Although the influence of paternal smoking on birth defects is of great public interest, epidemiological evidence concerning this potential relationship is extremely limited. A stratified random sample of 29 hospitals in the Shanghai Municipality, China, was used to select 1012 birth defects cases and controls. Mothers of the cases and controls were interviewed in the hospitals from October 1986 to September 1987. A modest relationship between paternal smoking and overall birth defects in offspring was identified [odds ratio (OR) = 1.21, 95% confidence interval (CI): 1.01-1.45]. More markedly elevated risks were identified for anencephalus (OR = 2.1), spina bifida (OR = 1.9), pigmentary anomalies of the skin (OR = 3.3) and varus/valgus deformities of the feet (OR = 1.8). Our analysis also shows that paternal smoking is more likely to be associated with multiple rather than isolated malformations. A paternally-mediated effect of smoking on birth defects is suggested and further studies are encouraged.
PIP: The effect of paternal smoking on birth defects was examined using data from the Shanghai Birth Defects Monitoring Program in Shanghai Municipality from October 1986 to September 1987. A stratified random sample of 29 hospitals was selected. A total of 75,756 births with weights of 1000 gm or over were recorded. The final sample included 1012 cases and 1012 controls without adjustment for confounding factors. Maternal exposure to radiation, chemicals, and pesticides during pregnancy and the smoking and alcohol consumption habit of the husband were recorded. The relative risk (RR) of birth defects associated with paternal smoking was 1.2. Paternal smoking was associated with a 2.1- fold increase of anencephalus; infants whose fathers smoked were 3.3 times as likely to have had pigmentary anomalies of the skin, and 2.3 times as likely to have a diaphragmatic hernia. The odds ratio (OR) of spina bifida was 1.9 and varus or valgus deformities of feet had an OR of 1.8. The OR of these anomalies was also over 1.5: eye anomalies, microtia or absence of ear, nasal bone absence, cleft palate without cleft lip, brachydactylia or adactylia, undescended testicle, and polycystic kidney. The possible dose-response relationship between paternal smoking and birth defects was assessed in 3 groups: 1-9, 10- 19, and 20 or more cigarettes per day. Similar increased RRs across smoking levels were found for anencephalus, cleft palate, and pigmentary anomalies of the skin. Increasing risk among the heavier smokers was apparent for spina bifida, nasal bone absence, varus or valgus deformities of the feet, and diaphragmatic hernia. Paternal smoking was slightly more related to multiple defects than to single defects. This suggests a modest link between paternal smoking and total birth defects and a stronger effect of paternal smoking and anencephalus and spina bifida risk, consistent with a previous study.