Population-based cohort study investigates the effect of SARS-CoV-2 infection on pregnancy outcomes

By Dr. Priyom Bose, Ph.D.Jul 27 2022Reviewed by Aimee Molineux

Researchers have worked extensively hard to understand various aspects of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causal agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic.

Several studies are available that have focused on pregnancy outcomes of women who were infected with COVID-19 during their hospital stay for pregnancy termination or delivery. However, very few studies are available that assess the pregnancy outcome of women who were infected with SARS-CoV-2 during different stages of pregnancy. 

Background

Among the limited number of studies that evaluated the pregnancy outcomes of women infected with COVID-19 at varying stages of pregnancy, few reported their findings for the whole cohort. Further, this sub-group of studies failed to analyze the pregnancy outcomes by trimester of infection. Therefore, there is a gap in research related to pregnancy outcomes for women infected with SARS-CoV-2 during the early phase of their pregnancy.

Researchers stated that the timing of viral infection might be important for the fetal development, birth, and other health outcomes of newborns. Prior studies on the effect of influenza infection on pregnancy reported adverse outcomes with a higher rate of caesarian delivery and preterm birth (PTB) in women who contracted influenza in their later stages of pregnancy.

Research related to other coronaviruses, namely, Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV) revealed a high risk of spontaneous abortion and preterm delivery.

Scientists conducted a comparative study to understand the difference between the pregnancy outcomes in COVID-19-positive women and healthy women. This study revealed that PTB and low birth weight (LBW) were more highly associated with COVID-19-infected pregnant women than in healthy pregnant women.

However, the relationship between the timing of COVID-19 infection and the extent of the pregnancy outcomes has not yet been uncovered.

A new study

In a new study published in PLoS ONE, researchers have focused on evaluating small-for-gestational-age (SGA) rates and PTB in a large cohort. Scientists followed the participants for SARS-CoV-2 infection during their pregnancy and gestational age of infection. 

This Israel-based study was conducted in Maccabi Healthcare Services (MHS), which contained 2.5 million members representing every section of the Israeli population. MHS is a computerized database that includes demographic data of each patient, and their medical records, including the SARS-CoV-2 polymerase chain reaction (PCR) test.

Researchers identified all pregnant female members with non-ectopic pregnancy from the database between February 2020 (the first reported COVID-19 case in Israel) and July 2021. The current study defined PTB as less than 37 weeks of gestation. SGA was defined as the body weight of the infant at birth less the gender-specific 10th percentile for the gestational age. LBW was considered in infants who were less than 2500 grams at birth. Pregnancy loss (PL) included spontaneous and induced abortions up to 20 weeks of gestation.

Findings

The current study revealed a considerable risk of PTB in women who contracted SARS-CoV-2 in their third trimester of pregnancy. However, such an outcome was not observed in patients infected with COVID-19 at their earlier stage of pregnancy. This finding is consistent with a previous study that reported an increased risk of PTB in pregnant women who contracted COVID-19 during the third trimester and exhibited symptomatic infection.

Scientists revealed that the rate of induced labor was higher in women infected in the third trimester compared to their matched healthy women. Although a higher rate of PTB was observed among COVID-19-infected women, no variation in SGA rates was observed between the infected and their matched healthy group. This finding is extremely reassuring because SARS-CoV-2 infection during pregnancy does not affect intrauterine growth restriction.

Previous studies have reported an elevated risk of miscarriage during MERS and SARS-CoV outbreaks. However, in the current COVID-19 scenario, such an outcome was not observed, i.e., no difference in PL rates between infected and matched non-infected women was observed.

Conclusion

One of the main strengths of this study is its large cohort size, which is representative of the population of Israel. A limitation of the study is the non-assessment of the delivery mode, as it was not provided in the MHS database.

Additionally, hospital discharge records were not evaluated for the entire study cohort due to the lack of availability. However, the authors strongly suggested that gestational age at the time of SARS-CoV-2 infection plays an important role in pregnancy outcomes. It reports that women in their third trimester, particularly after 34 weeks of gestation, must strictly practice social distancing to avoid risks of adverse pregnancy outcomes.