Does smoking in the father increase the risk of birth defects?

This study investigated if smoking in the father before conception is associated with birth defects (BD) in the child. They found that smoking in the father may be associated with BDs including heart disease. 

Smoking is a known cause of birth defects (BDs). Women that smoke during pregnancy are more likely to give birth to a baby with lower birth weight and BDs. These include heart diseases and limb abnormalities. For this reason, women are encouraged to avoid smoking during pregnancy.

The influence of smoking in the father and BDs is unclear. Some studies suggest that preconception paternal smoking (PPS) may increase the risk of BDs. Most of these studies have also included maternal smoking. This can make it difficult to determine if PPS alone increases the risk. A large controlled study could be used to answer this question. It is unclear if PPS contributes to BDs in the offspring. 

This study included 566,439 couples that had a successful pregnancy. PPS was evaluated in these couples. This group had low rates of maternal smoking (1%). Smoking patterns during and after pregnancy were also measured. This was compared to birth defect reports. 

The rate of PPS was 28.7%. In babies with BDs, this rate was 36.8%. The risk of BDs was 87% higher in infants who continued to smoke.

13.3% of the fathers decreased smoking during pregnancy. 8.7% of the fathers stopped smoking while 6.6% of fathers continued smoking. The risk of BD was 41% higher with fathers that decreased smoking. There was no difference in BDs between babies from fathers who stopped smoking early after conception and those who did not smoke before conception.

Continued smoking was associated with an increased risk of congenital heart disease (CHD) and limb abnormalities. It was also associated with neural tube defects (NTD; abnormalities in the brain) and defects of the digestive tube. 

The authors concluded that smoking before conceiving in the father may be associated with BDs including heart disease.

This study did not investigate BDs that may emerge later in infancy. Couples self-reported their smoking habits. This could bias the data.