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A large head circumference is more strongly associated with unplanned cesarean or instrumental delivery and neonatal complications than high birthweight

Published:August 05, 2015DOI:https://doi.org/10.1016/j.ajog.2015.07.045

      Objective

      Fetal size impacts on perinatal outcomes. We queried whether the fetal head, as the fetal part interfacing with the birth canal, might impact on obstetric outcomes more than birthweight (BW). We examined associations between neonatal head circumference (HC) and delivery mode and risk of perinatal complications as compared to high BW.

      Study Design

      This was an electronic medical records–based study of term singleton births (37-42 weeks’ gestation) from January 2010 through December 2012 (N = 24,780, 6343 primiparae). We assessed risks of unplanned cesarean or instrumental delivery and maternal and fetal complications in cases with HC or BW ≥95th centile (large HC, high BW) vs those with parameters <95th centile (normal). Newborns were stratified into 4 subgroups: normal HC/normal BW (reference, n = 22,548, primiparae 5862); normal HC/high BW (n = 817, P = 213); large HC/normal BW (n = 878, P = 265); and large HC/high BW (n = 537, P = 103). Multinomial multivariable regression provided adjusted odds ratio (aOR) while controlling for potential confounders.

      Results

      Infants with HC ≥95th centile (n = 1415) were delivered vaginally in 62% of cases, unplanned cesarean delivery 16%, and instrumental delivery 11.2%; 78.4% of infants with HC <95th centile were delivered vaginally, 7.8% unplanned cesarean, and 6.7% instrumental delivery. Odds ratio (OR) for unplanned cesarean was 2.58 (95% confidence interval [CI], 2.22–3.01) and for instrumental delivery OR was 2.13 (95% CI, 1.78–2.54). In contrast, in those with BW ≥95th centile (n = 1354) 80.3% delivered vaginally, 10.2% by unplanned cesarean (OR, 1.2; 95% CI, 1.01–1.44), and 3.4% instrumental delivery (OR, 0.46; 95% CI, 0.34–0.62) compared to infants with BW <95th centile: spontaneous vaginal delivery, 77.3%, unplanned cesarean 8.2%, instrumental 7.1%. Multinomial regression with normal HC/normal BW as reference group showed large HC/normal BW infants were more likely to be delivered by unplanned cesarean (aOR, 3.08; 95% CI, 2.52–3.75) and instrumental delivery (aOR, 3.03; 95% CI, 2.46–3.75). Associations were strengthened in primiparae. Normal HC/high BW was not associated with unplanned cesarean (aOR, 1.18; 95% CI, 0.91–1.54), while large HC/high BW was (aOR, 1.93; 95% CI, 1.47–2.52). Analysis of unplanned cesarean indications showed large HC infants had more failure to progress (27.7% vs 14.1%, P < .001), while smaller HC infants had more fetal distress (23.4% vs 16.9%, P < .05).

      Conclusion

      A large HC is more strongly associated with unplanned cesarean and instrumental delivery than high BW. Prospective studies are needed to test fetal HC as a predictive parameter for prelabor counseling of women with “big babies.”

      Key words

      Classic obstetrics describes the 3 P’s: passageway, passenger, and power of the uterus, and the dangers inherent in a mismatch. The fetal head represents the point of interface between “passenger” and “passageway.”
      The literature of anthropology and human evolution addresses the issue of the obstetric dilemma of bipedalism and encephalization: ie, the tension at the point of meeting of the human fetal head and the bipedal female pelvis,
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      We queried how fetal head dimensions might impact the passage of the fetus through the birth canal and affect obstetric outcomes, primarily delivery mode. In our earlier work we showed
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      that delivery of a fetus with large HC significantly increased the risk of intrapartum levator ani trauma.
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      of prolonged second stage of labor, obstructed labor, unplanned cesarean delivery (UCD) or instrumental delivery, shoulder dystocia, brachial or facial nerve injuries, trauma to the clavicle and humerus, birth asphyxia, maternal postpartum hemorrhage, and trauma to the birth canal, bladder, or pelvic floor complex,
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      with their attendant potential long-term effects. These clinical observations led to attempts to estimate fetal weight, clinically and in recent decades sonographically, to inform management decisions to reduce risks of fetal and maternal complications in labor and delivery of macrosomic fetuses. Professional guidelines devote considerable attention to big babies and the optimal delivery approach for them.
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      We posed the question whether the dimensions of the fetal head might be more important than fetal weight in determining the likelihood of cesarean or instrumental delivery. As a first step in answering this question, we designed an electronic medical records (EMR)-based study to test the notion whether HC impacts delivery mode more than baby weight. Here we aimed to determine the relationship between neonatal HC and mode of delivery and frequency of complications in labor, and to compare this with the relationship between birthweight (BW) and delivery mode and labor complications.

