1. Volume 349, Issue 9062, Pages 1398-1399 (May 1997)
Twinning rates 
Mike Murphy, Eate Hey 
The Lancet 
Volume 349, Issue 9062, Pages (May 1997)
DOI: /S (05)
Copyright © 1997 Elsevier Ltd Terms and Conditions

2. Indirectly age-adjusted twin rates in England and Wales
1970 rates in 5-year maternal age-groups used as standard; 1981 rates are unreliable and omitted.
The Lancet  , DOI: ( /S (05) )
Copyright © 1997 Elsevier Ltd Terms and Conditions