Materials and Methods
This was a secondary analysis of the randomized trial in 10,154 nulliparous women who received vitamin C and E or placebo daily from 9-16 weeks' gestation until delivery; the trial was conducted at the 16 clinical centers that were members of the
Eunice Kennedy Shriver National Institute of Child Health and Human Developmental Maternal-Fetal Medicine Units Network between 2003 and 2008. Full details of the study design and technique of data collection have been described previously.
8- Roberts J.M.
- Myatt L.
- Spong C.Y.
- et al.
Vitamins C and E to prevent adverse outcomes with pregnancy associated hypertension.
Women who were included in the trial had blood samples that were collected at randomization, at 24 and 32 weeks' gestation, and at admission for delivery. Information about whether the women fasted for ≥12 hours (even though they were not specifically instructed to fast for any of these visits) was collected. Women were included in this secondary analysis if they had a blood sample that had been collected from 22-26 weeks’ gestation and had fasted for ≥12 hours before the blood collection. The study was approved by the Institutional Review Boards of each clinical site and the data coordinating center.
The diagnosis of hypertension was based on blood-pressure measurements that had been obtained during or after the 20th week of pregnancy, excluding intraoperative blood pressures and intrapartum systolic pressures. Severe pregnancy-associated hypertension was defined as a systolic pressure of ≥160 mm Hg or a diastolic pressure of ≥110 mm Hg on 2 occasions 2-240 hours apart or a single blood-pressure measurement that was severely elevated that led to treatment with an antihypertensive medication. Mild pregnancy-associated hypertension was defined as a systolic pressure of 140-159 mm Hg or a diastolic pressure of 90-109 mm Hg on 2 occasions 2-240 hours apart. Mild preeclampsia was defined as mild pregnancy-associated hypertension with documentation of proteinuria within 72 hours before or after an elevated blood-pressure measurement. Proteinuria was defined as total protein excretion of ≥300 mg in a 24-hour urine sample or ≥2+ on dipstick testing or a protein-to-creatinine ratio of ≥0.35 if a 24-hour urine sample was not available. Severe preeclampsia was defined as preeclampsia with either severe pregnancy-associated hypertension or protein excretion of ≥5 g in a 24-hour urine sample or as mild pregnancy-associated hypertension with oliguria (<500 mL in a 24-hour urine sample), pulmonary edema (confirmed by radiography), or thrombocytopenia (platelet count of <100,000 per cubic millimeter). Preeclampsia included mild and severe preeclampsia, HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome, and eclampsia. To determine the diagnosis of preeclampsia, deidentified medical charts of all women with pregnancy-associated hypertension were reviewed centrally by at least 3 reviewers.
Determination of insulin resistance
Insulin resistance was calculated from fasting maternal plasma glucose and insulin concentrations that had been obtained between 22 and 26 weeks' gestation. Insulin resistance was calculated with the use of the surrogate indices of homeostasis model assessment of insulin resistance (HOMA-IR) and also the quantitative insulin sensitivity check index (QUICKI).
9- Matthews D.R.
- Hosker J.P.
- Rudenski A.S.
- Naylor B.A.
- Treacher D.F.
- Turner R.C.
Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man.
, 10- Katz A.
- Nambi S.S.
- Mather K.
- et al.
Quantitative insulin sensitivity check index: a simple, accurate method for assessing insulin sensitivity in humans.
Surrogate indirect indices describe glucose-insulin homeostasis by empiric nonlinear equations. The intent of the empiric equations is to accommodate glucose ranges, to ensure reduced suppression of hepatic glucose production, and to allow the use of total insulin assays. The equations for the indirect indices are:
The surrogate indices impute a dynamic beta-cell function (insulin as stimulated by maternal glucose) from fasting steady state data.
11- Muniyappa R.
- Lee S.
- Chen H.
- Quon M.J.
Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage.
Insulin and glucose assays were performed at the Metabolism Core Laboratory at the University of Alabama at Birmingham. Glucose was measured on an automated spectrophotometric chemistry analyzer (Sirrus; Stanbio Laboratory, Boerne, TX) with a glucose-oxidase method. The intraassay coefficient of variation was 1.21%; the interassay coefficient of variation was 3.065%. Insulin was measured on a bench-top immunoassay analyzer (Tosoh Bioscience, San Francisco, CA) with a 2-site immunoenzymatic assay. The intraassay coefficient of variation was 4.42%; the interassay coefficient of variation was 1.49%.
