Assisted Hatching Risks and Possible Benefits

Computer artwork of an egg cell (centre) held in place by a tube (left) and about to be pierced by a micro- needle (right) to inject a single sperm cell.
CHRISTIAN DARKIN/Science Photo Library/Getty 

Assisted hatching is an assisted reproductive technology that is sometimes used in conjunction with conventional IVF treatment. Assisted hatching is thought to possibly help with the embryo implantation and is more likely to be recommended when there has been repeated unexplained IVF failure or for patients with a poor prognosis.

While some clinics use assisted hatching routinely, the American Society of Reproductive Medicine (ASRM) does not recommend this. This is because assisted hatching hasn’t been shown to improve live birth rates. Plus, as with any reproductive technology, there are additional costs and risks to using assisted hatching.

Has your doctor recommended assisted hatching for you? Here’s what you need to know.

How Do Embryos Hatch?

To understand assisted hatching, first, it would help to understand the natural hatching of an embryo.

Before you get an embryo, you start with an oocyte or egg. The oocyte has a protein-shell surrounding it known as the zona pellucida. The zona pellucida has many roles in embryo development, and these functions change as the embryo grows.

Before the egg becomes an embryo, the zona pellucida fuses with sperm cells. This is the start of the fertilization process. Once a single sperm cell penetrates the shell and fertilizes the egg, the zona pellucida hardens. This prevents more sperm cells from entering the now-fertilized zygote.

The hardened shell also helps prevent the embryo from implanting prematurely in the fallopian tubes (which would cause an ectopic pregnancy). It also keeps the many blastocyst cells together.

As the zygote travels down the fallopian tube and develops into the blastocysts stage, the zona pellucida expands and begins to thin and deteriorate. Around day four of development, the zona pellucida cracks open and the blastocyst/embryo emerges, leaving behind the thin-protein shell. This is the embryo hatching process.

Within a few days of hatching, the blastocyst implants itself into the endometrium. Without hatching, the blastocyst can’t implant itself into the uterine wall. This means pregnancy would fail to happen.

What Is Assisted Hatching?

During IVF treatment, fertilization takes place in the lab. But as any couple that has gone through an IVF treatment knows, having a fertilized embryo does not guarantee a pregnancy. The embryo transferred has to implant itself into the endometrium and “stick” for pregnancy to occur.

Up to 85 percent of embryos transferred do not “stick.” There are theories on why this occurs, and one of those theories is that the embryo doesn’t hatch properly. This may happen because the embryo intrinsically has an unusually hard shell, or because something in the lab environment (the cultures used to keep the embryo alive, cryopreservation chemicals, etc.) has artificially interrupted the hatching process.

Assisted hatching is meant to get over whatever hurdles are preventing hatching and improve the odds of implantation (and pregnancy) success.

Assisted Hatching Methods

You may assume that assisted hatching always involves making a small “break” or tear in the zona pellucida. But that’s not actually so. There are a few methods available, and every embryo lab approaches this differently. There are pros and cons to every way and the skill of the technician matters:

  • Mechanical hatching: With this technique, the embryologist keeps the embryo steady with the help of a pipette, while using a micro-needle to puncture through the zona pellucida, go just underneath the shell for a bit, and then come out the other end. (Imagine drawing a very thin line just alongside the embryo.) Then, the area between the two punctures is gently rubbed until a small tear occurs. It's difficult to control the size of the opening with this method.
  • Mechanical expansion of the shell: With this technique, the zona pellucida is not broken open. Instead, hydrostatic pressure is introduced just under the shell, to cause it to expand. The idea for this method comes from the natural expansion of the outer shell during the hatching process.
  • Chemical hatching: This technique involves using a chemical known as Tyrode’s acid. Tiny amounts of acid are applied to the zona pellucida until the shell is breached. Then, the embryo is quickly cleaned to avoid unnecessary acid exposure.
  • Drilling: With drilling, vibratory movements are used to create a conical opening. This technique uses something known as Piezo technology.
  • Laser-assisted hatching: Using a specialized laser to breach the zona pellucida is another possibility. Laser-assisted hatching allows much more control of the size of the hole created, more so than mechanical hatching with a needle (as described above).

