Normal ranges of the fetal weight determined by ultrasound in the population of the Hospital das Clínicas of the Faculdade de Medicina da Universidade de São Paulo

Objective

This study aimed to determine the normal range of fetal weight by ultrasound in pregnant women followed at the Obstetric Clinic of the Hospital das Clínicas of the Faculty of Medicine, University of São Paulo.

Methods

This retrospective cohort study included singleton pregnant women without associated maternal diseases, at 15–41 weeks of gestation, who underwent their last ultrasound up to 7 days before birth. Fetal parameters analyzed for the normal range were biparietal diameter, femur length, head and abdominal circumference. 3rd, 10th, 50th, 90th, and 97th weight percentiles were determined for each gestational age. Newborns were classified by birth weight as Small (SGA), Appropriate (AGA), or Large (LGA) for gestational age.

Results

Among 837 women admitted without maternal diseases, 136 were included and 379 examinations performed at 15–41 weeks of gestation. Multiple linear regression models were generated to develop the normal range of fetal weight. Three equations were selected, and six normal ranges were created considering the total population and stratified by fetal sex. Weight estimates were calculated for the 3rd, 10th, 50th, 90th, and 97th percentiles for each gestational age. Among the 136 newborns, 107 (78.7 %) were classified as AGA, 23 (16.9 %) as SGA, and 6 (4.4 %) as LGA.

Conclusion

The normal range of the fetal weight determined by ultrasound in this population showed a good correlation with gestational age, enabling the fetal weight gain pattern evaluation. The equation based on four parameters, including days before birth, presented the lowest percentage error variation to estimate the normal range.