Researchers in Scotland reported on Thursday that pregnant women with Covid were not only at greater risk of developing severe disease, but also more likely to lose their fetuses and babies in the womb or shortly after birth, compared with other women who gave birth during the pandemic.
The risk of losing a baby through stillbirth or the first month of life was highest among women who delivered their babies within four weeks of the onset of a Covid infection: 22.6 deaths for every 1,000 births, four times the rate in Scotland of 5.6 deaths per 1,000 births.
All of those deaths occurred in pregnancies among unvaccinated women, the researchers found. “Quite strikingly, no baby deaths occurred in women who had SARS-CoV-2 and were vaccinated,” said Dr. Sarah J. Stock, the paper’s first author, a maternal-fetal medicine specialist at the University of Edinburgh Usher Institute in Exeter.
The study also found a higher rate of preterm birth among women diagnosed with Covid, a rate that spiked if the baby was born within a month of the mother falling ill. More than 16 percent of these women gave birth before 37 weeks of pregnancy, compared with 8 percent among other women.
In Scotland, as in the United States, vaccination rates of pregnant women are low. Only one-third of pregnant women are vaccinated against the coronavirus, despite the protections afforded by immunization. Early research has found no evidence that the Pfizer-BioNTech or Moderna vaccines pose serious risks during pregnancy.
Indeed, the Scottish study found that the vast majority of infections among pregnant women were in those who were completely unvaccinated or were only partially vaccinated. Only 11 percent of the total infections were reported among fully vaccinated pregnant women.
Pregnant women who were unvaccinated were also four times as likely to be hospitalized, compared with vaccinated pregnant women.
Dr. Stock and her colleagues analyzed data collected by the Covid-19 in Pregnancy in Scotland study, a national cohort of all women who were pregnant or became pregnant after March 1, 2020, through the end of October 2021. The team tracked 144,546 pregnancies in 130,875 women during this period.
One weakness of the study is that the authors did not adjust for confounding factors, like maternal age or pre-existing medical conditions, which could lead to poor pregnancy outcomes regardless of coronavirus infection or Covid diagnosis (they also did not know whether women who were hospitalized were admitted because of Covid disease, or were just incidentally found to test positive at admission).
Vaccination rates are low among pregnant women across the board, but are particularly low among younger women and those from lower socioeconomic backgrounds, the study noted. Future analyses will take these demographic factors and other confounding factors into account, the authors said.
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Still, the discrepancies in hospitalization, premature birth and infant loss rates between vaccinated and unvaccinated women are so marked that those adjustments are unlikely to alter the conclusions, Dr. Stock and her colleagues said.
They urged pregnant women to get vaccinated, echoing the pleas of health officials in the United States.
“The key take home we’d love to get across is that really the best way to protect mother and baby is vaccination at the earliest opportunity, and that can be done at any stage of pregnancy,” said Aziz Sheikh, a population health researcher at the University of Edinburgh and another of the paper’s authors.
“We have enough information to bring the really strong message around promoting vaccination in pregnancy now,” said Rachael Wood, a consultant in public health medicine in Public Health Scotland, and a member of the study team.
