Pancreas Size and Fat Content Increase during Pregnancy and Correlate with Glycemic Control

The pancreas plays a critical role in adapting to the increased metabolic demands and insulin resistance of pregnancy. In rodents, beta cell proliferation during pregnancy induces pancreas growth, but whether similar changes occur in the human pancreas remains unknown. This study characterizes longitudinal changes in the size and composition of the pancreas during pregnancy and postpartum, and examines correlations with breastfeeding, adiposity, and metabolic assays.Sixty-one pregnant women were followed up to three visits during pregnancy (15, 25, and 35 weeks) and three postpartum (6 weeks, 6 months, and 12 months). MRI was conducted to assess pancreas, spleen, and kidney size as well as pancreas, liver, and whole-body adiposity. Glucose tolerance testing was performed at 24 to 28 weeks' gestation. In a subset of participants (<i>n</i> = 58), additional glucose assays were performed at 15 weeks' gestation. Pancreas size was normalized for concurrently measured body weight to calculate pancreas volume index (PVI).The size of the pancreas increased by approximately 20% from 15 to 35 weeks' gestation (<i>p</i> < 0.001) and declined postpartum. PVI was positively correlated with whole-body fat mass (<i>R</i> ² = 0.12) and fasting blood glucose (<i>R</i> ² = 0.18) at 15 weeks' gestation. Higher pancreas fat content at 15 weeks predicted impaired response to glucose challenge 10 weeks later (<i>R</i> ² = 0.33). PVI was low, and pancreatic fat was high at 15 weeks in two participants who were subsequently diagnosed with gestational diabetes mellitus. Any breastfeeding 1-year postpartum correlated with a smaller decline in PVI from 35 weeks' gestation to 1-year postpartum (<i>p</i> < 0.05).Pancreas size and fat content change dynamically during pregnancy and postpartum, and correlate with glucose levels, prenatal adiposity, and breastfeeding. · The pancreas adapts to the metabolic demands of pregnancy by increasing in size and shrinking postpartum.. · Small pancreas size and high pancreas fat content early in pregnancy may predict subsequent abnormal glucose tolerance.. · Breastfeeding 1-year postpartum was associated with a smaller decline in pancreas size compared to those who were not breastfeeding..