Study links COVID-19 infection to higher low birthweight and preterm birth rates

Study links COVID-19 infection to higher low birthweight and preterm birth rates | Image Credit: © weyo - © weyo - stock.adobe.com.

Increased risk of adverse outcomes

Adverse pregnancy outcomes were more common among women who became pregnant at the start of the COVID-19 pandemic, according to a recent study published in the Annals of Epidemiology.¹

Alongside being pregnant at the start of the COVID-19 pandemic, presenting with moderate to severe infection and having infection during the third trimester were associated with an increased risk of outcomes such as low birthweight, neonatal intensive care unit (NICU) admission, and preterm birth. This data expands knowledge about perinatal outcomes impacted by the COVID-19 pandemic.¹

“Due to their altered immune system, pregnant women are particularly vulnerable to severe infections,” said Xiaoming Li, PhD, director for the South Carolina Smart State Center for Healthcare Quality.¹ “The number of pregnant women who contracted SARS-CoV-2 during the pandemic raised concerns about the possible impacts on perinatal outcomes.”

Research has indicated a decline in preterm birth rates at the start of the COVID-19 pandemic, but investigators theorized mitigation and prevention efforts may have led to this reduction. Low birthweight and NICU admission rates have shown increases in other reports evaluating women infected during pregnancy, highlighting the disease’s impact.¹

Study methodology and data analysis

Data from a large group was obtained from electronic health records and assessed based on the timing of pregnancies within the pandemic and severity infections. Nearly 200,000 births from 2018 to 2021 were included in the analysis.¹

Deliveries before March 1, 2020, were included in the pre-pandemic group, while those conceived before and delivered during the pandemic were included in the partial overlap group.² Finally, the pandemic group included patients with conception and delivery occurring during the pandemic. The data was assessed using Modified Poisson Regression models.

Findings on birth outcomes

The odds of low birthweight were reduced among partial overlap patients vs pre-pandemic patients, with an adjusted relative risk (aRR) of 0.93. For preterm birth, the aRR among these patients was 0.91.²

Increased low birthweight risk was reported among the pandemic group, with an aRR of 1.10. Additionally, preterm birth and NICU rates increased, while breastfeeding initiation rates decreased, with aRRs of 1.10, 1.13, and 0.98, respectively.²

Preterm birth risk was also increased by moderate to severe symptoms, with an aRR of 1.34. Finally, low birthweight, preterm birth, and NICU admission were all more common among patients infected during the third trimester, with aRRs of 1.23, 1.18, and 1.17, respectively. This data highlighted the impact of COVID-19 infection and pandemic-related factors on perinatal outcomes.²

“These findings suggest that it is important to consider both the infection – including the timing and severity – and other pandemic-related factors, such as mitigation measures and timing of pregnancy, when working to optimize perinatal outcomes,” said Jihong Liu, ScD, corresponding author of the paper and professor at the Center for Healthcare Quality.¹

Supporting evidence from prior research

This data is support by prior research evaluating pregnancy outcomes among women with COVID-19 infection. A study published in the American Journal of Obstetrics & Gynecology highlighted increased odds of chronic villitis (CV) and specific histopathologic findings linked to COVID-19 infection.³

According to the data, the odds ratios of CV and severe SV were 1.56 and 2.36, respectively, among COVID-19 patients vs time-matched controls. These associations remained when controlling for gestational age, highlighting increased rates of histopathologic lesions among COVID-19 patients.

References

1. COVID-19 pandemic worsened mother, infant birth outcomes. Arnold School of Public Health. March 16, 2025. Accessed March 24, 2025. https://www.eurekalert.org/news-releases/1077072.
2. Sevoyan M, Liu J, Shih YW, Hung P, Zhang J, Li X. Associations of pregnancy timing relative to the COVID-19 pandemic, maternal SARS-CoV-2 infection, and adverse perinatal outcomes. Ann Epidemiol. 2025;102:94-101. doi:10.1016/j.annepidem.2025.01.006
3. Krewson C. COVID-19 linked to chronic villitis and placental lesions in pregnancy. Contemporary OB/GYN. January 28, 2025. Accessed March 24, 2025. https://www.contemporaryobgyn.net/view/covid-19-linked-to-chronic-villitis-and-placental-lesions-in-pregnancy.