The Centers for Disease Control and Prevention urged all pregnant women Wednesday to get the COVID-19 vaccine as hospitals in hot spots around the U.S. see disturbing numbers of unvaccinated mothers-to-be seriously ill with the virus.

Expectant women run a higher risk of severe illness and pregnancy complications from the coronavirus, including perhaps miscarriages and stillbirths. But their vaccination rates are low, with only about 23% having received at least one dose, according to CDC data.

"The vaccines are safe and effective, and it has never been more urgent to increase vaccinations as...