Cannabis abuse in pregnancy

Joseph CY WONG 黃志揚

HK Pract 2025;47:109-112

Summary

摘要

Introduction

Cannabis is a psychoactive illicit drug in Hong Kong with street names: “marijuana”, “hash”, “grass”, “weed”, etc. Tetrahydro-cannabinol (THC) is a cannabinoid giving the “high” sensation for abusers. It is ranked the fourth commonest type of drugs of abuse in 2023 (493, 24.9%), coming only after heroin, cocaine and ice.¹ With a growing social acceptance, it has become the second commonest abused drug among youngsters aged below 21. Therefore, cannabis abuse also has a growing prevalence among pregnant women. Primary care providers should acknowledge its impact on pregnant mothers and children and offer suitable advice and intervention during clinical encounters. Every clinical attendance can be a life changing opportunity for pregnant cannabis users to quit cannabis, if we, healthcare professionals, can offer a helping hand.

Prevalence

Data of drug abuse in Hong Kong is mainly gathered by the Security Bureau in the Central Registry of Drug Abuse (CRDA) which was based on a voluntary reporting system. Department of Pharmacology & Pharmacy of the University of Hong Kong (HKU) carried out analysis on data based on Accident & Emergency (A&E) attendance in public hospitals.² They organised drug abuse patterns from Clinical Data Analysis and Reporting System (CDARS) of the Hospital Authority (HA) and Poison Information and Clinical Management System (PICMS) of the Hong Kong Poison Information Centre (HKPIC). One quarter of women attended AED for substance abuse were during perinatal period, in which 13.3% women attended within one year before pregnancy, 6.9% were in 1-year period postpartum, and 5.9% were during gestation period.

Studies in the United States further evaluated the pattern of cannabis abuse among pregnant women.³ Four thousand pregnant women were included, prevalence of past-month cannabis use rose from 3.4% to 7.0% between 2002 to 2017. Daily or near daily cannabis use was also common (3.4%) among pregnant women. First trimester, in which foetus is believed to be the most sensitive to in-utero exposure to cannabis. Most exposure took place during first trimester (12.1%), compared with the second (4.0%) and third trimester (4.5%).

Neonatal risks

Three important prospective longitudinal studies following children to different endpoints (sample sizes: 698, 793 and 7531) established most of our understandings about the hazards of maternal use of cannabis.^4-6

Preterm birth, low birth weight, foetal growth restriction

In the past, evidence regarding preterm birth (PTB), low birth weight (LBW) and foetal growth restriction (FGR) was mixed: some showing correlations but some showing no clinical significance. Yet, recent meta-analysis and large retrospective cohort studies established dose-response relationship in maternal cannabis use with LBW (pooled odds ratio 1.77, pooled mean difference 109.42 g), PTB (pooled odds ratio 1.35) and FGR (growth reduction -14.44 g/week), with controlling tobacco smoking confounding effect.^7-9

Multiple congenital anomalies

Meta-analysis of recent retrospective cohorts demonstrated association of antenatal cannabis use and multiple congenital anomalies (MCA), especially for maternal infections, situs inversus, teratogenic syndromes and VACTERL association.¹⁰ Daily cannabis use was found to be the strongest predictor for all MCA.

APGAR score / perinatal death

Evidence regarding APGAR score and perinatal death was not consistent, but cannabis exposure led to more neonatal intensive care unit (NICU) admissions.¹¹

Neurodevelopment

Studies about cannabis exposure affecting children’s neurodevelopment were often with limited reproducibility, probably due to difficulties in controlling socioeconomic factors across families. Some neonates with in-utero exposure to cannabis were reported to have withdrawal syndrome presenting as increase in startles and tremors and reduced habituation to light.¹² When they grew up to preschool age, they might demonstrate difficulties with verbal and visual reasoning, features of attention deficits, hyperactivity, and impulsivity. As the child enters adolescence, symptoms of depression and anxiety would emerge and the children tend to have earlier cannabis use and poorer adolescent and early adulthood achievement.

Maternal risks

General risks and health hazards of cannabis use in adults would affect pregnant women including dependence, harmful use, withdrawal, tolerance. Tetrahydrocannabinol (THC) replacement therapy can reduce maternal risks but not neonatal risks. No specific treatment option showed superiority over one another, but treatment is better than none.¹³

Nausea and vomiting

Media often promote medical use of cannabis for its antiemetic use including for morning sickness during pregnancy. 92% pregnant women trying cannabis for antiemetic use found it effective or even extremely effective.¹⁴ Yet in observational studies, cannabis use before pregnancy has been associated with more nausea and vomiting during pregnancy.¹⁵ The subjective antiemetic effects may only be due to placebo effects or belief from popular culture, rather than strong evidencebased therapeutic benefit. Further health education is needed to boost the public awareness of the adverse effects of cannabis products.

