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Covid-19 vaccines in pregnancy not linked to miscarriage or stillbirth

The risks of catching covid-19, or being vaccinated against it, during pregnancy have been debated throughout the pandemic, with research now overwhelmingly supporting that pregnant people get vaccinated

Health 11 August 2022

A pregnant person receives the Pfizer/BioNTech vaccine against covid-19 in Schwenksville, Pennsylvania in February 2021

A pregnant person receives the Pfizer/BioNTech vaccine against covid-19 in Schwenksville, Pennsylvania, in February 2021

HANNAH BEIER/Reuters/Alamy

The most commonly used covid-19 vaccines are safe in pregnancy, a study has confirmed.

The risks of catching covid-19, or being vaccinated against it, during pregnancy have been debated throughout the pandemic. In the UK, covid-19 vaccines began being rolled out in December 2020 but were not offered to pregnant people until April 2021.

Worldwide, pregnant people are now broadly encouraged to get vaccinated. But in the UK alone, only three in five (59.5 per cent) women who gave birth in January 2022 had received at least one dose.

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To better understand the vaccines’ safety profile, Manish Sadarangani at the British Columbia Children’s Hospital Research Institute in Canada and his colleagues surveyed 191,360 people, aged 15 to 49, between December 2020 and November 2021. Over these 11 months, the alpha, beta, gamma and delta coronavirus variants were dominant in Canada.

The participants, from seven Canadian provinces, self-reported any health issues they may have experienced in the seven days after they received the first or second dose of a Pfizer/BioNTech or Moderna coronavirus vaccine. The team did not include people who received modified adenovirus vaccines, such as the Oxford/AstraZeneca vaccine, as only a relatively small number of pregnant people in Canada were immunised with this vaccine type.

The participants, of whom more than 97 per cent identified as women, were split into three groups: pregnant people who were vaccinated against covid-19, unvaccinated pregnant people and people who were vaccinated but not pregnant.

“This study was looking at whether there were any complications associated with [the coronavirus] vaccine doses during pregnancy,” says Allison McGeer at the University of Toronto, a co-author of the study. This study does not ask whether the vaccine protects pregnant people from severe covid-19, which is supported by other research, she says.

The researchers found that in the seven days after a first vaccine dose, 1.5 per cent of the 5597 vaccinated pregnant people reported a stillbirth or miscarriage, which resulted in hospitalisation in some cases. This is compared with 2.1 per cent of the 339 unvaccinated pregnant people who experienced a stillbirth or miscarriage in the seven days before they were surveyed.

For comparison, the researchers assessed the hospitalisation rate of the non-pregnant but vaccinated participants. Of these, just 0.6 per cent were admitted for any reason in the seven days after their first vaccine dose.

“The one thing that all women who are pregnant worry about is the baby,” says McGeer. “In this sizable study we were unable to detect any adverse events associated with pregnancy for those who got the vaccine.”

Other serious pregnancy complications – such as vaginal bleeding, abnormal foetal heart rate and reduced foetal movement – were rarely reported by any of the participants. Although the rate of these events was low, it was comparable between the pregnant participants, regardless of whether they had been vaccinated against covid-19.

“It is very reassuring that there is no evidence of any safety concerns associated with vaccination in pregnancy, especially as high levels of vaccination hesitancy in pregnancy persist,” says Sarah Stock at the University of Edinburgh in the UK.

The team also found that just 4 per cent of pregnant people reported less serious health issues, such as muscle pain and headaches in the seven days following their first vaccine dose, rising to 7.5 per cent in the week after a second dose.

Meanwhile, 6.3 per cent of the vaccinated non-pregnant people reported mild side effects in the week after dose one, increasing to 11.3 per cent in the seven days after dose two.

It is unclear why pregnant people experienced fewer mild symptoms after vaccination than non-pregnant people, says McGeer. It might be due to the way the immune system changes when someone is pregnant, she says.

The World Health Organization, NHS and Centers for Disease Control and Prevention (CDC) in the US all recommend that pregnant people get vaccinated against the coronavirus.

Past research has shown the potential risks of catching covid-19 in pregnancy. According to a study published in July, having covid-19 in late pregnancy is linked to a seven-fold higher risk of premature birth.

A more recent study review found that pregnant people with covid-19 are more likely to experience heart complications than those who are not pregnant.

Journal reference: The Lancet Infectious Diseases, DOI: https://doi.org/10.1016/S1473-3099(22)00426-1

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