Everything you need to know about hatching blastocysts
Starting from the top, hatching blastocysts are embryos that have reached an advanced and highly significant stage of development.
At this point, usually around day five or six after fertilisation, the embryo begins to break out of its protective outer shell, known as the zona pellucida. This process is called hatching, and it plays a vital role in enabling the embryo to implant into the lining of the uterus.
For implantation to occur, the embryo needs to hatch from the zona pellucida so it can interact with the uterine lining. Once free from the zona pellucida, the embryo is able to interact directly with the uterine lining, attach itself and begin the process that may ultimately lead to pregnancy.
Hatching blastocysts are often considered more viable for implantation because they have already demonstrated strong developmental potential. Reaching this stage indicates that the embryo has divided appropriately, formed specialised cell layers and sustained growth through several critical checkpoints.
For many patients undergoing fertility treatment, the presence of a hatching blastocyst represents an encouraging milestone and a hopeful step forward on the path towards conception and pregnancy.
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Hatching blastocyst deep-dive
Shifting gears and heading to South Africa, today we’re picking up with 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
- implantation of hatching blastocysts
Plus, loads more. Wijnland’s state-of-the-art medical equipment and its personalised approach make them a Centre of Excellence for fertility treatment in South Africa.
So, blastocysts. Let’s unpack what we mean by ‘hatching’ and how it affects implantation.
What are hatching blastocysts?
A blastocyst is an embryo that has developed to the blastocyst stage, usually around 5-7 days after fertilisation. To understand what a hatching blastocyst is, let’s break down the early stages of embryo development.
In the reproductive system, both eggs and embryos are surrounded by a protective protein shell called the zona pellucida (ZP). This shell plays a key role in the first few days after fertilization. Once an egg is fertilized, the ZP hardens to prevent multiple sperm from entering and to stop the embryo from implanting too early – for example, in the fallopian tube (which could lead to an ectopic pregnancy).
As the embryo grows and prepares for implantation in the uterus, the ZP naturally starts to thin. The blastocyst (the Day 5 embryo) releases enzymes and expands, eventually breaking through the ZP. When this happens before implantation, the embryo 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.
In Wijnland Fertility’s grading system, a size 5 blastocyst is considered to be hatching.
Is a hatching blastocyst a good sign?
All blastocysts must hatch in order to implant (similar to a chicken that has to “hatch” out of its egg when born).
Are hatching blastocysts good to see? In general, yes. Seeing a blastocyst beginning to hatch can be an encouraging sign of development, but hatching status alone cannot predict whether an embryo will implant or result in a live birth.
The bottom line – for an embryo to implant, it must eventually hatch from the zona pellucida. Hatching may occur before or after embryo transfer, depending on the embryo and the circumstances of treatment.
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 after embryo transfer and implantation can be around 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.)
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.Â
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.
Editor’s note: This article is one of our most popular reads, but 4+ years old – so please check with your healthcare provider. At the time this article was published (2022), Wijnland Fertility identified several circumstances in which its clinicians might consider assisted hatching, including:
- 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.
- Although assisted hatching has been proposed as a way to improve implantation, current evidence doesn’t show a significant improvement in live birth rates in fresh IVF cycles. Evidence for its benefit in other groups, including people with a poorer prognosis or undergoing frozen embryo transfer, remains insufficient.
- 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.
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On your reading list
- Short, long or something different? How this consultant starts, pivots & builds a personalised IVF treatment protocol
- Day 3 or Day 5 blastocyst embryos? An embryologist’s 101
- Handy Reddit chat covering hatching blasts, embryo transfer and success stories
Do you have a hatching blastocysts success story? If you’re happy to share, we’d love to hear from you! DM us on Insta, and we’ll be in touch.
