Antenatal diagnosis of early-onset small for gestational age: absolute and relative risks of adverse outcomes.

Abstract

To determine the absolute and relative risks of adverse maternal, perinatal, and longer-term child outcomes for pregnancies with antenatally detected early-onset small for gestational age fetuses, compared with baseline population rates. We linked ultrasound data from pregnancies with antenatally detected, nonanomalous, early-onset small for gestational age fetuses (estimated fetal weight and/or abdominal circumference <10th percentile at 16+0-31+6 weeks) from our tertiary referral center with provincial health and education databases. We compared risks of adverse pregnancy (eg, stillbirth, gestational hypertension/preeclampsia, cesarean section) and child outcomes (eg, infant death, intensive care unit admission, composite neonatal morbidity, cerebral palsy, Early Development Index score, and Ministry of Education special needs designation at school entry age) among pregnancies with early-onset small for gestational age fetuses to the general population of births in British Columbia, Canada. We calculated relative risks and absolute risk differences with 95% confidence intervals. Among 581 pregnancies with nonanomalous early-onset small for gestational age fetuses, risk ratios for adverse pregnancy outcomes ranged from 4-fold higher for gestational hypertension/preeclampsia (95% confidence interval: 3.8-5.1) to 10-fold higher for stillbirth (95% confidence interval: 5.6-16.6), compared with the rest of the 359,602 nonanomalous births in the province. These relative risks corresponded to 16.5 per 100 excess cases (95% confidence interval: 13.1-19.8) and 2.2 per 100 excess cases (95% confidence interval: 0.9-3.6), respectively. Risks of neonatal complications were similarly elevated (eg, composite neonatal morbidity was 31-fold higher). While Ministry of Education special needs designation was 3-fold higher (95% confidence interval: 2.1-5.6), corresponding to 7 per 100 excess cases (95% confidence interval: 2.0-11.5), there was only a trend toward a higher risk of cerebral palsy. Risks of adverse maternal and childhood outcomes are elevated in pregnancies with early-onset small for gestational age fetuses. Presenting these risks in relative and absolute terms from baseline population risks may facilitate clinical counseling and risk comprehension.