A simple regression model for estimating gestational age in later pregnancy by ultrasonography

Three hundred and six antenatal women with confirmed LMP underwent a single real time ultrasonographic examination between 32-40 weeks of gestation. Four parameters viz. BPD, HL, FL and AP having a positive correlation with gestational age were studied. A multiple regression model for predicting gestational age by a single ultrasonographic examination was developed by forward selection method after eliminating multicollinearity; as a high degree of intercorrelation was found between FL and HL, HL was eliminated from the data. The BPD does not have a significant role in predicting gestational age in later pregnancy. The proposed regression equation with FL and AP predicts gestational age 75% of time within +/- 10 days of 95% confidence limit.