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Among pregnant people with COVID-19, disease severity does not differ based on trimester of diagnosis, according to findings from a prospective, single-center cohort study.

Of more than 1,300 pregnant patients who presented with asymptomatic or mild COVID-19, there were no differences in disease progression by trimester of infection, reported Rachel Schell, MD, of the University of Texas Southwestern Medical Center in Dallas.

Additionally, there were no significant differences in maternal or neonatal outcomes based on the trimester of diagnosis, Schell said in a presentation at the Society for Maternal-Fetal Medicine virtual meeting.

Moderate, severe, or critical illness developed in 10% of pregnant patients who were initially asymptomatic, the researchers found.

"The frequency of COVID-19 disease progression does not differ by trimester of diagnosis," Schell said. "These results highlight the importance of preventive measures, including COVID-19 vaccination before or as early as possible during pregnancy."

Schell noted that COVID-19 vaccination rates remained low in their cohort. Of the patients who delivered between January and September 2021, 83% were unvaccinated.

COVID-19 infection rates in pregnancy have been comparable to the general population, but it has been linked to higher risk of developing severe illness. There is little data, however, showing how the timing of infection impacts disease severity in pregnancy, Schell said.

Schell's group conducted a prospective, single-center study to analyze the progression of COVID-19 severity in pregnant patients based on their trimester of diagnosis. All patients were treated at Parkland Hospital and Health system in Dallas, and were delivered between March 2020 and September 2021.

Beginning in May 2020, the health system adopted a universal testing protocol for all pregnant patients upon hospital admission, using molecular RT-PCR testing. The researchers grouped patients by their trimester of diagnosis and measured disease progression by reviewing medical records. They defined patients as asymptomatic, mild, moderate, severe, or critical based on . Additionally, they measured a composite obstetric outcome by trimester, which included delivery at less than 37 weeks, severe preeclampsia, abruption, stillbirth, and excess blood loss.

Overall, 1,306 pregnant patients with COVID-19 were included in the study. Approximately 8% of infections were diagnosed in the first trimester, 27% in the second trimester, and 65% in the third trimester. There were no significant differences in demographics across groups.

Hospital admission within 2 weeks of a COVID-19 diagnosis was likewise most common in the third trimester, with 90% of admissions being related to obstetric indications. After obstetric indications were excluded, there was no difference in hospital admissions by trimester.

Of all patients who were initially asymptomatic, 15% of patients diagnosed in the first trimester, 14% in the second trimester, and 10% in the third trimester developed symptomatic illness. However, the differences were not statistically significant.

Among patients who first reported asymptomatic or mild symptoms, 6% developed moderate, severe, or critical illness. Around 4% diagnosed in the first trimester, 5% in the second trimester, and 6% in the third trimester progressed to moderate, severe, or critical disease, but these differences were also not significant.

In a sub-group analysis, Schell's group compared disease severity and progression among patients who delivered before and during the Delta surge. Severe or critical illness increased during the Delta surge, from 4.2% to 7.8%. Progression of symptoms, however, was not significantly different during this time period.

Schell acknowledged that the study was limited by potential ascertainment bias, because diagnosis was based on testing protocols and some infections may be asymptomatic. Additionally, the study time period was defined by date of delivery rather than infection, which may have limited findings from the subgroup analysis on the Delta surge.

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