While pregnant women have been warned about their potential for more severe COVID-19 illness, a few early reports have suggested one positive finding for this population — that pandemic lockdown restrictions may have coincided with a decrease in preterm births.
Early studies have observed a decline in preterm birth rates during the lockdowns, highlighting a potential “silver lining” of the pandemic. But while these findings are encouraging, experts say there is still not enough data to know whether the reduction in preterm births was widespread, or what factors may have caused this outcome to drop in the first place.
“The jury is out, in terms of what’s the overall impact [of the pandemic] on preterm birth,” said Rahul Gupta, MD, MPH, chief medical and health officer at March of Dimes. While early data may provide some insight into lifestyle changes such as working from home and remote access to healthcare, Gupta said more information is needed before drawing conclusions about preterm birth reductions — and which populations were most affected.
Globally, preterm birth is the leading cause of death in children under 5 years old, according to the WHO. In the U.S., the preterm birth rate has been on a consistent upward trajectory, with 2019 being the fifth straight year in a row that the rate increased. Between 2018 and 2019, the preterm birth rate rose by 2%, according to the CDC.
Clinicians from Denmark and Ireland first began to notice a decline in preterm births last spring — specifically, those that were earliest and most critical. A preprint study from Denmark, which included more than 31,000 infants born between 2015 and 2020, showed around a 90% decrease in extremely preterm births (those born before 32 weeks’ gestation) during the lockdown period. In Ireland, another study published in BMJ Global Health observed a 73% reduction in extremely low birthweight deliveries, from January to April of last year.
Other studies have found that rates decrease for specific populations. A recent systematic review and meta-analysis in The Lancet Global Health found that while the overall preterm birth rate was not significantly different before and during the pandemic, the rate in high-income countries declined by 9%. Spontaneous preterm births in high-income countries saw an even greater reduction, falling by almost 20%.
“Interestingly, there are happy numbers mainly from high-income countries,” said the study’s lead author, Asma Khalil, MD, of St. George’s University Hospitals NHS Foundation Trust in London.
Some reports from the U.S. also reflected a decline, albeit a smaller one. Last April, Stephen Patrick, MD, MPH, of Vanderbilt University, wrote on Twitter that he noticed a lower number of infants in the neonatal intensive care unit (NICU) at his institution.
Last month, Patrick and colleagues published a study in JAMA Pediatrics showing the relationship between preterm birth and stay-at-home orders in Tennessee. Patrick’s team found that the risk of preterm birth fell nearly 15% during the lockdown period, after controlling for maternal age, race, education level, hypertension, and diabetes.
Naima Joseph, MD, MPH, a maternal-fetal medicine fellow at Emory University School of Medicine, said it could be that the decline is related to the environmental and lifestyle changes that occurred during the early months of the pandemic.
Alison Gemmill, PhD, of Johns Hopkins University, said that a number of changes during lockdown may have been associated with drops in the preterm birth rate. When most cars were off the roads, there may have been a decline in the number of preterm births associated with air pollution. Additionally, as pregnant people shifted to remote work and found themselves at home and off their feet, Gemmill said there may have been a decline in physical stress.
Another hypothesis, Gemmill added, is that the decrease in preterm births may have occurred simultaneously with an increase in stillbirths. Some reports have shown an increase in stillbirths during the pandemic (including Khalil’s analysis), but U.S. data has yet to confirm this increase.
Gemmill and colleagues published a study last week (which has not yet been peer-reviewed) showing that the preterm birth rate in the U.S. was one of several birth outcomes that was lower than expected in March and April of last year. But the group also observed that the rate dipped significantly again in November and December — coinciding with the months when infection rates climbed.
“Something is definitely going on,” Gemmill said in an interview. She added that the rates her group observed are crude, and do not describe how different demographic groups in the U.S. were affected. However, she said her research is “detecting a really important signal that doesn’t occur in birth outcomes research.”
Not all U.S. data confirm this pattern. A JAMA study of nearly 9,000 infants at the University of Pennsylvania showed that mothers in 2020 were at the same risk of preterm birth than they had been in years prior.
Gupta, of March of Dimes, stated that the U.S. is not a homogenous society, and preterm birth rates will look different across different populations. Black parents, for example, have a 50% higher chance of having a premature infant than white or Hispanic parents. And while preterm births may have coincided with remote work, that would not apply for the essential workers who continued their employment throughout lockdowns.
Regarding preterm birth outcomes during the pandemic, Gupta said that once scientists break down data by demographics, social determinants of health, and medical comorbidities, he expects there will be a “variety of outcomes.” There is no real-time, national birth surveillance data in the U.S. — so it will take time to understand these outcomes fully.
As far as the theories about which factors may have impacted preterm birth, Joseph said that “mostly, these data have led to more hypothesis generation than anything else more conclusive.”
Gupta agreed, adding that there is more research to be done about both the impacts of COVID-19 infection, as well as the indirect effects of the pandemic.
“I think we really have to better understand what factors during COVID — including lockdowns, unemployment, social interactions, mental health, adherence to medications, job loss — all played a role,” he said. “I think we should not take any of these one factors for granted.”