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

<table>Percentage of infants with relatively severe malformations and percentage of women who used antiasthmatics in early pregnancy in 21 counties in Sweden (2000–2008).</table>

Obstetrics and Gynecology International

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Figure 2

Figure 2: The Problem of Confounding in Studies of the Effect of Maternal Drug Use on Pregnancy Outcome 