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

Potential Applications

The potential applications of first-trimester volumetry are summarized in Table 2.

Birthweight Prediction

A strong correlation between placental size and birthweight was well demonstrated previously.[15] A recent study has showed that PV multiples of the median were reduced in SGA neonates (0.88), but increased in large-for-gestational-age neonates (1.09) compared with appropriate-for-gestational-age neonates (1.0).[15] A prospective study of 199 singleton low-risk pregnant women showed that EV during the first trimester of pregnancy correlates better with birthweight than CRL, GSV and PV.[16] A 10 mm3 increase in EV corresponds to a mean birthweight increase of 75 g, while a 1-mm increase in CRL corresponds to a birthweight increase of 113 g.[16] Further studies are required to confirm the usefulness of EV in the prediction of pregnancies complicated by macrosomia or low-birthweight fetuses.

Intrauterine Growth Restriction

Antenatal detection of pregnancies at risk of IUGR can reduce perinatal morbidity and mortality by four- to five-fold.[63] Measurement of PV or PQ may be an efficient method for the early and simple identification of impaired first wave of trophoblast invasion, and the subsequent development of IUGR.[11,12] In a prospective study of 1060 women, a small PV or PQ between 11 and 13 weeks was associated with high-resistance uterine perfusion in the second trimester.[11] Unlike uterine artery Doppler, PV and PQ did not show any dependency on age, gravidity, BMI or smoking habits.[11] In a study of 2489 consecutive singleton pregnancies, PQ at 12 weeks and uterine artery Doppler at 22 weeks had similar sensitivities (27.1 vs 28.1%) for predicting IUGR.[12] In a prospective study of 1199 women at 12 weeks' gestation, the PV was smaller in pregnancies subsequently complicated by SGA neonates with or without PE.[13] A PQ ≤10th centile occurred in 10% of pregnancies and its sensitivity in predicting complications including IUGR, PE or placental abruption was 22%.[14]

Preeclampsia

PE occurs in approximately 2% of pregnancies, but is a major cause of maternal and perinatal morbidity and mortality.[59] In a prospective study of 2489 consecutive singleton pregnancies, logistic regression models for the detection of PE had a sensitivity of 38.5% (PQ at 12 weeks) versus 44.8% (uterine artery Doppler at 22 weeks).[12] Taking a PQ that is ≤10th centile, the sensitivity for PE with and without SGA neonates was 30.8 and 20.0%, respectively. It appears that PQ is marginally less sensitive than uterine artery Doppler for the prediction of PE,[12] but similarly sensitive (~50%) in predicting the most severe complications, in which delivery took place before 34 weeks.[12]

Aneuploidy

An initial study in 2002 showed that the median PQ in a group of mixed chromosomal abnormalities (0.67) was significantly lower than that in normal fetuses (0.98),[17] and suggested that the inclusion of PV measurements as an additional marker to nuchal translucency may improve the sensitivity of first-trimester screening.[17] A subsequent study showed that the mean PV for GA was smaller in conjunction with trisomies 13 and 18 than in normal pregnancies.[18] However, no difference was observed between normal pregnancies and those with trisomy 21 or Turner syndrome.[18] Measurement of the PV, GSV and FV at 11–13 + 6 weeks of gestation is unlikely to be a useful predictor of major chromosomal defects.[18–21]

In early-onset IUGR caused by aneuploidy, a larger deficit in FV than CRL was observed.[21] This discrepancy can be explained by a larger growth rate of FV than CRL (five- to six-fold vs twofold) in normal fetuses at between 11 + 0 and 13 + 6 weeks.[8] FV may be a better first-trimester marker of IUGR than CRL. Compared with chromosomally normal fetuses, the fetal head volume for CRL was significantly smaller in conjunction with trisomy 21, trisomy 13 and Turner syndrome, but similar in association with trisomy 18 and triploidy.[19] The fetal trunk volume for CRL was significantly smaller in all chromosomal abnormalities except Turner syndrome.[19] It appears that the IUGR was symmetrical, with the head and trunk being equally affected in fetuses with trisomy 21 and Turner syndrome, but asymmetrical, with the trunk being more severely compromised than the head, in those with triploidy and trisomies 18 and 13.[19]

The mean GSV for GA was smaller in pregnancies with triploidy and trisomy 13 than in normal pregnancies, probably owing to a reduced amniotic fluid volume.[20]

Thalassemia

Fetal homozygous α0-thalassemia is the most common cause of hydrops fetalis in southeast Asia. Using placental thickness, the sensitivity to predict an affected pregnancy before 12 weeks of gestation was 72% with a specificity of 97%.[37]

In a preliminary study including 11 affected fetuses and 94 normal controls, the mean PQ in affected pregnancies was larger than that seen in unaffected pregnancies (1.37 [standard deviation: 0.65] vs 1.13 [standard deviation: 0.39]), although this difference was not significant.[27]

More recently, 106 pregnancies with a larger number of affected pregnancies (n = 26) were studied. Compared with unaffected pregnancies, the FV and FV/CRL quotients of affected pregnancies were significantly smaller at 9–14 weeks' gestation, although their CRLs were similar [Leung KY, Unpublished Data]. In addition, the PVs and PQs of affected pregnancies were significantly greater [Leung KY, Unpublished Data]. Early-onset IUGR and placentomegaly were probably caused by fetal anemia and hypoxia associated with homozygous α0-thalassemia. Consistent with another study,[8] it appears that 3D volumetry is more sensitive than CRL in detecting IUGR in early pregnancy. Further studies using a larger sample size are needed.

Multiple Pregnancy

In a prospective study on 290 consecutive twin and 37 triplet pregnancies at 11 + 0 to 13 + 6 weeks of gestation,[25] median twin and triplet PVs were 1.66 and 2.28 multiples of the median for singletons, respectively. It appears that PV in multiple pregnancies does not depend on chorionicity. There was no difference in the rate of placental growth between 11 and 13 + 6 weeks among singletons, twins and triplets.[25]

In a dichorionic twin pregnancy, discordance in growth with a distinctly small PV was associated with an abnormal twin with triploidy of maternal phenotype.[26]

Miscarriage

In a study of 111 pregnancies, including 30 ongoing pregnancy and 81 miscarriages, the correlation between the GSV and CRL or GA was weaker in cases of missed miscarriage than in ongoing pregnancies.[22] The GSV:EV ratio in missed miscarriages was significantly higher than those in ongoing pregnancies.[56] However, in another study on 86 patients, a logistical regression analysis showed no significant correlation between GSV and the outcome of missed miscarriages managed expectantly.[23] In a study of 125 asymptomatic pregnant women, YSV outside the 5th to 95th percentile or GSV less than the 5th percentile were associated with spontaneous miscarriage in univariate but not in regression analysis.[24] It appears that 3D volumetric assessment does not improve the diagnosis of miscarriage over conventional 2D sonographic measurements.[22–24]

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