Statistical analysis
Insulin resistance was evaluated across body mass index categories with the Cochran-Armitage test for trend. Other categoric variables were compared with the use of the χ2 test. Percentiles for each week of gestation were determined for insulin, glucose, HOMA-IR, and QUICKI with the use of the data from the women from this cohort who were normotensive and nonproteinuric. For each marker (insulin, glucose, HOMA-IR, QUICKI), the Breslow-Day test for homogeneity was used to determine whether there was a difference in the effect of body mass index among women who were Hispanic, African American, white, or other. Multivariable logistic regression analysis was used to calculate odds ratios and included race or ethnic group, body mass index, and blood pressure at study entry (9-16 weeks' gestational age), treatment group (vitamins, placebo), and gestational age at sampling. For all statistical tests, a nominal probability value of < .05 was considered to indicate statistical significance; no adjustments were made for multiple comparisons. Analyses were performed using SAS software (SAS Institute Inc, Cary, NC).
Results
A total of 10,154 women were assigned randomly in the parent trial; outcome data were available for 9969 women. Although 68% of these women had a study sample available between 22-26 weeks' gestation, only 1187 women (12%) had a ≥12-hour fasting sample available for analysis. Population characteristics of women with and without fasting samples are detailed in
Table 1. Body mass index was measured at study entry (9-16 weeks gestation). Fasting samples were available for 14.2% of the white women, 10.3% of the African American women, and 10.0% of the Hispanic women. Although there were statistically significant differences in maternal age, education level, and diastolic blood pressure, these differences were small and not clinically meaningful. Of the 1187 women who were included in this secondary analysis, 22% were African American, 26% were Hispanic and 52% white or other. Fifty-two percent of the women were under or normal weight, and 48% of the women were overweight or obese.
TABLE 1Population characteristics of women with and without fasting insulin and glucose measured from 22-26 weeks' gestation
Hauth. Insulin resistance and preeclampsia. Am J Obstet Gynecol 2011.
Insulin and glucose levels did not differ by whether women were in the vitamin- or placebo-treated group. The 75th percentile for insulin, glucose, and HOMA-IR results and the 25th percentile for QUICKI were chosen after other cutoffs were considered; the greatest significance was achieved with these percentiles. The frequency of glucose, insulin, and HOMA-IR results at ≥75th percentile and QUICKI levels at <25th percentile significantly increased with increasing body mass index (trend,
P < .0001). At midtrimester, obese women were approximately 2 times more likely than normal weight women to have a fasting glucose, insulin, and HOMA-IR results of ≥75th percentile and QUICKI level of <25th percentile (
Table 2).
TABLE 2Maternal body mass index and fasting glucose and insulin levels and insulin resistance at midgestation HOMA-IR, homeostasis model assessment of insulin resistance; QUICKI, quantitative insulin sensitivity check index.
Hauth. Insulin resistance and preeclampsia. Am J Obstet Gynecol 2011.
Hispanic women had a higher percentage of glucose, insulin, and HOMA-IR of ≥75th percentile and QUICKI level <25th percentile, compared with African American and white women (
P < .001;
Table 3). Compared with white women, African American women had a higher percentage of insulin and HOMA-IR results of ≥75th percentile and QUICKI level of <25th percentile (
P < .001,
Table 3) but not glucose of ≥75th percentile (
P = .86;
Table 3). There was a significant interaction between race and body mass index (under/normal weight, overweight/obese) for glucose, insulin and HOMA-IR level of ≥75th percentile and QUICKI of <25th percentile. Among the 568 overweight or obese women, 48% of the Hispanic women, 34% of the African American women, and 28% of the white women had a HOMA-IR result of ≥75th percentile.
TABLE 3Maternal race/ethnicity and fasting glucose and insulin levels and insulin resistance at midgestation
HOMA-IR, homeostasis model assessment of insulin resistance; QUICKI, quantitative insulin sensitivity check index.
Hauth. Insulin resistance and preeclampsia. Am J Obstet Gynecol 2011.
As expected, the 44 women (3.7%) in the cohort with gestational diabetes mellitus were significantly more likely to have glucose and HOMA-IR results of ≥75th percentile and QUICKI results of <25th percentile than women without gestational diabetes mellitus (glucose, 59% vs 26% [P < .0001]; HOMA-IR, 43% vs 25% [P = .007]; QUICKI 43% vs 25% [P = .007]). Although the women with gestational diabetes mellitus were more likely to have an insulin level of ≥75th percentile compared with nondiabetic women, this was not statistically significant (39% vs 25%; P = .05).
