Setting

Kaiser Permanente Northern California (KPNC) is an integrated health care delivery system that provides comprehensive medical services to >3 million members located in a 14-county region in Northern California. The sociodemographic characteristics of KPNC membership closely approximate the general population ethnically and socioeconomically and represent approximately 30% of the general population in the geographic areas covered.

We used data from the KPNC GDM registry to identify women who had a pregnancy complicated by GDM from 1997 through 2006. The registry used the KPNC hospital discharge and billing claim databases to identify all live births and stillbirths and referenced the KPNC laboratory database to obtain all plasma glucose values measured during screening glucose challenge tests and diagnostic 3-hour oral glucose tolerance tests (OGTTs). We restricted our cohort to women with GDM according to National Diabetes Data Group criteria (which were used for GDM diagnosis during the study period) who delivered from Jan. 1, 1997, through Dec. 31, 2006. During the study period, 96% of all pregnant women without preexisting diabetes who delivered an infant were screened for GDM. We limited our study population to GDM women who delivered at 12 medical centers in the KPNC region that referred at least some patients during the study period. We excluded women who delivered multiple births due to their increased risk of perinatal complications. Overall, we identified 11,435 women with GDM at the 12 medical centers, of whom 44.5% were referred to the perinatal service center.

Nurse-based management program

The KPNC Regional Perinatal Service Center is a nurse-based management program for women with GDM that offers supplemental care via telephone counseling to women with high-risk pregnancies, including those complicated by GDM, for the KPNC region. The program includes a call center with 32 registered nurses and 2 registered dietitians who offer telephone counseling 7 days a week on glucose monitoring and control, diet, and physical activity. Through a 1-800 number, the nurses are available to patients 24 hours a day, 7 days a week, while the dietitians are available to patients from 8 am -8 pm 5 days a week. In addition to the care provided by obstetricians, women referred to the center receive 1-2 counseling calls per week to help them manage their blood glucose levels during pregnancy; women can initiate additional calls if needed. The center also sends a laboratory slip for postpartum glucose testing and a reminder telephone call if the screening test was not performed.

The KPNC Regional Perinatal Service Center’s GDM program was first implemented in 1997 in 2 KPNC medical centers and gradually disseminated to 12 more KPNC medical centers. By 2006, the program was implemented in all KPNC medical centers. Due to the timeline for program implementation throughout the KPNC region, there was substantial medical center–level variation in the percent of GDM patients referred to the program. This quasi-experimental design allowed us to examine the association between referral to the program and infant adverse outcomes (eg, macrosomia and low birthweight) and to measure processes such as women’s postpartum glucose testing.

Infant outcomes

Infant birthweight was obtained from the electronic medical record. Macrosomia was defined as birthweight ≥4500 g. Low birthweight was defined as an infant weighing ≤2500 g.

Postpartum screening

Postpartum screening was defined as a fasting plasma glucose (FPG) or 75-g, 2-hour OGTT performed during the postpartum period. This definition excluded testing performed during the first 7 days postpartum, since several weeks may elapse before glucose metabolism returns to normal in most women with GDM. Both the American Diabetes Association and the American Congress of Obstetricians and Gynecologists recommend that postpartum glucose screening be performed at ≥6 weeks postpartum. We considered the postpartum screening performed only if it was done during the first year after delivery.

Covariates

Age, race-ethnicity, and maternal body weight measured during the beginning of the second trimester were ascertained from the computerized medical records. Use of insulin or glyburide during pregnancy was obtained from the electronic pharmacy database. Education was obtained by linkage with the state of California birth certificate database.

Early second-trimester body weight was obtained from an electronic database that collected weights reported at the time of the alpha-feta protein test, performed between 9-20 weeks’ gestation. Because we had data on body weight but not on height, a woman was considered obese if her weight was ≥90th percentile of the weight distribution of women of her race/ethnicity in this study population.

Statistical analysis

To characterize medical center referral practices, we categorized each medical center’s proportion of referrals according to the following predefined categories: <30%, 30-70%, or >70% for each year. Subsequently a woman was classified according to the annual referral proportion of her medical center for the year she delivered. The χ ² test was used to assess differences in women’s clinical characteristics by referral level.

Using the proportion from each woman’s delivery year, we assessed the association between referral level and women’s outcomes. The associations between annual referral proportion and outcomes of interest, with control for potential confounders, were examined via hierarchical mixed effects and logistic regression, with a random facility effect to account for the nonindependence among women nested within facilities.

The medical center annual referral proportion was calculated for patients at each center and odds ratios (ORs) and 95% confidence intervals (CIs) generated for the associations between category of medical center referral proportion to nurse management (<30%, 30-70%, and >70%) and outcomes. Centers with referral proportions <30% were considered the reference group.

Models were adjusted for the following variables: maternal age (18-24, 25-34, and ≥35 years), race-ethnicity (white, African American, Asian, Hispanic, other, and missing), obesity (yes, no, and missing), education (≤high school, some college, bachelor degree, graduate degree, and missing); FPG (continuous), and time period (1997 through 2001 and 2002 through 2006). We chose to adjust for FPG out of the 4 glucose measures available from the OGTT because the FPG association with macrosomia has been shown to be stronger than the associations observed with plasma glucose levels measured at the other time points of the OGTT.

This study was approved by the human subjects committee of the Kaiser Foundation Research Institute and the California State Institutional Review Board.