Olivia Munn and John Mulaney hadn’t finished raising their family when she was diagnosed with cancer — so they froze embryos. See how the process works during treatment.

Olivia Munn is sharing more about her breast cancer treatment in a new interview with Vogue. The 43-year-old actress – who was diagnosed with an aggressive form of breast cancer called luminal B in February following a risk assessment test – tells the magazine that she underwent a hysterectomy as part of her cancer treatment, which also included a double mastectomy. Munn says confronting how cancer treatment could affect her fertility led her and her partner John Mulaney — who are already parents to 2-year-old son Malcolm — to have a frank conversation about their family’s future.

“We decided to try one more round of egg retrieval because John and I talked about it a lot and we don’t feel like we’re done growing our family,” the former Essay star says. Although Munn had already frozen her eggs, at age 33 and again at 39, she and Mulaney wanted to increase their chances of having more children, with the help of a surrogate.

“We just wanted a few more eggs,” Munn told Vogue. “At my age, one in 10 eggs is healthy and we hoped to produce an embryo from this retrieval.”

The couple was ultimately able to create two healthy embryos, although undergoing assisted reproductive technology amid cancer treatment is not without its challenges. Here’s what you should know about preserving fertility during the process.

What is embryo freezing?

Embryos are eggs that have been fertilized with sperm. As with egg freezing, the first step in the embryo freezing process is to give the woman hormone injections (usually over the course of about 10 days) to stimulate the ovaries to produce multiple eggs in a single menstrual cycle. Another medication prevents ovulation, the process by which an egg is released from the ovary into the fallopian tube, where it would normally await fertilization. Dr.reproductive endocrinologist and infertility specialist at Northwestern University, told Yahoo Life.

Instead, doctors use a minimally invasive procedure that involves a long needle and suction to gently extract eggs from the ovaries. After that, the eggs themselves are frozen or fertilized with sperm (becoming embryos) and then frozen. Embryos can also be tested to ensure they are healthy enough and viable before being frozen. Embryos can remain frozen for at least 10 years, according to Johns Hopkins Medicine.

How is treatment different for cancer patients?

Some cancer treatments, including chemotherapy, can affect fertility. “Even if you are not receiving chemotherapy, in anyone with an estrogen-positive tumor, such as [Munn] has, for the long term ovarian suppressionn,” says Goldman. Ovarian suppression stops the ovaries from producing estrogen and fueling tumor growth, and can be done with medication or surgery to remove the ovaries. Munn initially tried medication but ultimately opted for surgery. “If a patient needs chemotherapy, it has two impacts on their fertility: they are at risk of loss of fertility due to chemotherapy and [also] due to time,” because fertility declines with age and may decline once someone finishes treatment, Goldman explains.

“It is extremely common for reproductive endocrinologists to work closely with oncologists and patients to create a window to preserve fertility,” Dr. Alan Copperman, director of the Division of Reproductive Endocrinology and Infertility at the Mount Sinai Health Systemand CEO and administrative director of New York RMAhe told Yahoo Life. Dr.head of fertility at Northwell Health, estimates that about a third of young women are still expecting to have children at the time they are diagnosed with breast cancer.

The process for freezing embryos is largely the same, but for people with estrogen-fueled forms of cancer like Munn’s, there may be some modifications. Hormone therapy used to stimulate the ovaries to produce more eggs can lead to estrogen spikes, so it’s usually given in lower doses, says Goldman; That was the case for Munn, according to her Vogue interview. Doctors may also use an additional medication to keep estrogen levels in the blood lower so that they do not lead to tumor growth or progression.

Are there risks?

“There are some important risks and experiences that the patient needs to be aware of” before starting the process of freezing eggs or embryos, whether or not they have cancer. Goldman says. Hormone injections used to increase egg production can cause ovarian hyperstimulation syndrome, which can cause the ovaries to swell painfully and leak fluid into the pelvis, abdomen and even around the lungs, according to Cleveland Clinic.

Exercise should also be avoided during the 10 to 14 days of treatment to avoid ovarian torsion or painful twisting of the organs. The egg extraction procedure, although minimally invasive, also presents a risk of infection.

But, in general, the process of freezing eggs or embryos is safe, and for cancer patients “the [cancer] The treatments they will face are much riskier, so this is often one of the easiest parts of the treatment” from a physical standpoint, says Goldman. “I say this with a caveat, because nothing about treatment and getting tested every day when facing a cancer diagnosis is easy; Patients may feel tired because of fluctuations in hormones, but they are also likely tired from coming into the office for monitoring so frequently.”

What is the next?

Although results vary, Goldman notes that freezing embryos gives the patient more “certainty” about their chances of having a baby. This is particularly important for cancer patients, who cannot afford the time needed to make multiple recoveries before undergoing chemotherapy or other treatments.

“The fact that [Munn and Mulaney] Having two healthy, tested embryos will give them a 60 to 70 percent chance of a healthy, live birth” with the help of a surrogate, says Goldman. “She was very lucky to have this outcome.”