Considering Egg Freezing? What to Know About Ovarian Reserve

Women are building families later in life than ever before, with more women giving birth in their 40s than their teens for the first time in U.S. history, according to a Centers for Disease Control and Prevention analysis. The paradigm shift is empowering women to reach new educational and professional heights and explore a world of interests before having children.

It also has brought the fertility window—and opportunities to stretch it, such as fertility banking—into focus.

“Fertility banking gives women more choices and more control over their reproductive health,” said Cedars-Sinai reproductive endocrinologist Erica Wang, MD.

The practice is exploding, enabling women to store their eggs and embryos and place them on ice until they are ready to have children. More than 40,500 eggs and 11,200 embryos were banked in 2023, according to the Society for Assisted Reproductive Technology.

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The Cryopreservation Process: From Hormone Injections to Pregnancy

In egg freezing, patients undergo 10 to 12 days of hormone injections to stimulate the ovaries to prepare a cluster of eggs. Their doctor checks on the eggs’ development using ultrasounds and blood tests.

When a patient’s eggs are ready, the clinic retrieves them through the vagina at a same-day surgery center while the patient is under anesthesia. The eggs are then frozen (cryopreserved) right away.

Embryo banking adds an extra step. In the lab, specialists fertilize the retrieved eggs with sperm, allow the embryos to mature over five to seven days, and then freeze them.

Later, if the patient wants to try to get pregnant with their frozen reserve, the lab will thaw their eggs or banked embryos. They will fertilize the eggs to become embryos, if needed, and the doctor will transfer the embryos into the patient’s uterus.

We don’t have the answer yet to extend the lifespan of eggs, but we do have the opportunity to freeze them in time.

Fertility Banking Reaches Maturity

Once considered experimental, egg freezing has come a long way.

Technological advances during the past decade—especially the move from a slow-freeze method to a flash-freeze method (vitrification)—have helped providers better protect and preserve the eggs. Faster freezing limits the formation of ice crystals, allowing a much higher rate of thawed eggs (95% for fast freezing versus 70% for slow freezing) to survive, according to Wang.

“It’s not a guarantee for the future,” Wang cautioned, “but it is the best option we have.”

Some eggs don’t fertilize or implant correctly, so women may undergo multiple rounds of freezing or embryo transfers to conceive. Typically, depending on the age at which the women froze their eggs, around one-third of women who use them will have a baby.

Wang added that awareness of the technology has spread, encouraging a new generation of women to consider freezing their eggs or embryos for later.

And as fertility treatments become more mainstream, California has mandated that private insurance cover fertility preservation and egg and embryo storage—driving demand for the services even higher.

“Freezing can help ensure you have children,” Wang said, “but we have to remember that the process does not ensure later fertility. We won’t know the outcome unless we use the frozen eggs or embryos.”

Understanding Your Ovarian Reserve and Fertility Window

Women are born with a complete set of around 1 million to 2 million eggs. Although everyone is different, a woman’s egg stockpile and its quality typically dwindle over time, gradually at first, then more rapidly after age 35.

An initial antral follicle count, ultrasound imaging performed by a reproductive endocrinology specialist, and an AMH blood test gauge your ovaries’ current egg supply.

Cedars-Sinai Reproductive Endocrinology and Infertility Department Director Margareta Pisarska, MD, suggests women think about future family-building plans in their mid to late 20s. If parenthood isn’t on the horizon at that time, ovarian reserve testing with a follicle count and AMH test can be helpful. Fertility preservation options should be weighed ideally in your late 20s to early 30s, unless your supply could be compromised or complicated by other factors.

“We need to be proactive,” Pisarska says. “An ovarian reserve test can’t predict future fertility, but if your ovarian reserve is already low, we might want to consider banking at an earlier age. We could end up with fewer eggs, but they may be of higher quality because you are younger. That potentially bodes better than if we waited.”

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Fertility specialists generally suggest banking 20 eggs as a starting point. You have about a 5% chance of a viable, successful pregnancy with one egg if you are under 35. By your mid to late 30s, the likelihood falls, with a steeper decline after age 40.  

“More eggs are going to be genetically unhealthy as we age,” Pisarska explained, “so the chances of success with each frozen egg goes down.”

An alternative to banking eggs is embryo banking. Older patients aiming to grow their family may use this form of fertility banking instead, using sperm from a partner or donor. Embryos are a step closer to getting pregnant and can provide more information on your chances.

“The assumption is that we can get pregnant at any time. However, despite the fact that women are aging slower and living longer, the reproductive lifespan of the ovary has not increased,” said Pisarska. “Egg depletion has been a constant, no matter what we have done in our goal to improve longevity.”

In a pivotal study, Pisarska, Computational Biomedicine Operations Director Nicholas Tatonetti, PhD, and other Cedars-Sinai investigators are digging into the mysteries of ovarian aging. The team is searching for more precise indicators and, ultimately, strategies to prolong the female biological clock.

In turn, the research could even unravel the secrets of a host of illnesses that strike later in life, some following menopause, including dementia, heart disease, osteoarthritis and osteoporosis. Early sex differences in the immune system—likely through hormonal ties—may be involved and pose a potential opportunity for earlier treatment to reduce long-term risks.

“We don’t have the answer yet to extend the lifespan of eggs, but we do have the opportunity to freeze them in time,” Pisarska stressed. “We will learn from that, too, because our eggs will be the same age as when they were frozen and younger than our bodies when we are ready to use them. How does that play a role?”

Setting Up Your Fertility for Success

Anyone embarking on a family-building journey should start by asking their primary care doctor or OB-GYN for a referral to a reproductive endocrinologist.

See a doctor before any treatment that could harm your fertility. People with certain genetic conditions, endometriosis, or those who will receive chemotherapy or other toxic treatments that can cause premature ovarian insufficiency (disrupted ovarian function before age 40) should think about fertility preservation earlier—before any potential impact to these organs.

Reproductive endocrinologists will consider your age alongside your egg supply, hormone levels, sperm access, goals (such as how many children you want) and medical history.

Fertility banking has some risks. In particular, the risk from high estrogen exposure needs to be addressed if you’re susceptible to hormone-driven conditions, such as breast or endometrial cancers or blood clots.

During the fertility banking process, Wang treats her patients as if they were already pregnant, starting them on prenatal vitamins and encouraging a healthy lifestyle. She also suggests limiting alcohol and caffeine, adopting a nutritious diet and getting moderate exercise.

“It’s a proactive decision to plan ahead for pregnancy,” she said.