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Pregnancy – Cannabis use linked to autism; alcohol raises miscarriage risk

Research suggests that children in Canada born to mothers who report using cannabis during pregnancy have about a 50% greater risk of developing autism, reports The Guardian. Other research, from Vanderbilt University, finds that each week a woman consumes alcohol during the first five to 10 weeks of pregnancy is linked with an 8% rise in miscarriage risk.

In The Guardian on 10 August 2020, Nicola Davis writes that the researchers looking at cannabis use during pregnancy found the results concerning – although more research was needed to unpick whether cannabis itself was behind the link. Their study was published in the journal Nature Medicine.

“There is an important parallel with alcohol use,” said Dr Daniel Corsi, an epidemiologist at Ottawa Hospital Research Institute, and a co-author of the study.

“Now the universal recommendation is no alcohol use in pregnancy and I think a similar recommendation should be made for no cannabis use in pregnancy,” he said, adding that it was particularly important given recreational cannabis use was legalised in Canada in 2018.

The team analysed data from around half a million live births in Ontario between 2007 and 2012. The children were followed up until 2017, with autism diagnoses recorded from 18 months. In total about 3,000 of the mothers reported using cannabis during pregnancy.


The results reveal that 2.2% of children born to mothers who used cannabis during pregnancy developed autism, compared with 1.4% of those born to mothers who did not.

To account for other factors that might explain the findings, the team matched 2,364 mothers who used cannabis to 170,671 who did not but who had similar characteristics such as age, education, health conditions and socio-economic status. They also used modelling to look at additional factors including pregnancy complications, reports The Guardian.

The results suggest children born to mothers who used cannabis during pregnancy had a 51% greater risk of developing autism than those born to mothers who did not.

However, the study was based on self-reported cannabis use, meaning occasional use was unlikely to be captured. It was also unable to look at the impact of different doses or frequency of cannabis use – or whether cannabis use changed over pregnancy.

Independent view

The Guardian cites Dr Sven Sandin, a statistician and epidemiologist at the Karolinska Institute in Sweden, who focuses on autism and who was not involved in the research, said the study was well conducted and took into account many factors that could explain the apparent link between cannabis use by mothers and autism in their offspring – including age of the mother and rates of pre-term births. But he said autism was relatively rare and the increased risk was small.

Furthermore, he noted that women who reported cannabis use had a higher risk of mental health problems, meaning that they might be self-medicating with cannabis but passing on genetic risk factors for autism to their children.

“We know autism is highly heritable. Could it therefore be that they transfer the risk to their children not through [using cannabis] … but just through passing on their genes?” he said, noting that the possibility was not fully ruled out by the study.

Sir Robin Murray, a professor of psychiatric research at King’s College London, said: “The finding of increased rates of autism in the offspring of mothers who used cannabis in pregnancy is not surprising given the evidence from animal studies showing how it can disrupt brain development,” The Guardian reports.

Murray noted that women who used cannabis when pregnant might also have engaged in unhealthy behaviours that could be behind the apparent link – meaning caution, and further studies, were needed.

“However, this is a useful warning given that many cannabis dispensaries in North America actively promote taking cannabis for morning sickness in pregnancy,” he said.


Maternal cannabis use in pregnancy and child neurodevelopmental outcomes

Nature Medicine. Published on 10 August 2020.


Daniel J Corsi, Jessy Donelle, Ewa Sucha, Steven Hawken, Helen Hsu, Darine El-Chaar, Lise Bisnaire, Deshayne Fell, Shi Wu Wen and Mark Walker.


Cannabis use in pregnancy has increased and many women continue to use it throughout pregnancy. With the legalisation of recreational cannabis in many jurisdictions, there is concern about potentially adverse childhood outcomes related to prenatal exposure.

Using the provincial birth registry containing information on cannabis use during pregnancy, we perform a retrospective analysis of all live births in Ontario, Canada, between 1 April 2007 and 31 March 2012.

We link pregnancy and birth data to provincial health administrative databases to ascertain child neurodevelopmental outcomes. We use matching techniques to control for confounding and Cox proportional hazards regression models to examine associations between prenatal cannabis use and child neurodevelopment.

We find an association between maternal cannabis use in pregnancy and the incidence of autism spectrum disorder in the offspring. The incidence of autism spectrum disorder diagnosis was 4.00 per 1,000 person-years among children with exposure compared to 2.42 among unexposed children, and the fully adjusted hazard ratio was 1.51 (95% confidence interval: 1.17–1.96) in the matched cohort.

The incidence of intellectual disability and learning disorders was higher among offspring of mothers who use cannabis in pregnancy, although less statistically robust. We emphasize a cautious interpretation of these findings given the likelihood of residual confounding.


Miscarriage risk increases each week alcohol is used in early pregnancy

Each week a woman consumes alcohol during the first five to 10 weeks of pregnancy is associated with an incremental 8% increase in risk of miscarriage, according to a study reported by the Vanderbilt University Medical Center on 10 August 2020.

The findings, published in the American Journal of Obstetrics and Gynecology, examine the timing, amount and type of alcohol use during pregnancy and how these factors relate to miscarriage risk before 20 weeks' gestation.

