Impairment of growth in fetuses destined to deliver preterm

OBJECTIVE: The objective of this study was to test the hypothesis that fetu ses destined to deliver preterm do not reach their individual growth potent ial. STUDY DESIGN: In a case control design, data on 44 preterm deliveries at le ss than or equal to 34 weeks were compared with data on a control group of next consecutive term deliveries. Criteria for inclusion were dating by ult rasonography at < 20 weeks and no medical or obstetric complications. For e ach fetus, GROW v.2 software was used to generate an Individual optimal gro wth curve and to calculate the percentile of achieved growth potential for birth weight based on 6 independent factors (maternal weight, height, parit y, ethnicity, fetal sex, and gestational age) identified as determining fet al weight from multivariate logistic regression analysis of 40,000 uncompli cated term pregnancies. Birth weight percentiles based on standard norms we re also calculated for each fetus. RESULTS: The number of fetuses with birth weight below the 5th, 10th, and 2 5th percentile of their growth potential was significantly higher in the pr eterm group (10, 13, and 18) compared with that in the control group (2, 2, and 6; P < .008, P < .001, and P < .008, respectively). There were no sign ificant differences in variables defining growth potential between the case and control groups; The number of fetuses below the 5th and 10th percentil e based on standard birth weight norms was not significantly different betw een preterm and term pregnancies (3 vs 1 and 5 vs 2; P = .37 and P = .27). Among preterm deliveries, those preceded by preterm premature rupture of th e membranes had significantly fewer fetuses > 75th percentile of their grow th potential (2 vs 8; P = .025). Fetuses with lower gestational ages at pre term delivery achieved lower median percentiles of their growth potential. CONCLUSION: A significant proportion of fetuses destined to deliver preterm do not reach their individual growth potential compared with those deliver ed at term. This finding challenges our concept of preterm delivery and man agement strategy aimed at tocolysis.