It started with doctors in Ireland and Denmark. Each team, unaware of the other’s work, crunched the numbers from its own region or country and found that during the lockdowns, premature births — especially the earliest, most dangerous cases — had plummeted. When they shared their findings, they heard similar anecdotal reports from other countries.

They don’t know what caused the drop in premature births, and can only speculate as to the factors in lockdown that might have contributed. But further research might help doctors, scientists and parents-to-be understand the causes of premature birth and ways to prevent it, which have been elusive until now. Their studies are not yet peer reviewed, and have been posted only on preprint servers. In some cases the changes amounted to only a few missing babies per hospital. But they represented significant reductions from the norm, and some experts in premature birth think the research is worthy of additional investigation.

“These results are compelling,” said Dr. Denise Jamieson, an obstetrician at Emory University’s School of Medicine in Atlanta.