Before you trust a fertility clinic's success rate - read this.

What actually goes into that number? Why does a standout success rate deserve more scrutiny, not less? And what should you be asking your clinic instead, before you hand over a deposit?

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I’ll start with a confession.

I never interrogated my clinic’s success rate. I looked at one clinic in Spain, not several, and the number played almost no part in my decision, because I didn’t know what it meant, and comparing felt impossible.

I was also panicking about my low AMH, worried I’d waited myself out of motherhood hoping Mr Right would appear.

€11,000 later, I understand what I should have asked. If you’ve found yourself hesitating on the headline numbers during your clinic research, or if you’ve wondered if you’re right to trust a shiny website for a clinic found on page 1 of a Google search, you’re right to be cautious.

Here’s why comparing clinics feels so difficult, and why some women eventually stop trying.

Clinics don’t all advertise the same metric. Some quote per embryo transfer; others quote per cycle started. Some report pregnancy rates; others report live birth rates. Time periods differ. Patient populations differ. Nobody flags this when you start looking.

So you try to compare two clinics’ numbers and something feels wrong, but you can’t name what. Eventually, most women abandon the comparison entirely.

What fills the gap?

Perhaps a recommendation from another woman in a fertility forum or a WhatsApp group, a woman who may have an entirely different diagnosis, or different circumstances to yours.

Or a doctor who sounded confident in the consultation, which doubles as a sales pitch, not a clinical assessment. (Profit-making clinics want your business.)

How about a website that looks clean and professional. A clinic within reasonable travelling distance.

You end up making one of the most significant decisions of your life on variables that felt more manageable than the numbers, because the numbers were unmanageable.

At 41, the cost of getting this wrong is higher than it would be at 31. A wrong clinic choice (made on a recommendation that doesn’t apply to you, or a number you couldn’t interrogate) doesn’t just cost money. It costs months.

And months are not a neutral variable when you’re working with your own eggs. A failed cycle at the wrong clinic doesn’t just set you back financially: it delays a timeline that’s already tight.

You don’t have the time or the money to waste on a decision made by default.

Understanding these numbers before you choose isn’t perfectionism. It’s the most efficient thing you can do.

A success rate is a fraction, and everything depends on what goes underneath it.

A rate quoted per embryo transfer counts only the women who got as far as a transfer. Every cancelled cycle, every cycle that produced no usable embryo, disappears from the maths, and past 40, those cycles are common. A rate quoted per cycle started includes them, which is why it’s always the smaller, more honest number.

Same clinic, same year, same patients: two very different percentages, depending on which one marketing preferred.

If a clinic tells you their over-40 success rate is 70%, the only useful response is to ask what they’re actually talking about. What exactly is the denominator?

This is the one that matters most for us, and the one a woman coming in fresh has no reason to suspect: an “over 40” success figure can blend own-egg and donor-egg outcomes.

Donor eggs come from young women, and their results are dramatically better, so a clinic treating plenty of donor-egg patients over 40 can publish an over-40 figure that has very little to do with your chances with your own eggs. This isn’t a fringe practice; some specialists openly acknowledge that headline numbers benefit from it.

The gap is not subtle. In the 2024 HFEA Fertility Trends report, women aged 43–44 using their own eggs had a birth rate of around 8% per embryo transferred, compared with 38% for patients aged 18–34.

With donor eggs, age matters far less, because the embryo's chromosomes reflect the donor's age, not the recipient's. Blend an own-egg population with a donor-egg population into a single "over-40" number, and the figure describes nobody.

What should happen instead? Every clinic should be able to provide patient-specific data: in your age group, their success rate with genetically normal embryos, and separately, their success rate with untested embryos.

If the breakdown exists, you’re allowed to see it. If it doesn’t exist, that tells you something too.

Here’s the perspective shift that would have changed how I read every clinic website.

Reputable clinics mostly perform within a similar band. You’ll see roughly the same success rates everywhere you go, but a huge difference in the quality of the care that’s delivered.

Which means a number that dramatically stands out from the cluster is not a reason to get excited. It’s a reason to ask questions. A standout figure usually reflects how the number was constructed or which patients the clinic accepts: clinics can protect a rate by declining the harder cases, and a woman over 40 with her own eggs is exactly who gets declined.

One prominent London clinic has claimed the UK’s highest success rates for three decades, and to its credit, its headline specifies the stricter measure, per treatment cycle started. But the claim sits beside miracle testimonials with no age-band or own-egg breakdown in sight.

It may be entirely defensible. You just can’t test it from the marketing, only from the clinic’s page on the HFEA register.

Also, the number tells you almost nothing about the thing that will actually vary: what the care is like when your cycle doesn’t go to plan.

Here are four questions that cut through the marketing.

Ask for answers in writing, and pay attention to how each clinic responds. A clinic that answers precisely is showing you what the care will be like when things don’t go to plan. A clinic that deflects, generalises, or gets defensive has answered a different question, and answered it clearly.

“What is your live birth rate per cycle started, not per transfer, for women my age, using their own eggs?”

A clear answer gives you a specific figure and explains exactly what it covers. An evasive answer talks about success rates in general terms, or pivots to overall clinic figures without breaking them down by age or egg type.

“Does that figure include donor-egg outcomes?”

A clear answer separates own-egg and donor-egg results without prompting. An evasive answer conflates them, or suggests the question isn’t relevant. It is, especially past 40, where donor-egg outcomes are significantly better and can inflate a headline figure substantially.

“How many women my age did you treat last year with their own eggs, and what was the average number of eggs collected?”

A strong percentage built on a very small patient volume is statistically unreliable: it tells you very little. If the answer is vague, or the volume is low, note it. Clinics with genuine experience treating women your age will be able to answer this directly.

“Who do you decline to treat (with their own eggs), and why?”

This is the question clinics don’t expect. A clinic that protects its success rate by declining harder cases (older women, lower AMH, previous failed cycles) will publish strong numbers that may have nothing to do with your situation. A clinic that answers this question directly is showing you something important about how it actually operates.

In the UK, verify published figures against the clinic’s page on the HFEA website rather than relying on the clinic’s own marketing. In other countries, ask who audits or verifies the numbers: in some jurisdictions, the honest answer is nobody.

Outside the UK, the picture varies considerably. In some countries, clinics report their own figures to professional bodies, with no independent verification. If you’re considering treatment abroad, it’s worth asking not just what the number is, but who collected it.

The success rate was never information about you. It’s marketing about them. The information about you comes from the questions they’re hoping you won’t ask. Part of the industry’s advantage is that patients don’t know what to ask.

After this briefing, you do.

Sarah

P.S. If you want this level of preparation behind every decision, not just this one, The Briefing Room Programme opens this Autumn: six weeks to build your bespoke treatment strategy before you spend a penny on treatment, with four independent expert sessions - an embryologist, a fertility doctor, a nutritionist, a therapist - all focused on women over 40. Applications are now open. Built for solo women over 40 who don’t have time or money to waste.