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 < 10(th) 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. RESULTS: Among 57,170 pregnancies meeting inclusion criteria, 319 (0.6%) pregnancies were complicated by stillbirth. The area under the receiver operating characteristics 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.