Differential Effects of Maternal and Fetal Betamethasone Injections in Late-Gestation Fetal Sheep

OBJECTIVE: To determine the effects of single or repeated intramuscular injections of betamethasone, given maternally or directly to the fetus, on chronically catheterized, late-gestation fetal sheep. METHODS: Fetal or maternal sheep received either repeated intramuscular injections of betamethasone (0.5 mg/kg body weight at 104, 111, and 118 days'gestation), single betamethasone injection (at 104 days ' gestation, followed by saline at 111 and 118 days ' gestation), or repeated saline injections; n = 6 or 7 per group. At approximately 130 days ' gestationfetuses were catheterizedfor serial measurements of heart rate, arterial pressure, blood gases, metabolites, and electrolytes. RESULTS: Repeated maternal betamethasone injections reduced birth weight (P =.03) without fetal hypoxemia or hypoglycemia. Circulating fetal calcium and lactate concentrations were reduced (P =.002 and P =.014, respectively) by repeated maternal betamethasone only. Fetal hematocrit tended to be lower afterfetal (P =.3) and maternal (P =.07) betamethasone. CONCLUSION: Growth restriction caused by repeated maternal betamethasone treatments is not due to overt chronic placental insufficiency but may be caused by alterations in hormonal mediators offetal growth or impairment of placental transport of specific nutrients. (J Soc Gynecol Investig 2003;10:474-9) Copyright 2003 by the Societyfor Gynecologic Investigation. KEY WORDS: Antenatal corticosteroids, intrauterine growth restriction, placenta. single course of antenatal corticosteroids for fetal mat-uration before preterm birth is supported by a great deal of evidence regarding the safety and efficacy of this therapy. 12 In recent years, treatment ofwomen who have recurring or persisting risk of preterm birth with repeated courses of antenatal corticosteroids became common (Planer B, Ballard R, Ballard P, et al. Use of antenatal corticosteroid