Stillbirth and the small fetus: use of a sex-specific versus a non-sex-specific growth standard

OBJECTIVE: To determine if the use of a sex-specific standard to define small-for-gestational age (SGA) will improve prediction of stillbirth. STUDY DESIGN: We performed a retrospective cohort study of singleton pregnancies excluding anomalies, aneuploidy, undocumented fetal sex or birthweight. SGA was defined as birthweight < 10th percentile by the non-sex-specific and sex-specific Alexander standards. The association between SGA and stillbirth using these standards was assessed using logistic regression. RESULT: Among 57 170 pregnancies meeting inclusion criteria, 319 (0.6%) pregnancies were complicated by stillbirth. The area under the receiver operating characteristic curve for the prediction of stillbirth was greater for the sex-specific compared to the non-sex-specific standard (0.83 vs 0.72, P < 0.001). CONCLUSION: Our findings suggest adoption of a sex-specific standard for diagnosis of SGA as it is more discriminative in identifying the SGA fetus at risk for stillbirth.