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

Table 2

Impact of various maternal variables on the risk for any relatively severe congenital malformation in the infants and on the use of antidepressant drugs.

	Relatively severe malformationa		Maternal use of antidepressants
Variable	OR	95% CI	OR	95% CI
Maternal age
<20	1.07	0.99–1.15	0.69	0.60–0.79
20–24	1.04	1.00–1.07	0.91	0.86–0.97
25–29	1.00	Reference	1.00	Reference
30–34	1.00	0.97–1.02	1.19	1.14–1.24
35–39	1.02	0.99–1.06	1.52	1.99–1.60
40–44	1.15	1.08–1.23	1.78	1.62–1.96
≥45	1.02	0.74–1.41	2.36	1.60–3.49
Parity
1	1.00	Reference	1.00	Reference
2	0.89	0.87–0.91	0.67	0.64–0.70
3	0.90	0.87–0.93	0.85	0.80–0.89
≥4	0.89	0.85–0.93	0.84	0.78–0.90
Smoking
None	1.00	Reference	1.00	Reference
<10 cigs/day	1.06	1.03–1.11	2.39	2.27–2.51
≥10 cigs/day	1.09	1.03–1.15	3.84	3.63–4.07
Body mass index
<19.8	1.00	0.96–1.04	1.03	0.96–1.20
19.8–25.9	1.00	Reference	1.00	Reference
26–29.9	1.09	1.06–1.11	1.22	1.17–1.27
30–39.9	1.15	1.11–1.20	1.49	1.41–1.57
≥40	1.39	1.23–1.56	2.19	1.92–2.50
Number of years of unwanted childlessness
0	1.00	Reference	1.00	Reference
1	1.02	0.95–1.09	0.89	0.88–0.99
2	1.08	1.01–1.15	0.90	0.81–1.01
3	1.12	1.02–1.29	0.66	0.56–0.78
4	1.30	1.17–1.45	0.80	0.65–0.98
≥5	1.30	1.25–1.41	0.82	0.71–0.95
Number of previous miscarriages
0	1.00	Reference	1.00	Reference
1	1.05	1.02–1.05	0.99	0.95–1.04
2	1.05	0.98–1.11	1.08	0.99–1.17
≥3	1.12	1.02–1.32	1.15	1.01–1.30

aAny congenital malformation with the exception of the following conditions which are common and variably registered: preauricular tag, patent ductus at preterm birth, undescended testicle, hip (sub)luxation, tongue tie, single umbilical artery, nevus.