Study: Examining the impact of trimester of diagnosis on COVID-19 disease progression in pregnancy. Image Credit: MIA Studio / Shutterstock

All trimesters of pregnancy carry the same risk of COVID-19

The outbreak of the COVID-19 pandemic in the US has led to more than 97 million infections and more than 1.06 million deaths. About 182,000 cases and 285 maternal deaths have been reported among pregnant women. Normal pregnancy is mainly associated with a 20-30% decrease in pulmonary functional residual capacity and a 20% increase in oxygen consumption. As a result, lower respiratory tract infections are poorly tolerated, especially in the third trimester.

It is known that pregnant patients are at higher risk of morbidity due to influenza infections. Recent studies suggest that pregnant patients are at higher risk for severe to critically severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) infection compared to non-pregnant women of the same age. Also, this disparity worsened during the rise of the Delta (B.1.617.2) variant. In addition, an increased risk of adverse neonatal and maternal outcomes is associated with severe COVID-19 during pregnancy. However, little is known about the impact of the timing of infection during pregnancy on such risks. Finally, vaccine acceptance among pregnant women is also lower than among other demographic groups.

a study American Journal of Obstetrics & Gynecology MFM The journal aimed to analyze the effect of the trimester of SARS-CoV-2 infection on disease progression in pregnant women.

Studies: Investigation of the effect of trimester diagnosed during pregnancy on the progression of COVID-19 disease. Image Credit: MIA Studio / Shutterstock

about the study

The study includes patients who tested positive for SARS-CoV-2 during pregnancy from March 18, 2020 to September 30, 2021. Before May 14, 2020, the diagnosis of COVID-19 was made based on symptoms or specific risk criteria, while after May 14, 2020, it was made using universal polymerase chain reaction (PCR) testing. For patients with multiple SARS-CoV-2 infections during pregnancy, only index infection was included in this study.

The severity of the disease was determined as mild, moderate, asymptomatic, severe, or critical, according to the National Institutes of Health (NIH). Pregnancy diagnosis week was determined and categorized according to trimester. For outpatients, assessment was made through telemedicine virtual visits, while the primary indication for hospital admission was COVID-19-related disease, non-obstetric, or obstetric.

Delivery was considered for patients with severe or critical COVID-19 infection at or near term. Diagnostic trimester determined assessment of maximum disease severity, disease progression, and indication for hospitalization. A comparison of baseline and demographic medical characteristics of patients infected during the first, second or third trimester of pregnancy was made. In addition, neonatal, maternal and obstetric information was obtained. Primary outcomes include preeclampsia with severe features, stillbirth, excessive blood loss at birth, abruption, and delivery less than 37 weeks. Secondary outcomes included need for neonatal respiratory support, umbilical blood pH less than 7, cesarean delivery, transfusion, abruption, stillbirth, gestational age at birth less than 37 weeks, excessive blood loss at birth, and severe preeclampsia. Finally, a subgroup analysis was performed to analyze disease severity and outcomes in patients infected before and during Delta variant upregulation.

Study findings

The results showed that a total of 1,326 pregnant patients tested positive for COVID-19 during the study period. Of these, 103 were first trimester patients, 355 second trimester patients, and 868 third trimester patients. It has been reported that first and second trimester patients diagnosed with COVID-19 are older and have chronic hypertension or pregestational diabetes mellitus than those diagnosed in the third trimester.

Of the 1,326 patients, 1,195 were reported to be asymptomatic or mild, while of the 436 patients who were initially asymptomatic, 45 later developed symptoms. 4 first trimester, 18 second trimester, and 49 third trimester patients developed moderate, severe, or critical COVID-19 disease. It has been reported that pregnancy loss during SARS-CoV-2 infection is more likely in first trimester patients. It has been reported that the mean gestational age is 7 weeks in the first week and 17 weeks in the second week. Stillbirth was recorded in 5 patients in the third trimester and occurred at an average of 33 weeks of gestation.

Composite obstetric outcomes were reported in 23 first, 96 second and 24 third trimester patients. Overall, it was reported that 83% of patients diagnosed with COVID-19 were not vaccinated even after the initiation of vaccination programs. Finally, a higher prevalence of severe or critical infections was observed during the rise of the Delta variant. This was most evident in patients diagnosed in the third trimester. In addition, it was observed that disease progression increased during the delta period.

Therefore, the current study shows that the frequency of progression of COVID-19 disease is not affected by the trimester of diagnosis. About 10% of pregnant patients develop mild, moderate or severe disease. However, there was an increased risk of disease severity during the Delta fluctuation period. Therefore, COVID-19 vaccinations and other preventive measures should be administered before pregnancy or as early as possible to avoid adverse consequences.


The study has certain limitations. There is a potential accuracy bias in the study. In addition, adverse pregnancy outcomes and critical or serious illness are underestimated in the study. Third, it may not be able to detect real differences in the frequency of disease progression. Finally, patients who were infected with the Delta variant but did not give birth before September 30, 2021 were excluded from the study.

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