Reference range of birth weight with gestation and first-trimester prediction of small-for-gestation neonates.

OBJECTIVE Firstly, to establish a reference range of birth weight with gestation at delivery; secondly, to identify maternal characteristics that are significantly associated with birth weight; and thirdly, to determine if combinations of maternal characteristics, fetal nuchal translucency thickness (NT), and serum concentrations of free beta-human chorionic gonadotrophin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A) are significant predictors of small-for-gestational-age (SGA) neonates in the absence of preeclampsia. METHOD Maternal characteristics were recorded; fetal NT, maternal serum free β-hCG and PAPP-A were measured at 11 weeks to 13 weeks 6 days in 33,602 women with singleton pregnancies. Regression analysis was used to determine the association of birth weight with gestation at delivery and to establish a reference range with gestation. Logistic regression analysis was used to determine if maternal factors, fetal NT, free β-hCG, and PAPP-A contribute significantly in predicting SGA in the absence of preeclampsia. RESULTS Birth weight increased with maternal weight and height; it was higher in parous than in nulliparous women and in those with a medical history of pre-pregnancy diabetes mellitus, and it was lower in cigarette smokers, in all racial groups other than in Caucasian women, and in those with a medical history of chronic hypertension and in those who previously delivered SGA neonates. In the SGA group compared with the unaffected group, there were lower median delta NT (0.10 vs 0.12 mm), free β-hCG [0.9 vs 1.0 MoM (multiples of median)], and PAPP-A (0.8 vs 1.0 MoM). The prediction of SGA provided by maternal factors was significantly improved by the addition of fetal NT and PAPP-A (34.0 vs 37.0% at a false-positive rate of 10%). CONCLUSION Prediction of the birth of SGA neonates in the absence of preeclampsia can be provided in the first trimester of pregnancy by a combination of maternal characteristics and measurements of parameters used in early screening for aneuploidies.