What Actually Happens to Your Embryo in the Lab? An Embryologist Explains
IVF & The Lab · Podcast Recap
What Actually Happens to Your Embryo in the Lab? An Embryologist Explains
A conversation with Dr. Tony Anderson, embryologist of 35+ years and founder of IVF Academy USA, on attrition, grading, lab environment, and what actually matters when choosing a clinic.
Key Takeaways
- IVF attrition is normal, not a sign of poor egg quality — of ~12 eggs retrieved, only 2-3 typically end up genetically normal and able to implant, which mirrors what naturally happens across roughly a year’s worth of ovulation cycles, just compressed into one.
- Embryos “arresting” between day 2-5 usually isn’t caused by anything the patient did — it happens when the embryo has to activate its own genome and take over its own metabolism, and this natural selection process sometimes just doesn’t proceed.
- Embryo grading (the letter/number system, like “4AA”) reflects real biological differences in implantation potential, but “BB”-range embryos are common and have pregnancy rates very similar to top-grade “AA” embryos.
- Lab environment matters, but maybe not in the way people assume — pH, osmolality, and temperature control are the critical, tightly regulated factors; more added technology isn’t always the differentiator it’s marketed as.
- If you’re considering egg freezing, sooner is generally better than later — attrition and abnormality rates both increase with age, meaning more eggs are typically needed for the same chance of success later on.
If you’ve gone through IVF, you’ve likely never met your embryologist, even though they play one of the most critical roles in the process. In a recent episode of the Fertility Confidence Podcast, host Kelsey sat down with Dr. Tony Anderson — founder and CEO of IVF Academy USA, a partner in the Positive Fertility Network, and an embryologist with over 35 years of experience — to pull back the curtain on what actually happens behind that closed lab door.
Why Embryo Attrition Isn’t a Red Flag
One of the most reassuring parts of the conversation was Dr. Anderson’s breakdown of the numbers. Using a patient under 35 as an example: out of roughly 12 eggs retrieved, about 10 are mature, 9 fertilize, and only about 4 make it to blastocyst stage by day 5. Of those, roughly half are genetically normal, leaving 2-3 embryos actually capable of implanting.
That might sound discouraging on its own, but Dr. Anderson reframed it in a way that’s worth sitting with: a natural cycle involves about 12 ovulations a year, and IVF essentially compresses that same year’s worth of chances into a single retrieval. Ending up with 2-3 normal embryos from one IVF cycle is, statistically, comparable to what the body does across an entire year of trying naturally.
“Each egg is a roll of the dice. The more times you can roll it, the more chances you’re going to get to get pregnant.”
Why Embryos Sometimes “Arrest” — And Why It’s Not Your Fault
Between day 2 and day 5, an embryo has to shift from living off the egg’s original maternal reserves to activating its own genome and producing its own proteins. Dr. Anderson described this as a kind of natural selection: not every fertilized egg is built to make that transition successfully, and when one doesn’t, it isn’t a reflection of anything the patient did.
His analogy: if every acorn became a tree, there’d be far too many trees. The same principle applies to embryos — some level of attrition is simply how the process is supposed to work, not a sign that something went wrong.
What Grading Actually Means (and Doesn’t)
Embryo grading — the letters and numbers you might see on your embryo report — reflects two things: how expanded/hatched the blastocyst is, and the quality of two distinct cell groups: the inner cell mass (which becomes the baby) and the trophectoderm (which becomes the placenta and does the actual work of implanting). Fewer cells in the trophectoderm generally means a less robust attempt at implantation.
But Dr. Anderson was clear that top grades aren’t the whole story: pregnancy rates for solidly mid-range “BB” embryos are very similar to top-tier “AA” embryos. Most embryos, he noted, land somewhere in that middle range — and that’s expected, not a disappointment.
Lab Environment: What Actually Matters
Dr. Anderson was refreshingly candid about which lab factors are genuinely critical versus which are more marketing than substance. In his view, three environmental factors are the ones that truly matter: pH, osmolality (the salt concentration of the culture media), and temperature — all of which require precise, continuous control. He shared that even when his lab’s air filtration system went down for an extended period years ago, pregnancy rates didn’t drop, which led his current lab to skip that particular technology investment and instead prioritize low-VOC lab materials and precise media control.
What to Ask When Choosing a Clinic
Dr. Anderson’s advice for evaluating a fertility clinic’s lab specifically:
- Ask to meet someone from the embryology team. A lab that’s confident in its process should be willing to have someone come speak with patients.
- Check published success rates. In the U.S., SART.org allows patients to look up individual clinics’ pregnancy rates and cycle volume.
- Trust matters as much in the lab as it does with your doctor. If a clinic isn’t transparent about their processes and safety systems, that’s worth taking seriously.
On Egg Freezing: Earlier Is Better
Dr. Anderson shared a personal note: his own 23-year-old daughter is now considering egg freezing, and his advice to her was not to wait past 30. While eggs can technically be frozen up to age 40, both egg quantity and the rate of genetic abnormality shift with age, meaning more eggs are typically needed later on to reach the same odds of success achievable with fewer eggs earlier.
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Book Your Clarity Call →Sources & Further Reading
- Fertility Confidence Podcast. “How an Embryologist Impacts Fertility with Dr. Tony Anderson.” Episode transcript.
- Dr. Tony Anderson, Founder & CEO, IVF Academy USA. LinkedIn: Tony Anderson / IVF Academy USA. Instagram: @ivfacademyusa.
