A new study has found that obese woman need a different dose of in vitro fertilization (IVF) medication than women of normal weight, in order to successfully harvest their eggs for the procedure.

In vitro fertilization is used to help women become pregnant by mixing the sperm and egg outside the body, then implanting the embryo into the woman’s uterus. In order to ensure success, women are given a type of medication called GnRH antagonist, which works to prevent early ovulation signals that may ruin the egg harvest. The researchers found that obese women in particular required special doses of the medication in order to ensure success.

“Our findings indicate obese women may need a different or increased dosing regimen to improve fertility treatment outcomes,” Dr. Nanette Santoro of the University of Colorado at Denver, an author of the study, said in a press release. “Given the cost of IVF and stress of infertility, it is important to maximize each woman’s chances of conceiving a child.”

The Centers for Disease Control and Prevention (CDC) states that one percent of all babies born in the U.S. per year are conceived through “assisted reproductive technology,” which refers to any procedure that involves “surgically removing eggs from a woman’s ovaries, combining them with sperm in the laboratory, and returning them to the woman’s body or donating them to another woman.”

“If the GnRH antagonist clears from a woman’s body too quickly, there is a risk that the brain will signal the body to discharge the eggs from the ovaries too early,” Santoro said in the press release. “We were surprised to find obese women were more likely to experience this, and it may be one reason why overweight and obese women have a higher rate of unsuccessful IVF cycles than normal weight women do.”

Research has shown that it may be more difficult for obese women to have successful in vitro fertilization — and healthy reproduction in general. One study, published in 2012, found that BMI could adversely affect egg quality in women. In order for eggs to be considered healthy and “mature,” they need one spindle attached to a set of chromosomes; the researchers found that among obese women, there was more of a chance of having eggs with multiple spindles and disorganized chromosomes. About 60 percent of eggs from obese women had two spindles, compared to only 35 percent among normal weight women.

Meanwhile, research has also shown that obese women are less likely to have successul IVF from their own eggs (and not donor eggs), due to poorer egg quality. There has even been a debate over banning obese women from IVF, or placing weight limits on women who are looking for assisted pregnancy.

This means that obese women can either attempt to lose weight, or else search for the possibility of receiving donor eggs. When it comes to IVF with donor eggs, obese women apparently have normal success rates. Another study published in 2013 claims that obese women are just as likely to have successful pregnancies from IVF using donor eggs as normal weight women (rather than their own). "Our study suggests that obesity does not significantly affect whether a women will become pregnant with donors eggs," Dr. Emily Jungheim, the study's author and assistant professor of obstetrics and gynecology at Washington University School of Medicine, said. "This supports the argument that doctors shouldn't discourage obese women from pursuing treatment if they need donor eggs to conceive."

More research is needed to better understand the problems for obese women who are trying to get pregnant. "Because of the complex nature of obesity and of reproduction, when an obese woman with subfertility presents for fertility treatment, an individualized yet systematic approach is needed," some researchers wrote in a study about obesity and reproduction, though they concluded that weight loss "improves ovulatory function" as well as pregnancy outcomes.