Anna Parker found the image online: a teal onesie with a handwritten note pinned to the front. “Someday,” it read.

It was a word Ms. Parker kept repeating to herself. She and her husband have been trying for four years to have a second baby and are now going through in vitro fertilization. She posted the photo on her Facebook page in January, along with a message about her weight, which was the highest it had been since her first pregnancy. Her blood sugar, too, was troublingly high.

“I’m scared to go into pregnancy,” she wrote in the Facebook post. “I’m so afraid being unhealthy will make me miscarry.”

Ms. Parker, 38, wrote in the post that she had just started taking a new diabetes medication, Mounjaro, which is also widely used for weight loss. She felt “miserable” after her first few doses, Ms. Parker said in an interview. She was recently cleaning out her 5-year-old son’s lunch box, and the smell of ketchup from his dinosaur-shaped chicken nuggets made her vomit into the sink.

Doctors say they are seeing more women like Ms. Parker try weight-loss medications in the hopes of having a healthy pregnancy, or of conceiving in the first place. Women with obesity are sometimes advised to lose weight before pregnancy, because some research suggests that excess weight can make it harder to get pregnant and can increase the risk of miscarriage and pregnancy complications.

For patients on these drugs, the side effects are only one challenge. What some said they find more alarming is just how little information there is on the risks of taking these drugs before or during pregnancy. With next to no data on Mounjaro, Ozempic and similar medications during pregnancy, doctors typically recommend that women stop taking them at least two months before trying to conceive.