American Journal of Obstetrics & Gynecology
Volume 201, Issue 2 , Pages 156.e1-156.e6, August 2009

Late recognition of pregnancy as a predictor of adverse birth outcomes

Presented at the National State of the Science Congress on Nursing Research, Washington, DC, Oct. 2-4, 2008.

  • Adejoke B. Ayoola, PhD, RN

      Affiliations

    • Department of Nursing, Calvin College, Grand Rapids, MI
    • Corresponding Author InformationReprints: Adejoke B. Ayoola, PhD, RN, Assistant Professor, Department of Nursing, Calvin College, 1734 Knollcrest Circle SE, Grand Rapids, MI 49546
    • ,
  • Manfred Stommel, PhD

      Affiliations

    • College of Nursing, Michigan State University, East Lansing, MI
    • ,
  • Mary D. Nettleman, MD, MS, MACP

      Affiliations

    • Department of Medicine, Michigan State University, East Lansing, MI

Received 7 January 2009; received in revised form 19 April 2009; accepted 10 May 2009.

Article Outline

Objective

We examined the relationship between the time of recognition of pregnancy and birth outcomes, such as premature births, low birthweight (LBW), admission to the neonatal intensive care unit (NICU), and infant mortality.

Study Design

A secondary analysis was performed using the Pregnancy Risk Assessment and Monitoring System (PRAMS) multistate data from 2000-2004. The sample consisted of 136,373 women who had a live childbirth. Analysis involved multiple logistic regression models, appropriately weighted for point and variance estimation to reflect the complex survey design of the PRAMS using STATA 9.2 (Stata Corp, College Station, TX).

Results

Approximately 27.6% recognized their pregnancy late (after 6 weeks of gestation). Late recognition was significantly associated with an increased odds of having premature births (odds ratio [OR], 1.09; 99% confidence interval [CI], 1.01-1.19), LBW (OR, 1.08; 99% CI, 1.01-1.15), and NICU admissions (OR, 1.12; 99% CI, 1.03-1.21).

Conclusion

These results provide a rationale and an impetus for developing interventions that promote early recognition of pregnancy.

Key words: birth outcomes, low birthweight, pregnancy recognition, Pregnancy Risk Assessment and Monitoring System, preterm birth

 

Early pregnancy is a critical period for fetal development. Within the first 4 weeks after conception, the heart begins to beat. By the eighth week all major organs have formed.1 Unfortunately, many women do not realize they are pregnant during this important time and may inadvertently continue risky behaviors, such as drinking and smoking.2, 3, 4 Studies have shown that women reduce or stop risky behaviors promptly once pregnancy is recognized, often before the first prenatal care (PNC) visit.3, 5, 6 Conversely, delays in recognition would be expected to increase the duration of fetal exposure to conditions that interfere with normal development.3, 7, 8, 9, 10, 11 Pregnancy recognition is also a necessary prerequisite to initiating prenatal care.

Although pregnancy recognition is potentially important, no study has examined whether the timing of pregnancy recognition affects birth outcome. This is a critical step in determining whether education about pregnancy recognition should become part of preconceptual health programs or whether studies should be done to improve the timing of recognition. Therefore, the current study used the Pregnancy Risk Assessment and Monitoring System (PRAMS) database to examine the relationship between late recognition of pregnancy and adverse birth outcomes: namely, prematurity, low birthweight (LBW), admission into the neonatal intensive care unit (NICU), and infant mortality.

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Materials and Methods 

Study design 

This study was a secondary analysis of 5 annual data cohorts (2000-2004) collected through the PRAMS program in the United States. The PRAMS data are derived from an ongoing, cross-sectional, population-based survey designed by the Centers for Disease Control and Prevention (CDC).12, 13, 14, 15 The data are representative of women of childbearing age in 29 US states, who had live births within the 2-6 months prior to being contacted for participation in the study.

The PRAMS data are also linked with birth certificates for each state to capture maternal marital status, age, parity, child's birthweight, and gestational age. The PRAMS data are weighted so that the results can be generalized to an entire state's population of women having a live birth.12 The PRAMS database does not contain individual identifiers, and its use and this study were approved by the Michigan State University Institutional Review Board.

