Bariatric Surgery and Consequences for Mother and Baby in Pregnancy - II

Background Glucose metabolism in pregnancy following bariatric surgery Bariatric surgery (BS) increases fertility and decreases obesity related risks associated with pregnancy such as macrosomia, gestational diabetes mellitus (GDM), and pre-eclampsia (1, 2, 3). However, BS is also associated with alterations to the glucose metabolism (4). These alterations have been shown to be more pronounced following Roux-en-Y gastric bypass (RYGB) compared to sleeve gastrectomy (SG) given that RYGB causes more extensive modifications to the gastro-intestinal system (5). Meals are associated with an exaggerated secretion of insulin, which can cause a mismatch between glucose and insulin levels with a risk of hypoglycemia, also known as post-bariatric hypoglycemia (4, 5). On the other hand, pregnancy is accompanied by a progressively decreasing insulin sensitivity (6), which could counteract the risk of hypoglycemia. Results from the first Bariatric surgery And consequences for Mother and Baby In pregnancy (BAMBI) study showed that hypoglycemia was present in both early and late pregnancy as measured by continuous glucose monitoring (CGM) and mixed meal test (7, 8). Surprisingly, the BAMBI study revealed a two-fold increase in time spent in hyperglycemia during CGM throughout pregnancy and in the postpartum period among pregnant women with RYGB compared to BMI-matched healthy pregnant controls (7). Therefore, identification of women with GDM is important. Oral glucose tolerance testing (OGTT) is not recommended among women with bariatric surgery given the risk of hypoglycemia following the glucose load as well as the lack of validated cut-offs (9). According to our current national guideline, diagnosis of GDM in post-bariatric pregnant women is based on self-monitoring of fasting glucose and glucose 1.5 hour following meals (10). However, as shown for both non-pregnant and pregnant individuals with previous bariatric surgery, nadir glucose appears at about 1.5 hour following meals (5, 8). Thus, we might underestimate the prevalence of gestational diabetes in this population. Given the risks associated with GDM for both the mother and the offspring (11), correctly identifying women with GDM is crucial.

Please see attached figure 1, a schematic overview of different outcomes in pregnancy following bariatric surgery.

Fetal growth During the initial 12 months post-surgery, the body is in a catabolic state characterized by a significant weight loss including both lean and fat body mass (12). As of now, it is recommended to postpone conception at least 12 months after BS in order to reduce the risk of insufficient gestational weight gain (GWG) and thereby restricted fetal growth (9). Small-for-gestational age (SGA) neonates are increased in prevalence following BS (13). Insufficient GWG have been associated with an increased risk of delivering SGA neonates, yet insufficient GWG only account for about half the cases (13, 14). The BAMBI study showed a tendency towards increased time spent in hypoglycemia and decreased time in hyperglycemia among the women with RYGB delivering SGA neonates as compared to the women with RYGB delivering appropriate-for-gestational age (AGA) neonates. Additionally, women with RYGB delivering large-for-gestational (LGA) neonates spent less time in hypoglycemia and more time in hyperglycemia as compared to the women with RYGB delivering AGA neonates (8). Unfortunately, the BAMBI study lacked power to show a statistical significant difference.

In Denmark, female infertility and BMI >35kg/m2 serve as eligibility criteria for BS (15). About 40% of people having BS are women of childbearing age, both nationally and internationally (16, 17). The number of bariatric surgeries performed among women of childbearing age have been increasing since 2015, and 890 women had bariatric surgery in Denmark in 2022 (16). Therefore, studies comparing RYGB and SG are needed to guide the women to the best possible pregnancy outcome when having BS before pregnancy.

Aims