Fetal volume and crown-rump length from 7 to 10 weeks of gestational age in singletons and twins

Abstract 

Objective(s)

We intend to verify if fetal volume and crown-rump length were different between singletons and twins in pregnancies aged from 7 to 10 weeks and to evaluate if fetal volume is more accurate to determine the gestational age than crown-rump length at this gestational age.

Study design

From 52 days (7 weeks and 3 days) to 73 days (10 weeks and 3 days) weekly three-dimensional ultrasonography was performed in 20 twin fetuses and 20 singletons. Crown-rump length and fetal volume using VOCAL were assessed in all examinations. The ‘true’ gestational age was based on oocyte retrieval.

Results

At the age of 52 days, the crown-rump length was 11.74±0.27mm (mean±S.D.) and 11.48±0.22mm (singletons and twins, respectively), while the fetal volume was 0.354±0.015cm³ and 0.324±0.012cm³. At the gestational age of 73 days, the crown-rump length was 36.19±0.90mm and 35.87±0.54mm and the fetal volume was 6.204±0.090cm³ and 6.083±0.081cm³. The total relative increase observed was much higher for fetal volume than for CRL: 1705±301% vs. 210±33% in singletons and 1827±305% vs. 214±25% in twins. The 95% limits of agreement (±2.3 days vs.±3.2 days, fetal volume vs. crown-rump length) and the intraclass correlation coefficients (0.989 vs. 0.978) between the “true” gestational age and that predicted by fetal volume were better than those predicted by crown-rump length. No significant difference was identified between singletons and twins for both fetal volume and crown-rump length.

Conclusion(s)

Twins and singletons had similar fetal volume and crown-rump length between the 7th and 10th week of gestational age. Additionally, fetal volume assessed by VOCAL was better than crown-rump length to estimate the gestational age at the evaluated period. However, the improvement was small and probably without clinical significance.

Condensation

Fetal volume and crown-rump length were similar between singletons and twins. Fetal volume relative increase was higher and the predicted gestational age was better.

Keywords: Gestational age, Ultrasonography, Twins