SWIFT: Study of Women, Infant Feeding and Type 2 Diabetes After GDM Pregnancy

The SWIFT study recruited women during pregnancy, and enrolled 1,035 women diagnosed with GDM who delivered a singleton, live born infant of at least 35 weeks gestation at a Kaiser Permanente Northern California hospital from 2008 to 2011, and met other study eligibility criteria. Women with recent GDM consented to three in-person research exams with the first exam at 6-9 weeks postpartum (study baseline) and the two follow up research exams continuing annually thereafter for two years post-baseline. SWIFT participants continued to be followed for clinical diagnoses of diabetes via the KPNC electronic health record system during the subsequent years through present. The study enrollment of participants began in late 2008 and ended in December 2011, and in-person follow up exams through 2014. The SWIFT cohort is racially and ethnically diverse (75% minority) with 35% Asian (1/3 South Asian, 1/3 Southeast Asian, 1/3 Chinese), 9% Black, 31% Hispanic, 23% White, and 2% mixed race/Native groups, and includes a longitudinal research Biobank, and research datasets, and clinical electronic health record data for diagnoses of diabetes and other clinical measures.

Each woman provided written informed consent for three in-person exams involving administration of the 2-hour 75 gram Oral Glucose Tolerance Test (OGTT) to reclassify glucose tolerance in women following GDM pregnancy, and numerous other research assessments. At baseline, 21 women were classified with overt diabetes and excluded from follow up, 2 women dropped out at baseline, and 2 women were ineligible. There were 1,010 women with recent GDM and no diabetes at baseline who were followed to evaluate the primary study outcome, the progression to glucose intolerance during the two year follow up period, defined as incident diabetes by American Diabetes Association (ADA) criteria from the 2-hour 75 gram OGTT glucose values, and/or clinical medical diagnosis of diabetes. The annual study follow up exams during the 2 years post-baseline occurred from 2009-2014. The study cohort continues in ongoing follow up for progression to diabetes and subsequent pregnancies via laboratory testing from the Kaiser Permanente electronic health records through present (72% remain KPNC health plan members). A 4th in person research exam is enrolling SWIFT participants in 2022-2024,

The primary exposure for the study is lactation intensity and duration assessed quantitatively using the method by Piper et al. 2001 to estimate a continuous lactation intensity and duration score up to 12 months postpartum. The study assessed infant feeding prospectively from prenatal telephone contacts to assess breastfeeding intention via a standardized method, inpatient hospital delivery records, participant infant feeding diaries, telephone contacts at 1 month postpartum, self-administered monthly mailed surveys (from 3 to 11 months postpartum), and from surveys at the three in-person annual study exams. Data collection during and after pregnancy was also obtained from electronic health records related to perinatal course (e.g., laboratory diagnosis of GDM phenotype severity: 3-hr OGTT z-score and GDM treatment, gestational age at GDM diagnosis, maternal pre-pregnancy BMI, gestational weight gain), medical history, prenatal measures, subsequent pregnancies, and the maternal and newborn outcomes.

Subsequent studies of metabolites preceding progression to overt diabetes after gestational diabetes pregnancy are underway. Investigations are ongoing to measure changes in metabolomics, proteomics and lipidomics at the baseline and follow up exams.

At each of three study exams, trained research staff assessed maternal characteristics (infant feeding, sociodemographics, medical and reproductive history, subsequent pregnancies, medication use, recurrence of GDM, physical activity, dietary intake, depression, and sleep habits/disorders), as well as breastfeeding intensity and duration, infant health, and complementary infant dietary intake using self- and interviewer-administered questionnaires. Trained research staff measured participant anthropometry and body composition via bioelectrical impedance assessment according to standardized research protocols, as well as collected, processed, and stored biospecimens from 2-hour 75 g OGTTs (fasting and 2-h plasma and buffy coat), and administered questionnaires at each in-person exam.