Impact of alcohol use rises through the ninth week of pregnancy, and risk accrues regardless of whether a woman reported having fewer than one drink or more than four drinks each week. Risk is also independent of the type of alcohol consumed and whether the woman had episodes of binge drinking.

Though most women change their alcohol use after a positive pregnancy test, consuming alcohol before recognising a pregnancy is common among both those with a planned or unintended pregnancy. Half of the 5,353 women included in the analysis reported alcohol use around conception and during the first weeks of pregnancy.

The median gestational age for stopping alcohol use was 29 days. Although 41% of women who changed their use did so within three days of a positive pregnancy test, those who stopped consumption near their missed period had a 37% greater risk of miscarriage compared to women who did not use alcohol.

"Abstaining from alcohol around conception or during pregnancy has long been advised for many reasons, including preventing fetal alcohol syndrome. Nonetheless, modest levels of consumption are often seen as likely to be safe," said Katherine Hartmann, MD, PhD, vice president for Research Integration at VUMC and principal investigator for the Right from the Start cohort, from which participants were enrolled in the study.

"For this reason, our findings are alarming. Levels of use that women, and some care providers, may believe are responsible are harmful, and no amount can be suggested as safe regarding pregnancy loss."

According to the researchers, one in six recognised pregnancies ends in miscarriage, which brings great emotional cost and leaves unanswered questions about why the miscarriage occurred.

Biologically, little is known about how alcohol causes harm during early pregnancy, but it may increase miscarriage risk by modifying hormone patterns, altering the quality of implantation, increasing oxidative stress or impairing key pathways.

Because alcohol use is most common in the first weeks – when the embryo develops most rapidly and lays down the pattern for organ development – understanding how timing relates to risk matters.

Risk did not peak in patterns related to alcohol use in specific phases of embryonic development, and there was no evidence that a cumulative "dose" of alcohol contributed to level of risk.

The study recruited women planning a pregnancy or in early pregnancy from eight metropolitan areas in Tennessee, North Carolina and Texas. Participants were interviewed during the first trimester about their alcohol use in a four-month window.

"Combining the facts that the cohort is large, comes from diverse communities, captures data early in pregnancy and applies more advanced analytic techniques than prior studies, we're confident we've raised important concerns," said Alex Sundermann, MD, PhD, the study's first author and recent graduate of the Vanderbilt Medical Scientist Training Program.

To avoid increased risk of miscarriage, the researchers emphasise the importance of using home pregnancy tests, which can reliably detect pregnancy before a missed period, and ceasing alcohol use when planning a pregnancy or when pregnancy is possible.


Week-by-week alcohol consumption in early pregnancy and spontaneous abortion risk: a prospective cohort study

American Journal of Obstetrics & Gynecology. Published on 12 July 2020.


Alexandra C Sundermann, Digna R Velez Edwards, James C Slaughter, Sarah H Jones, Eric S Torstenson and Katherine E Hartmann.


Half of women use alcohol in the first weeks of gestation, but most stop once pregnancy is detected. The relationship between timing of alcohol use cessation in early pregnancy and spontaneous abortion risk has not been determined.


This study aimed to evaluate the association between week-by-week alcohol consumption in early pregnancy and spontaneous abortion.

Study Design

Participants in Right from the Start, a community-based prospective pregnancy cohort, were recruited from 8 metropolitan areas in the United States (2000–2012).

In the first trimester, participants provided information about alcohol consumed in the prior 4 months, including whether they altered alcohol use; date of change in use; and frequency, amount, and type of alcohol consumed before and after change.

We assessed the association between spontaneous abortion and week of alcohol use, cumulative weeks exposed, number of drinks per week, beverage type, and binge drinking.


Among 5353 participants, 49.7% reported using alcohol during early pregnancy and 12.0% miscarried. Median gestational age at change in alcohol use was 29 days (interquartile range, 15–35 days). Alcohol use during weeks 5 through 10 from last menstrual period was associated with increased spontaneous abortion risk, with risk peaking for use in week 9.

Each successive week of alcohol use was associated with an 8% increase in spontaneous abortion relative to those who did not drink (adjusted hazard ratio, 1.08; 95% confidence interval, 1.04–1.12). This risk is cumulative. In addition, risk was not related to number of drinks per week, beverage type, or binge drinking.


Each additional week of alcohol exposure during the first trimester increases risk of spontaneous abortion, even at low levels of consumption and when excluding binge drinking.


[link url="https://www.theguardian.com/society/2020/aug/10/study-links-cannabis-use-during-pregnancy-to-autism-risk?CMP=Share_iOSApp_Other"]Study links cannabis use during pregnancy to autism risk[/link]


[link url="https://www.nature.com/articles/s41591-020-1002-5"]Maternal cannabis use in pregnancy and child neurodevelopmental outcomes[/link]


[link url="https://www.sciencedaily.com/releases/2020/08/200810102430.htm"]Miscarriage risk increases each week alcohol is used in early pregnancy[/link]


[link url="https://www.ajog.org/article/S0002-9378(20)30725-0/fulltext"]Week-by-week alcohol consumption in early pregnancy and spontaneous abortion risk: a prospective cohort study[/link]


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