SARS-CoV-2 infection in third trimester increases odds of preterm birth

Compared with women who did not have SARS-CoV-2, those who were infected during the third trimester of pregnancy had a higher risk for preterm birth, data in PLoS One showed.

The risk for preterm birth was not higher among women infected during the first or second trimesters, researchers said, and infection was not associated with pregnancy loss. However, they cautioned that the study was conducted before omicron became the predominant variant.

“Systematic reviews and meta-analyses of pregnancy outcomes in SARS-CoV-2-positive women reported that [preterm birth] and low birth weight were more probable in pregnant women with COVID-19 than pregnant women without COVID-19, though less is known regarding the extent to which these associations vary by timing of infection during pregnancy,” Noga Fallach, MSc, a biostatistician and epidemiologist at Kahn-Sagol-Maccabi (KSM) Research and Innovation Institute in Tel Aviv, Israel, and colleagues wrote.

Fallach and colleagues retrospectively identified 2,753 women with a positive SARS-CoV-2 reverse transcriptase polymerase chain reaction test during their pregnancy between Feb. 21, 2020, and July 2, 2021. They matched infected women 1:1 to noninfected women by age, date of last menstrual cycle, sector — meaning being Jewish or Arab — and residential area socioeconomic status to compare the risk for preterm birth, small for gestational age and pregnancy loss.

In total, 48.4% of women with SARS-CoV-2 were infected during their third trimester and 17.4% were infected during their first trimester. Symptomatic disease occurred in 17.6%, 51.3% and 46.7% of women infected during the first, second and third trimesters, respectively.

There were no significant differences in the incidence of preterm birth between women infected during their first and second trimesters and their matched controls. However, those infected during the third trimester were significantly more likely to have a preterm birth compared with controls (adjusted OR = 2.76; 95% CI, 1.63-4.67). The odds were even greater in women infected after 34 weeks’ gestation (aOR = 7.1; 95% CI, 2.44-20.61).

The risk for preterm birth was also greater among symptomatic women infected during the third trimester compared with controls, according to the study (aOR = 4.28; 95% CI, 1.94-9.41).

Results showed there was no significantly higher risk for small for gestational age or pregnancy loss with SARS-CoV-2 infection, regardless of when infection occurred during pregnancy.

“The results are encouraging and reassuring that COVID-19 infection during pregnancy is not associated with any type of pregnancy loss,” Tal Patalon, MD, LLB, MBA, head of the KSM Research and Innovation Institute, said in a press release. “However, it should be remembered that the research group tested the COVID pre-delta variants, and does not refer to the dominant variant today, which is omicron. We continue to conduct research to provide real-world data and knowledge to the public and decision-makers.”

References:

• Fallach N, et al. PLoS One. 2022;doi:10.1371/journal.pone.0270893.
• Higher rates of preterm birth in women infected with COVID-19 in late pregnancy. https://e3.eurekalert.org/news-releases/958770. Published July 20, 2022. Accessed July 20, 2022.