Pregnancy changes a performer’s body, making breathing and the vibration of vocal cords more difficult. Paul E. Kwak, MD, notes that the blood vessels on the surface of the vocal cords can become engorged during pregnancy, requiring extra energy and breath to make sounds. “The breath is shallower and the tissue is thicker, so it vibrates less easily,” Dr. Kwak tells The New York Times.

Acid reflux, a common complaint in pregnancy, can also make singing painful. “It’s like having heartburn in your throat,” says Aaron Johnson, PhD, MM. “The tissue is raw, possibly swollen, making it more difficult to get the voice out.” Not every singer experiences vocal changes during pregnancy, says Dr. Johnson.

Read more from The New York Times.