Significance and Outcomes of Fetal Growth Restriction Below the 5th Percentile Compared to the 5th to 10th Percentiles on Midgestation Growth Ultrasonography

Objective: To determine whether there are differences in neonatal and pregnancy outcomes in pregnancies complicated by severe fetal growth restriction, defined as estimated fetal weight below the 5th percentile, compared with estimated fetal weight in the 5th to 10th percentiles at midgestation.

Methods: We conducted a retrospective review of singleton nonanomalous gestations with estimated fetal weight at or below the 10th percentile (Hadlock et al. Radiology 1991; 181:129-133) at 18 to 24 weeks' gestation. The cohort was divided into fetuses with estimated fetal weight below the 5th percentile and estimated fetal weight in the 5th to 10th percentiles. Antenatal and neonatal outcomes were compared across the groups.

Results: Of the 254 growth-restricted fetuses, 91 had estimated fetal weight below the 5th percentile, and 163 were in the 5th to 10th percentiles. Fetuses below the 5th percentile were 2.82 times more likely to be born small for gestational age compared to fetuses at the 5th to 10th percentiles (P = .001). Fetuses with estimated fetal weight below the 5th percentile had higher rates of hypertensive disorders of pregnancy (relative risk [RR], 1.79; P = .04), abnormal umbilical artery Doppler waveforms (RR, 6.27; P = .01), labor induction (RR, 1.45; P = .002), neonatal intensive care unit admission (RR, 1.73; P = .02), and Apgar scores of less than 7 at 1 minute (RR, 2.05; P = .04).

Conclusions: Severely growth-restricted fetuses with an estimated fetal weight below the 5th percentile at 18 to 24 weeks are born smaller and have worse antepartum and neonatal outcomes than those with an estimated fetal weight in the 5th to 10th percentiles. These findings suggest that severely growth-restricted fetuses at midgestation should be treated and counseled differently than those in the 5th to 10th percentiles.