Effects of Dexamethasone on Offspring Survival and Intrauterine Growth Restriction

The placenta is the primary organ responsible for deactivating maternal glucocorticoids and reducing fetal exposure. Glucocorticoid use during pregnancy is a common treatment for asthma, allergies, and COVID-19. Several studies have reported adverse effects including intrauterine growth restriction as a result of glucocorticoid exposure, yet little is known about the mechanisms by which short and long-term maternal glucocorticoid exposures affect placental biology and fetal development. To better understand the role of glucocorticoids on placental and fetal outcomes, we used a mouse model exposed to the synthetic glucocorticoid, dexamethasone (Dex), prior to and throughout gestation. We conducted a randomized controlled trial in mice with a treatment arm of Dex exposure and water exposure as control. Virgin C57Bl/6J female mice were single-housed at 11 weeks of age, and Dex was introduced in the drinking water as a 1mg/kg/day dose. After one week of treatment, mice were bred with age-matched virgin males. Dam body composition, food, and water intake were monitored weekly. Maternal insulin sensitivity, pup survival rate, litter size, and pup birth weight at postnatal day (PND) 0.5 were also assessed. Dams treated with Dex lost significant lean mass after one week of treatment. Dex treatment did not appear to affect the dams’ ability to get pregnant, as both groups carried pups to term with similar lengths of gestation (p=0.838). Water and Dex-treated dams gained comparable weight during the first and second trimesters of pregnancy, however, the Dex group gained less lean mass than the water group during the third trimester. At PND0.5, Dex dams had fewer pups with a 40% reduction in litter size (p=0.01) and lighter pups with a 37% reduction in offspring weight (p<0.001), indicating substantial intrauterine growth restriction. All pups of Dex-treated dams died by PND1. Attempts to rescue pups of Dex-dams by cross-fostering with water-treated nursing dams or by feeding the pups 10% glucose at PND0.5 failed by PND1. These results demonstrate a novel finding regarding the chronic use of glucocorticoids before and during conception and pregnancy. The reduction in both pup weight and late-pregnancy maternal weight gain suggests potential growth restriction or placental insufficiency. Further molecular studies during multiple time points of gestation will help elucidate the mechanisms at play.