      Materials and Methods

      This was a cross-sectional study based on EMR performed in the Hadassah-Hebrew University Medical Centers Jerusalem, comprising 2 campuses of a tertiary care center. Our institutional ethical review board reviewed and approved the study (#0085-13-HMO; Feb. 14, 2013). All singleton term deliveries (37+0-42+0) occurring from January 2010 through December 2012 were eligible for inclusion. Multiple births were excluded. Data were collected in blinded fashion by research staff who were not involved in any stage of perinatal care; midwives and obstetricians caring for laboring women and nursery physicians and nurses caring for their infants were unaware of the study. Data were extracted for maternal demographic and obstetric parameters including type of delivery and length of second stage of labor
      ACOG
      Operative vaginal delivery. Practice bulletin no. 17. In: Clinical Management Guidelines for Obstetricians and Gynecologists.
      • Spong C.Y.
      • Berghella V.
      • Wenstrom K.D.
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      • Saade G.R.
      Preventing the first cesarean delivery: summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, and American College of Obstetricians and Gynecologists Workshop.
      (defined as prolonged if >3 hours for primipara with epidural anesthesia, 2 hours without; 2 hours for multipara with epidural anesthesia, 1 hour without), maternal hemorrhage (defined as >500 mL or requiring transfusion of packed cells), and gestational diabetes mellitus, and neonatal parameters including BW, neonatal HC, infant sex, meconial fluid, umbilical cord (arterial) pH, 5-minute Apgar score, and neonatal intensive care unit admission. Infants with BW or HC ≤5th centile (n = 1780) were excluded from further analysis; our aim was to examine HC and BW to improve prelabor counseling and inform management decisions in big babies, and the subgroup at the opposite end of the spectrum includes a high proportion of pregnancies with complications such as preeclampsia, fetal growth restriction, and fetal anomalies, which elevate the risk for cesarean delivery and are managed under well-established protocols (Figure 1).
      Figure thumbnail gr1
      Figure 1Cohort selection flowchart
      BW, birthweight; EMR, electronic medical records; HC, head circumference; IUGR, intrauterine growth restriction.
      ∗EMR was found to lack the birth weight (n=20) head circumference (n=1588), or both (n=8).
      Infants with HC or BW at or below the 5% centile, which include a high proportion of pregnancies with maternal and/or fetal complications such as preeclampsia, IUGR, fetal anomalies, etc., are at very high risk of operative delivery for fetal distress.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      BW was recorded in the delivery room; HC was measured in the newborn nursery 6-18 hours after delivery, with a flexible metal tape measure, passed around the baby’s head above the eyebrows anteriorly and at the posterior protuberance of the occipital bone posteriorly.
      • Low A.
      Measurements of infants at birth.
      Outcomes were analyzed for primiparae and for the whole cohort. Infant sex was analyzed as a possible modifier. Statistical analyses were performed with SPSS 20 for Windows (IBM, Armonk, NY) and Excel (Microsoft Seattle, WA). Dichotomous variables were analyzed with the χ2 test to determine proportions of each outcome differing from expected, and correlation between the variables. Fisher exact test was applied as appropriate in analyzing cells with small numbers of cases. Odds ratios (ORs) for 4 delivery modes (spontaneous vaginal, elective cesarean, instrumental [vacuum or forceps assisted], and unplanned cesarean) were determined for neonates with HC ≥95th centile and BW ≥95th centile, as compared to the expected risk in the whole cohort. Risks of the outcome parameters UCD or instrumental delivery were calculated for 7 percentile subgroups (5th, 10th, 25th, 50th, 75th, 90th, 95th) of HC and BW (Figure 2).
      Figure thumbnail gr2
      Figure 2Proportions of unplanned cesarean and instrumental deliveries in seven percentile subgroups of HC and BW
      Proportions of mode of delivery (cesarean [C/S] and instrumental) for 5th, 10th, 25th, 50th, 75th, 90th, and 95th centile subgroups of A, head circumference (HC) and B, birthweight (BW) for whole cohort (n = 26,560) and of C, HC and D, BW in primiparae (n = 6990). Data points represent increments, eg, 5th centile includes infants up to and including 5th centile, 95th represents infants ≥95th-100th centile.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      Multinomial multivariable regression was used to obtain adjusted OR (aOR) of the mode of delivery for HC or BW ≥95th centile, with vaginal delivery as the reference group, while controlling for maternal age, primipara status, gestational age at delivery, and infant sex, as well as examining interactions between these variables. ORs and aORs are reported with 95% confidence intervals (CI).
      An interaction term between HC and BW was found significant (P < .001). However, not all neonates with large HC had high BW, and vice versa. To assess and compare the impact of HC and BW in neonates of differing proportions, a multinomial multivariable regression model for modes of delivery was analyzed according to 4 strata of HC and BW, where normal was defined as (>5th centile and <95th centile): normal HC/normal BW; large HC/normal BW; normal HC/high BW; and large HC/high BW.
      To assess the feasibility of applying prenatal HC evaluation to prelabor counseling, fetal HC and EFW were compared to neonatal HC and BW to determine the degree of correlation between them. Ultrasound data were drawn from a subset of our study population undergoing ultrasound examination in our ultrasound units, including fetal biometry, within 3 days of delivery. Postnatal measurements were performed in identical fashion for all infants, and nursery caregivers were unaware of the prenatal ultrasound results. Prenatal sonographic HC and EFW were performed according to International Society of Ultrasound in Obstetrics and Gynecology guidelines.
      • Salomon L.J.
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      • et al.
      Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan.
      Sonographic EFW was derived from standard fetal biometry (abdominal circumference, femur length, biparietal diameter, and HC) with the Hadlock formula.
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      Bland-Altman plots
      • Bland J.M.
      • Altman D.G.
      Statistical methods for assessing agreement between two methods of clinical measurement.
      and interclass correlation coefficients were applied to compare prenatal HC and EFW with postnatal measurements.

