1. Modem epidemiology;Rothman,1986
2. Multicentre randomised clinical trial of chorion villus sampling and amniocentesis;Lancet,1989
3. Transabdominal versus transcervical routes for chorion villus sampling;Bovicelli;Lancet,1986
4. Transvaginal CVS versus transabdominal CVS (our randomised cases);Tomassini,1988
5. Transabdominal versus transcervical chorionic villus sampling: a randomized trial;Brambati;Hum Reprod,1988