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

Abstract

OBJECTIVE 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. STUDY DESIGN We linked ultrasound data from pregnancies with antenatally-detected, non-anomalous, early-onset SGA fetuses (estimated fetal weight and/or abdominal circumference <10th percentile at 16+0 to 31+6 weeks) from our tertiary referral centre with provincial health and education databases. We compared risks of adverse pregnancy (e.g., stillbirth, gestational hypertension/ preeclampsia, caesarean section) and child outcomes (e.g., 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 SGA fetuses to the general population of births in British Columbia, Canada. We calculated relative risks and absolute risk differences with 95% confidence intervals (CI). RESULTS Among 581 pregnancies with non-anomalous early-onset SGA fetuses, risk ratios for adverse pregnancy outcomes ranged from 4-fold higher for gestational hypertension/ preeclampsia [95% CI: 3.8 to 5.1], to 10-fold higher for stillbirth [95% CI: 5.6 to 16.6], compared with the rest of the 359,602 non-anomalous births in the province. These relative risks corresponded to 16.5 per 100 excess cases [95% CI: 13.1 to 19.8] and 2.2 per 100 excess cases [95% CI 0.9 to 3.6], respectively. Risks of neonatal complications were similarly elevated (e.g. composite neonatal morbidity was 31-fold higher). While Ministry Special Needs designation was 3-fold higher [95% CI: 2.1 to 5.6], corresponding to 7 per 100 excess cases [95% CI: 2.0-11.5], there was only a trend towards a higher risk of cerebral palsy. CONCLUSION Risks of adverse maternal and childhood outcomes are elevated in pregnancies with early-onset SGA fetuses. Presenting these risks in relative and absolute terms from baseline population risks may facilitate clinical counselling and risk comprehension.