      Results

      A total of 28,168 term singleton deliveries occurred at our hospitals during the study period. Electronic data for HC and/or BW were missing in a small number of files: 1588 (5.6%) had no HC, 20 (0.07%) no BW, and 8 had neither parameter recorded. These cases were excluded from further analysis. The remaining cohort of 26,560 was analyzed for percentiles cutoffs; infants found to have HC and/or BW ≤5th centile were excluded from further analysis. A total of 24,780 singleton births therefore were included; 6343 were first deliveries (Figure 1).
      Background parameters of the study cohort and the 95th centile BW or HC subgroups are shown in Table 1. One quarter of the patients in the cohort were primiparae (25.6%), while 9.7% were grand-multiparae. Rates of gestational diabetes mellitus did not differ significantly among the groups. The rates and ORs of delivery mode outcomes (spontaneous vaginal delivery being the reference group) in large HC and high BW babies, among the whole cohort and primiparae, are shown in Table 2.
      Table 1Demographic characteristics of the study cohort and 95th centiles of head circumference and birthweight
      DemographicCohort
      Excluding infants with HC and/or BW measurements ≤5th centile
      ≥95th centile HC≥95th centile BWP value
      P values were calculated for χ2 test for dichotomous variables for subgroup with HC ≥95th centile or BW ≥95th centile vs the cases with HC or BW measuring >5th and <95th centiles.
      n = 24,780n = 1415n = 1354
      Maternal age, mean (± SD)30.14 (5.56)30.93 (5.56)31.02 (5.36)< .001
      Parity, n (%)
       Primipara6343 (25.6)368 (26)216 (16)< .001
       Multipara16,037 (64.7)857 (60.6)893 (66)
       Grandmultipara2400 (9.7)190 (13.4)245 (18.1)
      GA at delivery, median (range)39 (37–42)40 (37–42)40 (37–42)< .001
      Infant sex, n (% female)11,811 (47.7)315 (22.3)448 (33.1)< .001
      Current smoker, n (% yes)851 (3.5)23 (1.7)25 (1.9)< .001
      GDM, n (%)824 (3.4)54 (3.8)53 (3.9)NS
      HC, mean (range)34.46 (32.3–41)36.74 (36.2–41)35.96 (33–40)< .001
      BW, mean (range)3351.1 (2600–5250)3899.8 (2664–5250)4214.42 (4018–5250)< .001
      BW, birthweight; GA, gestational age; GDM, gestational diabetes mellitus; HC, head circumference; NS, not significant.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Excluding infants with HC and/or BW measurements ≤5th centile
      b P values were calculated for χ2 test for dichotomous variables for subgroup with HC ≥95th centile or BW ≥95th centile vs the cases with HC or BW measuring >5th and <95th centiles.
      Table 2Rates and ORs of modes of delivery comparing infants with large head circumference or high birthweight (≥95th centile) to the populations <95th centiles
      Variable% of all deliveriesHead circumferenceBirthweight
      Rate of delivery mode in ≥95th centile, %Rate of delivery mode in <95th centile, %OR (95% CI) (≥95th vs <95th centile)Rate of delivery mode in ≥95th centile, %Rate of delivery mode in <95th centile, %OR (95% CI) (≥95th vs <95th centile)
      Spontaneous vaginal delivery
      Reference category.
       Cohort77.46278.4Reference category80.377.3Reference category
       Primiparae63.43863.4Reference category56.562.2Reference category
      Instrumental
       Cohort6.911.26.72.13 (1.78–2.54)3.47.10.46 (0.34–0.62)
       Primiparae17.123.116.82.29 (1.74–3.03)10.617.40.68 (0.43–1.06)
      Elective cesarean
       Cohort7.410.77.21.9 (1.59–2.27)6.17.40.79 (0.63–0.99)
       Primiparae4.66.84.52.53 (1.62–3.94)6.94.51.69 (0.97–2.92)
      Unplanned cesarean
       Cohort8.3167.82.58 (2.22–3.01)10.28.21.2 (1.01–1.44)
       Primiparae16.332.115.33.5 (2.7–4.51)25.915.91.79 (1.3–2.48)
      CI, confidence interval; OR, odds ratio.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Reference category.
      Rate of vaginal delivery was 78.4% when HC <95th centile vs 62% in HC ≥95th centile. Risk of UCD was 7.8% when HC <95th centile and increased to 16% when HC ≥95th centile. Risk of instrumental delivery was 6.7% and 11.2% in babies with HC below and above the 95th centile, respectively. (Results for infants ≥97.5 centile are shown in Supplemental Table 1; Appendix.) The OR for UCD was 2.58 (95% CI, 2.22–3.01) and for instrumental delivery OR 2.13 (95% CI, 1.78–2.54) for babies with HC ≥95th centile as compared to those with HC in normal range.
      Babies with BW ≥95th centile delivered vaginally in 80.3% of cases, while 10.2% were delivered by UCD and 3.4% by instrumental delivery. BW ≥95th centile showed weaker association with UCD (OR, 1.2; 95% CI, 1.01–1.44) than HC, and was associated with significantly lower odds of instrumental delivery (OR, 0.46; 95% CI, 0.34–0.62). (Supplemental Table 2 compares ORs in infants at 95 and 97.5 centile subgroups.)
      Multinomial regression modeling controlling for maternal age, gestational age at delivery, sex of the fetus, and primipara status showed that HC ≥95th centile more than doubled the risk of UCD (aOR, 2.65; 95% CI, 2.22–3.17) while BW ≥95th centile had no significant effect (OR, 0.91; 95% CI, 0.73–1.12) (Table 3). Interaction terms between infant sex and HC and BW were nonsignificant (data not shown).
      Table 3Multinomial regression model showing adjusted ORs of modes of delivery in the cohort, adjusted for maternal age, GA at delivery, infant sex, and parity
      VariableVaginal delivery (reference group)Instrumental delivery aOR (95% CI)Elective cesarean aOR (95% CI)Unplanned cesarean aOR (95% CI)
      BW and HC stratum
