Methods	Central randomisation (unknown) and stratified according to age 35-38, >= 39 and centre
Participants	Participants from 12 centres in Canada. Eligible women - aged 35 years or older at time of delivery or those referred for fetal chromosome analysis. Less than 12 weeks’ gestation. Viable singleton intrauterine pregnancy confirmed by ultrasound. Women excluded if dead or disorganized embryo, multiple pregnancy, Rh isoimmunisation, untreated cervical infection or gestation greater than 12 weeks. 2787 women randomised. 396 ineligible following randomisation. 1391 randomised to CVS (200 ineligible). 1396 randomised to amniocentesis (196 ineligible).
Interventions	TC versus second trimester AC.
Outcomes	Technical difficulties, abnormal karyotype, pregnancy complications, perinatal loss, neonatal complications and cytogenetic accuracy
Notes
Risk of bias
Item	Authors’ judgement	Description
Allocation concealment?	Yes	A - Adequate