“The biological clock and the career clock are in total conflict with each other,” Indra Nooyi said recently, speaking on why women still can’t have it all. “Total, complete conflict.” And so, women in their 30’s are increasingly turning to a seemingly miraculous way of pausing their biological clocks: egg freezing.

The procedure offers the possibility to unwind the conflict Nooyi describes, to extend those childbearing years until careers are settled, savings are amassed, and priorities, shifted. For this, we applaud it, as we should applaud anything that increases reproductive options for women, single or married, but all working and busy and not ready for the demands of motherhood.

However – and this is a big however: Egg freezing is being packaged and sold not as preservation of eggs, but as fertility preservation, as a conclusive solution to a timing problem — and it is far from that.

It’s important to see this technology for what it really is: a glimmer of hope that the odds will work in one’s favor one day. And let’s recognize definitively what egg freezing is not: an ironclad insurance policy of fertility preservation. Glossy pamphlets, fawning press, and the enticing women’s lib angle obfuscate these facts. But true reproductive choice necessarily includes the ability to make informed decisions, and women deserve to see the fine print on this particular medical marvel.

What is egg freezing?

A brief introduction to the egg freezing process, so we’re all starting from the same set of facts: Egg freezing is the process by which a woman’s egg production is stimulated, and eggs are harvested, frozen and preserved for later use. Fertility hormones taken prior to harvesting ensure the woman produces more eggs than usual in a monthly cycle and increase the likelihood that eight or more eggs can be harvested in a single session. (Each cycle, i.e., month, is a separate retrieval or “treatment,” with a cost attached and no guaranteed success rate.) After the harvesting process, a lab determines how many of those eggs are mature enough for freezing (usually about 75%). These unfertilized eggs are then cryogenically frozen in a lab and preserved for future use.

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This is all pretty straightforward, explained in any egg freezing service’s pamphlet or website. But there are a number of additional and very real factors often left out or glossed over. Women need to be aware that:

1. The process of harvesting the eggs is physically grueling; hormone injections are required every day for weeks and usually cause weight gain and mood changes.
2. It’s expensive.
3. The success of the process is critically dependent on the quality of the facility and the technical capabilities of the staff freezing and thawing the eggs.
4. There is no way to know at the time of the procedure if you are harvesting eggs with chromosomal abnormalities that will render the eggs unviable when you later thaw them.
5. Frozen eggs don’t negate other possible fertility challenges couples may face, many of which worsen with age.

We’ll skip an in-depth look at factors 1 through 3; they are relatively self-explanatory: The process is a pain, physically and emotionally, it’s financially prohibitive for most, and it can be a total waste if the lab makes any mistakes in the very complicated and technically precise thawing process.

Does egg freezing really preserve fertility?

Let’s revisit, for a moment, Point #4, the one about not knowing at the time of harvesting whether the eggs you’re freezing are actually viable. We all know that eggs age over time and that older eggs are more susceptible to abnormalities (which is why older women are more at risk of miscarriages in normal pregnancies). It’s important to remember that freezing eggs only preserves the eggs at the time they were frozen; a woman who freezes her eggs at 40 is preserving 40-year old eggs (freezing does not reverse the aging process of those eggs). Ironically, the women who would have the greatest success rates with this process – women in their early 20’s – are also the least likely to be at a stage in life where they’re worrying about infertility.

The uncertainty lies here: There is no way to find out whether an egg has a potentially fatal chromosomal abnormality until it has been fertilized.  This means that, even after undergoing the whole egg freezing process, you would not find out what proportion of your eggs were viable – and viable genetic combinations with your partner’s genetic material – until you unfroze and fertilized them years later… when it could be too late to pursue other fertility options.

Consider this statistic, drawn from data on egg freezing in the U.S.: a 35-year old woman who manages to have six eggs harvested, frozen and then thawed successfully, still only has an 18% chance of that process resulting in a live birth. In other words, this process is rife with uncertainty and potential pitfalls, even assuming some best-case scenarios regarding technological successes.

More uncertainty lies in Point #5 above: There are many other factors that play a role in determining the likelihood of a live birth from frozen eggs. Even if a viable egg is frozen, thawed, and fertilized successfully, that only addresses one type of age-related fertility issue. There are a host of other factors that worsen with age and could impact a couple’s ability to conceive, beyond the existence of a healthy egg: male infertility (whether sperm motility or chromosomal viability), and uterine or cervical inefficiency (i.e., structural problems that prevent a healthy fetus from being carried to term).

(And of course, there are a host of other, additional potential fertility problems that are not impacted by age, but that a couple would only learn of when they started trying to conceive.)

Put simply, since 2009, when medical associations began compiling statistics on this process, the overall chances of experiencing a live birth from frozen eggs have been between 20-24% – hardly the statistic you would expect of a procedure that’s being marketed as a rock-solid backup plan.

Freezing eggs is certainly an important innovation, and a great option for women seeking to increase their chances at delayed fertility. But it’s also not magic. In the name of true reproductive freedom, let’s make sure women approach an expensive and potentially difficult process fully aware of its risks and limitations; let’s not sell them snake oil, even if it is cryogenically-preserved.