The combined sample size for the 2000-2004 PRAMS surveys was 157,692 respondents. The analysis sample included 136,373 after the exclusion of respondents with missing information on key variables and cases with obvious errors on key variables, such as a gestational age of 77 weeks. Excluded women were more likely to be unmarried (odds ratio [OR], 1.22; P < .01), have less than a high school education (OR, 1.96; P < .01), and be a member of a minority ethnic/racial group (OR, 1.56; P < .01). This is consistent with other studies that have shown that higher attrition and nonresponse rates are related to individual characteristics.16

Measures 

The main outcomes were gestational age at birth, birthweight, admission to the NICU, and infant mortality (death before 1 year of age). Gestational age was calculated from the first day of the last menstrual period and was recoded into “premature births” (gestational age < 37 weeks) and “term births” (gestational age of ≥ 37 weeks). Birthweight was also dichotomized into “LBW” (≤ 2500 g) and “normal birthweight” (> 2500 g). NICU admission is the admission of a baby into the NICU during the neonatal period (ie, any time between the birth and the 28th day of life).

The predictor variable was the time of recognition of pregnancy. It was reported as a continuous variable and was dichotomized into “early” and “late” recognition for the final analysis. There is no standard definition of late pregnancy recognition. For the purposes of the study, we defined “late pregnancy recognition” as recognition occurring after 6 weeks of pregnancy/gestation, which was considered achievable for most women17, 18 and was consistent with the cutoff used in older studies.3 The PRAMS question that was used to measure time of recognition of pregnancy was: How many weeks or months pregnant were you when you were sure you were pregnant? (for example, you had a pregnancy test or a doctor or nurse said you were pregnant).

There were several potential confounders that were entered into the analytic model. These included maternal age, parity, marital status, level of education, insurance status, race/ethnicity, smoking and drinking behavior during pregnancy, having multiple births, prior premature birth, prior baby with LBW, and prepregnancy body mass index (BMI).7, 19, 20, 21, 22 Time lag to initiation of PNC was included and measured in terms of the difference between time of recognition of pregnancy (PR) and initiation of PNC and was computed as PNC minus PR equals time lag, using weeks as the unit of measurement.

This was necessary, because the time of pregnancy recognition could be a proxy to PNC initiation and is likely to be highly correlated, which increases the possibility of collinearity. Maternal race/ethnicity is coded as non-Hispanic white, black, Hispanic, or other (American Indian, Alaska Native, Asian/Hawaiian, and Pacific Islander).

The variable insurance status was created from 4 merged responses from the PRAMS variable and coded into 3 categories: no insurance, had Medicaid sometime before or during pregnancy, and had private insurance only.

Previous LBW and premature births were coded based on women's responses as either had no previous LBW or had a previous LBW and either had no previous premature birth or had previous premature birth, respectively. Based on the PRAMS questions, smoking status was coded into 3 categories: nonsmoker, quitter or attempted quitter (smoked > 100 cigarettes in past 2 years but not in third trimester), or continued smoker (smoked during third trimester). Drinking behavior included 3 levels: nondrinker, quitter or attempted quitter (drank any alcohol in the past 2 years but not in the third trimester), or continued drinker (drank in the third trimester). Maternal prepregnancy BMI was categorized into morbidly obese (BMI > 40 kg/m2), obese (BMI 30-39 kg/m2), overweight (BMI 26-29 kg/m2), or normal weight (BMI ≤ 25 kg/m2).

The data were analyzed using univariate and bivariate statistics, including percentages, means, and χ2 test. Logistic regression models were used for the multivariate analysis. The PRAMS data combine separate state surveys and use complex cluster designs. Thus, all point estimation needs to take account of the differential weighting of cases, and variance estimation needs to reflect the division into primary sampling units and strata.23 This means that all statistical estimates, whether simple percentages or adjusted odds ratios from multivariate regression models, refer to the target population of 5.5 million pregnant women to which the PRAMS data can be generalized. SES were estimated using the Taylor series linearization method incorporated into the “svy” command of STATA (version 9.2; Stata Corp, College Station, TX). Given the number of outcome variables and the very large sample size, the statistical significance level was set to a cutoff point of P = .01.

