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 ± 0.27 mm (mean ± S.D.) and 11.48 ± 0.22 mm (singletons and twins, respectively), while the fetal volume was 0.354 ± 0.015 cm3 and 0.324 ± 0.012 cm3 . At the gestational age of 73 days, the crown-rump length was 36.19 ± 0.90 mm and 35.87 ± 0.54 mm and the fetal volume was 6.204 ± 0.090 cm3 and 6.083 ± 0.081 cm3 . 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.