Background: Estimating neonatal birthweight (NBW) is an essential part of labor management. Most rural hospitals in Thailand use symphysis-fundal height (SFH) to predict NBW, but the possibility of maternal and neonatal morbidities associated with incorrectly estimated extreme NBW remains a major problem.
Objective: To identify a formula for predicting NBW using maternal physical parameters in singleton pregnancies prior to
delivery.
Material and Method: A cross-sectional study was performed of three hundred and ten singleton pregnant women who were assessed for maternal physical parameters during the 7-day period prior to delivery by a single researcher (Manovit. S). Pregnant women with non-vertex presentation, intrauterine death, or major structural or abnormal chromosomal fetuses were excluded. Parameters which were significantly related to NBW were evaluated using regression equations and formulae were constructed for predicting NBW.
Results: Five maternal physical parameters were significantly related to NBW: body weight (BW), height (Ht), symphysisfundal
height (SFH), back-fundal height (BFH), and transverse abdominal diameter (TAD). The most accurate formula in the present study was found to be EFW = (-21,062.57) + (0.97 x gestational age (weeks)2) + (-0.06 x body weight (kg)2) + (242.11 x height (cm)) + (-0.73 x height (cm)2) + (39.13 x back-fundal height (cm)) +(0.94 x symphysis-fundal height (cm)2) + (19.68 x transverse abdominal diameter (cm)). This formula showed a correlation of 0.674, absolute percentage error of 7.26% (SD, 5.71), 90.3% prediction within 15% of NBW, area under ROC curve of 0.90 for prediction of NBW >3,500 grams, sensitivity of 87.0% and specificity of 90.5% at a cutoff value of 3,226 grams.
Conclusion: This study proposes a novel formula for the prediction of NBW which might be very useful in evaluating parturients with large fetus in primary health care or low-resource settings.

Keywords: Neonatal birthweight, Maternal physical parameters, Symphysis-fundal height, Back-fundal height, Transverse abdominal diameter