       HC ≥95th centile12.67 (2.18–3.27)3.23 (2.57–4.06)2.65 (2.22–3.17)
       BW ≥95th centile10.34 (0.24–0.47)1.14 (0.86–1.51)0.9 (0.73–1.12)
       Maternal age (continuous, years)11.03 (1.02–1.04)1.12 (1.1–1.13)1.08 (1.07–1.09)
       GA (continuous, 37-42 wks)11.12 (1.07–1.17)0.32 (0.3–0.34)0.95 (0.92–0.99)
      Infant sex
       Female1
       Male11.3 (1.17–1.44)0.85 (0.76–0.94)1.33 (1.2–1.46)
      Parity
       Parity>11
      Primipara status
       Primipara17.49 (6.67–8.41)1.38 (1.19–1.6)5.93 (5.34–6.6)
      BW, birthweight; CI, confidence interval; GA, gestational age; HC, head circumference; aOR, odds ratio.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      Large HC does not always accompany high BW (Figure 3): only in 24% of big fetuses, ie, those with HC or BW ≥95th centile, did both parameters occur together. Some 2.2% of the whole study cohort had both HC and BW ≥95th centile. An interaction term between HC and BW was found significant (P < .001) in multinomial multivariable regression analysis for mode of delivery adjusted to the above parameters (model not shown). To investigate this further we analyzed modes of delivery according to 4 strata, where normal was defined as (>5th centile and <95th centile): normal HC/normal BW; large HC/normal BW; normal HC/high BW; and large HC/high BW (Table 4). Rates of spontaneous vaginal delivery in the subgroups were highest in the normal HC/normal BW and normal HC/high BW subgroups: 78.1% and 85.1%, respectively. Large HC/normal BW babies were delivered vaginally in only 55.4% of cases, and large HC/high BW babies, 73%.
      Figure thumbnail gr3
      Figure 3Venn diagram showing breakdown of large HC and high BW infants, and overlap between them
      BW, birthweight; HC, head circumference.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      Table 4Multinomial multivariate regression model showing aORs of modes of delivery in the whole cohort and in primiparae in 4 HC/BW subgroups
      VariableVaginal delivery rate, % (reference group)Instrumental deliveryElective cesareanUnplanned cesarean
      Rate, %aOR (95% CI)Rate, %aOR (95% CI)Rate, %aOR (95% CI)
      BW and HC stratum (cohort)
      Adjusted for maternal age, GA at delivery, infant sex, and parity
       Normal HC/Normal BW (n = 22,548)78.16.87.37.8
       Large HC/Normal BW (n = 878)55.415.83.03 (2.46–3.75)11.33.26 (2.52–4.21)17.53.08 (2.52–3.75)
       Normal HC/High BW (n = 817)85.13.20.52 (0.35–0.78)3.71.08 (0.73–1.6)8.11.18 (0.91–1.54)
       Large HC/High BW (n = 537)733.70.59 (0.37–0.94)9.93.71 (2.65–5.2)13.41.93 (1.47–2.52)
      BW and HC stratum (primiparae)
      Adjusted for maternal age, GA at delivery, infant sex.
       Normal HC/Normal BW (n = 5862)63.416.94.515.2
       Large HC/Normal BW (n = 265)34.427.52.67 (1.94–3.68)64.32 (2.37–7.86)32.13.3 (2.41–4.53)
       Normal HC/High BW (n = 213)64.69.70.52 (0.28–0.99)5.33.69 (1.51–8.99)20.41.28 (0.79–2.09)
       Large HC/High BW (n = 103)47.611.70.81 (0.43–1.53)8.76.36 (2.89–13.99)322.36 (1.48–3.75)
      Rates of delivery modes in the 4 strata are shown.
      aOR, adjusted odds ratio; BW, birthweight; CI, confidence interval; GA, gestational age; HC, head circumference.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Adjusted for maternal age, GA at delivery, infant sex, and parity
      b Adjusted for maternal age, GA at delivery, infant sex.
      Normal HC/normal BW babies underwent instrumental delivery in 6.8% of cases, as compared to 15.8% of large HC/normal BW cases. This is in contrast to a low rate in normal HC/high BW and large HC/high BW infants, who were delivered by vacuum extraction 3.2 and 3.7% of the time, respectively.
      Normal HC/normal BW babies were delivered by UCD in 7.8% of cases, and normal HC/high BW cases, 8.1%. In contrast, 17.5% of large HC/normal BW cases were delivered by UCD, and 13.4% of large HC/high BW infants. Risk of interventional delivery was higher in all subgroups among primiparae.
      Multinomial multivariable regression applying these HC/BW strata to mode of delivery and adjusted for the parameters above showed that the risk of UCD for the large HC/normal BW group was 3 times (aOR, 3.08; 95% CI, 2.52–3.75) that of the normal HC/normal BW group. The risk of instrumental delivery was aOR 3.03 (95% CI, 2.46–3.75). Among primiparae, risk of UCD rose to 3.3 (95% CI, 2.41–4.53) while risk of instrumental delivery decreased slightly to 2.67 (95% CI, 1.94–3.68). In the 2 high BW subgroups (with or without large HC) the risk of UCD was nearly doubled among the large HC/high BW infants (aOR, 1.93; 95% CI, 1.47–2.52), but not significantly increased in normal HC/high BW cases (aOR, 1.18; 95% CI, 0.91–1.54). Notably, high BW cases with large or normal HC were significantly less likely to undergo instrumental delivery (aOR, 0.59; 95% CI, 0.37–0.94 and aOR, 0.52; 95% CI, 0.35–0.78, respectively). Table 4 summarizes rates and aORs of delivery modes in the 4 strata. Among primiparae, risk of UCD among high BW infants was 2.36 (95% CI, 1.48–3.75) when HC ≥95th centile, but was not elevated when HC was normal (aOR, 1.28; 95% CI 0.79–2.09); large HC/normal BW was associated with increased risk of instrumental delivery (aOR, 2.67; 95% CI, 1.94–3.68). The normal HC/high BW stratum was at reduced risk for instrumental delivery (aOR, 0.52; 95% CI, 0.28–0.99) while large HC/high BW stratum showed a nonsignificant reduction in risk of instrumental delivery (aOR, 0.81; 95% CI, 0.43–1.53).
