Egg Freezing (Oocyte Cryopreservation)

Each month the ovaries usually release one mature egg, while the other eggs that started to develop that month are lost. In egg freezing, hormone medicines rescue more of these eggs so that several mature at once. They are collected before ovulation, checked under a microscope, and the mature ones are frozen. Clinics today use vitrification, an ultra-rapid freezing method that turns the egg into a glass-like state without ice crystals, which greatly improved survival after thawing compared with older slow-freezing methods. The eggs are then stored in liquid nitrogen at about minus 196 degrees Celsius, where they do not age. When you decide to use them, the eggs are warmed and fertilised with sperm by intracytoplasmic sperm injection (ICSI), and the resulting embryos are grown for a few days before one is transferred to the uterus. Freezing embryos instead of eggs is an alternative for women who have a partner.

Medical egg freezing is offered before treatments that can damage the ovaries, such as chemotherapy, pelvic radiotherapy or surgery on the ovaries, and to some women with conditions that may lead to early menopause, such as certain genetic conditions, endometriosis affecting the ovaries or a family history of very early menopause. Before cancer treatment the timing is urgent, and stimulation can start at any point in the menstrual cycle so that cancer treatment is delayed as little as possible. Personal, or elective, egg freezing is chosen by women who want to keep the option of a genetic child later, for example because they do not have a partner yet or are not ready for parenthood. Fertility specialists often suggest considering it in the early to mid thirties, because the number and quality of eggs fall with age, and more steeply after the mid thirties. Eggs are also sometimes frozen during IVF when sperm is unexpectedly not available on the day.

Treatment usually starts at the beginning of a menstrual cycle, or at any point when time is short. For about 10 to 14 days you inject hormones under the skin, usually once or twice a day, to stimulate the ovaries, with a second medicine to stop early ovulation. Vaginal ultrasound scans and blood tests every few days track the growing follicles, the fluid-filled sacs that hold the eggs, and doses are adjusted. When the follicles are ready, a trigger injection completes the maturation of the eggs, and egg collection follows about 36 hours later. Under sedation or a brief general anaesthetic, a thin needle guided by vaginal ultrasound passes through the vaginal wall into each ovary and draws out the follicle fluid. The procedure takes about 15 to 30 minutes and leaves no external cut. In the laboratory, embryologists identify the eggs, assess which are mature and vitrify the mature ones on the same day.

Most healthy women of reproductive age can freeze eggs. Before starting, an ovarian reserve assessment estimates how many eggs you might collect: a blood test for anti-Müllerian hormone (AMH) and an ultrasound count of the small follicles in the ovaries. These tests predict the response to stimulation rather than the chance of pregnancy, and they help the specialist advise how many cycles may be useful. Screening for HIV and hepatitis B and C is required before eggs are stored. The specialist discusses your age, health and goals, how many eggs are realistic, and the possible need for more than one cycle. You also review the consent forms, which cover storage duration, renewal and what happens to the eggs in different situations. International patients can often have the first scans and blood tests near home and travel for the last part of stimulation, the collection and the freezing.

After egg collection you rest for a few hours and go home the same day with someone to accompany you, because of the sedation. Mild cramping, bloating and light spotting are common for a few days, and simple painkillers are usually enough. Most women return to work the next day, and the next period usually comes about one to two weeks later. For planning, the clinic needs you nearby for part of the two weeks: early monitoring can sometimes be done near home, but the last scans, the trigger injection and the collection must be timed closely, so arriving by about day 6 to 8 of stimulation is common. Flying is usually fine 1 to 3 days after collection if you feel well, but if your abdomen keeps swelling, you gain weight quickly or you feel short of breath, contact the clinic before travelling. Storage contracts, renewal dates and the option of moving eggs to another clinic later should be agreed in writing.

Egg freezing is generally safe. The main medical risk is ovarian hyperstimulation syndrome (OHSS), where the ovaries over-respond, causing abdominal swelling, nausea and fluid shifts; careful monitoring and modern trigger medicines have made severe OHSS uncommon. Egg collection carries small risks of bleeding, infection and injury to nearby organs, and mood changes, headaches and bloating can occur during stimulation. The question of results lies in the future. Not every egg survives thawing, fertilises or develops into an embryo able to implant, and the chance of a live birth from a set of frozen eggs falls with your age at freezing and rises with the number of eggs stored. Women who freeze eggs in their early thirties generally need fewer eggs for a reasonable chance than women who freeze in their late thirties or forties. Your clinic should give you an individual estimate based on your age and egg numbers, without promises.