Three-dimensional sonographic volumetry of the placenta and the fetus between weeks 15 and 17 of gestation

Abstract

Objectives: Three-dimensional sonographic volume measurement enables for the first time direct comparison of the increase in size of different but closely interacting structures like the placenta and fetus. Our aim was to calculate the fetal and placental volumes between weeks 15 and 17 of gestation, to monitor the difference in the increase of the fetal and placental sizes and to determine their mutual relationship.

Methods: Fetal and placental sonographic volume measurements were made in 356 singleton pregnancies. To measure the relationship between fetal and placental volumes, a quotient was calculated. Regression analyses were performed to analyze the dependence of the fetal and placental volumes and placental quotient on the week of gestation and other influencing variables.

Results: The mean of the fetal volume increased markedly from 67.8 to 76.6 mL (by 13%) within the 3 weeks of observation, whereas placental volume increased only slightly (111.1 to 114 mL (by 2.6%)). The random variation of placental volumes around the mean in all three gestational weeks was considerably higher than that of fetal volumes, indicating that in this early period of gestation there is little correlation between fetal and placental sizes. Fetal volume correlated better to gestational week than did placental volume.

Conclusion: The quotient of fetal and placental volume might assist in the diagnosis of high-risk pregnancies and the assessment of a normal or large fetus with a small placenta.