title: Twin growth discrepancy in early pregnancy.
abstract: OBJECTIVE
  To assess whether early fetal growth restriction in a twin, expressed as the intertwin discrepancy in crown-rump length (CRL) between two viable twins at 7 + 0 to 9 + 6 weeks' gestation, is predictive of subsequent single fetal loss.
  
  
  METHODS
  This was a retrospective analysis of data collected prospectively over 3 years. Women attending an early pregnancy unit underwent a transvaginal ultrasound examination. In women with a viable twin pregnancy between 7 + 0 and 9 + 6 weeks of gestation, the CRL ratio between the two embryos was calculated. Women were followed up and the intertwin discrepancy in CRL at the 7 + 0 to 9 + 6-week scan was compared between cases in which there was spontaneous reduction to a singleton and those in which both twins remained viable at the 11-14-week scan.
  
  
  RESULTS
  There were 77 women included in the study and nine (12%) of these had a single fetal loss. Pregnancies with subsequent single fetal loss were more likely to have a larger median CRL discrepancy (42.0%; interquartile range (IQR), 23.8-64.3%) than were those which retained two viable fetuses (6.1%; IQR, 2.2-12.5%) (P < 0.0001). The median CRL discrepancy in subsequently viable monochorionic diamniotic twins (10.9%; IQR, 1.9-17.5%) was no different from that in dichorionic diamniotic twin pregnancies (5.9%; IQR, 2.1-12.3%) (P = 0.305). Regardless of chorionicity, there was a relationship between increasing CRL discrepancy and single fetal loss; the likelihood of a subsequently viable twin pregnancy was 97% if the discrepancy was < 20%, while if the discrepancy was > 60% there were no cases of both twins remaining viable (P < 0.0001). Receiver-operating characteristics curve analysis of CRL discrepancy in predicting single fetal loss gave an area under the curve of 0.93, with an optimum cut-off point of 16.9% discrepancy (sensitivity, 88.9%; 95% CI, 51.8-99.7; and specificity, 86.7%; 95% CI, 76.3-93.8).
  
  
  CONCLUSIONS
  There is a significant relationship between CRL discrepancy at 7 + 0 to 9 + 6 weeks and the likelihood of subsequent single intrauterine fetal loss. This suggests that spontaneous fetal demise of one twin may be preceded by growth restriction in the first trimester.
authors.affiliation: Department of Obstetrics & Gynaecology, St George's, University of London, London, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Bora
authors.forename: T
authors.initials: T
authors.lastname: Bourne
authors.forename: C
authors.initials: C
authors.lastname: Bottomley
authors.forename: E
authors.initials: E
authors.lastname: Kirk
authors.forename: A T
authors.initials: AT
authors.lastname: Papageorghiou
mesh_terms: D000022:Abortion, Spontaneous / Q000209:etiology*; D000328:Adult; D018568:Crown-Rump Length; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First; D012189:Retrospective Studies; D014427:Twins / Q000502:physiology*; D016216:Ultrasonography, Prenatal