FETAL GROWTH AND THE ETIOLOGY OF PRETERM DELIVERY

Objective: To confirm that preterm delivery is associated with fetal g rowth restriction (FGR), and to determine if the various etiologies of preterm delivery are associated with the same degree and type of FGR. Methods: Two hundred ninety young, primarily minority gravidas who ha d routine initial ultrasound examinations also had subsequent ultrasou nd examinations at 32 weeks' gestation. Fetal growth characteristics w ere compared between preterm (less than 37 weeks' gestation) and term deliveries, and among preterm deliveries with medical or obstetric ind ications, premature rupture of membranes (PROM), and spontaneous prete rm labor. Results: Forty-six infants (15.9%) were born preterm. At 32 weeks' gestation, all fetuses later delivered preterm were already sma ller than fetuses later delivered at term (P < .05) for all dimensions : head circumference (HC), abdominal circumference (AC), biparietal di ameter (BPD), and femur length (FL). However, after stratifying by cau se of preterm delivery for those fetuses later delivered for medical o r obstetric indications, we found that only AC was decreased (P < .01) and that the HC-AC ratio was elevated (asymmetric FGR). Neonates deli vered after unsuccessfully treated PROM or preterm labor were symmetri cally smaller in all characteristics (HC, AC, BPD, and FL). Conclusion : By 32 weeks' gestation, fetuses later delivered preterm are already significantly smaller than fetuses later delivered at term. However, w hen stratified by the etiology of preterm delivery, infants delivered preterm for medical or obstetric indications had asymmetric growth pat terns, which suggests a growth failure late in pregnancy. Infants deli vered preterm after PROM or after failed or no tocolysis for spontaneo us preterm labor were proportionately smaller, implying an overall slo wing of growth that may originate early in pregnancy and possibly demo nstrate a more chronic stress.