      In analysis of the main indications for cesarean delivery (other than elective indications) we found that infants with large HC were more likely to undergo cesarean delivery for failure to progress (27.7% vs 14.1%, P < .001), while smaller infants were more likely to be delivered by cesarean for fetal distress (23.4% vs 16.9%, P < .05) (data not shown).
      Large HC impacted other outcome parameters. HC ≥95th centile was significantly associated with prolonged second stage of labor and maternal hemorrhage. Infants with HC ≥95th centile were more likely to be hospitalized in the special care nursery or neonatal intensive care unit, to have Apgar score ≤7, and to have umbilical cord pH ≤7.1 (Table 5, Supplemental Tables 1 and 2).
      Table 5Rates of maternal and fetal complications of the whole cohort (N = 24,780) and in primiparae (n = 6343) comparing infants with head circumference or birthweight ≥95th centile to the population (<95th centile)
      VariableTotalHead circumferenceBirthweight
      <95th centile≥95th centile<95th centile≥95th centile
      Prolonged second stage
       Cohort1325 (5.3%)1062 (5.3%)131 (12.2%)1128 (5.8%)65 (5.8%)
       Primiparae755 (14.3%)657 (13.5%)80 (29.3%)722 (14.1%)33 (19.6%)
      Maternal postpartum hemorrhage
       Cohort2695 (10.9%)2460 (10.5%)235 (16.6%)2481 (10.6%)214 (15.8%)
       Primiparae962 (15.2%)871 (14.6%)91 (24.7%)897 (14.6%)65 (30.1%)
      Meconial fluid
       Cohort1763 (7.1%)1641 (7%)122 (8.6%)1652 (7.1%)111 (8.2%)
       Primiparae574 (9%)534 (8.9%)40 (10.9%)550 (9%)24 (11.1%)
      Apgar <7
       Cohort29 (0.1%)25 (0.1%)4 (0.3%)27 (0.1%)2 (0.1%)
       Primiparae17 (0.3%)13 (0.2%)4 (1.1%)16 (0.3%)1 (0.5%)
      pH ≤7.1
       Cohort182 (0.9%)164 (0.9%)18 (1.5%)175 (1%)7 (0.7%)
       Primiparae86 (1.7%)76 (1.6%)10 (3.2%)83 (1.7%)3 (1.7%)
      NICU
      Admission to the special care nursery or neonatal intensive care unit (NICU).
       Cohort57 (0.2%)48 (0.2%)9 (0.6%)53 (0.2%)4 (0.3%)
       Primiparae25 (0.4%)20 (0.3%)5 (1.4%)25 (0.4%)0
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Admission to the special care nursery or neonatal intensive care unit (NICU).
      All subgroups showed increased frequency of maternal hemorrhage as compared to normal HC/normal BW infants. Mothers at the highest risk of maternal hemorrhage in the whole cohort were in the large HC subgroups, both those with normal and high BW (16.6%). In primiparae, however, the highest risk was observed in mothers of infants with normal HC/high BW (31.9%), as compared to 23.4% and 28.2% in high HC infants with normal and high BW, respectively (Table 6).
      Table 6Rates of maternal and fetal complications in the 4 subgroups, in the whole cohort and in primiparae
      VariableNormal HC and normal BW, % (n)Large HC and normal BW,
      Large HC or high BW ≥95th centile
      % (n)
      Normal HC and high BW,
      Large HC or high BW ≥95th centile
      % (n)
      Large HC and high BW,
      Large HC or high BW ≥95th centile
      % (n)
      P value
      Prolonged second stage
       Cohort5.5 (1029)15 (99)4.7 (33)7.7 (32)< .001
       Primiparae13.5 (661)30.3 (61)14.6 (14)24.6 (19)< .001
      Maternal postpartum hemorrhage
       Cohort10.4 (2335)16.6 (147)15.3 (125)16.6 (89)< .001
       Primiparae14.2 (835)23.4 (62)31.9 (36)28.2 (29)< .001
      Meconium stained amniotic fluid
       Cohort7 (1557)8.5 (75)7.8 (64)8.8 (47).11
       Primiparae8.9 (522)10.6 (28)10.6 (12)11.7 (12).56
      5-minute Apgar <7
       Cohort0.1 (23)0.5 (4)0.2 (2)0.01
       Primiparae0.2 (12)1.5 (4)0.9 (1)0< .001
      Arterial cord pH ≤7.1
       Cohort0.9 (162)1.7 (13)0.3 (2)1.2 (5).04
       Primiparae1.6 (74)3.9 (9)2.2 (2)1.2 (1).06
      NICU
      Admission to special care nursery or neonatal intensive care unit (NICU).
       Cohort0.2 (45)0.9 (8)0.4 (3)0.2 (1)< .001
       Primiparae0.3 (20)1.9 (5)00< .001
      BW, birthweight; HC, head circumference.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Large HC or high BW ≥95th centile
      b Admission to special care nursery or neonatal intensive care unit (NICU).
      To evaluate the feasibility of prenatal HC evaluation in prelabor counseling, we undertook to assess the reliability of prenatal measures of HC and EFW as compared to neonatal HC and BW. Data are based on a subgroup of our cohort comprised of patients (n = 2806) who underwent prenatal ultrasonography in our ultrasound units, including HC and fetal weight estimation, within 3 days of delivery. Prenatal and postnatal measurements of HC and BW were found to correlate strongly (intraclass correlation coefficient, 0.83 and 0.91, respectively). Bland-Altman plots
      • Bland J.M.
      • Altman D.G.
      Statistical methods for assessing agreement between two methods of clinical measurement.
      (Figure 4) show that prenatal HC was smaller than neonatal HC by a mean of 1.02 cm (95% CI of the mean, 0.98–1.05; SD ± 0.91; relative percentage error, 2.88%), consistently across the gestational weeks studied, while EFW overestimated BW by a mean of –77 g (95% CI of the mean, –86.2 to –68.2; SD ± 252.5; relative percentage error, 6.63%) this difference was also maintained over the weeks studied.
      Figure thumbnail gr4
      Figure 4Bland-Altman plots
      Bland-Altman plots
      • Bland J.M.
      • Altman D.G.
      Statistical methods for assessing agreement between two methods of clinical measurement.
      for prenatal and neonatal A, head circumference (HC) measurements and B, estimated fetal weight (EFW) and birthweight.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.