- SART (Society for Assisted Reproductive Technology) — sart.org, for publicly available clinic-level IVF success rate data.
There’s a 50% Chance Male Fertility Is Keeping You From Getting Pregnant
Half of all infertility cases involve a male factor. Yet sperm testing is still the last thing most couples are told to do — and the numbers being called “normal” are far from it.
- Male factor is involved in 50–70% of infertility cases — yet sperm testing is still routinely the last step, not the first.
- The WHO’s lower limit for “normal” sperm concentration is 15 million/mL — the 5th percentile. At that level, estimated per-cycle pregnancy odds are around 5%.
- Optimal sperm concentration sits at the 50th percentile of men who successfully conceived: approximately 60–73 million/mL.
- Below 30 million/mL, pregnancy probability drops off sharply. Above 50 million/mL it plateaus near the natural per-cycle ceiling of 20–25%.
- Sperm concentration is not fixed. A targeted, data-driven approach can produce significant improvement — often within 3–6 months.
When a couple struggles to conceive, the instinct — in clinical settings and at home — is to start with her. Her cycle, her hormones, her ovulation. This is understandable. It is also costing couples months, and sometimes years, they do not need to lose.
The data is unambiguous: male factor is involved in somewhere between 50 and 70% of infertility cases. Not as a rare secondary concern — as a primary driver, half the time. Yet semen analysis is still treated as the test you run after everything else has been checked, if it gets run at all.
What the statistics actually show
Infertility is clinically defined as 12 consecutive months of trying to conceive without a pregnancy. When researchers break down the causes, the picture looks like this:
This does not change based on prior pregnancies. Sperm quality and concentration shift over time, affected by age, health, stress, illness, and lifestyle. A previous successful conception — in this relationship or a past one — is not a current result. Testing still matters.
Why “normal” doesn’t mean what it sounds like
The reference range most clinics use comes from WHO guidelines. Under those guidelines, a sperm concentration of 15 million per millilitre is considered normal. A man who hits that number is typically told everything looks fine.
What that framing leaves out: 15 million/mL is the 5th percentile. It was derived from a dataset of men who did achieve pregnancy with their partners within 12 months — but the threshold was drawn at the very bottom of that group. Ninety-five percent of those men had better numbers. The threshold was not placed where success is likely. It was placed at the floor of the range where it has occasionally been shown to work.
At 15 million/mL, the estimated per-cycle probability of conception is approximately 5%. That is the number being rubber-stamped as acceptable in clinical semen analysis reporting.
The 50th percentile of that same dataset — the midpoint of men who successfully conceived — sits around 73 million per millilitre. A practical target for optimisation is above 60 million/mL. That gap, between what clears the bar and what actually reflects fertility potential, is not a minor technical distinction. It is where most couples who are told “nothing is wrong” are quietly losing time.
Where the real drop-off happens
Pregnancy probability by sperm concentration is not a linear curve. The steepest decline happens below 30 million/mL — which is still well above the WHO minimum threshold that triggers no clinical concern.
Above 50 million/mL, per-cycle pregnancy probability plateaus near 20–25% — a ceiling that reflects biological limits, not sperm count. Getting from 60 million to 100 million makes little practical difference. Getting from 15 million to 60 million makes a significant one.
Subfertility vs. infertility — and why the gap matters
One reason male factor gets missed is that clinical concern is triggered by infertility thresholds, not subfertility. If a result clears 15 million/mL, it does not prompt a referral or a follow-up conversation. But a man at 25 million/mL is not in the same position as one at 70 million/mL — and treating those results as equivalent is how couples end up in a prolonged stretch of “keep trying” that didn’t need to last as long as it did.
Subfertility — results that are technically within range but far from optimal — is common and, in many cases, improvable. The research base for male fertility nutrition, lifestyle, and supplementation is more robust than most people realise, partly because sperm concentration is a measurable, repeatable endpoint that is straightforward to study. Randomised controlled trials exist. The evidence base is there. But it cannot be applied well without knowing what the actual numbers are.
Getting tested — and reading the results correctly
A clinical semen analysis — where the sample is produced and analysed on-site at a lab — remains the most reliable method. At-home testing has improved; one option used in fertility-focused clinical programmes is Fellow, which runs morphology and returns actual numerical data rather than a simplified pass/fail result. If at-home results come back low or irregular, confirming with a clinical sample before building any treatment plan is the sensible next step.
When results come back, the question is not just whether concentration clears 15 million/mL. It is where concentration sits relative to the 50th-percentile target. Below 60 million/mL, there is room for improvement. Below 30 million/mL, understanding why — structural, hormonal, or lifestyle-related — should come before any intervention is started.
Testing is the beginning of a plan, not the end of a conversation.
The Sperm Count Blueprint
A focused resource for anyone whose sperm concentration is below optimal — or who doesn’t yet know where it stands. Covers how to interpret your numbers, the most common reasons concentration is low, and how to build a targeted plan based on what the research actually supports.
Get the Blueprint → Includes the Full Male Lab GuideReferences
- World Health Organization. (2021). WHO laboratory manual for the examination and processing of human semen (6th ed.). WHO Press. https://www.who.int/publications/i/item/9789240030787 — Source for sperm concentration reference ranges, including the 5th percentile lower threshold of 15 million/mL used in clinical semen analysis reporting.