Methods	Random telephone allocation using a table of random numbers.
Participants	Women requesting fetal karyotyping on the basis of advanced maternal age prior to 12th completed week. Exclusions included: multiple pregnancies, menstrual gestational age greater than 11 plus 6 weeks, or an indication for cytogenetic analysis other than advanced maternal age. 503 randomised to CVS group and 508 to the amniocentesis group
Interventions	Transcervical CVS performed from 9th to 13th week of pregnancy using round tipped curved steel forceps after initial ultrasound scan. Procedure performed under direct ultrasound guidance. Amniocentesis was performed from the 15th to 18th week of pregnancy using 22 G needle under direct ultrasound guidance
Outcomes	Diagnostic success and fetal loss rate.
Notes	Trial prematurely discontinued when second trimester serum biochemistry screening was introduced 110 women miscarried before the assigned procedure; 68 in the CVS group and 42 in the amniocentesis group. In total, the assigned procedure was performed in only 67% of randomised women (681/1011)
Risk of bias
Item	Authors’ judgement	Description
Allocation concealment?	Yes	A - Adequate