Covid-19 vaccination during pregnancy does not appear to raise risk of preterm birth or stillbirth

Researchers report that vaccination against Covid-19 during pregnancy is not related to an increase in risk of preterm birth, small size for gestational age at birth or stillbirth.

The findings appeared on August 17, 2022 in The BMJ/British Medical Journal.

“Our findings – along with extant evidence that 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, fetal, and neonatal outcomes – can inform evidence-based decision making about Covid-19 vaccination during pregnancy,” the researchers said.

As background, the authors noted that other research has shown that Covid-19 infection during pregnancy is associated with higher risks of complications such as admission to hospital, maternal death, preterm birth and stillbirth.

Prior research has also indicated that Covid-19 vaccination during pregnancy is effective against adverse Covid-19 outcomes in mothers and newborns.

This is the first large study to evaluate data on pregnancy outcomes after Covid-19 vaccination during pregnancy, specifically risk of preterm birth, small size for gestational age at birth, and stillbirth.

The investigators used a population-based birth registry and identified all liveborn and stillborn infants with a gestational age of at least 20 weeks or birth weight of at least 500g in Ontario, Canada between 1 May and 31 December 2021. They correlated this information to records of all Covid-19 immunizations in the same province.

They adjusted their analysis for mother’s age at delivery, pre-pregnancy body mass index, reported smoking or substance use during pregnancy, pre-existing health conditions, number of previous live births and stillbirths and area of residence and income.

They reported that out of 85,162 births, 43,099 mothers had gotten one dose or more of a Covid-19 vaccine during pregnancy, and of these 42, 979 (99.7%) received an mRNA vaccine.

They reported no association of vaccination during pregnancy with an 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%).

They also found no increase in the risk of small size for gestational age at birth (9.1% v 9.2%) or stillbirth (0.25% v 0.44%). 

‘Findings were similar by trimester of vaccination, mRNA vaccine product, and number of doses received during pregnancy,” they said.

“Future studies to assess similar outcomes after immunization with non-mRNA covid-19 vaccine types during pregnancy should be a research priority,” they added.