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Results 

The mean age of women in the study population was 27 years. The women were predominantly non-Hispanic white (65.6%) and married (67.1%). A substantial percentage of the population (41.2%) was comprised of first-time mothers (had no prior birth). About 40% of the women received Medicaid sometime before or during their pregnancy, and 44% were on public assistance. Fourteen percent of the women continued to smoke during pregnancy, and 6.1% drank alcohol during their third trimester.

Recognition of pregnancy occurred an average of 5.9 weeks after the last menstrual period (99% confidence interval [CI], 5.89-5.98), ranging from 1-39 weeks. More than a quarter (27.6%; 99% CI, 27.09-28.12%) of the women recognized their pregnancy late (ie, after 6 weeks of gestation). The mean for the time of recognition of pregnancy was 4.1 weeks for early recognizers and 10.6 weeks for late recognizers.

Demographic characteristics of early and late recognizers are presented in Table 1. The χ2 analysis revealed significant differences between the early and late recognizers in terms of the women's race/ethnicity, marital status, number of prior births, insurance status, socioeconomic status, and the maternal level of education (P < .001).

TABLE 1. Characteristics of the women in the study by time of pregnancy recognition
CharacteristicsPercent among early recognizers (n = 96,168a)Percent among late recognizers (n = 40,205b)P valuec
Age (y)
Range12-5311-51
Mean2825.4<.001
99% CI27.9-28.125.3-25.5
Race/ethnicity (% of total)
Non-Hispanic white70.951.4<.001
Black12.525.3<.001
Hispanic11.217.4<.001
Other4.55.1<.001
Missing0.90.8
Marital status (% of total)
Married53.5913.55<.001
Not married18.7714.05<.001
Missing0.040.0
Parity (% of total)
0 prior birth (nullipara)40.543.1<.001
≥ 159.456.9<.001
Missing0.090.1
Insurance status (% of total)
No insurance4.35.3<.001
Medicaid32.759.7<.001
Private insurance63.035.0<.001
Socioeconomic status (% of total)
Public assistance36.462<.001
No public assistance63.638<.001
Maternal education (% of total)
< high school13.228.6<.001
High school29.337.2<.001
≥ some college56.733.3<.001
Missing0.90.9
Smoking status
Nonsmoker75.268.7<.001
Smoker but quit12.113.1<.001
Smoked during third trimester12.517.9<.001
Missing0.30.4
Drinking behavior
Nondrinker33.744.7<.001
Drinker but quit59.449.7<.001
Drank during third trimester6.55.0<.074
Missing0.40.6

All the values are based on the population estimate for this study. Total population estimate = 5,509,817.

CI, confidence interval.

Ayoola. Late recognition of pregnancy predicts adverse birth outcomes. Am J Obstet Gynecol 2009.

aPopulation estimate for early recognizers = 3,988,999; early recognizers = 72.4%, 99% CI, 71.88-72.91;

bPopulation estimate for late recognizers = 1,520,818; late recognizers = 27.6%, 99% CI, 27.09-28.12;

cP value for χ2 test of early vs late recognition and main demographic variables.

There was also a significant difference (P < .001) between the time of pregnancy recognition and the women's smoking status (Table 1). However, among the drinkers, there was no significant difference between the group of women who were quitters or attempted quitters and those who drank in the third trimester (P = .074).

The mean gestational age of the babies born to the women was 38.7 weeks (99% CI, 38.69-38.72). The gestational age at birth ranged from 22-43 weeks, and 8.9% of births were premature. The mean birthweight was 3326 g (99% CI, 3320-3331 g). Seven percent of babies were born with LBW. The mean weight of LBW infants was 1994 g. The mean weight for non-LBW babies was 3429 g. More than a quarter of the LBW babies (26.2%) were born to women aged 21-25 years, and 46.2% were born to first-time mothers. Eleven percent of infants were admitted to the NICU. Less than 1% of the infants born to the women in the study were deceased at the time the mothers were surveyed.

