Growth restricting effects of a single course of antenatal betamethasone treatment and the role of human placental lactogen

Betamethasone (BET) is a widely used treatment for women who are at high risk of preterm delivery. In sheep, BET-induced growth restriction was found to be associated with reduced placenta lactogen (PL), a key regulator of fetal growth. We therefore hypothesized that also in humans a single course of BET administration is associated with a reduction of PL, associated with a deceleration in fetal growth. Objective To investigate effects of a single course of antenatal BET in humans on birth weight and PL. Methods Women exposed to BET (2 × 12 mg; n = 44) with normally grown fetuses between 23 + 5 and 34 + 0 wks (weeks + days of gestation) who delivered between 23 + 5 to 42 + 0 wks were compared to gestational age-matched controls ( n = 49). Maternal gestational blood samples were obtained before, during and after BET treatment and at the time of birth. Main outcome measures BET effects on fetal anthropometrics, placental morphometry and placental PL-protein and maternal plasma levels. Results The mean duration of days between BET administration and birth was 52 days. BET treatment was associated with decreased birth weight (−18.2%), head circumference (−8.6%), body length (−6.0%), and placental width (−5.5%), as compared to controls. These changes were irrespective of possible maternal confounders (gestational age at birth, maternal age, maternal BMI gain during pregnancy, smoking etc.). However, neither PL-plasma levels within 48 h after BET treatment nor placental PL-protein levels and maternal plasma levels at birth were changed after BET treatment. In central regions of the placenta, BET treatment increased the circumference of syncytiotrophoblast nuclei by +4.7% and nucleus surface area by +9.4% compared to controls, but these changes were not related to placental PL-protein or maternal PL-plasma levels at birth. Conclusion A single course of BET treatment was accompanied with reduced fetal growth, but this growth restricting effect was not associated with altered placental or maternal plasma PL levels. Altered expression of PL appears not to be causal for BET-induced fetal growth restriction in the human.