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April 7, 2004

Risk of Twinning as a Function of Maternal Height and Body Mass Index

Author Affiliations

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2004;291(13):1564-1566. doi:10.1001/jama.291.13.1564-c

To the Editor: Rates of twinning declined from the 1950s through the 1970s in many countries1,2 even after controlling for age and parity2 but began to increase again in the 1980s.1 Monozygotic twinning is considered an essentially random event with constant rates around the world, although recent evidence suggests that it may be more likely among women undergoing infertility treatment.1 Changes in twinning rates are thus largely attributable to dizygotic twinning, which is influenced by maternal age, race, family history,1,3 and, possibly, height and weight.3,4 Widespread use of infertility drugs is presumably the main cause of the recent increase in dizygotic twinning in most industrialized countries.1 We examined the relationship between twinning and maternal height and body mass index (BMI) in a large national cohort.

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