In the overall cohort, 85 women experienced preeclampsia; 592 women remained normotensive and nonproteinuric, and 510 women had an elevated blood pressure or proteinuria, but not preeclampsia. Only 8 of the 85 women who had preeclampsia had gestational diabetes mellitus. Fasting maternal glucose, insulin, and HOMA-IR results of ≥75th percentile and QUICKI results of <25th percentile were significantly more likely among those who subsequently had preeclampsia, compared with women who remained normotensive and nonproteinuric (
P < .05;
Table 4). A HOMA-IR result of ≥75th percentile had a sensitivity of 40% and specificity of 75% for subsequent preeclampsia, with a positive predictive value of 19% and a negative predictive value of 90% (values for the QUICKI analyses were identical to the HOMA-IR). Multivariable analyses confirmed midtrimester fasting insulin and HOMA-IR results of ≥75th percentile and QUICKI results of <25th percentile to be associated significantly with preeclampsia, compared with women with no hypertension or proteinuria (
Table 4). The 510 women with an elevated blood pressure or proteinuria level were similar to the normotensive, nonproteinuric women in regard to a HOMA-IR result of ≥75th percentile or QUICKI of <25th percentile (24% vs 25%;
P = .8).
TABLE 4Midgestation fasting glucose, insulin, insulin resistance, and subsequent preeclampsia
HOMA-IR, homeostasis model assessment of insulin resistance; QUICKI, quantitative insulin sensitivity check index.
Hauth. Insulin resistance and preeclampsia. Am J Obstet Gynecol 2011.
Comment
After the data were controlled for body mass index, race, ethnicity, treatment group, enrollment blood pressure, and gestational age at sampling, midtrimester fasting HOMA-IR results of ≥75th percentile and QUICKI of <25th percentile remain significant risk factors for subsequent preeclampsia. In low-risk nulliparous women, increasing body mass index and Hispanic/African American ethnicity/race were associated significantly with HOMA-IR result of ≥75th percentile and QUICKI of <25th percentile between 22 and 26 weeks gestation.
Insulin resistance describes a decreased sensitivity to insulin in regard to glucose disposal and to the inhibition of hepatic glucose production. The gold standard for direct testing of insulin resistance is by euglycemic glucose clamp testing.
12- DeFronzo R.A.
- Tobin J.D.
- Andres R.
Glucose clamp technique: a method for quantifying insulin secretion and resistance.
Direct testing is time consuming, labor intense, and expensive, requires an experienced operator, and is not feasible for epidemiologic studies, large clinical trials, or routine clinical use. We used 2 indirect surrogates in this analysis, the HOMA-IR and QUICKI methods. These indirect indices are dependent on a required fasting basal state (≥12 hours), glucose in the normal range, and the assumption that insulin levels are stable and that hepatic glucose production is constant. Glucose homeostasis is a feedback loop that involves hepatic glucose production and insulin secretion from beta cells.
9- Matthews D.R.
- Hosker J.P.
- Rudenski A.S.
- Naylor B.A.
- Treacher D.F.
- Turner R.C.
Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man.
The HOMA-IR and QUICKI methods describe the glucose-insulin homeostasis loop by empiric nonlinear equations. They accommodate glucose ranges, ensure reduced suppression of hepatic glucose production, allow the use of total insulin assays, and impute a dynamic beta cell function (insulin stimulated by glucose) from fasting steady-state data.
10- Katz A.
- Nambi S.S.
- Mather K.
- et al.
Quantitative insulin sensitivity check index: a simple, accurate method for assessing insulin sensitivity in humans.
, 11- Muniyappa R.
- Lee S.
- Chen H.
- Quon M.J.
Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage.
In nonpregnant women, HOMA-IR and QUICKI results have a reasonable linear correlation with direct evaluation that uses the glucose clamp to assess insulin sensitivity/resistance.
11- Muniyappa R.
- Lee S.
- Chen H.
- Quon M.J.
Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage.
, 13Insulin sensitivity and its measurement: structural commonalities among the methods.
, 14- Wallace T.M.
- Levy J.C.
- Matthews D.R.
Use and abuse of HOMA modeling.
We are not aware of any reports that have compared the glucose clamp with the HOMA-IR or QUICKI method in pregnant women.
The use of indirect indices of insulin resistance may not be generalizable from a single testing facility because of the lack of a standardized insulin assay.
15- Staten M.A.
- Stern M.P.
- Miller W.G.
- Steffes M.W.
- Campbell S.E.
Insulin Standardization Workgroup
Insulin assay standardization: leading to measure of insulin sensitivity and secretion for practical clinical care.
, 16- Marcovina S.
- Bowsher R.R.
- Miller W.G.
- et al.
Standardization of insulin immunoassays: report of the American Diabetes Association Workgroup.
, 17- Manley S.E.
