Rapid karyotyping in the second and third trimesters for fetuses at risk of chromosomal abnormalities at Chulalongkorn Hospital.

Transabdominal fetal blood sampling under ultrasonic guidance was performed in 20 fetuses at 18 to 34 weeks gestation. Pure fetal blood was obtained in all cases; 11 from the umbilical veins at the placental cord insertion, 7 from the fetal intrahepatic veins and 2 from the fetal hearts. Rapid karyotype was obtained within 7 days by fetal lymphocyte culture. Chromosomal abnormality was detected in 5 (25.0%) fetuses. Abnormal karyotype was found in 4 of 8 fetuses with structural malformations detected by antenatal ultrasound and in 1 of 5 fetuses of elderly mothers at advanced gestational ages. This suggested that in fetuses at risk of chromosomal abnormality, rapid karyotype should be obtained and fetal blood sampling is justified in the second or third trimester.