Causes & Treatment

Everything You Need to Know About Hatching Blastocysts

Eloise Edington  |   27 Jan 2022

Starting from the top, hatching blastocysts are embryos that have reached an advanced stage of development, where they begin to break out of their protective outer shell, known as the zona pellucida. This process, called hatching, is a crucial step for successful implantation in the uterus, during fertility treatments like IVF.

Hatching blastocysts are typically considered more viable for implantation, as they’ve demonstrated the ability to progress to this advanced stage of development. This stage marks an exciting milestone in the journey towards conception and pregnancy.

Here, we’ve asked our partners in South Africa, Wijnland Fertility Clinic and Sperm Bank, to give us the deep-dive on:

  • what we mean by ‘hatching blastocysts’
  • who assisted hatching might be suitable for
  • the implantation of hatching blastocysts
  • … and more of your hatching blastocyst questions

Wijnland’s state-of-the-art medical equipment and its personalised approach make them a Centre of Excellence for fertility treatment in South Africa.  Check out their website by clicking here.

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Back to blastocysts. Let’s unpack what we mean by ‘hatching’ and how it affects implantation.

Over to Wijnland…

What are hatching blastocysts?

A blastocyst is a Day 5 embryo yet to fully understand what a hatching blastocyst is, we need to explain the early development of an embryo.

In the reproductive system, embryos and eggs naturally have a protective protein shell called the zona pellucida (ZP). The ZP has multiple functions, especially during the first few days of fertilization and development. Once fertilization has occurred, the ZP hardens to prevent additional sperm from penetrating the egg and prevents premature implantation in the fallopian tube (ectopic pregnancy).

Whilst the embryo develops, preparing to implant into the uterus wall, the ZP thins as the blastocyst (the day 5 embryo) secretes enzymes and increases in size. When an embryo breaches the ZP before implanting into the uterus, it is considered to have hatched.

What do hatching blastocysts look like?

How are embryos graded?

Each laboratory has its own grading system and embryos are usually graded by the embryologists to categorize the embryo quality. Wijnland Fertility grades embryos according to three parameters.

The first parameter refers to the size of the blastocyst and is graded from 1 (smallest) to 5 (largest). The second parameter refers to the inner cell mass (ICM), which develops into the fetus and is graded A to C. The third parameter refers to the trophectoderm, which develops into the placenta and is graded A to C.

Hatching embryos are graded as a size 5 blastocyst.

Is it a ‘good sign’ and are hatching blastocysts more likely to implant?

All blastocysts must hatch in order to implant (similar to a chicken that has to “hatch” out of its egg when born). A hatching embryo is a good sign and should start on day 5 of development. Most embryos, however, would hatch once transferred into the uterus. A failure to hatch could be a contributing factor to implantation failure.

Can you get pregnant even if you don’t get to the blastocyst stage?

Yes, you can get pregnant if an embryo is transferred earlier (day 3) but it must reach the blastocyst stage within the uterus.

What is assisted hatching?

IVF laboratories provide numerous “add-on” treatments to improve IVF outcomes and the possibility of taking home a baby. Assisted hatching (AH) is one of these add-ons and was first suggested in the 1980s.

Naturally, implantation takes place approximately 7 days after fertilization but during IVF, the implantation process starts immediately after embryo transfer and implantation occurs 2-3 days hereafter. Assisted hatching is the artificial thinning or disruption of a section of the ZP to assist the embryo in hatching from the ZP. Assisted hatching is usually performed on either Days 3, 4 or 5 of embryo development.

There are a few techniques that can be used to perform AH and the most popular technique is by the aid of a laser. (Other techniques include chemical thinning, mechanical disruption with a microneedle and piezoelectric pulses.) Laser-assisted hatching is currently the safest, fastest, and most effective technique.

How are hatching blastocysts linked with PGS and PGT-A screening?

In cases where preimplantation genetic screening (PGS) or now known as preimplantation genetic testing for aneuploidy (PGT-A), assisted hatching is one of the techniques used by laboratories prior to biopsy to optimize the biopsy procedure. Embryos that have undergone hatching prior to biopsy have been shown to have improved IVF outcomes in comparison to non-hatching embryos. Assisted hatching is, therefore, a valuable technique to use in the laboratory for PGT-A cases.


Is assisted hatching suitable for me?

Remember that fertility treatment add-ons usually come at an additional cost so you’ll need to speak with your fertility doctor to understand if assisted hatching is right for you. Wijnland emphasizes that additional treatments like assisted hatching should only be offered to cases that meet the criteria – so assisted hatching isn’t suitable for every patient going through IVF.

Wijnland suggest assisted hatching when:

  • The ZP is abnormally thick or hard as this could make it more difficult for the embryo to hatch and implant. By assisting with embryo hatching, the process of implantation is started.
  • Embryos reach day 5 of development but haven’t hatched. Performing assisted hatching on these embryos could facilitate embryo hatching and possibly improve the chances of implantation.
  • A patient is older than 38 years old or has poor embryo quality, has had previous implantation failure, is using frozen-thawed embryos and has high follicle-stimulating hormone (FSH) levels.
  • A small piece of the embryo’s “placenta” needs to be biopsied (PGT-a) for testing.

Is it worth pushing to blastocyst stage even with low ovarian reserve where there are few embryos?

We would definitely push for the blastocyst stage (day 5) due to the “extra” information that we get from the development from day 3 to day 5 (impact of the sperm dominance from day 3 onwards). Embryo selection for single embryo transfer is much easier due to the better embryo developing more strongly from day 3 to day 5.

What are the benefits of assisted hatching?

  • Assisted hatching is safe and doesn’t cause damage to the embryo.
  • Some evidence suggests increased clinical pregnancy rates but no significant increase in the live birth rate.
  • For people who meet the criteria for assisted hatching increased IVF success has been observed.

What are the risks of assisted hatching?

  • Some evidence suggests a hatching blastocyst is more likely to split into twins although other studies have found no significant increase.
  • Assisted hatching can be expensive.
  • There is no guarantee of an improved live birth rate.

When an embryo struggles to develop into a hatched blastocyst, assisted hatching can be a viable fertility treatment add-on for suitable patients. Scientific evidence suggests slightly improved chances of clinical pregnancy rates and with increased medical advances, a clearer understanding of the benefits of assisted hatching can be reached.

Thank you to Wijnland for their expertise and detailed explanation of hatching blastocysts and assisted hatching during fertility treatment.

To book an appointment with Wijnland, a leading fertility clinic and sperm bank in South Africa, click here.

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