Advanced Embryology

advanced embryology

Harley Street Fertility Clinic’s laboratory uses state of the art techniques within the field of assisted reproduction.

Some of the advanced and innovative techniques available to our patients are listed below.

Blastocyst culture and transfer

Historically embryo transfer following IVF or ICSI took place two or three days after egg collection when the embryo contains around six to eight cells.  However, laboratory advances have meant that we can now culture embryos for five or six days. By this stage, the embryos have numerous cells (approximately 80 – 100) and start to form two distinct layers. The embryos are then known as blastocysts.

Culturing embryos in the laboratory to day five or six gives the embryos more opportunity to prove their developmental potential. Some fertilised eggs may even arrest (stop developing) prior to day 5. This ‘natural selection’ enables the embryologist to more accurately choose the best embryo for transfer which offers the most likely chance of pregnancy.

  1. Blastocyst grading

    Blastocyst grading or quality is determined by evaluating the outer ring of cells, known as the trophectoderm or trophoblastic cells, that will eventually form the placenta; the inner cell mass or ICM, which is made up of the stem cells that the baby will develop from.
    Scoring of blastocysts is an imperfect science, and some very nice-looking blastocysts do not necessarily produce a pregnancy. However, the basic rule of thumb is that the best embryos make it to the blastocyst stage, and therefore has a greater chance statistically of producing an ongoing pregnancy than a lesser quality one.

  2. Transfer and implantation

    During natural conception, eggs and sperm fertilise in the fallopian tube, in which they continue to divide and only reach the uterus on Day 5 post fertilization at this blastocyst stage. Therefore a Day 5 transfer mirrors this physiological timing. Scientific evidence shows that blastocyst transfer success rates are higher than the transfer of day three embryos.

  3. Freezing (vitrification)

    Harley Street Fertility Clinic promotes eSET (Elective Single Embryo Transfer) as recommended by the Human Fertilisation and Embryo Authority (HFEA). This means that there are often additional blastocysts remaining after embryo transfer. If the blastocysts are of good quality, they can be stored for use in a frozen embryo replacement cycle (FET) at a later date. The freezing process is known as vitrification. Currently, scientific reports indicate that the chances of pregnancy using blastocysts that have been vitrified is almost equal to those used in a fresh embryo transfer cycle.

Laser Assisted Hatching

Whether embryos are transferred on Day 3 or 5, for implantation and therefore pregnancy to occur, the embryos have to “hatch” out of the zona pellucida (embryo shell) so that the cells of the embryos can come into direct contact with the cells lining the womb. Some studies have suggested that a possible reason for the failure of embryos to implant following IVF treatment may be the inability of embryos to undergo this hatching process.

It is possible to assist this hatching process in the laboratory by using a laser to make a small hole in the shell of the embryo. This process is known as assisted hatching.

There is no evidence of benefit in the routine use of assisted hatching in every cycle and in view of the theoretical risk (<1%) of damage during the procedure it may only be suggested in select cases:

  • couples whose embryos are noted to have thickening of the zona by or highly experienced embryological team.
  • couples with a history of recurrent implantation failure
  • couples with an advanced maternal age.

There is emerging evidence that for a minority of patients – particularly those with poor prognosis – Assisted Hatching improves the clinical pregnancy rate.

The following paper in Nature provides the latest evidence for Assisted Hatching.

Assisted hatching increases the risk of monozygotic twinning.


EmbryoGlue is an embryo transfer medium used in the final step of IVF treatment. It’s been developed to closely resemble the environment in the womb, which can help to encourage successful implantation.

EmbryoGlue isn’t glue as you know it; it’s made with a substance – hyaluronan – that makes the embryo more likely to stick to the lining of the womb.

Hyaluronan is a type of carbohydrate found everywhere in the body. In EmbryoGlue it acts like a bridge between the embryo and the womb, which helps them stick together. It’s rich in the carbohydrates, amino acids and protein the embryo needs to develop properly, and it also helps to thicken the EmbryoGlue, which reduces how much the embryo can move around.

If you decide to use EmbryoGlue your treatment procedure will not change. The only difference is that, just before we transfer the embryo, we’ll place it in the EmbryoGlue transfer medium.

Further reading

The treatments listed above are adjuncts to IVF and not recommended for all patients. Please speak to your consultant about whether it might be beneficial for you.

Please refer to the regulator’s web page regarding treatment “add-ons” for further information: HFEA

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