Cannabis in pregnancy

Cannabis during pregnancy is clearly discouraged by BAG, SGGG and ACOG. Meta-analyses show higher risk of low birth weight (–110 g on average), preterm birth and NICU admission (Gunn 2016, Metz 2018). THC crosses the placenta and affects fetal brain development (Volkow 2017). No safe amount is known — abstinence is the only evidence-based recommendation.

TL;DR

  • THC crosses the placenta and reaches the fetus.
  • Studies (Metz 2018, Volkow 2017): increased risk of preterm birth and low birth weight.
  • Long-term effects: mild cognitive and executive deficits at school age (OPPS, Fried).
  • Clear FOPH, SGGG, ACOG recommendation: no cannabis, including CBD.

Why CBD is not recommended either

CBD products often contain trace THC. Also, no controlled safety studies exist in pregnancy.

Preclinical data suggest interference with placental development (Feinshtein 2013).

The endocannabinoid system and fetal brain development

The endogenous cannabinoid system plays a fundamental role in early embryonic development and the formation of the central nervous system. Already in the first weeks of pregnancy, this physiological system controls neuronal migration, axonal pathfinding, and synaptogenesis in the fetal brain. When exogenous cannabinoids such as THC cross the placental barrier into the fetal circulation, they bind to the receptors there. This unphysiological activation can disrupt the highly sensitive, precisely timed developmental steps and have a lasting impact on the child's neural networking.

Since the fetal liver does not yet possess fully developed enzymatic degradation pathways, the active substances and their metabolites remain in the fetal circulation significantly longer than in the maternal organism. In addition, the amniotic fluid represents a potential reservoir in which lipophilic substances can accumulate. The impairment affects not only the neural structure but also the placental function itself, as cannabinoids can negatively affect blood flow to the uterus and thus the continuous supply of oxygen and nutrients to the unborn child.

  • Key function of the endocannabinoid system in fetal brain maturation
  • Dysregulation of neuronal migration by exogenous cannabinoids
  • Prolonged half-life of THC in the fetal organism due to immature enzymes
  • Restriction of placental blood flow and nutrient supply

Swiss legal framework, prevention and advice

In Switzerland, the legal situation regarding cannabis is clearly regulated: products with a total THC content of over one percent are considered illegal under the Narcotics Act (BetmG). For pregnant women, this means that the consumption of such substances also has legal relevance. Since August 2022, medical cannabis has been prescribable by a doctor without a BAG exceptional permit, but due to the insufficient safety data, such a prescription is only issued to pregnant women after the strictest benefit-risk assessment and in absolute exceptional cases.

Swiss authorities such as the BAG and Swissmedic work closely with gynecological professional societies to raise awareness among medical staff about the risks of consumption during pregnancy. In the event of questions or uncertainties following accidental consumption, Tox Info Suisse provides an initial, confidential point of contact via the emergency number 145. In addition, Swiss hospitals and maternal consultants are trained to advise affected women in a non-judgmental and evidence-based manner in order to support a rapid cessation of consumption in the interest of child protection.

  • Legal limit of less than one percent total THC for legal products
  • Prescription requirement for medical cannabis since August 2022 without BAG authorization
  • Free and anonymous consultation at Tox Info Suisse via the telephone number 145
  • Interdisciplinary cooperation between BAG, Swissmedic and gynaecological services

Risks during breastfeeding and postnatal accumulation

The risks do not end with birth, as lipophilic substances such as THC pass into breast milk to a high degree. Due to the high fat content of breast milk, cannabinoids accumulate heavily there, and the concentration in the milk can exceed that in the maternal blood plasma many times over. The infant ingests these active substances through feeding, after which they accumulate in the child's fatty tissue and developing brain. This can lead to sedation, poor feeding, and delays in motor development.

Professional organisations therefore recommend strict cannabis abstinence throughout the entire breastfeeding period. If a mother is unable to stop consumption, it must be weighed up in consultation with paediatrics whether weaning is the safer option for the child. In addition to the direct pharmacological effects via breast milk, the consumption of psychoactive substances also impairs the cognitive presence and responsiveness of caregivers, which has been proven to increase the risk of accidents in the home environment.

  • Strong accumulation of lipophilic cannabinoids in high-fat breast milk
  • Delay in motor development and sedation in the breastfed infant
  • Strict recommendation of abstinence during the entire breastfeeding period
  • Increased risk of accidents due to impaired responsiveness of the parents

FAQ

I used unknowingly — what now?

Don't panic: stop immediately and talk to your OB/GYN. Single exposures are rarely catastrophic, but avoid chronic use.

How long does THC remain detectable in a pregnant woman's body after consumption?

The detectability of THC depends on the frequency of consumption and individual metabolism. Since THC is highly fat-soluble, it accumulates in fatty tissue and is only slowly released from there. In the case of one-off consumption, THC is usually only detectable in urine for a few days. With regular consumption, however, detection in urine can be established for several weeks up to a month or longer, which also means ongoing exposure of the fetus.

Does the recommendation for abstinence also apply to second-hand cannabis smoke?

Yes, the passive inhalation of cannabis smoke should also be strictly avoided during pregnancy. When exposed to second-hand smoke in enclosed spaces, measurable amounts of THC and harmful combustion products such as carbon monoxide can enter the maternal bloodstream. Carbon monoxide impairs oxygen transport in the blood, which directly compromises the oxygen supply to the fetus via the placenta and increases the risk of developmental delays.

Is there a difference between smoked cannabis and the consumption of edibles during pregnancy?

Although consuming cannabis-containing foods eliminates the harmful substances of combustion smoke, the risk to the unborn child remains just as high. During oral consumption, the psychoactive active ingredient THC is converted in the liver into an even more potent metabolite. This also reaches the fetus directly via the bloodstream and the placenta. The unpredictable concentration of the active ingredient and the delayed onset of action of edibles also increase the risk of an overdose.