First-Trimester Ultrasound Volumetry

Measurement Techniques and Potential Application in the Prediction of Pregnancy Complications

Kwok Yin Leung; Teresa Ma; Betty YT Lau; Min Chen

Disclosures

Expert Rev of Obstet Gynecol. 2012;7(4):379-386. 

In This Article

Placental Volume

After automatic acquisition of 3D volume, the placenta is defined by the basal and chorionic border with the uterine wall carefully excluded.[43] Common measurement techniques include the VOCAL method with a 30° rotation angle[10,22] or the multiplanar method.[27] Inter- and intra-observer correlations were good, ranging from 0.8 to 0.99 in some studies,[10,22,23] but relatively poor in another study.[27] XI VOCAL cannot be used interchangeably with VOCAL or multiplanar techniques in measuring PV at 11–14 weeks' gestation because of inferior reproducibility and in vivo validity.[44]

There was a strong correlation between PV and CRL or GA from 7 to 13 + 6 weeks.[4,16,18] PV increased from 1.7 ml at 7 weeks, through 42.6 ml at 10 + 6 weeks, to 91 ml at 13 + 6 weeks.[4,18] While CRL increased only 4.4-times from 9 to 40 mm, the mean PV increased 10.5-times.[4]

Placental quotient (PQ) equals PV divided by the fetal CRL,[12] and is a simple first-trimester parameter to indicate whether a placenta is large or small for a given fetus.[3] Neither PV nor PQ are associated with maternal plasma cell-free fetal DNA levels, which may reflect the extent of placental apoptosis[45] or other unknown mechanisms.

There are limitations in using placental volumetry for clinical applications because of the physiological variations in placental shape, weight and volume[46] at each stage of gestation,[47] the heterogeneous nature of placental growth,[13] and the reproducibility and accuracy of measuring the volume of the placenta, an irregular structure.[39]

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