Neurodevelopmental impacts of betamethasone administered in the late preterm period: An experimental study in CD-1 mice

The safety of antenatal corticosteroid administration during the late preterm period is currently questioned. This experimental study conducted in a CD-1 mouse model aimed to determine if exposure to betamethasone in the late preterm period 1) induces behavioral changes in adulthood and 2) alters cerebral anatomy. In the prenatal group, four gravid mice were randomly assigned to receive 0.1 mg of betamethasone (around 1.82 mg/kg based on an average body weight of 55 g) or an equivalent volume of phosphate buffered saline (PBS) on gestation day 18, and yielded a total of 43 pups. This model was selected to test the impact of cumulative exposure to exogenous and endogenous steroids. In the postnatal group, six gravid mice yielded a total of 69 pups which were randomly assigned to receive betamethasone or PBS. Pups in the intervention group received 0.03 mg of betamethasone subcutaneously on postnatal day 5, at which time mouse brain development is equivalent to that of humans at 34–36 weeks' gestation. To evaluate objective 1, pups were subjected to behavioral tests on postnatal days 21–50. On postnatal day 60, structural magnetic resonance imaging (MRI) was performed to assess objective 2. Outcomes were compared between treatment groups using linear mixed models including random effects for litter and a fixed term for the interaction of treatment and sex. We used a statistical significance threshold of p < 0.05. Male mice exposed to betamethasone ante- or postnatally engaged in more social contact than those exposed to PBS (interaction of betamethasone and male sex: prenatal β = 0.09, 95 % CI (0.02, 0.17), p = 0.02; postnatal β = 0.08, 95 %CI (0.01, 0.14), p = 0.03), while female mice engaged in less social contact. MRI showed that male mice exposed to betamethasone prenatally had larger habenulas and smaller amygdala than those exposed to PBS (interaction of betamethasone and male sex: habenula β = 0.01, 95 %CI (0.004, 0.02), p = 0.01, amygdala β = −1.43, 95 %CI (−2.67, −0.21), p = 0.03), while female mice had larger amygdala and smaller habenulas. Postnatal exposure to betamethasone was associated with lower combined volume of the parietal cortex and hypothalamus (interaction of betamethasone and male sex: β = −0.32, 95 %CI (−0.58, −0.03), p = 0.04). No other significant differences in behavioral outcomes or brain volumes were identified. These results suggest that exposure to betamethasone in the late preterm period is associated with small but significant sex-specific disruptions of the limbic system, associated with social behavior disturbances.