Research setting

The study population was drawn from a combined membership of >650,000 at 2 regions: Kaiser Permanente Hawaii (KPH) and Kaiser Permanente Northwest (KPNW). Both regions’ memberships are ∼20% of the areas’ general populations and reflect their demographic/socioeconomic characteristics. Overall at KPH, the majority (75%) of members are non-white compared to 74% for state census. For KPNW membership, 16% overall are non-white compared to 15% in the states of Oregon and Washington. In Hawaii, low-income individuals enroll under the state health insurance plan for Medicaid, >12% of KPH population. KPNW serves ∼8% of Medicaid members through the Oregon Health Plan, a population demographically similar to the area population. All members in both regions have access to medically necessary services from Kaiser Permanente or by referral from their primary care physician.

Both regions maintain administrative and clinical electronic databases on inpatient admissions and deliveries, outpatient visits, laboratory tests, pharmacy dispenses, chronic-disease registries, and outside claims/referrals. Institutional review boards of both Kaiser Permanente regions and the State of Hawaii Department of Health approved this study.

Sample selection

Inclusion criteria were women 18 years and older, members at KPH or KPNW through their entire pregnancy, who delivered singleton live births during 1995 through 2010 (n = 73,016). Mothers with preexisting diabetes would not be eligible for GDM screening, and were excluded from analysis when known (n = 675 [1%], based on prior diabetes diagnosis in the electronic medical record (EMR) or if listed as a medical risk factor on the birth certificate), resulting in 72,341 women potentially eligible for screening. EMR data were not available to determine preexisting diabetes status in the earlier years for both regions, and for most of the study years for KPH, so it was not possible to exclude all women with preexisting diabetes by EMR diagnosis status. However, as clinicians would not order GDM screening for women with preexisting diabetes, women with preexisting diabetes would be reflected in our “untested” group. Based on US data for women of childbearing age, we estimate there were ≥1500 women with preexisting diabetes we could not identify (who would thus not be screened for GDM). Both regions universally screen for GDM, and among the 72,341 women, we had available GDM screening laboratory measurements on 64,687. Reasons for not screening include history of GDM in previous pregnancy (n = 624) and thus presumably treated directly without testing, preterm birth (n = 1313), and an estimated 1500 women with preexisting diagnosed diabetes we could not identify by EMR. The final study sample was 64,687.

Glucose testing and GDM diagnosis

Both KPH and KPNW universally screen for GDM, initially using a 50-g, 1-hour GCT. For those who failed the GCT (>140 mg/dL); a 100-g, 3-hour OGTT is performed to diagnose GDM. We stratified GDM screening by gestation (<24, 24-28, and >28 weeks); there were 4073 (6.3%) women who had repeat GDM screening (screened in 2 different gestational periods), and 62 women who had repeat GDM screening in all 3 gestational periods. Reasons for repeat GDM screening would be individualized but would include borderline screening the first time (eg, 1 of 4 positive OGTT glucose values), and/or later identification of conditions that may accompany GDM such as macrosomia, polyhydramnios, or persistent glucosuria. For women screened more than once during pregnancy, we only used 1 screening test in our analysis. We prioritized the included screening test for analysis as follows: (1) 24-28 weeks’ gestation; (2) <24 weeks’ gestation (some high-risk women have earlier screening and if positive are treated/not retested); and (3) >28 weeks’ gestation. The average gestational age of GDM screening was 27.5 weeks’ gestation ( Table 1 ).

Both the National Diabetes Data Group (NDDG) and Carpenter and Coustan (C&C) criteria for GDM diagnosis require that ≥2 of the 4 possible glucose concentrations measured with the 100-g OGTT are positive, although they have different threshold cutoffs. The NDDG require the ≥2 values to exceed these thresholds (in mg/dL): fasting ≥105 mg/dL; 1-hour ≥190 mg/dL; 2-hour ≥165 mg/dL; and 3-hour ≥145 mg/dL. The more recent C&C criteria have lower thresholds: fasting ≥95 mg/dL; 1-hour ≥180 mg/dL; 2-hour ≥155 mg/dL; and 3-hour ≥140 mg/dL. Currently, both regions use C&C criteria. However, as our evaluation began in 1995, when both regions were using NDDG criteria, we have calculated GDM using both criteria sets. Additionally, as women with a very high initial GCT (>200 mg/dL) are typically treated clinically in our practice as presumed GDM without further OGTT, we also evaluated this group separately. We stratified maternal glucose screening results into 7 mutually exclusive categories: (1) normal GCT (referent group); (2) +GCT, normal OGTT; (3) one abnormality on the OGTT by C&C criteria (1 hr, 2 hr, or 3 hr post-OGTT); (4) one abnormality on the OGTT by C&C criteria (fasting ≥95 mg/dL); (5) GDM by the lower C&C criteria but not by NDDG (≥2 abnormalities are required to diagnose GDM); (6) GDM by NDDG criteria; (7) women with a GCT >200 mg/dL (these women were not included in any OGTT category even if performed). For subgroup analyses, glucose screening was collapsed into 3 mutually exclusive categories: (1) no GDM (ranging from normal GCT to 1 abnormality on OGTT); (2) GDM by either C&C or NDDG criteria; (3) GCT >200 mg/dL.

