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Obstetrics and Gynecology International
Volume 2012, Article ID 148616, 16 pages
Review Article

The Problem of Confounding in Studies of the Effect of Maternal Drug Use on Pregnancy Outcome

Tornblad Institute, Lund University, 223 62 Lund, Sweden

Received 12 August 2011; Accepted 29 August 2011

Academic Editor: Gideon Koren

Copyright © 2012 Bengt Källén. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In most epidemilogical studies, the problem of confounding adds to the uncertainty in conclusions drawn. This is also true for studies on the effect of maternal drug use on birth defect risks. This paper describes various types of such confounders and discusses methods to identify and adjust for them. Such confounders can be found in maternal characteristics like age, parity, smoking, use of alcohol, and body mass index, subfertility, and previous pregnancies including previous birth of a malformed child, socioeconomy, race/ethnicity, or country of birth. Confounding by concomitant maternal drug use may occur. A geographical or seasonal confounding can exist. In rare instances, infant sex and multiple birth can appear as confounders. The most difficult problem to solve is often confounding by indication. The problem of confounding is less important for congenital malformations than for many other pregnancy outcomes.