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

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

Gestational Sac Volume

The gestational sac consists of the amniotic cavity and the exocelomic cavity in the first trimester. GSV is commonly measured using the VOCAL method with a 30° rotation angle.^[9,33] Intraobserver variability was excellent, with an average difference between measurements of 0.5 cm³.^[9] GSV can be measured with reliably in VR, but the results were on average 19.8% smaller than the GSV calculated using the ellipsoid formula.^[55]

There was a high correlation between GSV and GA or CRL.^[1,9,16] Mean GSV increased from 8.50 cm³ at 7 weeks to 44.35 cm³ at 10 weeks,^[15] and 69 ml at 11 weeks to 144 ml at 13 + 6 weeks.^[20] GSV increased from 5.00 to 50.28 cm³ for a CRL increase from 0.9 to 4 cm.^[9]

GSV is closely related to amniotic fluid volume, which is an ultrafiltrate of maternal plasma. GSV may reflect uteroplacental function in the first trimester,^[56] and may potentially have predictive value for adverse pregnancy outcomes.^[24]

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Table 1. Reference data of first-trimester volumetry measured by different 3D ultrasound techniques.
3D parameters	3D measurement techniques	Gestation (weeks)							Ref.
3D parameters	3D measurement techniques	6	7	8	9	10	11	12	Ref.
EV/FV (cm³)	Multiplanar VOCAL™ (30°) XI VOCAL Virtual reality	0.04 0.07 0.04	0.19 0.40 0.20 0.31	0.74 0.99 1.02	2.31 2.31 2.45	5.84 4.62 5.12 5.35	11.84 8.65 9.71	19.29 14.25 22.20	[1] [2] [10] [40]
VOCAL vs SonoAVC	Mean difference of -76.5% with limit of agreement ranging from -159.6 to 6.7%							[51]
GSV (cm³)	Multiplanar VOCAL	4.36 3.8	7.52 8.3	12.97 16.2	22.38 26.0	38.61 47.1	66.61 67.9	114.93 90.8	[1] [5]
Gestational sac fluid volume (cm³)	VOCAL Virtual reality	2.18	3.97 4.86	5.87 9.82	13.75 18.20	23.33 32.36	53.70	87.10	[33] [40]
Yolk sac volume (cm³)	Multiplanar VOCAL Virtual reality XI VOCAL	0.04 0.05	0.07 0.06 0.08 0.06	0.10 0.10 0.08	0.12 0.12 0.10	0.13 0.16 0.15 0.16	0.13 0.18	0.12 0.12	[1] [6] [40] [10]
PV (ml)	Multiplanar VOCAL	Median: 41.3 ml (CRL: 35–44 mm), 48.5 ml (CRL: 45–54 mm), 59.2 ml (CRL: 55–64 mm) PV = 1.73 × exp(0.076 × CRL)							[3] [4]

CRL: Crown—rump length; EV: Embryo volume; FV: Fetal volume; GSV: Gestational sac volume; PV: Placental volume; SonoAVC: Sonography-based automated volume count; VOCAL: Virtual organ computer-aided analysis; XI: Extended imaging.

Table 2. Potential applications of first-trimester volumetry.
Area	Main findings	Ref.
Birthweight	The embryonic volume during the first trimester of pregnancy correlates better with birthweight than the crown–rump length	[15,16]
IUGR	Placental quotient at 12 weeks and uterine artery Doppler at 22 weeks have similar sensitivities (27.1 vs 28.1%) for predicting IUGR	[11–14]
Preeclampsia	The detection of preeclampsia had a sensitivity of 38.5% (placental quotient at 12 weeks) versus 44.8% (uterine artery Doppler at 22 weeks)	[12]
Aneuploidy	First-trimester volumetry is unlikely to be a useful predictor of major chromosomal defects In early-onset IUGR caused by aneuploidy, a larger deficit in fetal volume than crown–rump length was observed	[17–21]
Homozygous α⁰-thalassemia	Compared with unaffected pregnancies, the placental quotient of affected pregnancies was greater, while fetal volumes were smaller at 9–14 weeks' gestation	[27]
Multiple pregnancy	Median twin and triplet placental volumes were 1.66 and 2.28 multiples of the median for singletons, respectively. There was no difference in the rate of placental growth between 11 and 13 + 6 weeks among singletons, twins and triplets	[25,26]
Miscarriage	3D volumetric assessment does not improve the diagnosis of miscarriage over conventional 2D sonographic measurements	[22–24]

IUGR: Intrauterine growth restriction.

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