Unfused amnion and chorion after 14 weeks of gestation: associated fetal structural and chromosomal abnormalities

Objective To assess possible associations between delayed chorioamniotic fu sion after the end of the first trimester and fetal structural and/or chrom osomal abnormalities. Design We prospectively studied 492 fetuses from highrisk pregnancies betwe en 14 and 18 weeks of gestation by transabdominal ultrasonography. Of these , 60 (12%) had unfused amnion and chorion. Results No additional abnormalities were detected in 28/60 fetuses (47%). K aryotyping was performed in 27/28 cases, and one fetus had trisomy 13 (4%). Ten of 24 fetuses (42%) of this group attending a second mid-trimester sca n after 18 weeks of gestation had abnormal sonographic findings not noted a t the initial scan. Thirty-two of 60 (53%) fetuses had additional abnormali ties at the initial scan: cystic hygroma (n = 12), increased nuchal translu cency (n = 10) and other abnormalities (n = 10). Karyotyping revealed aneup loidy in 13 of 28 fetuses (46%) tested: trisomy 21 (n=5), Turner's syndrome (n=3), trisomy 18 (n = 3) and trisomy 13 (n = 2). Additional fetal abnorma lities were detected only at the second scan after 18 weeks of gestation in three of eight fetuses (38%). Conclusions These preliminary data suggest that the sonographic finding of unfused amnion and chorion after 24 weeks of gestation may be associated wi th fetal structural and/or chromosomal abnormalities.