1. Births: maternities with multiple births: rates per 1,000 maternities, age of mother, 1938–2004, all maternities;Office for National Statistics,2006
2. Trends in twin and triplet births: 1980–97;Martin;Natl Vital Stat Rep,1999
3. Five decades of progress in management of the infertile couple;Chen;Fertil Steril,1994
4. The best possible start to life – a consultation document on multiple births after IVF;Human Fertilisation and Embryology Authority,2007
5. Dramatic reduction in triplet and higher order births in England and Wales;Simmons;BJOG,2004