Cannabis use and pregnancy

Cannabis is the most commonly used illicit drug among women of reproductive age or 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 and their partners 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 testosterone levels. It is also thought 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-tetrahydrocannabinol), the main psychoactive ingredient in cannabis, is known to pass from the mother to the developing foetus through the placenta. This means that the foetus is affected by any amount of cannabis taken by the pregnant woman, placing it at a greater risk of complications occurring. The effect of the passive inhalation of cannabis as a result of breathing in the smoke of others is not clear, but it should be avoided.

Any form of smoking can disrupt the supply of oxygen and nutrients to the foetus, which can result in restrictions to the growth of the foetus (including overall length, foot length, head size and body weight), and in rare cases, premature birth, miscarriage and stillbirth.

Can cannabis use affect the baby?

There is some evidence that women who use cannabis during pregnancy are more likely to give birth to babies with lower birth weight, delayed commencement of breathing, an increase in features similar to those found in foetal alcohol syndrome, exaggerated startle response, tremors, poorer eye-sight, poorer ability to adapt to new aspects of the environment, and a hole in the heart (ventricular septal defect).

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.

Research suggests that, at ages three to four years, children of mothers who used cannabis while pregnant have poorer verbal, memory and reasoning ability; poorer motor skills and shorter length of play; and are more likely to be fearful, impulsive, inattentive, hyperactive and delinquent. These difficulties appear to persist to age 10 years, when they may be accompanied by increased depression and anxiety, along with reading and spelling problems and general underachievement at school. Such deficits may also continue into adolescence and early adulthood, along with an increased risk of initiation to tobacco and cannabis use.

In addition, there exists some evidence that mothers cannabis use during pregnancy increases the risk of their children developing childhood cancers, including non-lymphoblastic leukaemia, rhabdomyosarcoma (a rare, highly malignant tumour that can occur anywhere in the body), and astrocytoma (a type of brain tumour).

Preliminary research suggests that fathers cannabis use in the year prior to their children s birth is associated with an increased risk of rhabdomyosarcoma in their children, and that fathers cannabis use during conception, pregnancy or postnatally is associated with an increased risk of Sudden Infant Death Syndrome (SIDS) in their infants. Furthermore, some research suggests that children of fathers who experience cannabis dependence at least at some point in their lifetimes are more likely to experience negative outcomes during childhood, such as poor attachment relationships with their caregivers and psychosocial impairments, including depression and conduct problems.

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 help is available?

Women who are pregnant or who are planning to become pregnant as well as their partners, should be advised to stop using cannabis. Continued use should be discussed with a general practitioner, specialist or midwife who can provide help and support to cut down or quit cannabis use or refer patients on to specialist alcohol and other drug services.

Factsheet published August 1, 2008. Updated October 1, 2011.