Assisted hatching is a lab technique sometimes used during IVF in which an embryologist creates a small opening in the outer shell of an embryo before it’s transferred to the uterus. The idea is to help the embryo “hatch” out of that shell so it can attach to the uterine lining and implant. Despite its widespread use at many fertility clinics, current evidence shows it does not significantly improve live birth rates, and the American Society for Reproductive Medicine (ASRM) recommends against using it routinely.
How Assisted Hatching Works
Every embryo is surrounded by a protein shell called the zona pellucida. Think of it as a protective jacket. In a natural pregnancy, the embryo sheds this shell on its own around five or six days after fertilization, allowing it to burrow into the uterine wall. During IVF, some scientists theorized that the lab environment or the freezing process could toughen this shell, making it harder for the embryo to break free. Assisted hatching was developed in the early 1990s as a way to give the embryo a head start.
The procedure itself is done in the lab, shortly before the embryo transfer. An embryologist makes a small hole or thins a section of the shell using one of three methods:
- Laser: The most common approach today. A precise infrared laser fires brief pulses (each lasting about half a millisecond) to open the shell. It’s fast, controlled, and reproducible.
- Chemical: A small amount of acidic solution is applied to dissolve a tiny area of the shell. This was the original method but takes longer in the lab.
- Mechanical: A fine needle is used to physically puncture or partially cut the shell.
Studies comparing laser and chemical methods found no difference in pregnancy or implantation rates. The main advantage of the laser is speed. One clinic analysis estimated that switching from chemical to laser hatching saved about 46 hours of lab time per year across their caseload, simply because each procedure was about four minutes shorter.
What the Evidence Says About Success Rates
This is where the picture gets complicated, because many clinics still offer assisted hatching despite evidence that it doesn’t reliably help. A large Cochrane review pooling data from 39 randomized trials and over 7,200 women found that assisted hatching may slightly increase clinical pregnancy rates (the odds went up by about 20% on paper), but the quality of that evidence was rated low, and much of the apparent benefit disappeared in more carefully controlled analyses.
More importantly, when researchers looked specifically at live births (which is the outcome that actually matters), assisted hatching made no meaningful difference. Across 14 trials involving nearly 2,850 women, the live birth rate was about 28% without assisted hatching and somewhere between 27% and 34% with it. Statistically, that’s indistinguishable.
The ASRM’s 2022 guideline summarized it bluntly: there is moderate evidence that assisted hatching does not significantly improve live birth rates in fresh IVF cycles, and insufficient evidence for its benefit in frozen embryo transfers.
Does It Help Specific Groups?
One of the most persistent arguments for assisted hatching is that it might help certain subgroups, particularly older patients or those who’ve had repeated failed cycles. The data don’t support this either.
For women with a good prognosis (under 39, first or second IVF cycle, good-quality embryos), studies showed virtually identical outcomes with or without hatching: live birth rates of 47% versus 46%, clinical pregnancy rates of 53% versus 54%, and miscarriage rates of 13% versus 15%. None of these differences were statistically significant.
For women over 37 or those with recurrent implantation failure (more than two failed cycles), the results were similarly flat. Clinical pregnancy rates after assisted hatching were 15.1% versus 21% in older women and 27.1% versus 26.9% in women with repeated failures. Neither comparison showed a benefit.
Perhaps the most striking finding involves women with diminished ovarian reserve. A large analysis of national U.S. data from 2004 to 2011 found that live birth rates were actually significantly lower when assisted hatching was performed in these patients. Women over 39 undergoing their first IVF cycle also saw lower live birth rates with assisted hatching when day-3 (cleavage-stage) embryos were transferred. When blastocysts (day-5 embryos) were transferred instead, hatching had no effect either way.
Day 3 Versus Day 5 Transfers
Assisted hatching was originally developed when most clinics transferred embryos on day 3 of development, before they’d reached the blastocyst stage. At that point the shell is still thick and intact. By day 5 or 6, the embryo naturally begins thinning and breaking through the shell on its own, which is one reason many experts question whether hatching adds anything to blastocyst transfers.
The data back this up. In women over 39, assisted hatching was associated with lower live birth rates when day-3 embryos were transferred but had no measurable effect on outcomes after blastocyst transfer. Since most modern IVF clinics now culture embryos to the blastocyst stage before transfer, the theoretical window where hatching could help has become even narrower.
Risks to Consider
Assisted hatching isn’t a high-risk procedure in the traditional sense. It doesn’t require surgery or sedation, and embryo damage from the technique itself is rare in experienced hands. But it does carry one notable concern: a higher rate of multiple pregnancies. The Cochrane review found that the multiple pregnancy rate rose from about 9% without hatching to between 10% and 14% with it. Multiple pregnancies carry real risks for both mother and babies, including preterm birth and low birth weight.
There has also been a theoretical concern about identical twinning. When the shell is breached artificially, there’s a possibility that the inner cell mass could split as it squeezes through the opening, resulting in monozygotic (identical) twins. Identical twins conceived through IVF carry higher complication rates than fraternal twins because they often share a placenta.
Why Clinics Still Offer It
If the evidence is this underwhelming, you might wonder why assisted hatching remains on the menu at so many fertility clinics. Part of the answer is historical momentum. The technique became popular before large, well-designed trials were available, and once a procedure becomes standard practice it’s hard to walk back. Some clinics also charge an additional fee for it, typically a few hundred dollars, which creates a financial incentive to keep offering it.
Another factor is that the procedure is low-risk from the clinic’s perspective. It takes only minutes to perform, doesn’t harm the embryo in most cases, and gives patients the feeling that “everything possible” is being done. For patients who have already invested thousands of dollars in IVF, an extra add-on can feel like a reasonable insurance policy, even when the data suggest it isn’t one.
The ASRM’s current position is clear: laser-assisted hatching should not be routinely recommended for all IVF patients, and there isn’t enough data to recommend it for any specific subgroup, including those with poor prognosis. If your clinic suggests it, it’s worth asking what evidence they’re basing that recommendation on and whether it applies to your particular situation.