Late recognition of pregnancy was associated with increased adjusted odds of having 3 of the 4 adverse birth outcomes: namely, premature birth, LBW, and NICU admission (Table 2). This effect was independent of potentially confounding variables included in the analysis. Late recognition of pregnancy was not significantly associated with infant mortality.

TABLE 2. Logistic regression model predicting birth outcomes
Predictor variablesPrematuritya OR (99% CI)LBWa OR (99% CI)NICU admissiona OR (99% CI)Infant mortalitya OR (99% CI)
Adjusted OR associated with late recognition of pregnancyb1.09(1.01-1.19)c1.08(1.01-1.15)c1.12(1.03-1.21)c1.02(0.74-1.40)
Unadjusted OR associated with late recognition of pregnancyb1.22(1.14-1.32)c1.34(1.28-1.42)c1.28(1.19-1.37)c1.32(0.99-1.76)

CI, confidence interval; LBW, low birthweight; NICU, neonatal intensive care unit; OR, odds ratio.

Ayoola. Late recognition of pregnancy predicts adverse birth outcomes. Am J Obstet Gynecol 2009.

aAdjusted for multiple births, parity, marital status, level of education, previous LBW birth, previous premature birth, age of mother, race, insurance status, alcohol consumption, smoking, body mass index, and time lag between recognition and prenatal care;

bReference group: early recognition;

cP <.01.

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Comment 

Late recognition of pregnancy was significantly associated with adverse birth outcomes, including increased odds of preterm birth, LBW, and NICU admission. The associations between the time of pregnancy recognition and adverse birth outcomes might appear moderate, with odds ratios usually not deviating from unity by more than 10%. However, it is important to note that these odds ratios reflect associations after adjusting for smoking, drinking, and other variables known to be associated with adverse outcomes. Given the 6.4 million pregnancies that occur annually in the United States,24 late recognition of pregnancy is likely to account for a large number of poor birth outcomes in the United States.

More than a quarter of the women had delayed recognition of their pregnancy. Delayed recognition creates the potential for inadvertent exposure to unhealthy conditions and behaviors that could harm the fetus.1, 9, 25 Of note, approximately 3% of women at risk for pregnancy take medications that are potentially teratogenic, and others are exposed to environmental toxins.1, 9, 26, 27, 28 Late recognition of pregnancy delays discontinuation of behaviors, medications, and exposures to teratogenic substances. It also delays prenatal care, which cannot be initiated until the pregnancy is recognized. Therefore, early recognition of pregnancy provides opportunities for women to reconsider their behaviors early in pregnancy and adopt health-promoting behavior before permanent harm is done to the developing fetus,5, 6, 7, 25 even before the initiation of PNC. Adoption of health-promoting behaviors, such as taking daily multivitamins with adequate (400 μg) folic acid content, smoking cessation, abstinence from alcohol, and adequate nutrition, has been associated with better birth outcomes.1, 5, 7, 26, 27

It is not surprising that late recognition of pregnancy was associated with increased NICU utilization, because preterm births and LBW have been associated with complications that increase the risk of admission into NICU.29, 30, 31, 32 The lack of a significant association between the time of recognition of pregnancy and infant mortality may reflect the fact that infant mortality is a more general measure of pregnancy-related and postpregnancy-related mortality in the first year after birth. For example, infant mortality includes deaths related to sudden infant death syndrome, cosleeping, shaken baby syndrome, and other conditions.

The health-promotion model posits that health-promoting behavior is linked to the benefit that people expect to achieve from the behavior.33 Given the strong emotional impact of pregnancy and the maternal desire to promote fetal welfare,8 it is not surprising that pregnant women stop or reduce risky behaviors at high rates once they recognize their pregnancy.3 The timing of pregnancy recognition is likely to be a modifiable behavior. A recent randomized, controlled trial showed that women who were supplied with free home pregnancy test kits were more likely to suspect they were pregnant and more likely to test if they suspected.34 Thus, it is reasonable to consider that women at risk for pregnancy would be open to measures that promote early recognition of pregnancy.

