First trimester 3D volumetry. Association of the gestational volumes with the birth weight.

Objective: To evaluate the three dimensional ultrasound (3D) in the volume assessment of the gestational contents during the 1st trimester of pregnancy. Our aim was to correlate the embryo, gestational sac, and placenta volume with the birth weight. To monitor the increase of these volumes according to the gestational age.

Method: Prospective study of 199 singleton low risk pregnant women undergoing the 1st trimester ultrasound for fetal anomalies. In these women, gestational volumetry was performed and it was compared with the crown-rump length (CRL). Regression models were computed in order to analyze the dependence of birth weight with the volumes.

Results: The embryo volume reveals the strongest association with the birth weight at delivery (β = 0.24), followed by the CRL (β = 0.20) and the gestational sac volume (β = 0.20). The placenta volume appears the weakest association with fetal weight at delivery (β = 0.16). All volumes increased significantly from 11(+0)-11(+6) to 13(+0)-13(+6) weeks of gestation (p < 0.001). Ten cubic millimeter increase in embryo volume corresponds to a mean birth weight increase of 75 g, while 1 mm increase in the CRL corresponds to a birth weight increase of 113 g.

Conclusion: Our results provide evidence that the embryo volume during the first trimester of pregnancy correlates better with birth weight than the CRL. This might assist in the identification of the high risk pregnancies caring macrosomic and low birth weight fetuses.