Every year on World No Tobacco Day, we're reminded how bad smoking is for our health; the tar and chemicals stick to our clothes, skin, and the inside of our lungs. Cigarette smoking can affect our entire body, reducing our health in general, like our fertility. Couples who smoke are less fertile than non-smokers, and are more likely to take over a year to get pregnant.

Lifestyle factors, such as smoking, have been linked to reproductive health problems for both men and women. For example, in male smokers, the sperm and semen quality may deteriorate. Female smokers trying to conceive risk developing fertility problems, such as damaged eggs, increased miscarriage, and problems with the fallopian tubes — where eggs travel from the ovaries to the uterus.

Read More: Why Can't I Get Pregnant? Failed Fertility Treatment Linked To Future Cardiovascular Problems

There are a million reasons not to smoke; for couples who want to get pregnant, here are six ways smoking can lead to infertility in both men and women.

Smoking Effects On Female Fertility

Harder To Get Pregnant

Smoking has been linked to several fertility problems in women. Female smokers are 60 percent more likely than nonsmokers to be infertile. Previous research has found the risk of infertility in women smokers versus non-smokers was 1.60 compared to the baseline 1.0 for nonsmokers. Moreover, women smokers have an ovarian age that is two or three years older than their biological age, and a 40 percent lower success rate with reproductive assistance technologies, such as IVF. 

Increases Risk Of Miscarriage

Another reason women should kick the habit before becoming pregnant — early miscarriage. A 2010 study found Japanese women who smoked heavily early in pregnancy, and who also had a past pregnancy, were more than twice as likely as nonsmokers to suffer a miscarriage in their first trimester. This effect was more pronounced in women who smoked at least 20 cigarettes per day.

Although most miscarriages happen in the first trimester, and experts believe they're mostly due to random genetic abnormalities, we also know that lifestyle habits like smoking have been linked to an increased risk of miscarriage. Carbon monoxide and cyanide in inhaled cigarette smoke pass through the placenta and into the fetus. This can cause constriction of the blood vessels in the placenta, a lack of blood flow, and miscarriage at an early stage, or fetal growth restriction and death at a later stage in pregnancy.

Increases Risk Of Ectopic Pregnancy

The chemical cotinine, found in cigarette smoke, can cause a reaction that can lead to ectopic pregnancies, according to a 2010 study. Researchers observed a protein, known as "PROKR1", raised the risk of an egg implanting outside the womb. PROKR1 can allow the egg to implant correctly inside the womb, but when it's in the fallopian tubes, it's believed to increase the risk of this occurring outside the womb.

Women who smoked and developed an ectopic pregnancy had two times more PROKR1 in their fallopian tubes as women who did not smoke, and had an earlier healthy pregnancy. They hypothesize too much PROKR1 inhibits the muscles in the walls of the fallopian tubes from contracting, which prevents the transfer of the egg to the womb.

Smoking Effects On Male Fertility

Decreases Sperm Count

Cigarette smoking can decrease sperm count in men who smoke. A 2003 study found sperm count, motility, and morphology, or form, were significantly affected in smokers, while another 2015 review did not see any significant changes. Although research may be inconclusive, the American Society for Reproductive Medicine has stated smoking can affect basic semen parameters, such as its appearance, volume, pH, viscosity, and count. 

Read More: Can Smoking Pot Lower Male Fertility?

Increases Sperm DNA Fragmentation

Male smokers are more likely to have a significantly higher level of DNA fragmentation compared to non-smokers. Sperm has a DNA fragmentation index (DFI), which is a ratio that states the percent of fragmented, or broken, sperm DNA. Therefore, a higher DFI percentage means more DNA in the sperm is broken, which is believed to decrease male fertility.

A 2006 study found cigarette smoking has harmful effects on sperm quality and sperm DNA fragmentation. However, the semen analysis of count, morphology, and motility was normal in these men. The American Society for Reproductive Medicine notes that the clinical value of DNA fragmentation testing is not recommended to evaluate male infertility. But, this coincidence is worth exploring at the molecular level, since other factors that influence fertility also tend to be normal.

Changes Sperm's Epigenetic Profile

Smoking is believed to change the epigenetic profile of sperm. Epigenetics refers to "extra" information "sprinkled" to the top of our DNA related to our environment. This means smoking can alter our DNA, affecting how the body reads it, and how these changes can be passed on to future generations. In a 2016 study, researchers found smokers had DNA methylation changes that affected more than 7,000 genes; many of the genes are linked to heart disease and cancer, which are known to be caused by smoking.

Smoking can make us feel good in the short term, but it can quickly damage our health, and even influence our fertility.

See Also:

Mothers Who Smoke While Pregnant Or Breastfeeding Decrease Their Son's Chances Of Being Fertile

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