Methods	Central telephone randomisation. Random allocation in balanced blocks and stratified by centre. Finland - consecutively numbered, sealed, opaque envelopes
Participants	3248 recruited from 31 centres in Europe (21 in the UK, 4 in Italy, 2 in the Netherlands and 1 in Finland, Denmark, Switzerland and Germany). Prenatal diagnosis due to maternal age. Other indications were anxiety and previously affected child with chromosome anomaly. Centres eligible if each participating obstetrician had performed at least 30 procedures with > 10 mg of tissue in 23 out of 25 most recent cases. 1609 randomised to CVS and 1592 to AC
Interventions	First trimester CVS TC or TA approach versus second trimester AC
Outcomes	Pregnancy outcome, abnormal karyotype, antenatal complications and diagnostic accuracy
Notes
Risk of bias
Item	Authors’ judgement	Description
Allocation concealment?	Yes	A - Adequate