Trimester differences in COVID-19 severity do not exist and women remain at risk of developing severe COVID regardless of trimester, according to new research presented at the Society for Maternal-Fetal Medicine’s (SMFM) annual meeting.

Research shows that pregnant people who contract COVID-19 are at increased risk of severe complications, including hospitalization, ventilation, and death, compared to pregnant people without COVID-19. However, little is known about how the timing of COVID-19 infection during pregnancy might impact a pregnant person’s risk of developing severe symptoms.

“Regardless of what trimester they are in, pregnant people are at risk of developing severe COVID illness,” said one of the study’s authors, Rachel Schell, MD, a maternal-fetal medicine fellow at the University of Texas Southwestern Medical Center in Dallas.

Researchers identified a group of pregnant people at a single urban hospital in Dallas, Parkland Hospital, and followed the progression of their COVID-19 symptoms. From March 18, 2020 to May 31, 2021, 1,092 pregnant people were diagnosed with COVID-19. Sixty-seven people (6%) were diagnosed in the first trimester, 309 (28%) in the second trimester, and 716 (66%) in the third trimester. There were no significant demographic differences between the groups.

Results found no trimester differences in COVID-19 severity. Across all trimesters, 993 out of 1092 people (90.9%) were either asymptomatic or had mild COVID-19 symptoms, and 35 out of 345 people (10.1%) who were initially asymptomatic developed moderate, severe, or critical symptoms. Among pregnant patients who were initially asymptomatic or had mild symptoms in any trimester, 5% developed moderate, severe, or critical illness.

“This research is helpful for us in counseling patients who test positive for COVID,” said another one of the study’s authors, Emily Adhikari, MD, a maternal-fetal medicine subspecialist at the University of Texas Southwestern Medical Center and medical director of perinatal infectious diseases at Parkland Hospital. “There is no reason to be hesitant to get vaccinated because you are early in your pregnancy. You’re still at risk of getting really sick from COVID in your first trimester.”

Researchers are in the process of expanding their research to look at whether there are significant differences or changes in COVID severity by trimester due to the Delta variant.

SMFM, the CDC, and the American College of Obstetricians and Gynecologists recommend all pregnant people get vaccinated against COVID-19, noting that the vaccines are safe and effective. Vaccination rates among pregnant people continue to remain low despite evidence showing vaccines can help to prevent severe illness during pregnancy. The latest figures from the CDC  show that fewer than 36% of pregnant people are vaccinated; vaccination rates are even lower among pregnant people who are Black and Hispanic.