It is known that mothers who smoke are at a greater risk of miscarriage if they continue to smoking during pregancy. However, the effect of a partner smoking (passive smoking) during pregnancy on the risk of miscarriage has not been clearly resolved. A joint American and Chinese study, published in the May 15 2004 issue of the American Journal of Epidemiology, has found that if a woman’s partner smokes, the risk of miscarriage is raised. And if the partner smokes more than 20 cigarettes a day, the risk is significantly increased.
Below we look at the issue in more depth:
How was the study carried out?
The joint American and Chinese study looked at 526 newly married women who did not smoke or drink from 1996 to 1998. They were all textile workers in China and they were put into groups according to the number of cigarettes a day their husbands smoked: more than 20 cigarettes a day, less than 20 cigarettes a day and no cigarettes (nonsmoker).
The researchers tested the women’s urine every day to see whether or not they had become pregnant. When the women did become pregnant, their pregnancy was followed closely.
What did the study find?
There was little difference between the groups of women as to their likelihood to become pregnant. Therefore, in this study, the smoking habits of the father did not seem to affect the chance of pregnancy.
However, the number of cigarettes the father smoked did seem to have an effect on the risk of spontaneous miscarriage within the first six weeks:
- of the women whose partners smoked more than 20 cigarettes a day, nearly one-third of the women lost their babies within six weeks of conceiving
- of the women whose partners did not smoke at all, roughly one-fifth of the women had a miscarriage within the first six weeks of conceiving
Also, the number of cigarettes the father smoked seemed to have an effect on the likelihood of eventually becoming pregnant and giving birth:
- of the women whose partners smoked more than 20 cigarettes a day, 76 percent became pregnant and gave birth
- of the women whose partners did not smoke at all, 84 percent became pregnant and gave birth
What are the conclusions from these findings?
The researchers from the study concluded that heavy smoking by the father increased the risk of early pregnancy loss. They suggest that this is either due to exposure of the male sperm to the effects of smoking, or due to the mother being exposed to the effects of passive smoking.
Why does smoking raise the risk of miscarriage?
The researchers believe that smoking by the father could damage the chromosomes in his sperm, making the sperm less likely to produce viable babies. Also the researchers think that the father’s cigarette smoke is inhaled passively by the mother and this can affect the developing fetus. It is thought that tobacco smoke may alter a pregnant woman’s levels of female sex hormones and that it may reduce the amount of blood that flows through the placenta and nourishes the baby.
What can be done to lower the risk of miscarriage?
It is worth remembering that miscarriage is a common event and many women experience two miscarriages, purely by chance. Often there is no underlying problem when a miscarriage occurs and there is every chance of a successful pregnancy in the future.
In over 60 percent of miscarriages, there is a problem with the way genetic material from the egg and sperm has combined and the resulting baby is unable to develop. There is no other reason for this than bad luck. Another cause is the embryo failing to implant into the lining of the womb. Doctors don’t full understood why this happens, but sometimes it can be due to a hormone imbalance.
Miscarriage is not thought to be caused by stress or lack of rest. However, it is helpful for both partners to stop smoking before trying to conceive and remain smoke-free once pregnancy has begun.
If you experience three consecutive miscarriages, it is advisable to visit your doctor to undergo tests to rule out any possible specific cause such as hormonal imbalances, abnormalities of the uterus or a problem with the immune system.