The lambda sign at 10–14 weeks of gestation as a predictor of chorionicity in twin pregnancies

Abstract

Chorionicity was prospectively determined in 369 twin pregnancies by ultrasound at 10-14 weeks of gestation. Pregnancies were classified as monochorionic if there was a single placental mass in the absence of the lambda sign at the inter-twin membrane-placental junction, and dichorionic if there was a single placental mass but the lambda sign was present, or the placentas were not adjacent to each other. In 81 (22%) cases, the pregnancies were classified as monochorionic and in 288 (78%) as dichorionic. Pregnancy outcome was available in 279 cases and all 63 of these pregnancies classified as monochorionic resulted in the delivery of same-sex twins. Similarly, all 100 different-sex pairs were correctly classified as dichorionic. These findings demonstrate the high reliability of ultrasound examination at 10-14 weeks of gestation in determining chorionicity in twin pregnancies.

Prevalence and perinatal outcome of dichorionic and monochorionic twins with nuchal translucency above the 99th percentile and normal karyotype

“…Crown-rump length (CRL) was measured in each twin and NT was measured following The Fetal Medicine Foundation's guidelines 9 . Chorionicity was determined, the pregnancy being considered monochorionic in the presence of a single placenta and absent lambda sign, and dichorionic when the placentae were not adjacent or in a single placental plate and the lambda sign was present 10 . The intertwin discordance in CRL and NT was calculated as a percentage of the larger measurement: (CRL1 − CRL2/CRL1 × 100 and NT1 − NT2/NT1 × 100).…”

Monozygotic twins discordant for trisomy 13: counselling and management issues

“…Monochorionicity was confirmed on ultrasound scan. 3 Nuchal thickness in the first twin (twin A) was normal at 0.8 mm and no structural malformations were identified. Detailed scan of the second twin (twin B) showed alobar holoprosencephaly and a proboscis.…”

Aneuploidy and Anomaly Screening

“…The performance of screening can be improved by the addition of maternal serum biochemistry, but appropriate adjustments are needed for chorionicity (Sepulveda, et al, 1996). In dichorionic twins at 11 to 13 weeks, the levels of maternal serum free β-hCG and PAPP-A are about twice as high as in singleton pregnancies, but in monochorionic twins the levels are lower than in dichorionic twins Nicolaides, 2000, 2003;Spencer et al, 2008;Linskens et al, 2009).…”