- Luzio S.D.
- Stratton I.M.
- Wallace T.M.
- Clark P.M.
Preanalytical, analytical, and computational factors affect homeostasis model assessment estimates.
, 18- Manley S.E.
- Stratton E.M.
- Clark P.M.
- Luzio S.D.
Comparison of 11 human insulin assays: implications for clinical investigation and research.
Thus, cutoff points for insulin resistance require development of the 75th percentile HOMA-IR and the 25th percentile for QUICKI at each testing facility. It is also important to note that population differences may have an effect on the usefulness of surrogate indices to reflect insulin resistance. Alvarez et al
19- Alvarez J.A.
- Bush N.C.
- Hunter G.R.
- Brock D.W.
- Gower B.A.
Ethnicity and weight status affect the accuracy of proxy indices of insulin sensitivity.
found that surrogate indices may be more accurate in African American vs white American women and more accurate in overweight vs normal weight adults.
Parretti et al
20- Parretti E.
- Lapolla A.
- Dalfrà M.
- et al.
Preeclampsia in lean normotensive normotolerant pregnant women can be predicted by simple insulin sensitivity indexes.
assessed insulin sensitivity in 829 pregnant women at 16-20 and 26-30 weeks gestation. Their HOMA-IR and QUICKI insulin sensitivity analysis results were similar and, at 16-20 weeks’ gestation, had a sensitivity of 79-85% to predict subsequent preeclampsia, with a specificity of 97% for both analyses. Our data confirm a significant relationship with a HOMA-IR result of ≥75th percentile and QUICKI level of <25th percentile at 22 to 26 weeks gestation with subsequent preeclampsia, although with a lower sensitivity of 40% and specificity of 75%. The higher sensitivity and specificity of the report of Parretti et al may relate to their more homogeneous population (Italian women of white race), their exclusion of women with gestational diabetes mellitus, their selection of women with a body mass index of between 19 and 25 kg/m,
or to their method of calculation of the 75-100 percentile (HOMA-IR) or the 0-25 percentile (QUICKI) quartiles. In our report, race, ethnicity, and maternal weight significantly increased the percentage of women whose HOMA-IR result was ≥75th percentile and whose QUICKI result was <25th percentile. Sierra-Laguado et al
21- Sierra-Laguado J.
- Garcia R.G.
- Celedón J.
- et al.
Determination of insulin resistance using the homeostatic model assessment (HOMA) and its relation with the risk of developing pregnancy-induced hypertension.
have also reported that midtrimester log-HOMA analysis was associated significantly with subsequent preeclampsia. Within their cohort of 572 normotensive pregnant women at a gestational age of <30 weeks, the 18 women who experienced preeclampsia had a higher log-HOMA result than did 72 control subjects who were matched by body mass index and gestational and maternal age at enrollment.
Roberts and Gammill
22Insulin resistance in preeclampsia.
have emphasized the importance of controlling for maternal weight and for insulin resistance testing before the clinical appearance of preeclampsia. Parretti et al
20- Parretti E.
- Lapolla A.
- Dalfrà M.
- et al.
Preeclampsia in lean normotensive normotolerant pregnant women can be predicted by simple insulin sensitivity indexes.
enrolled lean pregnant women, and Sierra-Laguado et al
21- Sierra-Laguado J.
- Garcia R.G.
- Celedón J.
- et al.
Determination of insulin resistance using the homeostatic model assessment (HOMA) and its relation with the risk of developing pregnancy-induced hypertension.
matched the women for maternal weight. Pregnant women in both reports were assessed early in pregnancy before clinically evident preeclampsia had occurred. We also determined fasting glucose and insulin concentrations before clinically evident preeclampsia (22-26 weeks' gestation), and our analyses controlled for maternal weight and other potential risk factors for preeclampsia. Roberts and Gammill
22Insulin resistance in preeclampsia.
concluded that, even if the midtrimester HOMA-IR result is only 20% predictive of subsequent preeclampsia, the result would be similar to the “gold standard” of uterine artery Doppler imaging (also 20%) which would entail more complex and costly assessment of risk.
23- Papageorghious A.T.
- Yu C.K.
- Nicolaides K.H.
The role of uterine artery Doppler in predicting adverse pregnancy outcome.
In summary, maternal midtrimester insulin resistance increased significantly (HOMA-IR result of ≥75th percentile or QUICKI result of <25th percentile) with increasing body mass index among Hispanic and African American women. Midtrimester maternal insulin resistance is associated with a significantly increased risk of subsequent preeclampsia.
