January is the most popular month of the year for women to find out they’re pregnant, but that discovery sometimes comes with pesky side effects.

Morning sickness has always affected pregnant women, some more than others, and researchers are just now discovering why, said KSTP’s health expert Dr. Archelle Georgiou.

Researchers from the University of Southern California and the University of Cambridge recently published a study reporting that the hormone GDF15 causes morning sickness in pregnant women and a condition called hyperemesis gravidarum in a small percentage of pregnant women.

Hyperemesis gravidarum causes morning sickness so severe the patient usually has to be hospitalized. Hyperemesis also usually occurs throughout the entire pregnancy, as opposed to just the first trimester.

The hormone GDF15 is normally found in the body at a low level, but during pregnancy, the placenta creates the hormone at a high level, according to Dr. Georgiou.

Researchers are now giving women at high risk for hyperemesis gravidarum a small dose of a medicine that increases the production of GDF15 before pregnancy to test if exposure to the hormone reduces morning sickness during pregnancy.