COVID Vaccine in Pregnancy Not Tied to Adverse Outcomes

Pregnant women who received a COVID-19 vaccine faced no additional risks of adverse birth outcomes compared to those who were not vaccinated, according to a retrospective cohort study.

COVID-19 vaccination in pregnancy was not associated with an increased risk of preterm birth (adjusted hazard ratio [aHR] 0.91, 95% CI 0.82-1.01) or of small-for-gestational-age (SGA) at birth (aHR 0.95, 95% CI 0.87-1.03), reported Heather Lipkind, MD, MS, of Yale University in New Haven, Connecticut, and colleagues in Mortality and Morbidity Weekly Report.

However, only 21.8% of the more than 40,000 pregnant women in the study were vaccinated, the researchers noted.

Lipkind and colleagues added that while the absolute risk of severe morbidity associated with COVID-19 in pregnancy is low, pregnant women with symptomatic illness have an increased risk of ICU admission, invasive ventilation, life support, and even death versus non-pregnant women with COVID-19. Additionally, researchers are gathering more evidence about the benefits of COVID-19 vaccination in pregnancy, such as the presence of antibodies in cord blood.

“Together, these findings reinforce the importance of communicating the risks for COVID-19 during pregnancy, the benefits of vaccination, and information on the safety and effectiveness of COVID-19 vaccination during pregnancy,” Lipkind’s group stated.

The CDC recommends COVID-19 vaccination during pregnancy, and additionally suggests that all adults — including those who are pregnant, breastfeeding, or trying to get pregnant — get a booster shot. The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine recommend COVID-19 vaccination during pregnancy.

Lipkind and colleagues analyzed 46,079 singleton pregnancies from December 2020 to July 2021, obtaining data from eight health centers in the CDC Vaccine Safety Datalink (VSD) project. They included women, ages 16 to 49, who were expected to deliver between February and July 2021.

In the vaccinated group (n=10,064), the mean age was 32.2 years, 43% were non-Hispanic white, 25.6% were Asian, and 24.5% were Hispanic. Mean age in the unvaccinated group (n=36,015) was 29.8 years, while 38.4% were Hispanic, 32.2% were white, and 15.7% were Asian. Obesity, defined as a BMI ≥30 before pregnancy or during the first trimester, was the most common comorbidity in both groups.

The authors collected data from standardized VSD files, electronic health records, insurance claims, and state or local immunization databases to identify those who received a COVID vaccine during pregnancy. Vaccine doses that were administered from a woman’s last menstrual period through 3 days before delivery were included.

Lipkind’s group then compared rates of preterm and SGA at birth (defined as a birthweight less than the 10th percentile for gestational age) between the vaccinated and unvaccinated groups, conducting separate analyses based on the number of doses received and the trimester of administration.

Nearly all those who were vaccinated received their shot(s) in the second (37%) or third trimester (62%).

Most of the vaccinated individuals received an mRNA vaccine — 54% Pfizer/BioNTech, 41% Moderna — and 4% received the Johnson & Johnson vaccine. For those who received an mRNA vaccine, 82% had both doses.

The overall prevalence of preterm birth and SGA at birth was 6.6 and 8.2 per 100 live births, respectively. COVID-19 vaccination was not associated with an increased risk of either outcome, and no association was seen when analyzed by mRNA vaccine dose or trimester of vaccination, the researchers found.

Study limitations included the fact that it may not have captured all vaccinations during pregnancy, which potentially biased results towards the null. Additionally, the authors were unable to adjust for some confounders, including previous history of preterm or SGA at birth, and previous infection with COVID-19 that may have affected vaccination. The researchers added that very few study participants were vaccinated in the first trimester, and future studies should explore the safety of vaccination during this time period.