Acknowledgments
We thank the following Subcommittee members: Sabine Bousleiman, RNC, MSN, MPH, and Margaret Cotroneo, RN, protocol development and coordination between clinical research centers; Elizabeth Thom, PhD, protocol/data management and statistical analysis, and Gail D. Pearson, MD, ScD, protocol development and oversight.
The following individuals comprise the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network: D.J. Rouse, A. Northen, P. Files, J. Grant, M. Wallace, K. Bailey (University of Alabama at Birmingham, Birmingham, AL); S. Caritis, T. Kamon, M. Cotroneo, D. Fischer (University of Pittsburgh, Pittsburgh, PA);P. Reed, S. Quinn (LDS Hospital), V. Morby (McKay-Dee Hospital), F. Porter (LDS Hospital),> R. Silver, J. Miller (Utah Valley Regional Medical Center), K. Hill (University of Utah, Salt Lake City, UT); S. Bousleiman, R. Alcon, K. Saravia, F. Loffredo, A. Bayless (Christiana), C. Perez (St. Peter's University Hospital), M. Lake (St. Peter's University Hospital), M. Talucci (Columbia University, New York, NY); K. Boggess, K. Dorman, J. Mitchell, K. Clark, S. Timlin (University of North Carolina at Chapel Hill, Chapel Hill, NC); J. Bailit, C. Milluzzi, W. Dalton, C. Brezine, D. Bazzo (Case Western Reserve University-MetroHealth Medical Center, Cleveland, OH); J. Sheffield, L. Moseley, M. Santillan, K. Buentipo, J. Price, L. Sherman, C. Melton, Y. Gloria-McCutchen, B. Espino (University of Texas Southwestern Medical Center, Dallas, TX); M. Dinsmoor (Evanston NorthShore), T. Matson-Manning, G. Mallett (Northwestern University, Chicago, IL); S. Blackwell, K. Cannon, S. Lege-Humbert, Z. Spears (University of Texas Health Science Center at Houston, Houston, TX); J. Tillinghast, M. Seebeck (Brown University, Providence, RI); J. Iams, F. Johnson, S. Fyffe, C. Latimer, S. Frantz, S. Wylie (The Ohio State University, Columbus, OH); M. Talucci, M. Hoffman (Christiana), J. Benson (Christiana), Z. Reid, C. Tocci (Drexel University, Philadelphia, PA); M. Harper, P. Meis, M. Swain (Wake Forest University Health Sciences, Winston-Salem, NC); W. Smith, L. Davis, E. Lairson, S. Butcher, S. Maxwell, D. Fisher (Oregon Health & Science University, Portland, OR); J. Moss, B. Stratton, G. Hankins, J. Brandon, C. Nelson-Becker, G. Olson, L. Pacheco (University of Texas Medical Branch, Galveston, TX); G. Norman, S. Blackwell, P. Lockhart, D. Driscoll, M. Dombrowski (Wayne State University, Detroit, MI); E. Thom, T. Boekhoudt, L. Leuchtenburg (The George Washington University Biostatistics Center, Washington, DC); G. Pearson, V. Pemberton, J. Cutler, W. Barouch (National Heart, Lung, and Blood Institute, Bethesda, MD); S. Tolivaisa (Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD).
Article Info
Publication History
Accepted:
February 3,
2011
Received in revised form:
January 14,
2011
Received:
December 9,
2010
Footnotes
The other members of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network are listed in this full-length article.
The racing flag logo above indicates that this article was rushed to press for the benefit of the scientific community.
Supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) ( HD34208 , HD27869 , HD40485 , HD40560 , HD40544 , HD34116 , HD40512 , HD21410 , HD40545 , HD40500 , HD27915 , HD34136 , HD27860 , HD53118 , HD53097 , HD27917 , and HD36801 ), the National Heart, Lung, and Blood Institute , and the National Center for Research Resources ( M01 RR00080 , UL1 RR024989 ). The University of Alabama at Birmingham, Metabolism Core Laboratory is supported by the Nutrition Obesity Research Center (NORC, P30-DK56336 ), Diabetes Research and Training Center (DRTC, P60DK079626 ), and Center for Clinical and Translational Science (CCTS, UL1RR025777 ).
The contents of this article do not necessarily represent the official view of the National Institute of Child Health and Human Development, the National Heart, Lung, and Blood Institute, the National Center for Research Resources, or the National Institutes of Health.
Cite this article as: Hauth JC, Clifton RG, Roberts JM, et al. Maternal insulin resistance and preeclampsia. Am J Obstet Gynecol 2011;204:327.e1-6.
Copyright
© 2011 Mosby, Inc. Published by Elsevier Inc. All rights reserved.