BMJ  2005;330 (9 April), doi:10.1136/bmj.330.7495.0-b

Folic acid may not increase twinning

In vitro fertilisation is a strong confounder in assessments of the correlation between using folic acid during pregnancy and giving birth to twins, and the findings from a recent Swedish study—that folic acid was associated with an increase in dizygotic twinning—are probably incorrect. Berry and colleagues (p 815) used models based on Swedish records for 1995-9 to establish whether failure to adequately adjust for a reported misclassification of use of in vitro fertilisation could have led to the false finding. They found that even when misclassification of in vitro fertilisation was reduced to 5%, the bias persisted in the adjusted model.

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Relevant Article

Impact of misclassification of in vitro fertilisation in studies of folic acid and twinning: modelling using population based Swedish vital records

R J Berry, R Kihlberg, and O Devine
BMJ 2005 330: 815. [Abstract] [Full Text] [PDF]

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