The predictive value of first trimester fetal volume measurements, a prospective cohort study

Objectives: To determine if fetal volume (FV) measurements with three-dimensional ultrasound in the first trimester of pregnancy can detect the fetus at risk for preterm birth and/or low birth weight. Methods: In this prospective cohort study, 538 participants were included during the routine first trimester ultrasound examination. Volume measurements were performed with VOCAL (9 degrees). Firstly, the relation between FV and gestational age for a set of participants with normal pregnancies (training set), was assessed using multiple linear regression analysis, which was then used to determine the expected normal values. Secondly, for a new set of participants with normal pregnancies and a set of participants with complicated pregnancies (preterm birth and/or low birth weight), i.e. the validation set, the observed fetal volumes (FVobserved) were compared with their expected normal values (FVexpected) and expressed as a percentage of the expected normal value. The difference in mean percentage was then assessed with independent-samples t-test. Finally, logistic regression analysis was applied to the validation set to analyze the ability to predict the pregnancy outcome with Pi calculation. Results: Linear regression analysis of FV as a predictor of preterm birth and/or low birth weight did not result in significant (p = 0.630 and 0.290, respectively) or clinical relevant results (standardized effect sizes of 0.061 and 0.179, respectively). The predicting quality was also very low (AUC = 0.508 and 0.545 respectively). Conclusions: Fetal volume measurements in the first trimester of pregnancy are not useful as a prognostic tool for predicting pregnancies of high risk for preterm birth or a low birth weight.