Lockdown may not have many obvious benefits, but research suggests the "stay at home" restriction has reduced the number of babies being born premature.
Medics in Tennessee noticed fewer newborns were admitted to neonatal intensive care units in the weeks after the state introduced measures to control its coronavirus outbreak.
After analysing data, the medics have found premature birth rates were 14% lower than the previous four years.
They have put this down to "essentially enforced bed rest" due to pregnant women, along with the rest of the population, being told to stay at home.
Although fewer premature babies were delivered, the medics noted more infants required "respiratory assistance at birth", suggesting the newborns were "sicker", which "warrants further investigation".
Watch: Premature births decline amid pandemic
"Preterm birth affects one-in-10 infants nationwide, taking a substantial toll on children, families and communities," said study author Dr Stephen Patrick, from the Vanderbilt Center for Child Health Policy in Nashville.
"Our study, coupled with similar studies from Europe, provide initial evidence COVID-19 [the disease caused by the coronavirus] stay-at-home orders were associated with reductions in spontaneous preterm birth.
"While encouraging, we need to ensure other pregnancy complications, like stillbirth, did not increase during this time period."
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This comes after the Lullaby Trust charity warned cot death may be increasing during the pandemic due to social restrictions preventing fathers from attending antenatal appointments, where parents learn how to reduce the risk.
Babies born at less than 37 weeks "have higher morbidity and mortality risks", the Tennessee medics wrote in the journal JAMA Pediatrics.
This affects around eight in every 100 babies in the UK alone.
It is possible for an infant to survive if delivered at around 24 weeks, but they may be left with a severe disability.
Tennessee's initial lockdown spanned 22 March to 30 April, 2020.
To better understand the restriction's impact on pregnancy, medics from Vanderbilt University Medical Center, the Tennessee Department of Health and the Centers of Disease Control and Prevention (CDC) compared 2020 data over that period to the same 38 days between 2015 and 2019.
Results reveal the premature birth rate – defined as delivery at 34 to 35 weeks – was 10.2% in 2020, compared with 11.3% in the previous years.
The number of infants born "late pre-term" – 35 to 36 weeks – also fell from 6.5% to 5.8%.
"The overall decrease in preterm birth we saw during Tennessee COVID-19 stay-at-home order was driven by reductions among infants born late preterm, 35-36 weeks gestation," said lead author Dr Elizabeth Harvey, from the CDC's division of reproductive health.
After accounting for other factors that influence premature birth risk, like a mother's age and conditions such as diabetes, the results reveal the odds reduced by 14% in 2020 compared to the same period from 2015 to 2019.
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The medics put this down to more mothers benefiting from bed rest while at home.
"Although we saw less infants born preterm, we also saw infants born during this time required more respiratory assistance at birth, which may suggest they were sicker and warrants further investigation," said Dr Harvey.
It may be possible for a pregnant woman with the coronavirus to pass the infection to her baby before it is born. "When this has happened, the babies have got better," according to the NHS.
There is no evidence the coronavirus causes miscarriages or affects how an unborn baby develops.
Future research could explore if the same Tennessee patterns occurred in other US states, as well as whether interventions for foetal or maternal complications were behind the results, added the medics.
"Reducing preterm birth is a public health priority and understanding mechanisms to reduce preterm births may lead to more effective interventions," they wrote.
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