The karyotype of fetuses with anomalies detected by second trimester ultrasonography.

Objective: To determine the incidence of abnormal karyotype among fetuses with anomalies detected by detailed second trimester ultrasonography.

Methods: A total of 573 patients underwent amniocentesis following the detection of anomalies by detailed second trimester ultrasonography.

Results: Thirty-six (6.3%) fetuses with abnormal karyotype were detected. The most common abnormal karyotypes were: trisomy 18, 11 cases; trisomy 21, 8 cases; 45XO, 7 cases; trisomy 13, 3 cases; and triploidy, 2 cases. Abnormal karyotype was detected in 20/111 (18%) fetuses with more than one anomaly, 15/182 (8.2%) with cystic hygroma, and 1/38 with nuchal thickening. No abnormal karyotype was detected among 108 fetuses with choroid plexus cyst, 58 with hydronephrosis, 25 with ventriculomegaly, 16 with a single umbilical artery, 18 with cardiac anomalies.

Conclusions: (1) Half of the cases with abnormal karyotype occurred in fetuses with more than one anomaly. (2) Cystic hygroma was the isolated malformations most commonly associated with abnormal karyotype. (3) Isolated malformations such as choroid plexus cyst or hydronephrosis were not associated with abnormal karyotype.