What is ovarian hyperstimulation syndrome? Here's what you should know about this IVF side effect.

Heather Bray thought the hard part was over. At 34, the lifestyle influencer had spent more than a week injecting herself with hormones so that she could undergo egg retrieval as part of her in vitro fertilization journey. Yet just days after her procedure, she noticed something odd.

“I started gaining weight very rapidly, and my stomach started swelling,” she tells Yahoo Life. “I stepped on the scale and you could see I was 10 to 15 pounds heavier.”

Bray, now 36, says she “looked pregnant” — the extra weight came from fluid retention. She was “very uncomfortable,” and had difficulty breathing. Even rolling over in bed was challenging. She spoke to her doctor doing her IVF treatments, who she says instructed her not to go to the hospital.

Then, in the middle of the night, she woke up and “felt like everything was closing in around me.”

“It was very scary,” she recalls. “I’m screaming to my husband, ‘Call 911, something is not right.’ I try to walk, and I fall to the ground. I completely faint and pass out.”

Bray was suffering from a complication known as ovarian hyperstimulation syndrome (OHSS). It is one of the most common risks of fertility treatments, as the injectable hormone medications that stimulate the development of eggs in the ovaries can cause them to swell and become painful.

Bray went to the hospital, where she received a paracentesis, a procedure to drain excess fluid from the abdomen. It provided her some relief — until the fluid returned the next day, sending her back to the hospital. The second time, she says, she felt immense relief.

Still, the experience was jarring.

“It caused a lot of pain and discomfort,” Bray says. Plus, she learned that “when the ovaries get big and swollen like that, they can end up twisting, and the blood supply can get cut off,” referring to a complication known as ovarian torsion.

“That’s an emergency surgery, and they might not be able to save your ovary,” she says.

Ultimately, Bray — who welcomed her son from this round of IVF — says she was ill-prepared for this complication.

“It’s a risk, but my doctor ... brushed over it,” she recalls. “They say the risk of it happening is so low. ... It’s not as talked about. I don’t know anyone who went through it.”

Why does ovarian hyperstimulation syndrome occur?

OHSS is a potential side effect of stimulating the ovaries to produce multiple eggs at the same time either during the first part of an IVF cycle or when planning to freeze eggs, reproductive endocrinologist Dr. Jill Attaman of Boston IVF, tells Yahoo Life.

“With either, eggs are eventually removed during a procedure called an egg retrieval,” she explans. “The eggs are either frozen for future use or fertilized with sperm.”

OHSS may be caused by “an excess of substances made by the hyperstimulated ovaries that increases leakage of fluid rich in protein out of the blood vessels, where it needs to be, to other spaces like the abdomen and pelvis," Attaman explains. “This can result in dehydration and cause symptoms. The syndrome can be mild, moderate or severe.”

According to women's health expert Dr. Jennifer Wider, certain people are at greater risk for developing OHSS. That includes women who have polycystic ovarian syndrome (PCOS) and those who have received high doses of human chorionic gonadotropic (hCG) injections; hCG is the hormone that helps increase the likelihood of pregnancy.

What are the symptoms?

There are several symptoms to look out for that indicate you may be experiencing OHSS — and that you should seek medical attention immediately. They include:

• abdominal pain

• bloating

• nausea

• difficulty breathing

• vomiting

• dehydration

In rare cases, OHSS can kidney failure as well as blood clots; in very rare cases, OHSS can be life-threatening: In 2022, a 23-year-old woman from India died during an IVF procedure as OHSS caused fluid to build up in her lungs.

While serious complications are possible, "the majority of OHSS is mild or moderate, with recovery soon after egg retrieval," says Dr. Stephanie Thompson, a reproductive endocrinology and infertility specialist at The Institute for Reproductive Medicine and Science and member of the CCRM Fertility network.

Is it possible to avoid OHSS?

Attaman notes that proper planning by a doctor can lower the risk of OHSS for fertility patients. She says the first step to avoid OHSS is to “talk to your doctor about your history and your health,” followed by testing one’s ovarian reserve, which is useful in selecting the dose of hormones and medication used in treatment.

“Once the treatment is started, your doctor and clinic will keep a close eye on you by looking at an ultrasound of the ovary or ovaries and evaluating hormone levels to estimate of how many eggs are growing,” Attaman explains. “Dosing of hormones and medicines can be adjusted to help maximize egg production but also decrease the risk of OHSS. There are different options for hormones and medicines that can be used to trigger maturation of the oocytes prior to a planned egg retrieval that help reduce risk as well.”

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