Social cognitive theory35, 36 also provides a framework for changing the environment to influence behaviors.37 Population-based interventions could be designed to make the environment more conducive for early pregnancy recognition. This might include financial coverage for home pregnancy test kits or educational interventions designed to inform women and men about early fetal development and the importance of early recognition. Promotion of early recognition of pregnancy could be an important tool for preconceptual health programs. Ideally, interventions would be studied in clinical trial settings.

This study is the first population-based study to demonstrate the relationship between early recognition of pregnancy and important birth outcomes. It is based on a large dataset acquired over 5 years, providing a form of statistical robustness and stability. Of note, the PRAMS population includes only women with live births. Therefore, the effect of pregnancy recognition on birth outcomes could have been underestimated, because fetal deaths and stillbirths were not included.

The study is subject to some limitations. Recognition of pregnancy was a self-reported variable, which could be subject to some biases, including recall bias. As an observational study, the results can describe only associations and cannot assign causality. Future studies are needed to examine the process of recognition of pregnancy to gain a deeper understanding of the antecedent factors in pregnancy recognition. The study used a cutoff of 6 weeks to define delayed recognition, based on older conventions.3 Almost three-fourths of women in the population recognized their pregnancies within 6 weeks, which makes this an achievable goal. Although this definition is useful for analysis of large datasets, it is not meant to be used as a guideline for clinical care. Fetal development begins at conception, and women should be encouraged to recognize their pregnancies as early as possible.

In summary, delayed pregnancy recognition was associated with adverse fetal outcomes. These results provide a foundation and a rationale for future trials designed to improve the timing of recognition of pregnancy.

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Acknowledgments 

We acknowledge the suggestions and guidance provided by Larry Hembroff, Audrey Gift, Renee Canady, and Linda Spence, of Michigan State University, during the design and analysis of this study. The authors also acknowledge the support of all the PRAMS Working Groups: Alabama, Albert Woolbright, PhD; Alaska, Kathy Perham-Hester, MS, MPH; Arkansas, Gina Redford, MAP; Colorado, Alyson Shupe, PhD; Florida, Helen Marshall; Georgia, Carol Hoban, MS, MPH; Hawaii, Limin Song, MPH, CHES; Illinois, Theresa Sandidge, MA; Louisiana, Joan Wightkin; Maine, Kim Haggan; Maryland, Diana Cheng, MD; Michigan, Yasmina Bouraoui, MPH; Minnesota, Jan Jernell; Mississippi, Linda Pendleton, LMSW; Montana, JoAnn Dotson; Nebraska, Jennifer Severe-Oforah; New Jersey, Lakota Kruse, MD; New Mexico, Ssu Weng, MD, MPH; New York City, Candace Mulready, MPH; New York State, Anne Radigan-Garcia; North Carolina, Paul Buescher, PhD; North Dakota, Sandra Anseth, RN; Ohio, Amy Davis; Oklahoma, Dick Lorenz; Oregon, Ken Rosenberg, MD, MPH; Rhode Island, Sam Viner-Brown; South Carolina, Jim Ferguson, DrPH; Texas, Tanya J. Guthrie, PhD; Utah, Laurie Baksh; Vermont, Peggy Brozicevic; Washington, Linda Lohdefinck; West Virginia, Melissa Baker, MA; and the CDC PRAMS Team, Applied Sciences Branch, Division of Reproductive Health.

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 This study was supported in part by the American Nurses Foundation/Midwest Nursing Research Society, Blue Cross Blue Shield of Michigan Foundation, and Michigan State University.

 Cite this article as: Ayoola AB, Stommel M, Nettleman MD. Late recognition of pregnancy as a predictor of adverse birth outcomes. Am J Obstet Gynecol 2009;201:156.e1-6.

PII: S0002-9378(09)00505-5

doi:10.1016/j.ajog.2009.05.011

American Journal of Obstetrics & Gynecology
Volume 201, Issue 2 , Pages 156.e1-156.e6, August 2009

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