Methods	Telephone randomisation. Random allocation list computer generated
Participants	4368 participants in 12 centres. Inclusion criteria: prenatal diagnosis due to maternal age, newborn baby with a chromosomal abnormality, viable fetus with a crown rump length of 20-50 mm on ultrasound and consent to enter the trial. Exclusion criteria were: previous open neural tube defect detected by prenatal diagnosis, molecular or biochemical disorders found on prenatal tests, non viable fetus, multiple pregnancy, failed CVS, fetal anomaly or oligohydramnios, active vaginal bleeding, alloimmunised patient, recurrent unexplained miscarriages, intrauterine contraceptive device in utero, previous CEMAT trial randomisation
Interventions	Both groups underwent detailed fetal anomaly ultrasound examination at 15 and 20 weeks. Early amniocentesis group had amnio performed between 11 and 12 gestational weeks and second trimester between 15 and 16 weeks. All amniocentesis were performed under direct ultrasound guidance using 22 G, 9 cm or 14 cm needles
Outcomes	Pregnancy outcome, congenital anomalies, abnormal karyotype and technical difficulty
Notes
Risk of bias
Item	Authors’ judgement	Description
Allocation concealment?	Yes	A - Adequate