Women who smoke take longer to become pregnant and are more likely never to become pregnant than women who don't smoke. Exposure to passive smoke is almost as harmful to female conception as active smoking. Smoking affects female fertility by affecting the ovaries, the fallopian tube and by reducing the quality of eggs produced. The quantity and quality of sperm is also reduced in men who smoke.
Smoking and Ovarian Function
The effect of smoking on the human ovaries is threefold. First, women who smoke lose functioning eggs from their ovaries more rapidly than women who don't smoke. Smoking accelerates the onset of menopause, shortening a woman's reproductive lifespan. Secondly, ovaries exposed to toxins in smoke are less able to make estrogen needed for normal reproductive function and fertility. Finally, the eggs of women who smoke are more likely to have genetically or functionally abnormal eggs, which inhibit normal fertilization or cause genetic abnormalities in the fertilized egg.
Smoking and Fallopian Tube Function
The fallopian tubes are essential for conception because fertilization of the egg by sperm occurs in the fallopian tubes. The cells lining the tubes are covered with tiny hair-like structures that move the ovulated egg from the ovary into the tube for fertilization. After the egg is fertilized, these cells propel the embryo onward to the uterus where the embryo implants. Smoking disrupts the normal function of these fallopian tube cells and the fertilized egg may not move out of the tube properly, resulting in a tubal (ectopic) pregnancy which is a non-viable pregnancy that is dangerous to the mother. In some cases, the fertilized egg may be propelled to the uterus too soon and fail to properly implant, making miscarriage more likely.
Smoking and Fertility Treatments
In addition to the negative effect of smoking on natural conception, the success rate of assisted reproductive technology (ART) treatments is also reduced in women who smoke. Women who smoke are more likely to need twice as many ART treatments to become pregnant. In addition, smokers often need more stimulation medications (gonadotropins) to stimulate their ovaries to produce eggs, which increases the both the cost of the treatment and the risk of side effects. Women who smoke typically have fewer eggs at retrieval and are less likely to achieve pregnancy even if embryos are transferred to the uterus. If women who smoke conceive, they are more likely to have a miscarriage or underweight baby. In summary, the reduced fertility caused by smoking may not be reversible even with ART treatments.
Smoking and Male Fertility
Numerous studies have shown a negative effect of smoking on sperm quality and quantity. Smokers tend to have fewer sperm and the sperm they have are more likely to have shape abnormalities and poor swimming ability. However, because sperm quality can be poor and conception can still occur, the absolute effect of smoking on conception is still being researched. Men who smoke are more likely to experience erectile dysfunction, which also impairs natural conception.
