Estimation of foetal weight in third trimester using thigh measurements

Estimation of foetal weight is essential in daily obstetric practice particularly close to term. It guides clinicians to finalize important obstetrical decisions. Low birth weight and excessive foetal weight at delivery both are associated with an increased risk of neonatal complications during labour and the puerperium. The objectives of this cross sectional study were to estimate the foetal weight using only two thigh parameters and its comparison with birth weight. This study was conducted in Radiology Department PNS Shifa during 1st June, 2007 to 30 Nov, 2007.

All pregnant females coming to Radiology Department for Ultrasound examinations in 3rd trimester were the Subjects of study. All infants were delivered with in 48 hour of ultrasound examination. 100 patients were included in this study. Thigh measurements were made by conventional two-dimensional ultrasonography. The Isobe formula was compared with already established Aoki's formula and actual birth weight using paired sample t-test.

Isobe's formula showed a significant correlation with the actual birth weight. In 90% of cases estimated foetal weight was within 10% of the actual birth weight.

The Isobe's formula was found to be convenient among all the established formulas for estimated foetal body weight. Measurement of head circumference was not necessary near term.