Cannabinoid hyperemesis syndrome has been reported by Emergency Medicine journals in the recent decade.¹⁶ Its diagnosis was based on chronic marijuana use, acute-onset nausea, vomiting and abdominal pain. These symptoms typically lasted for one to two days and could be relieved by hot showers. Treatment options include topical capsaicin cream, haloperidol and benzodiazepines. In the long term, cannabis cessation is important.

Postpartum risks

THC can pass from mothers to babies through breastfeeding, as it is very soluble in fats. In chronic heavy users, the level of THC in milk can be eight times as high as in plasma and its metabolites could be found in infant faeces and urine, posing hazards to neonates.¹⁷

Mothers smoking cannabis products could result in second-hand exposure or accidental ingestion by infants, which is an independent risk factor for sudden infant death syndrome. Mothers abusing cannabis could also lead to impaired childcare, inflicting domestic accidents or child neglect.

Recommendations

American College of Obstetrics and Gynaecology and American Academy of Paediatrics made similar recommendation:

1. Encourage cessation of cannabis use in individuals who are planning for pregnancy or during gestational period.


2. Healthcare providers should ask pregnant women about cannabis use and concurrent use of tobacco or other substance abuse, in order to provide appropriate counselling of the potential risks of continued use during pregnancy.

Key messages

1. Cannabis is one of the commonest illicit drugs of abuse among adolescents and young adults in Hong Kong. A quarter of women attending A&E for drug abuse were perinatal.


2. Cannabis exposure during pregnancy and postpartum can bring adverse outcomes in neonates (including growth, development, congenital anomalies, and perinatal deaths) and mothers (general hazards and hyperemesis).


3. Counselling for cannabis cessation during pregnancy and breastfeeding i s generally recommended, but universal testing is not indicated unless clinically indicated and with informed consent from mothers. Healthcare professionals need to be aware of limitations of diagnostic tools for cannabis testing (e.g. halflife of cannabis differs between samples and testing methods).


4. Neonates with in-utero exposure of cannabis in Hong Kong are usually admitted to SCBU for monitoring and their mothers would be referred to CCDS for multidisciplinary follow-up.



3. For pregnant women using cannabis for medical use, alternative treatment options with more pregnancy-safety data should be considered.


4. Cannabis use should be discouraged during lactation.


5. Universal testing is not indicated, and tests should only be done if indicated and with consent from clients.


6. Healthcare professionals should also be aware of the limitations of different diagnostic tools, as cannabis’ biological half-life differs in various samples and diagnostic tests. Clinicians should refer to the instructions of specific drug test kits.

Local practice

There is no general recommendation or guidelines provided by local expert bodies. But in general practice, mother at-risk of substance abuse would be referred to Comprehensive Child Development Service (CCDS) for follow-up of mother-and-child wellbeing. Antenatally, CCDS provides counselling for mothers, urine testing and psychiatric or drug rehabilitation service. Postnatally, it provides toxicology for mothers and children and organises multidisciplinary case conference (MDCC) or social welfare plan meeting if needed. Infants would also be admitted to special care baby unit (SCBU) for monitoring of withdrawal effects after delivery. For cannabis users planning on pregnancy, cannabis rehabilitation services via the government and non-government organisations (NGOs) can provide cessation counselling. The Social and Welfare Department (SWD) has two Centres for Drug Counselling (CDCs) and eleven Counselling Centres for Psychotropic Substance Abusers (CCPSAs) for prevention and rehabilitation of cannabis use for the general public. NGOs operates thirteen residential drug treatment and rehabilitation services units in Hong Kong for drug abusers who wish to seek voluntary residential drug treatment and rehabilitation for social integration. General Practitioners can refer at-risk individuals to these programmes for cannabis abstinence and other social interventions. Healthcare professionals can also screen any illicit drug use of the spouse as well, to facilitate early intervention for at-risk families.

Conclusion

Primary healthcare providers, midwives, obstetricians and paediatricians should be aware of the growing popularity of cannabis use in the young population and actively offer advice and assistance for pregnant women having cannabis abuse whether necessary. Early social intervention can be provided by CCDS in Hong Kong for mothers with cannabis abuse. More studies are needed to explore the physical and psychosocial impacts of child development in families with cannabis abuse and their intervention, as well as those with multiple drug abuse.

References

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