      Comment

      Principal findings of the study

      In this study based on high-quality EMRs with data entered prospectively prepartum, intrapartum, and postpartum, we demonstrate that large HC showed stronger association as compared to high BW with perinatal complications. We showed that infants with HC ≥95th centile had higher risk for interventional delivery (instrumental or UCD). Large HC infants were delivered by UCD about twice as frequently as those with HC in normal range, regardless of BW. Among infants of primiparae the risk was doubled again within all groups.
      Large HC was associated with higher risk of instrumental delivery among infants with normal BW; high BW infants had significantly lower risk of instrumental delivery. Our protocols mandate clinical EFW in the delivery room when fetal macrosomia is suspected, but do not require sonographic measurement of HC. Owing to the risks of instrumental delivery to the fetus and mother in suspected fetal macrosomia, it is less likely to be attempted in these fetuses.
      Women delivering fetuses with HC ≥95th centile showed consistently greater risk of prolonged second stage, most markedly in infants with normal BW. Indeed, fetuses with large HC were more likely to undergo UCD for failure to progress, while those with normal HC more often underwent UCD for fetal indications. This supports our hypothesis of a role for HC in prelabor evaluation.
      In our preliminary analyses of rates of UCD and other outcome parameters among the study cohort, we observed significant increase in rate of operative delivery in very small fetuses (Figure 1), which are recognized as being at increased risk of placental insufficiency, preeclampsia, intrauterine growth restriction, and therefore fetal distress in labor. Since our study aim was to assess large HC and its impact on intrapartum outcomes, we excluded this subgroup from further analysis.

