Assisted fertilization

How many oocytes do I need to freeze to get pregnant in the future?

In recent decades, women have been driven to freeze their eggs to try to preserve fertility over time. Waiting to recover from a tumor , waiting to find job stability, waiting for the right man or the right time to become a mother.

Once that time has come, what are the chances of successfully carrying on a pregnancy thanks to frozen eggs?

And how many oocytes need to be frozen and at what age to increase the chances of success?

Those are two very important questions. To date, many women have spent thousands of euros (or dollars worldwide) to preserve their eggs, and many have had to deal with a bitter reality. That is, that of having frozen an insufficient number of oocytes or having done so at the wrong age.

The answers are arriving in recent months, based on the data that have been collected in recent years and thanks to the increase in available cases.

It’s not that easy

When they tell us about egg freezing, they often make it sound safe and simple. You freeze the oocytes, have them preserved with the currently most effective method ( vitrification ), then come back after a few years to have them fertilized, certain that pregnancy will come.

It’s not quite that simple.

When it comes to human reproduction, mother nature isn’t very efficient.

On average, a woman is born with 1-2 million oocytes, but only some of them will have the chance to become children. Similarly, when a certain number of oocytes are frozen, it is not guaranteed that all of them will conceive.

A frozen egg cell does not necessarily equate to a baby.

How many oocytes to freeze to have hope of getting pregnant?

Many clinics advised women to freeze 10 to 20 eggs, regardless of their age or situation. But this is absolutely not a correct procedure since the eggs decrease in quality and quantity as the woman gets older.

For this reason, a more personalized approach is now recommended , which also includes evaluating what a woman is willing to spend. Let’s not forget that storing your own eggs costs money. And the more they are kept, the more the price increases. Just as it increases if you want to keep them frozen for longer than expected by the clinic.

An important study published in Human Reproduction in April 2017 tried to shed light on the probability of having a baby (and therefore of carrying a pregnancy to term) based on the woman’s age at the time of freezing of the oocytes and the number of oocytes frozen .

Number of oocytes frozen, age at time of freezing and pregnancy success

A 36-year-old woman who decides to cryopreserve 10 oocytes has a 60% chance of carrying a pregnancy to term. At 37, she has a 50% chance. And at 39, she has a 39% chance.

The authors of the study have also created a calculator, which you can find here , through which by entering age and the number of frozen oocytes, it returns the probability of having one, two or three pregnancies.

Tabella da“Predicting the likelihood of live birth for elective oocyte cryopreservation: a counseling tool for physicians and patients,” Human Reproduction, 2017.

From frozen egg to born baby

The assisted fertilization treatment starting from oocyte freezing includes many phases with many oocytes or embryos, which are “lost” along the way.

Initially the eggs have to be thawed, then they are fertilized with sperm. Then once fertilized they are left in a petri dish to mature into what are called blastocysts. A portion of those blastocysts may be abnormal. Some embryos have genetic abnormalities. Then seemingly healthy embryos are transferred to a woman’s body.

Some nestle in the endometrium and some don’t.

If they nestle, abortion is still possible.

To make an estimate as correct as possible, the researchers took all these steps into account.

Each of the percentages indicated represents a fraction of the oocytes or embryos that survived the previous step.

  • Thawing: 85-95%
  • Fertilization: 70%
  • Blastocyst: 40-50%
  • Normal chromosomes: 57% for oocytes retrieved when woman was 35 years of age or younger, 13% for eggs retrieved at 44 years of age or older
  • Plant: 70-75%
  • Birth of a child: 60% (assuming chromosome testing and other steps above go smoothly)

In the end it all boils down to numbers: The more eggs that are stored, the greater the chances of selecting the best cells and the greater the chances of having a baby.

Dr Kathryn Barlow

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

Leave a Reply

Your email address will not be published. Required fields are marked *