Vaccination against Covid-19 in pregnancy is not linked to a higher risk of preterm birth or stillbirth, a large observational study has suggested.

Infection with SARS-CoV-2 during pregnancy has been associated with higher risks of admission to hospital, admission to an intensive care unit, and death, the Canadian researchers wrote in The BMJ.

Covid has also been linked with a higher risk of preterm birth, foetal growth restriction, postpartum haemorrhage, and stillbirth, they noted.

Yet despite many countries recommending vaccination against Covid-19 during pregnancy, vaccine coverage in pregnant women remained lower than among women of reproductive age.

For this population-based retrospective cohort study, the researchers analysed birth registry data from Ontario, Canada, from 1 May to 31 December 2021, including all liveborn and stillborn infants from pregnancies conceived at least 42 weeks before the end of the study period and with gestational age of 20 weeks or more or birth weight of 500g or more.

Among the 85,162 births, around half (43,099) were in individuals who had received one or more doses of a Covid vaccine while pregnant, with almost all of those people receiving an mRNA vaccine.

The researchers found that vaccination during pregnancy was not associated with any increased risk of overall preterm birth (6.5% among vaccinated v 6.9% among unvaccinated), spontaneous preterm birth (3.7% v 4.4%), or very preterm birth (0.59% v 0.89%).

In addition, no increase was found in risk of small for gestational age at birth (9.1% v 9.2%) or stillbirth (0.25% v 0.44%) when taking the vaccination during pregancy.

‘These results – based on more than 43,000 foetuses exposed to at least one dose of mRNA Covid-19 vaccine – did not differ by trimester of vaccination, number of doses received during pregnancy, or mRNA vaccine product,’ the researchers added.

‘Our findings – along with extant evidence that Covid-19 vaccination during pregnancy is effective against Covid-19 for pregnant individuals and their newborns, and that Covid-19 during pregnancy is associated with increased risks of adverse maternal, foetal, and neonatal outcomes – can inform evidence-based decision making about Covid-19 vaccination during pregnancy.’

The researchers were unable to assess vaccination before pregnancy or around the time of conception or the effect of booster doses, and they called for studies assessing similar outcomes after immunisation with non-mRNA Covid-19 vaccine types during pregnancy to be prioritised.

In a letter, sent in January to health bodies – including community pharmacy-led vaccination services – NHS England and NHS Improvement (NHSE&I) asked maternity service leads to coordinate with vaccination programme leads so that every woman attending a maternity service has easy, timely access to vaccine confidence conversations and co-located vaccination offers.

This comes after at trial earlier this year found a bivalent protein-based respiratory syncytial virus (RSV) vaccine given to pregnant women is safe and elicits neutralizing antibodies which transfer to their offspring, according to a planned interim analysis of a Phase IIb trial.