It is feasible and reproducible to undertake volumetry of the placenta, fetus, gestational sac, gesational sac fluid and york sac in the first trimester using 3D ultrasound.[1–6,33] Although the traditional prediction method focuses on clinical history, 2D sonographic parameters and biochemical markers,[28–32] first-trimester volumetry may represent an important tool for the prediction of birthweight and pregnancy complications.[11–27] There was a strong correlation between PV and EV measured by 3D ultrasound, and CRL or GA in the first trimester.[4,7,9,10] Measurement of PV/PQ is an early method to identify impaired trophoblast invasion, and its use can predict the subsequent development of IUGR at a sensitivity of 27.1% or PE at 38.5%. However, this method alone probably cannot predict all cases of at-risk pregnancies. At between 11 + 0 and 13 + 6 weeks, an increase in FV is greater than CRL. In early-onset IUGR caused by aneuploidy or homozygous α0-thalassemia [Leung KY, Unpublished Data], a larger deficit in fetal volume than CRL was observed. Further studies, including pathological examinations, are required to investigate the pathophysiology.
The accuracy of volumetry depends on the measurement technique, the object being measured and the observer. A wide discrepancy in reported normal volumes of first-trimester embryo and other structures (Table 1) was probably a result of inconsistencies in the measurement technique used, inadequate assessment of technique repeatability and validity, and a diversity of mutually incompatible 3D imaging formats and software measuring tools. As the placenta is an irregular structure, the influence of measurement error is larger than it is for the fetus, which is relatively regular and symmetrical.[42,44] The clinical use of placental volumetry is further limited by physiological variations in placental shape, weight and volume at each stage of gestation, and the heterogeneity of placental growth.
Expert Rev of Obstet Gynecol. 2012;7(4):379-386. © 2012 Expert Reviews Ltd.