Gestational weight gain, bariatric surgery, and adverse maternal and infant outcomes

Abstract

Gestational weight gain is a crucial predictor for various adverse maternal and infant outcomes. In 2009, the U.S. Institute of Medicine (IOM) introduced optimal ranges for gestational weight gain based on a woman's pre-pregnancy BMI. Since then, the IOM recommended guidelines for gestational weight gain have found widespread application in both clinical practice and research. Despite this, their calculation of recommended weight gain relies on traditional methods, and these conventional approaches have inherent limitations. Specifically, gestational weight gain is calculated by subtracting pre-pregnancy weight from the woman’s weight before delivery, overlooking the influence of gestational duration on the potential for gaining weight. For instance, a woman delivering preterm (at week 30) will have less time to gain weight, compared to a woman delivering her infant at full term (40 weeks), which would produce a biased association between low gestational weight gain and the risk of preterm birth.

Gestational weight gain z-scores are a method that addresses the impact of gestational duration on gestational weight gain by standardizing weight gain according to gestational age. While early-pregnancy body mass index (BMI) specific z-score charts have been established for Swedish pregnant women, using these charts to determine optimal ranges for gestational weight gain remains unexplored. Currently, there is limited research on the relationship between gestational weight gain z-scores and adverse pregnancy outcomes, both generally as well as among women who have undergone bariatric surgery. This thesis explores the association between gestational weight gain z-scores and adverse pregnancy outcomes, both generally as well as specifically among women who have undergone bariatric surgery, providing evidence to contribute to determining optimal ranges of gestational weight gain z-scores.

The first study in this thesis is a cohort study comprising singleton pregnancies (n=174,953) that explored the association between gestational weight gain z-scores and various delivery outcomes in each early-pregnancy BMI weight status group. For women with a normal weight, overweight, or obese weight status at the start of pregnancy, increased gestational weight gain was associated with an elevated risk of cesarean section, induction of labor, and postpartum hemorrhage. Low weight gain reduced the risk of cesarean delivery among all early-pregnancy BMI weight status categories, except for underweight.

The second study in this thesis is a cohort study comprising singleton pregnancies (n=131,164) that investigated the association between gestational weight gain z-scores - in early pregnancy and before diagnosis - and gestational diabetes. With the exception of women with an obese class III weight status at the start of pregnancy, high gestational weight gain before diagnosis was associated with an increased risk of gestational diabetes. Additionally, for women with an extremely obese status (obese class III) at the start of pregnancy, low gestational weight gain before diagnosis was associated with a reduced risk of gestational diabetes. In women with an overweight status at the start of pregnancy, high gestational weight gain in early pregnancy was associated with an increased risk of gestational diabetes. Meanwhile, in women with an obese weight status (obese I, II, and III) at the start of pregnancy, low weight gain in early pregnancy was associated with a reduced risk gestational diabetes.

The third study in this thesis is a matched cohort study comprising singleton pregnancies with a history of bariatric surgery (n=6388) and without (n=6388). The study compared gestational weight gain between women with and without a history of bariatric surgery and investigated whether gestational weight gain differed by surgical procedure, surgery-to conception interval, and/or surgery-to-conception weight loss. Women with a history of bariatric surgery had lower gestational weight gain than matched controls with similar early pregnancy characteristics. While gestational weight gain was lower in women with a shorter surgery-to-conception interval or lower surgery-to-conception weight loss, it did not differ by surgical procedure.

The fourth study in this thesis is a cohort study comprising singleton pregnancies with a history of gastric bypass (n=8284) investigating predictors, including gestational weight gain, of delivering a small-for-gestational-age (SGA) infant after gastric bypass surgery, among both nulliparous and parous women, separately. Low gestational weight gain and smoking were both associated with an increased risk of SGA, while having an overweight/obese weight status at the start of pregnancy or high gestational weight gain was associated with a decreased risk of SGA.

Overall, the findings from this thesis indicate that excessive gestational weight gain is associated with an increased risk of cesarean section, induction of labor, postpartum hemorrhage and gestational diabetes in women starting pregnancy with a normal weight, overweight, or obese weight status. In these same women, inadequate gestational weight gain is associated with a reduced risk of cesarean section. Additionally, inadequate gestational weight is associated with a reduced risk of gestational diabetes only among women with an obese class III weight status. In women with a history of bariatric surgery, gestational weight gain is lower than for women who have not undergone this surgery, and increased gestational weight gain is associated with a decreased risk of delivering an SGA infant. However, to determine the optimal gestational weight gain range, further studies are required to investigate the association between gestational weight gain and long-term outcomes.