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

Table 6

Importance of the mother’s country of birth on the occurrence of relatively severe malformations in the infant. Odds ratios adjusted for year of birth, maternal age, parity, smoking, and BMI. Reference is infants born by mothers born in Sweden. Data for years 2000–2008.

Geographic area	Number of infants	% of all infants	% malformed infants	OR	95% CI
Sweden	727166	81.9	2.7	1.00	Reference
Other Nordic countries	16612	1.9	2.5	0.87	0.79–0.96
Western Europe,; Northern America,; Australia,; New Zealand	10504	1.2	2.6	0.96	0.85–1.08
Eastern Europe and former Soviet Union	25855	2.9	2.5	0.89	0.83–0.97
Sub-Saharan Africa	15488	1.7	2.7	0.97	0.88–1.08
North Africa and Middle East	54186	6.1	2.9	1.04	0.98–1.09
Asia	27405	3.1	2.2	0.82	0.75–0.89
South and Middle America	10373	1.2	2.4	0.84	0.74–0.96
All non-Nordic countries	143811	16.2	2.6	0.94	0.91–0.98