ARE NATURAL TWINNING RATES CONTINUING TO DECLINE

During the 1960s and 1970s, the maternal age-specific twinning rates w ere declining in England and males and many other countries, However, around 1980 this change reversed and since then twinning rates have be en increasing, The question arises whether this increase is simply a c onsequence of hormonal induction of ovulation and various other techni ques of assisted reproduction. The question assumes some importance be cause the level of 'natural' twinning may be an index of reproductive (and other) health. Nationwide data on the prevalence of medically ass isted conceptions are not available, so indirect methods have to be us ed to answer the question, It is tentatively concluded here that the ' natural' twinning rate has recently been increasing in England and Wal es and Belgium, These conclusions are based on two assumptions: (i) th at in England and Wales, conceptions by young women are infrequently p receded by medical assistance; and (ii) in Belgium, the rate of medica lly assisted conceptions is not lower in East Flanders than in the res t of Belgium. Direct data on these points would test these conclusions .