title: Fetal volume and crown-rump length from 7 to 10 weeks of gestational age in singletons and twins.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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 cm(3) and 0.324+/-0.012 cm(3). 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 cm(3) and 6.083+/-0.081 cm(3). 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.
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Escola de Ultra-sonografia de Ribeirão Preto (EURP) e Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FMRP-USP), Ribeirão Preto, São Paulo, Brazil. wpmartins@gmail.com
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
authors.forename: Carolina O
authors.initials: CO
authors.lastname: Nastri
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Barra
authors.forename: Paula A A S
authors.initials: PA
authors.lastname: Navarro
authors.forename: Francisco
authors.initials: F
authors.lastname: Mauad Filho
authors.forename: Rui A
authors.initials: RA
authors.lastname: Ferriani
mesh_terms: D000328:Adult; D018568:Crown-Rump Length; D005260:Female; D005307:Fertilization in Vitro; D005333:Fetus / Q000033:anatomy & histology*; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D014427:Twins; D016216:Ultrasonography, Prenatal / Q000379:methods*