NCPIC - National Cannabis Prevention and Information Centre

5: Cannabis use and fertility, pregnancy and breastfeeding

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Cannabis is the most commonly used illicit drug by women who are pregnant.

Even though there has been little research into the effects of cannabis use upon the unborn child, it is strongly recommended that pregnant women do not use alcohol or any other drug due to the potential harmful effects on the developing baby.

Can cannabis use affect fertility?

Heavy use of cannabis has been linked to decreased fertility in both men and women.

In females, there is evidence that cannabis use may disrupt the menstrual cycle. In males, cannabis is thought to decrease sperm quality and production and testosterone levels. It has also been shown to decrease the ability of sperm to move quickly and has been linked to sperm abnormalities. These factors can make it difficult for a woman to become pregnant.

Can cannabis use affect pregnancy?

THC (delta-9-hydrocannabinol), the principal psychoactive ingredient in cannabis, is known to pass from the mother to the developing foetus through the placenta, increasing the risk of complications.

Any form of smoking can disrupt the supply of oxygen and nutrients to the foetus, which can result in premature birth. Women who smoke cannabis even once a week are more likely to give birth to babies with a lower birth weight, which may place the child at a higher risk of developing breathing problems and possible infections. Other risks can include reduced foot length, head circumference and body length.

There is evidence of the damage caused by smoking tobacco during pregnancy, including:

  • miscarriage
  • still-birth
  • Sudden Infant Death Syndrome (SIDS)

Because most people who smoke cannabis also smoke tobacco at the same time, it is believed that these complications could also occur if a woman smokes cannabis and tobacco during pregnancy.

Can cannabis use affect the baby?

There is some evidence that babies born to women who use cannabis during pregnancy are more likely to startle, have higher levels of tremors and may not see as well compared to those babies who are not exposed to cannabis. These symptoms, however, are not evident after the first month. Other effects may include delays in the commencement of breathing at birth and a higher rate of defects in the walls of the heart.

Other studies have found that in the first six months of life, babies who have been exposed to cannabis in utero are also at greater risk of developing asthma, chest infections, and other breathing problems such as wheezing.

Can cannabis use affect breast milk?

When a breastfeeding mother uses cannabis, THC passes into the breast milk and thus into the baby, where it can be stored in the baby’s fatty tissue for several weeks.

Using cannabis while breastfeeding may cause the baby to be unsettled and disrupt feeding cycles. As a result, cannabis use should be avoided when breastfeeding.

Can using cannabis impact on pregnancy care?

Other problems can be experienced by pregnant women using cannabis because they are less likely to disclose their use of cannabis to healthcare workers. The stigma associated with their use, as well as fear, guilt and shame about what they may have exposed their unborn baby to, may prevent these women from giving a full history to their obstetricians or midwives.

This may impact on the quality of care for both the woman and her developing baby as healthcare workers do not have a complete history.

What can your patient do?

If your patient is planning to become, or is pregnant and using cannabis, then it is a good time to advise them to stop using. If they have been using cannabis during their pregnancy, talk to them about their use and/or refer them for more specialized treatment to help them cut down or quit their cannabis use. There is no evidence that cannabis withdrawal increases the risk of miscarriage.