OBJECTIVE: We examined whether maternal smoking and use of nicotine substitutes during the first 12 weeks of pregnancy increased the prevalence of congenital malformations in general and of certain congenital malformations in particular.
METHODS: In the Danish National Birth Cohort (1997–2003) we identified 76,768 pregnancies (and their subsequent singleton births); 20,603 were exposed to tobacco smoking during the first 12 weeks of pregnancy. Birth outcomes were collected by linkage to the Central Population Register, the National Patients Register, and the National Birth Register. We identified congenital malformations from the Hospital Medical Birth Registry as they were recorded at birth or in the first year of follow-up.
RESULTS: Smoking mothers were younger, weighed less, consumed more alcohol, and had received less education. Children exposed to prenatal tobacco smoking had no increase in congenital malformations prevalence compared with the nonexposed children in both crude and adjusted analyses. Children born to nonsmokers, but who used nicotine substitutes, had a slightly increased relative congenital malformations prevalence ratio; relative prevalence rate ratio was 1.61 (95% confidence interval 1.01–2.58), which represents a 60% increased risk. When the analysis was restricted to musculoskeletal malformations, the relative prevalence rate ratio was 2.63 (95% confidence interval 1.53–4.52).
CONCLUSION: Our results showed no increase in congenital malformations related to prenatal tobacco smoking. However, we identified an increase of malformations risk in nonsmokers using nicotine substitutes. This finding needs to be replicated in other data sources.
LEVEL OF EVIDENCE: II-2
The risk of congenital malformations is not increased with prenatal smoking, but there is an increased prevalence of musculoskeletal malformations in nonsmokers using nicotine substitutes.
From the 1Unit of Public Health and Environmental Care, Department of Preventive Medicine, University of Valencia, Valencia, Spain; 2Unit of Clinical Epidemiology, Dr. Peset University Hospital, Valencia, Spain; 3Institute of Public Health, Epidemiology, University of Southern Denmark, Odense, Denmark; 4Danish Epidemiology Science Centre, University of Aarhus, Aarhus, Denmark; and 5Department of Epidemiology, School of Public Health, University of California Los Angeles, Los Angeles, California.
Supported by a grant from the Danish Research Agency (No. 1105-93 and 11099-96). Financing from the Danish National Research Foundation resulted in the Danish National Birth Cohort. Additional support was obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, and the Augustinus Foundation.
Corresponding author: María Morales-Suárez-Varela, Unit of Public Health and Environmental Care, Department of Preventive Medicine, University of Valencia, Avda, Vicente Andrés Estellés s/n, 46100 Burjasot, Valencia, Spain; e-mail: firstname.lastname@example.org.