Classification of incident gestational insulin use

ACOG recommends treatment with insulin when dietary management fails to maintain glycemic targets. Treatment for all GDM patients in both regions is by protocol: a referral to a registered dietician for dietary counseling, instruction in home blood glucose monitoring and insulin administration (if needed), weekly review of blood sugar logs with one of our GDM nurse case managers, and modifications to treatment regimens as determined by the supervising obstetrician. Regional protocols are similar, but also region specific. Both regions currently use the following whole blood (capillary) glucose target ranges to determine when medication initiation, or further titration, is needed: fasting glucose <95 mg/dL; either 1-hour postprandial <140 mg/dL or 2-hour postprandial glucose <120 mg/dL. If dietary intervention does not achieve glycemic goals (eg, ≥2 self-monitored blood glucose values exceed target range or <75% self-monitored blood glucose values in target range), GDM women in both regions receive medication treatment (insulin). Oral hypoglycemic medications are infrequently used for GDM treatment in either region. Among the 64,687 women, only a total of 99 (0.15%) women received oral hypoglycemic medications. Use was split evenly among metformin (0.08%) and sulfonylureas (0.07%). Ten women who received oral agents also received insulin. Distribution of oral hypoglycemic therapy by glucose testing group was similar to insulin therapy.

To classify incident insulin use in pregnancy, we reviewed each individual woman’s entire history of pharmaceutical dispensing of insulin in our pharmacy databases, as well as with outside claims and referrals. Women for whom their first dispense of insulin occurred during the pregnancy were classified as incident insulin users.

Classification of ethnicity and other covariates

Ethnicity classification was based on the mother’s reported race on the states’ official birth certificates. As per state algorithms for classifying race, if the mother reported being any part Native Hawaiian, ethnicity is classified as Native Hawaiian. If she did not list Native Hawaiian, but a non-Caucasian race, then we classified the woman into that group. Race was classified as white only if no other race/ethnicity was reported. Maternal age, maternal prepregnancy weight, baby gender, and baby birth-weight were recorded in the electronic medical records. State birth-certificate records were used to validate baby birth-weight and also provided mother’s reported parity and weight gain in pregnancy. Maternal prepregnancy measured weight was available in the EMR in a subsample of 27,017 women from both regions (the outpatient EMR was phased in at KPH starting in 2004 and at KPNW starting in 1995).

Statistical analyses

We conducted all statistical analyses using the SAS Statistical Analysis System version 9.2 (SAS Institute, Cary, NC).

We conducted all initial analyses for KPH and KPNW separately and overall. We used Pearson χ ² and Fisher exact tests to compare incident insulin use between glucose levels. We tested increasing need for insulin treatment based on GDM screening category using the Mantel-Haenszel test for trend. All the statistical tests that we report are 2-sided; the term statistically significant implies a P value < .05.

Incident insulin use during pregnancy, based on maternal GCT and OGTT results

Table 2 presents the prevalence of incident insulin use during pregnancy based on maternal GDM screening results for each region separately, and combined. Consistent with a greater prevalence of high-risk racial groups for GDM in Hawaii, the overall prevalence of GDM (by C&C criteria) was 6% in Hawaii and 4.4% in the KPNW region. Moreover, the overall need for insulin use among all pregnant women was double in Hawaii vs KPNW (2.97% vs 1.25%, P < .001).

In both regions, women with only 1 of 4 abnormal values on OGTT (ie, not diagnostic for GDM), were >4 times as likely to need insulin if the fasting plasma glucose was ≥95 mg/dL, compared to an isolated postprandial (1-, 2-, or 3-hour OGTT) abnormality ( P < .0001) ( Table 2 ). For diagnosed GDM (≥2 of 4 glucose values [fasting, 1 hour, 2 hour, 3 hour] positive on OGTT), women who met NDDG-GDM criteria were more than twice as likely to need insulin compared to the “mild” GDM by C&C criteria alone (odds ratio [OR], 2.8; 95% confidence interval [CI], 2.3–3.4). Notably, women with an initial GCT >200 mg/dL were the highest-risk group for needed incident insulin use during pregnancy, with a rate that was >3 times greater than women with any diagnosed GDM (OR, 3.7; 95% CI, 3.1–4.4). Overall in both regions, 50% of women with a GCT >200 mg/dL required insulin treatment during their pregnancy ( Table 2 ).

Sensitivity analyses in subgroups

There are several risk factors for GDM, including obesity, race/ethnicity, and obstetrical history. We found that women who were obese or overweight had a much higher rate for needing insulin treatment than women with normal prepregnancy weight ( Table 3 ). The population in general has become more obese, and we also found a small cohort effect of increased incident insulin for GDM in more recent years ( Table 3 ). There were 610 women screened who had a known history of GDM in prior pregnancies from the EMR; the rate of insulin treatment in the current pregnancy was 35% with a history of GDM by either C&C or NDDG criteria. Moreover, women with GDM by C&C criteria in a previous pregnancy were more likely to have more severe GDM (ie, meet NDDG criteria vs C&C criteria in the current pregnancy; P < .0001).

Table 3

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. How best to diagnose and treat the small-for-gestational-age fetus
2. Maternal preeclampsia and bone mineral density of the adult offspring
3. Supplement to September 2012 (vol. 207, no. 3, page S63)
4. Functional and anatomic comparison of 2 versus 3 suture placement for uterosacral ligament suspension: a cadaver study

Stay updated, free articles. Join our Telegram channel

Join