Of all the methods, laser-assisted hatching may be the safest and most effective. However, not every embryology lab is equipped to perform this specific technology. Chemical hatching is more commonly used. With all of these methods, the skill and experience level of the embryologist can make a big difference.

Risks

Any manipulation or interference with an embryo is going to involve some risk. One possible risk to assisted hatching is that the embryo will become lethally damaged. This could occur before embryo transfer or after. In either case, pregnancy would not result.

Somewhat ironically, another risk of assisted hatching is the embryo’s natural hatching process will be thrown off and the embryo will fail to fully hatch from the zona pellucida.

Another risk of assisted hatching is twinning, specifically monozygotic twinning. Monozygotic twins are identical twins, who come from one egg and one sperm. Twinning is already increased during conventional IVF treatment, and research has found that assisted hatching my further increase that risk. While all multiple pregnancies carry risk, monozygotic twin pregnancies come with even higher risks for the mother and babies. Still, the risk of twinning is low, occurring less than 1 percent of the time.

You may be wondering if assisted hatching increases the risk of birth defects. A large retrospective study of over approximately 35,000 cycles found that the risk of congenital anomalies was not significantly increased with embryos that were manipulated with assisted hatching, compared to IVF cycles where assisted hatching did not take place.

Does Assisted Hatching Improve IVF Success Rates?

The big question is, of course, is it worth it? Does assisted hatching to help you take home a baby? The answer is a bit complicated.

A Cochrane review on assisted hatching—that considered 31 studies, totaling 1,992 pregnancies and 5,728 women—found that assisted hatching just slightly improved clinical pregnancy rates. However, live birth rates did not improve.

Live birth rates are more important to consider that the clinical pregnancy rate since the goal in any fertility treatment is taking home a baby—not just getting a positive pregnancy test.

Unfortunately, most of the research on assisted hatching has only reported clinical pregnancy rates, and not live birth rates. Those that did look at live birth rates didn’t find an advantage. More research must be done.

Another study found that when assisted hatching was done on “good quality” embryos, pregnancy rates went down. The results varied depending on age group when assisted hatching was done on fair to poor quality embryos. This would imply that assisted hatching not only won't help those with a good prognosis, but it may harm their chances of success.

Who Might Benefit From Assisted Hatching?

There is evidence that assisted hatching may improve clinical pregnancy rates with patients who:

  • Have experienced two or more failed IVF cycles
  • Have poor embryo quality
  • Are older than age 38

It was thought that assisted hatching might be worth trying with frozen embryo transfer cycles, but this may not be the case. In fact, one study found that assisted hatching in a frozen embryo cycle may slightly decrease the odds of a live birth.

Cost

Despite the recommendations of the ASRM, who advise against the routine use of assisted hatching, some clinics still offer it to every patient. In these clinics, the cost for assisted hatching may already be “included” in the overall IVF fee.

For clinics who add-on assisted hatching, the cost can range from $200 to $700, on average. There are also a few clinics which offer the technology for "free," if they think it may be beneficial.

A Word From Verywell

When discussing IVF treatment, it can be tempting to accept or want to use every possible technological “add-on” offered. It may seem like more help should always lead to a better chance of success. But more doesn’t always mean better. 

Because there is not enough evidence to show assisted hatching improves live birth rates, the ASRM recommends against the routine use of the technology. If your clinic does use assisted hatching with every patient, talk to your doctor about why they think this is best for you. You can turn the technology down.

However, for particular patient groups, assisted hatching may be beneficial. As always, talk to your doctor about your personal situation.

Was this page helpful?
Article Sources