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

Table 5

Importance of maternal education or non-cohabitation for occurrence and diagnosis of congenital malformations in Sweden. Odds ratios (ORs) with 95% confidence intervals (95% CI) for various malformation groups at different maternal education levels. For educational level, the reference is 12 years of education, for non-cohabitation, the reference is cohabitation. Adjustment for year of birth, maternal age, parity, smoking, and BMI.

	<12 years of education		≥14 years of education		Non-cohabiting in early pregnancy
Malformation group	OR	95% CI	OR	95% CI	OR	95% CI
Relatively severe malformations	1.05	1.00–1.10	0.97	0.93–1.00	0.99	0.95–1.06
Chromosome anomalies	1.04	0.86–1.26	0.96	0.84–1.10	0.99	0.75–1.29
Neural tube defects	0.75	0.40–1.16	0.97	0.73–1.30	1.49	0.89–2.48
Orofacial clefts	0.99	0.81–1.21	0.89	0.77–1.03	0.95	0.71–1.26
Cardiovascular defects	1.02	0.94–1.61	0.97	0.87–1.08	1.08	0.97–1.22
Severe kidney malformation	1.07	0.78–1.46	0.98	0.86–1.13	0.99	0.62–1.57
Hypospadias	1.24	1.06–1.45	0.78	0.62–0.98	0.85	0.66–1.10
Pes equinovarus	0.86	0.69–1.07	0.94	0.69–1.26	1.00	0.75–1.33
(Sub)luxation of hip	0.90	0.80–1.01	0.98	0.64–1.49	0.76	0.63–0.91
Craniostenosis	0.75	0.53–1.07	1.01	0.68–1.51	0.94	0.58–1.54