      Clinical significance

      We posed our research question ultimately to improve prelabor counseling and clinical management of mothers with big babies. As a first step, before undertaking a prospective cohort study, we sought to test the notion that fetal head size, as the point of meeting between the fetus and the mother’s birth canal, might be an indicator of risk of cesarean or instrumental delivery. In our study we observed that the dimensions of the fetal head are more important than BW in assessing the likelihood of cesarean or instrumental delivery. This observation challenges us to reexamine the current emphasis on EFW in predicting the likelihood of a vaginal delivery when evaluating the suspected macrosomic fetus. Further, it has implications for prospective research into the value of HC vs EFW with ultrasound or clinical estimation in the prediction of vaginal or interventional delivery. Pending examination in a prospective study, our results show that prenatal HC is a reliable measure, reflecting neonatal HC well. Its availability makes it a feasible tool for practitioners involved in prelabor counseling. It appears that large BW fetuses, which are generally grouped together as “macrosomic” and counseled accordingly, are differentiated in their risk of complications by their head dimensions. Indeed, the subgroup of fetuses with BW >95th centile, but HC below it, achieved spontaneous vaginal delivery more frequently than any other subgroup. Pending support of our results from prospective studies, mothers, particularly multiparae, whose big baby is shown to have HC measurement <95th centile, may be reassured that they are not at significantly increased risk of UCD. These results may also have implications for women desiring vaginal birth after cesarean and for those considering elective cesarean because of macrosomic fetus. In addition, among women with large fetuses who are candidates for induction of labor, HC may be more useful than EFW, as the parameter more strongly associated with outcomes.
      Few studies have investigated the impact of HC on the odds of operative delivery in nulliparae,
      • Elvander C.
      • Hogberg U.
      • Ekeus C.
      The influence of fetal head circumference on labor outcome: a population-based register study.
      • Kennelly M.M.
      • Anjum R.
      • Lyons S.
      • Burke G.
      Postpartum fetal head circumference and its influence on labor duration in nullipara.
      • Larson A.
      • Mandelbaum D.E.
      Association of head circumference and shoulder dystocia in macrosomic neonates.
      • Mujugira A.
      • Osoti A.
      • Deya R.
      • Hawes S.E.
      • Phipps A.I.
      Fetal head circumference, operative delivery, and fetal outcomes: a multi-ethnic population-based cohort study.
      rather focusing on EFW.
      • Campbell S.
      Fetal macrosomia: a problem in need of a policy.
      The earlier studies showed that the odds of operative delivery and prolonged second stage of labor
      • Elvander C.
      • Hogberg U.
      • Ekeus C.
      The influence of fetal head circumference on labor outcome: a population-based register study.
      • Kennelly M.M.
      • Anjum R.
      • Lyons S.
      • Burke G.
      Postpartum fetal head circumference and its influence on labor duration in nullipara.
      • Larson A.
      • Mandelbaum D.E.
      Association of head circumference and shoulder dystocia in macrosomic neonates.
      increased as HC increased, and found as we did that infants of higher BW were less likely to show signs of fetal distress than smaller fetuses with similar HC.
      • Elvander C.
      • Hogberg U.
      • Ekeus C.
      The influence of fetal head circumference on labor outcome: a population-based register study.
      However earlier studies did not address the varying effects of large HC and BW in parous women, which we found to differ significantly from those observed in primiparae. Since all big babies are a management challenge, we explored the impact of HC and BW in our whole cohort as well as focusing on primiparae. We also addressed the impact of large HC on other maternal and neonatal outcomes, which have not been widely investigated previously.
      Prenatal and postnatal measures of HC are inherently different, in that the postnatal measure includes skin and hair, and may be affected by edema resulting from the birth itself, while the prenatal scan measures around the skull. However, the 1-cm difference was consistent across gestational weeks studied here, suggesting that a similar cutoff can be applied prenatally. Recent large studies have shown the consistency of prenatal and postnatal size distribution across populations with adequate nutritional status
      • Villar J.
      • Papageorghiou A.T.
      • Pang R.
      • et al.
      The likeness of fetal growth and newborn size across non-isolated populations in the INTERGROWTH-21st Project: the Fetal Growth Longitudinal Study and Newborn Cross-Sectional Study.
      • Papageorghiou A.T.
      • Ohuma E.O.
      • Altman D.G.
      • et al.
      International standards for fetal growth based on serial ultrasound measurements: the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project.
      and support a roughly 1-cm difference.
      Our results need to be confirmed in a prospective study based on prenatal measures of HC to determine its strength as a predictor of delivery mode and maternal and fetal complications.

      Study strengths and limitations

      Our study has several strengths and limitations. This is a very large cohort of 24,780 singleton births, based on EMR. Very few cases were excluded from the patient population, and those only for inadvertent omission of ≥1 of the studied parameters (HC and BW); there is no reason to suppose that big babies were more likely to be missing information. In addition, since exposures and outcomes were recorded nearly simultaneously, there is little danger of either selection or recall bias. However, as our results are based on a single institution, there may be some limitation in the generalizability of our results to centers with differing population mix. In addition, this is a retrospective study, with the limitations inherent in that approach. We could not analyze results for shoulder dystocia,
      • Ecker J.L.
      Cesarean delivery for suspected macrosomia: inefficient at best.
      for example. While this complication was recorded in ∼0.2% of deliveries, owing to the problematic, subjective reporting of this complication, informative analyses were not possible.

      Conclusion

      A large HC is more strongly associated with interventional delivery, as well as maternal and fetal complications, than a high BW. These findings call for prospective studies to determine the role of prenatally determined HC in predicting vaginal or interventional delivery. Pending the results of prospective studies, it may be time to reweigh professional recommendations regarding the macrosomic fetus, to include HC among the parameters considered.

