Fetal biometric parameters: Reference charts for a non-selected risk population from Uberaba, Brazil

OBJECTIVE To establish reference charts for fetal biometric parameters in a non-selected risk population from Uberaba, Southeast of Brazil. METHODS A retrospective cross-sectional study was performed among 5656 non-selected risk singleton pregnant women between 14 and 41 weeks of gestation. The ultrasound exams were performed during routine visits of second and third trimesters. Biparietal diameter (BPD) was measured at the level of the thalami and cavum septi pellucidi. Head circumference (HC) was calculated by the following formula: HC = 1.62*(BPD + occipital frontal diameter, OFD). Abdominal circumference (AC) was measured using the following formula: AC = (anteroposterior diameter + transverse abdominal diameter) × 1.57. Femur diaphysis length (FDL) was obtained in the longest axis of femur without including the distal femoral epiphysis. The estimated fetal weight (EFW) was obtained by the Hadlock formula. Polynomial regressions were performed to obtain the best-fit model for each fetal biometric parameter as the function of gestational age (GA). RESULTS The mean, standard deviations (SD), minimum and maximum of BPD (cm), HC (cm), AC (cm), FDL (cm) and EFW (g) were 6.9 ± 1.9 (2.3 - 10.5), 24.51 ± 6.61 (9.1 - 36.4), 22.8 ± 7.3 (7.5 - 41.1), 4.9 ± 1.6 (1.2 - 8.1) and 1365 ± 1019 (103 - 4777), respectively. Second-degree polynomial regressions between the evaluated parameters and GA resulted in the following formulas: BPD = -4.044 + 0.540 × GA - 0.0049 × GA2 (R2 = 0.97); HC= -15.420 + 2.024 GA - 0.0199 × GA2 (R2 = 0.98); AC = -9.579 + 1.329 × GA - 0.0055 × GA2 (R2 = 0.97); FDL = -3.778 + 0.416 × GA - 0.0035 × GA2 (R2 = 0.98) and EFW = 916 - 123 × GA + 4.70 × GA2 (R2 = 0.96); respectively. CONCLUSION Reference charts for the fetal biometric parameters in a non-selected risk population from Uberaba, Southeast of Brazil, were established.