Date Published: August 1, 2017
Publisher: Public Library of Science
Author(s): L. M. Sorbye, R. Skjaerven, K. Klungsoyr, N. H. Morken, Ronald C. W. Ma
Abstract: BackgroundBeing overweight is an important risk factor for Gestational Diabetes Mellitus (GDM), but the underlying mechanisms are not understood. Weight change between pregnancies has been suggested to be an independent mechanism behind GDM. We assessed the risk for GDM in second pregnancy by change in Body Mass Index (BMI) from first to second pregnancy and whether BMI and gestational weight gain modified the risk.Methods and findingsIn this observational cohort, we included 24,198 mothers and their 2 first pregnancies in data from the Medical Birth Registry of Norway (2006–2014). Weight change, defined as prepregnant BMI in second pregnancy minus prepregnant BMI in first pregnancy, was divided into 6 categories by units BMI (kilo/square meter). Relative risk (RR) estimates were obtained by general linear models for the binary family and adjusted for maternal age at second delivery, country of birth, education, smoking in pregnancy, interpregnancy interval, and year of second birth. Analyses were stratified by BMI (first pregnancy) and gestational weight gain (second pregnancy). Compared to women with stable BMI (−1 to 1), women who gained weight between pregnancies had higher risk of GDM—gaining 1 to 2 units: adjusted RR 2.0 (95% CI 1.5 to 2.7), 2 to 4 units: RR 2.6 (2.0 to 3.5), and ≥4 units: RR 5.4 (4.0 to 7.4). Risk increased significantly both for women with BMI below and above 25 at first pregnancy, although it increased more for the former group. A limitation in our study was the limited data on BMI in 2 pregnancies.ConclusionsThe risk of GDM increased with increasing weight gain from first to second pregnancy, and more strongly among women with BMI < 25 in first pregnancy. Our results suggest weight change as a metabolic mechanism behind the increased risk of GDM, thus weight change should be acknowledged as an independent factor for screening GDM in clinical guidelines. Promoting healthy weight from preconception through the postpartum period should be a target.
Partial Text: Worldwide, overweight has reached epidemic proportions [1, 2], with serious consequences for reproductive health. Being overweight during pregnancy increases the risk of complications in pregnancy, in childbirth, and for the newborn child [3–7] and is an important risk factor for Gestational Diabetes Mellitus (GDM) [8–11]. GDM is defined as glucose intolerance of various degrees that is first detected during pregnancy , and the prevalence of GDM has increased, with variation by countries [11, 13–15]. GDM increases the risk of immediate adverse pregnancy and infant outcomes  and, in the long term, the risk of metabolic syndrome and Type 2 Diabetes Mellitus in the mothers [17–19]. Children born to GDM mothers have an increased risk of high birthweight and being overweight in adolescence .
A total of 24,198 mothers were included in the main analysis. Of these, 12,078 (50%) women had information on gestational weight gain (GWG) in their second pregnancy and were included in the analysis evaluating effect modification by GWG. Population characteristics by GDM in second pregnancy are shown in Table 1.
Women who increased their weight by ≥1 BMI unit from first to second pregnancy had increased risk of GDM in the second pregnancy compared to women with stable weight (−1 to <1 BMI unit change). This applied to women with prepregnant BMI below and above 25 in the first pregnancy; however, the strongest association was found in women with BMI < 25. We found a preventive effect on GDM in overweight women (first pregnancy) who reduced their weight by ≥2 BMI units until the second pregnancy. Our results support a metabolic mechanism behind the increased risk of GDM, represented by the weight change itself. Source: http://doi.org/10.1371/journal.pmed.1002367