Unvaccinated Pregnant People With COVID-19 Have Increased Risk of Poor Birth Outcomes

COVID-19 vaccination is recommended for pregnant people, and vaccination has been proven not to increase the risk of preterm birth or small-for-gestational-age at birth.

However, pregnant people who contract COVID-19 and are not vaccinated are more likely to experience poor birth outcomes, even if they did not experience severe respiratory problems during their infection.

Research led by the Institute for Systems Biology and published in The Lancet studied the impact of maternal COVID-19 infection on birth outcomes. The retrospective cohort study used clinical data from Providence St Joseph Health for electronic records of pregnant people who delivered in the US at the Providence, Swedish, or Kadlec sites in Alaska, California, Montana, Oregon, or Washington.

The study included people who had PCR-tested positive for COVID-19 during pregnancy, subdivided by the trimester of infection. No one in this cohort had been vaccinated for COVID-19 at the time they contracted the virus.

The control group consisted of people with at least one negative COVID-19 PCR-based test and no positive tests during their pregnancy. The cohorts were matched based on common covariates affecting birth outcomes, and the investigators conducted univariate and multivariate analysis to investigate risk factors and predict birth outcomes. The primary study endpoint was gestational age at delivery with preterm birth classification.

People positive for COVID-19 were more likely to be Hispanic, a race other than Asian or White, Medicaid insurance, lower age, higher BMI, and lower level of education, all factors known to be associated with negative birth outcomes. Investigators adjusted the study accordingly, using statistical matching to control for confounding variables.

From the study period March 5, 2020-July 4, 2021, the investigators observed 882 people infected with COVID-19 during their pregnancy (first trimester n=85; second trimester n=226; third trimester n=571) and 19769 people who did not test positive for COVID-19 during their pregnancy.

COVID-19 infection, especially during the first and second trimesters, increased the risk of preterm birth (p<0·05) and stillbirth (p<0·05). Gestational age at COVID-19 infection was found to be associated with gestational age at delivery (p<0·01). The study participants had mild-to-moderate COVID-19 infection, and COVID-19 severity was not correlated with gestational age at delivery (p=0·31).