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COVID vaccination not linked to premature birth or unusually small babies – CDC study

COVID vaccinations during pregnancy present no greater risk of premature birth or of unusually small babies than for vaccinated women, a US study has reported.

The findings of one of the first studies to examine the health of babies born to women vaccinated during pregnancy were reassuring, said the researchers. Low-birthweight babies and infants born early are more likely to experience developmental delays and other health problems.

An earlier study had found that women vaccinated during pregnancy did not face a higher risk of miscarriage than the unvaccinated.

The latest study looked at 46,079 pregnancies that resulted in a live birth, including 10,064 among women who received one or more doses of the COVID vaccine between 15 December 2020, and 22 July 2021, during their pregnancies.

Most had received the Pfizer-BioNTech or Moderna shots, and most were inoculated during their second or third trimester.

Overall, 6,6% of the babies were born prematurely, before 37 weeks of pregnancy, and 8,2% were born small for their gestational age, weighing less than 2,4kg. Researchers found no difference in the rates among mothers who had been vaccinated while pregnant and those who had not.

“We plan to do follow-up studies on infants and their development, but there hasnʼt been enough time to do them yet,” said Dr Heather Lipkind, a maternal foetal medicine specialist at Yale University and lead author.

The study was conducted by the US Centers for Disease Control and Prevention (CDC), in collaboration with Lipkind, HealthPartners Institute, Kaiser Permanente researchers and the Harvard Pilgrim Health Care Institute. It was published on the CDC site Morbidity and Mortality Weekly Report.

The risks of pre-term birth, which appear to be higher when pregnant women are infected with the coronavirus, are well established, she said: “With each week of gestation, the brain develops more. If you have COVID and have to deliver preterm, that can also affect long-term development.”

Another benefit to vaccination is that women may pass on coronavirus antibodies to their infants, helping to protect them from illness, she added.

Pregnant women who become infected face a higher risk of developing severe disease, and federal health officials have implored them to get vaccinated. Nevertheless, vaccination rates remain low among pregnant women — about 31% as of late September.

Vaccination rates also vary widely by community. While almost half of all pregnant Asian Americans are vaccinated, only 25% of pregnant Hispanic women are, and only 15% of pregnant black women, according to the CDC.

“Anecdotally, in my practice women who are not vaccinated are getting way sicker,” Lipkind said, “and weʼre seeing pre-term birth in pregnant women who had COVID and loss of pregnancy. Itʼs very, very tragic.”

She strongly encourages her patients to get vaccinated, but she often faces fierce resistance, she said.

“I think people are just afraid of the unknown in general with pregnancy, but this latast research help them feel a little better about vaccination.”

Study details

Receipt of COVID-19 Vaccine During Pregnancy and Preterm or Small-for-Gestational-Age at Birth — Eight Integrated Health Care Organizations, United States, December 15, 2020–July 22, 2021

Published in CDC’s Morbidity and Mortality Weekly Report on 4 January 2022

Heather Lipkind; Gabriela Vazquez-Benitez; Malini DeSilva; Kimberly Vesco; Christina Ackerman-Banks; Jingyi Zhu; Thomas Boyce; Matthew Daley; Candace Fuller; Darios Getahun; Stephanie Irving; Lisa Jackson; Joshua Williams; Ousseny Zerbo; Michael McNeil; Christine Olson; Eric Weintraub; Elyse Kharbanda.


What is already known about this topic?
Pregnant women with COVID-19 are at increased risk for severe illness and adverse birth outcomes, yet many remain reluctant to be vaccinated.

What is added by this report?
In a retrospective cohort of >40,000 pregnant women, COVID-19 vaccination during pregnancy was not associated with preterm birth or small-for-gestational-age at birth overall, stratified by trimester of vaccination, or number of vaccine doses received during pregnancy, compared with unvaccinated pregnant women.

What are the implications for public health practice?
These data support the safety of COVID-19 vaccination during pregnancy. CDC recommends COVID-19 vaccination for women who are pregnant, recently pregnant, who are trying to become pregnant now, or who might become pregnant in the future.


MMWR article – Receipt of COVID-19 Vaccine During Pregnancy and Preterm or Small-for-Gestational-Age at Birth — Eight Integrated Health Care Organizations, United States, December 15, 2020–July 22, 2021 (Open access)


See more from MedicalBrief archives:


Delta variant increases COVID-19 risks for pregnant women


Pfizer/Moderna vaccine side effects in breastfeeding women and infants


COVID increases pregnancy and birth complications — French hospital study


Effectiveness of Pfizer vaccine in pregnancy — Clalit Health Services study


Pregnant women pass COVID antibodies to their babies — Weill Cornell



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