Between April 1, 1996 and May 31, 2010, 33,179 women were screened for GDM and thus met initial study inclusion criteria. A total of 1082 women were diagnosed by NDDG criteria, and 1542 would be diagnosed by CC criteria. This represents a 42.5% increase in GDM diagnoses, from 3.3% (1082/33,179) to 4.6% (1542/33,179), using the more inclusive criteria. On average, an additional 33 women would be diagnosed with GDM per year in our cohort.
Of the 33,179 women screened, 5454 screened positive for GDM based on a 50g, 1-hour glucose load ≥140 mg/dL and were neither diagnosed with GDM based solely on this result nor excluded based on established criteria. Eighty-five percent (4659/5454) underwent a diagnostic 100 g, 3-hour OGTT and had results available in our database to confirm or exclude GDM diagnosis (). Those who were otherwise eligible but did not have a 3-hr OGTT result (795/5454, 15%) were more likely to be Caucasian (40% vs. 36%) or African-American (18% vs. 12%) and less likely to be Hispanic (37% vs. 45%) (p<0.001). These women had median 1-hour glucose load values of 150 mg/dL [144-162], comparable to the negative OGTT study group (153 mg/dL [145-163]) and lower than those of the CC only group (158mg/dL [149-173]) and the NDDG group (169mg/dL [155-188]). As a sensitivity analysis, we included these 795 women in the negative OGTT group, but the magnitude and statistical significance of the associations between study group and the perinatal outcomes did not change.
Flow diagram of inclusion and exclusion criteria for three study groups (CC only, NDDG, and negative OGTT) of women eligible for gestational diabetes (GDM) screening
Of the 4659 women who had a 3-hour OGTT, 23% (1082/4659) were diagnosed with and treated for GDM by NDDG criteria, comprising the NDDG group. An additional 10% (460/4659) would have been diagnosed by CC criteria, the CC only group. The 67% who screened positive (3117/4659) but were not diagnosed by either criteria comprised the negative OGTT group (). Maternal characteristics of the three groups are shown in . The CC only group had median 1-hour glucose screening results (158 mg/dL [149-173]) lower than the NDDG group (169 mg/dL [155-188], p<0.001) and higher than the negative OGTT group (153 mg/dL [145-163], p<0.001) ().
Maternal characteristics by study group: Carpenter-Coustan (CC only) vs. National Diabetes Data Group (NDDG) and Carpenter-Coustan (CC only) vs. negative oral glucose tolerance test (negative OGTT)
As shown in , in unadjusted analysis, the CC only group was more likely to develop gestational hypertension and pre-eclampsia than either the NDDG or negative OGTT study groups. The CC only group was also more likely to deliver by cesarean section and less likely to have a normal spontaneous vaginal delivery than the negative OGTT group.
Bivariate analysis of perinatal outcomes: Carpenter-Coustan (CC only) vs. National Diabetes Data Group (NDDG) and Carpenter-Coustan (CC only) vs. negative oral glucose tolerance test (negative OGTT)
Two continuous variables, birthweight and gestational age at delivery, are represented in . At statistically similar gestational ages at delivery, infants born to CC only women weighed statistically more than infants born to negative OGTT women (3483 g vs. 3387 g, p<0.05). Compared to infants born to NDDG women, those born to CC only women were also born at a statistically greater gestational age (39.3 weeks vs. 39.0 weeks, p<0.001) with a statistically greater birthweight (3483 g vs. 3360 g, p=0.005).
Inset of weeks 38 to 40 to show relationship between gestational age at delivery and birthweight for the three study groups with symbols placed at the median gestational age at delivery.
In multivariable regression models, adjusted and unadjusted models did not differ in statistical significance or overall precision when each potential covariate assessed in bivariate analysis was considered. Only results of adjusted models are reported, controlling for parity, maternal delivery age over 35, ethnicity, and delivery year. Models evaluating cesarean and operative deliveries also controlled for prior cesarean delivery.
Compared to the NDDG group, women in the CC only group were more likely to have hypertensive disorders of pregnancy including gestational hypertension (aPR 1.54, 95% CI 1.01 – 2.37) and pre-eclampsia (aPR 1.70, 95% CI 1.23 – 2.35). Compared to the negative OGTT group, women in the CC only group were at greater risk of both gestational hypertension (aPR 1.48, 95% CI 1.02 – 2.13) and pre-eclampsia (aPR 1.47, 95% CI 1.02 – 2.13), as they were in comparison to the NDDG group. The CC only group was more likely to have a cesarean delivery (aPR 1.16, 95% 1.04 – 1.30), and their infants were more likely to have macrosomia >4000g (aPR 1.25, 95% CI 1.01 – 1.56). ().
Adjusted prevalence ratios (aPR) comparing women diagnosed with GDM by: Carpenter-Coustan (CC only) vs. National Diabetes Data Group (NDDG) and Carpenter-Coustan (CC only) vs. negative oral glucose tolerance test (negative OGTT)
Women in the CC only group were equally likely to have an infant admitted to the NICU as those in each of the other two groups in unadjusted bivariate analysis. Infants of CC only women with a NICU admission, however, were less likely to stay in the NICU for over 48 hours than infants of women in the NDDG group (43% vs. 56%, p=0.017) (). In adjusted models, there were no significant differences in NICU admission or length of stay > 48 hours among the three groups ().
Body mass index (BMI) and gestational weight gain have been included in the UNC Perinatal Database for the past 2 years and were available for 325 women. We conducted a sensitivity analysis to evaluate the impact of these missing data on this subset of women, including and excluding BMI from our models. The significant differences or similarities for each perinatal outcome were not altered by inclusion of BMI.