Embryo Arrest: Why Embryos Stop Growing Before Day 5

The fertilization report looked good. You had eggs. They fertilized. Day three looked fine. Then came the call. Nothing made it past day five, or one did, and it was graded poor, and the cycle was over. You were told it was egg quality, or it was a numbers game, or that you have to try again.

Here is what that explanation leaves out. An embryo does not run on one engine the whole way. For the first two to three days it runs almost entirely on the egg, on the proteins, the messenger molecules, and the energy the egg packed during its final growth phase. Then, around the four to eight cell stage on day three, the embryo activates its own genome and takes over, and the paternal contribution comes online.

That handover changes where you look. If development stalls in the first three days, you start with the egg and its energy supply. If it looked strong on day three and stalled before the blastocyst, you start with the sperm and its DNA. Same line in the report. Two completely different first moves. Most workups examine neither. They adjust the protocol and go again.

In this episode, I walk through the seven factors that shape whether an embryo keeps dividing, and what most clinics never review before they tell you it was your eggs. Pull it up, take notes, and bring it to your next appointment.

TIMESTAMPS
00:00 The day five call and what the explanation leaves out
00:55 If this show has helped you, leave a review
01:05 Who reviews your case at Fab Fertile
03:50 Number one: the day three handover and where to look first
06:10 Number two: the egg's energy supply was built before the cycle
08:05 Number three: sperm DNA fragmentation and the standard semen analysis
09:20 Number four: the full thyroid panel, including antibodies
10:20 The Embryo Audit Checklist
10:40 Number five: blood sugar and insulin, for both of you
11:45 Number six: inflammation, the gut microbiome, oxidative stress
12:40 Number seven: the ninety day window and why repeating a cycle repeats the result
13:45 Why the data driven approach works for left brain people
14:30 Chromosomal quality is information, not a verdict
14:55 The Functional Fertility Second Opinion

WHAT THE RESEARCH SHOWS
A standard semen analysis measures count, motility, and shape. It does not measure the integrity of the DNA inside the sperm. Sperm carrying damaged DNA can still fertilize an egg and produce a normal-looking embryo on day two or three, and development can stall after the genome handover.

In a 2025 retrospective analysis of 870 fresh single blastocyst ICSI cycles, each one percent increase in sperm DNA fragmentation was associated with roughly 2.5 percent lower odds of obtaining a top quality blastocyst on day five. The same analysis found that fragmentation was not predictive of clinical pregnancy outcomes. It speaks to why an embryo stalled, not to whether a pregnancy will happen.

Thyroid autoantibodies have been detected in follicular fluid at concentrations that correlate with blood levels, which is one reason a complete thyroid panel may include Free T3, Free T4, Reverse T3, TPO antibodies, and thyroglobulin antibodies rather than TSH alone. These are not established diagnostic tests for embryo arrest. They can provide context that a single TSH result cannot.

THE EMBRYO AUDIT CHECKLIST
If your embryos have arrested and you want to walk through what to review before the next cycle repeats the same result, we built the Embryo Audit Checklist for exactly this.
Download it at https://fabfertile.com/pages/embryo-audit-checklist
Or email hello@fabfertile.ca, subject line CHECKLIST.

FUNCTIONAL FERTILITY SECOND OPINION
This is a call where I review your cycle, your labs, your history, and your partner's picture together in one place. You leave knowing what your embryos may be telling you and what the next cycle would be built on, instead of repeating the same outcome. Whatever you decide afterward is yours, but it gets made with information your workup did not give you.
Book at https://fabfertile.com/pages/book
Or email hello@fabfertile.ca, subject line FERTILE.

ABOUT THE HOST
I'm Sarah Clark, founder of Fab Fertile and host of Get Pregnant Naturally, a podcast with over one million downloads. My functional fertility team works with couples navigating low AMH and failed IVF, reviewing functional lab results, gut microbiome, food sensitivity, vaginal microbiome, nutrigenomics, HTMA, DUTCH, toxin testing, and bloodwork alongside nervous system work, to help identify patterns that may not have been considered. We work alongside your medical team, not instead of them. Subscribe to Get Pregnant Naturally for weekly episodes on fertility optimization, IVF preparation, and the lab work your doctor probably isn't running.

Sarah Clark, founder of Fab Fertile, host of Get Pregnant Naturally (1M+ downloads), and author of Fabulously Fertile.

If this episode helped you make sense of your own numbers, leave a review wherever you listen. It is how another woman, being told the same thing, finds her way here.

REFERENCES

1. Machałowski T, Machałowska J, Gill K, et al. Sperm DNA Fragmentation Impairs Early Embryo Development but Is Not Predictive of Pregnancy Outcomes: Insights from 870 ICSI Cycles. International Journal of Molecular Sciences. 2025. doi:10.3390/ijms26167923
2. Monteleone P, Parrini D, Faviana P, et al. Female infertility related to thyroid autoimmunity: the ovarian follicle hypothesis. American Journal of Reproductive Immunology. 2011.
3. American Urological Association and American Society for Reproductive Medicine. Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline. 2020.