      Appendix

      Supplemental Table 1Rates of modes of delivery and maternal and fetal complications comparing infants with head circumference or birth weight 97.5 centile to the population (<97.5 centile)
      VariableTotalHead circumferenceBirthweight
      <97.5 centile≥97.5 centile<97.5 centile≥97.5 centile
      MODE OF DELIVERY
      Vaginal
       Cohort19189 (77.4%)18540 (78.3%)649 (59.6%)18661 (77.4%)528 (78.5%)
       Primiparae3931 (63.4%)3826 (63.2%)105 (36%)3883 (62.2%)48 (49%)
      Instrumental
       Cohort1717 (6.9%)1590 (6.7%)127 (11.7%)1701 (7.1%)16 (2.4%)
       Primiparae1087 (17.1%)1021 (16.9%)66 (22.6%)1079 (17.3%)8 (8.2%)
      Elective cesarean
       Cohort1824 (7.4%)1702 (7.2%)122 (11.2%)1771 (7.3%)53 (7.9%)
       Primiparae293 (4.6%)273 (4.5%)20 (6.8%)284 (4.5%)9 (9.2%)
      Unplanned cesarean
       Cohort2050 (8.3%)1859 (7.8%)191 (17.5%)1974 (8.2%)76 (11.3%)
       Primiparae1032 (16.3%)931 (15.4%)101 (34.6%)999 (16%)33 (33.7%)
      MATERNAL AND FETAL COMPLICATIONS
      Prolonged second stage
       Cohort1325 (5.3%)1082 (5.5%)111 (13.8%)1167 (5.8%)26 (4.8%)
       Primiparae755 (14.3%)684 (13.5%)71 (33.8%)742 (14.3%)13 (19.1%)
      Maternal postpartum hemorrhage
       Cohort2695 (10.9%)2512 (10.6%)183 (16.8%)2592 (10.8%)103 (15.3%)
       Primiparae962 (15.2%)889 (14.7%)73 (25%)934 (15%)28 (28.6%)
      Meconial fluid
       Cohort1763 (7.1%)1669 (7%)94 (8.6%)1716 (7.1%)47 (7%)
       Primiparae574 (9%)540 (8.9%)34 (11.6%)566 (9.1%)8 (8.2%)
      Apgar <7
       Cohort29 (0.1%)26 (0.1%)3 (0.3%)28 (0.1%)1 (0.1%)
       Primiparae17 (0.3%)14 (0.2%)3 (1%)17 (0.3%)0
      pH ≤7.1
       Cohort182 (0.9%)167 (0.9%)15 (1.6%)178 (0.9%)4 (0.7%)
       Primiparae86 (1.7%)78 (1.6%)8 (3.1%)84 (1.7%)2 (2.5%)
      NICU
      Admission to the special care nursery or neonatal intensive care unit (NICU).
       Cohort57 (0.2%)49 (0.2%)8 (0.7%)55 (0.2%)2 (0.3%)
       Primiparae25 (0.4%)20 (0.3%)5 (1.7%)25 (0.4%)0
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Admission to the special care nursery or neonatal intensive care unit (NICU).
      Supplemental Table 2ORs for delivery modes and maternal and fetal complications, comparing the ≥95th centile and ≥97.5th centile
      VariableHead circumferenceBirthweight
      OR (95% CI) (≥95th centile vs <95th centile)OR (95% CI) (≥97.5th centile vs <97.5th centile)OR (95% CI) (≥95th centile vs <95th centile)OR (95% CI) (≥97.5th centile vs <97.5th centile)
      Mode of delivery
       Vaginal
      Vaginal (reference group) vs instrumental or elective cesarean or emergency cesarean, for prolonged second stage vs not prolonged and for maternal hemorrhage vs no maternal hemorrhage
      1111
       Instrumental2.13 (1.78–2.54)2.28 (1.87–2.78)0.46 (0.34–0.62)0.33 (0.2–0.55)
       Elective cesarean1.9 (1.59–2.27)2.05 (1.68–2.5)0.79 (0.63–0.99)1.06 (0.79–1.4)
       Unplanned cesarean2.58 (2.22–3.01)2.94 (2.48–3.47)1.2 (1.01–1.44)1.36 (1.07–1.74)
      Maternal and fetal complications
       Prolonged second stage2.42 (1.99–2.94)2.77 (2.25–3.12)1 (0.78–1.3)0.83 (0.56–1.23)
       Maternal postpartum hemorrhage1.69 (1.46–1.96)1.7 (1.45–2)1.59 (1.36–1.85)1.5 (1.21–1.86)
       Meconial fluid1.25 (1.03–1.51)1.25 (1.00–1.55)1.18 (0.96–1.44)0.98 (0.73–1.32)
       Apgar <72.65 (0.92–7.63)2.52 (0.76–8.33)1.28 (0.3–5.4)1.3 (0.17–9.41)
       pH ≤7.11.72 (1.05–2.8)1.84 (1.08–3.14)0.68 (0.32–1.46)0.79 (0.29–2.12)
       NICU
      Admission to special care nursery or neonatal intensive care unit (NICU).
      3.1 (1.52–6.35)3.57 (1.7–7.56)1.3 (0.47–3.62)1.3 (0.32–5.36)
      CI, confidence interval; OR, odds ratio.
      Lipschuetz. Relationship between head circumference and mode of delivery. Am J Obstet Gynecol 2015.
      a Vaginal (reference group) vs instrumental or elective cesarean or emergency cesarean, for prolonged second stage vs not prolonged and for maternal hemorrhage vs no maternal hemorrhage
      b Admission to special care nursery or neonatal intensive care unit (NICU).

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