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OP33.04: Prediction of birth weight using 3D ultrasound measurement of fetal thigh volume

was analyzed. Birth weight was standardized for gestational age (z-score) and a multivariate regression analysis was performed to determine the relation between z-score as dependent variable and BMI, GWG, maternal age, infant sex, parity, educational status, smoking, hemorrhage, hypertensive syndrome of pregnancy and gestational diabetes, as independent variables. Results: Mean preconceptional BMI was 25.7 ± 5.2 Kg. Mean GWG was 14.5 ± 7.1 Kg. BMI was positively correlated to birth weight zscore and was associated with LGA and cesarean section. GWG was also positively correlated to birth weight z-score. Pregestational BMI (0,08), GWG (0,04), infant sex (0,31) and hypertensive syndrome of pregnancy (−0.29) explained 13.2% of birth weight Z-score. Maternal age did not contribute to the model. Parity, educational status, smoking, hemorrhage and gestational diabetes, were not related to birth weight in this model. Conclusions: Birth weight was mainly determined by infant sex and pregestational BMI. In the population studied, pregestational BMI had a stronger influence than GWG. Overweight and obese women should be careful of their GWG, but should be even more attentive to weight before conception. This is important as it is the only modifiable factor. This data does not allow concluding a specific BMI or GWG to decrease perinatal mortality, since only the effect on weight birth was studied.