03:59 9th December 2013 | In-Vitro Fertilisation
Embryo Grading Embryo Transfer Cervix FSH Injections Uterus Assisted Hatching Blastocyst Transfer Zona Pellucida PGD PGS
The next step in the IVF treatment process after the Egg collection process is the Embryo grading and transfer.
Embryo grading takes place on the day of embryo transfer. Embryos are graded visually looking at them under the microscope. We look at the shape of the embryo’s cells and assess how smoothly the cells are dividing by looking for fragmentation. Ideally, there should be no fragmentation as in a grade one embryo. Fragments are small pieces of cell which have broken away during cell division. We think that the more fragmentation that occurs, the less likely the embryo is to implant in the uterus and result in a pregnancy. Research has shown that grade 1 and 2 embryos grow equally well, whereas grades 3 and 4 did less well. However pregnancies have followed the transfer of a single grade 4 embryo. There is no relationship between the quality of embryos transferred and the chance of a baby being born with an abnormality.
Some clients will need a “mock” embryo transfer to rule out any abnormality of the cervix that could become an obstacle to the real embryo transfer. This decision is usually taken by the doctor depending on the appearance of the cervix on vaginal examination. This is usually performed before the commencement of the FSH injections (second injection). You will be told to come with a full bladder for embryo transfer. The doctor will first tell you about your embryos and then show them to you on the TV screen. Two or three embryos are then transferred into the uterus. The procedure usually only takes a few minutes and is usually quick and painless. You may go home immediately after the procedure. Resting or lying down does not improve the success rate. You may also empty your bladder if necessary.
Although utmost care and control is taken, complications or difficulties may be encountered i.e:
The egg is surrounded by a thick outer shell called the zona pellucida and the fertilised egg (embryo) has to hatch from this to implant into the lining of the womb. This outer shell may be too thick in some cases and this may disturb implantation. There is some evidence that making a hole in the zona with either a chemical solution or
using Laser energy improves hatching and pregnancy rates. Although the benefits of assisted hatching is controversial, it can be used for the treatment of the eggs of older women or women where the day 3 follicle stimulating hormone (FSH) is elevated.
One of the major challenges of In Vitro Fertilisation is the selection of the embryo with implantation potential from the available pool of embryos. A blastocyst is an embryo that has developed for five days after fertilisation. The implantation rate is better with the transfer of blastocysts than the usual practice of transferring embryos on Day 2.
This has the advantage of reducing the risk of multiple pregnancies by reducing the number of embryos transferred, indeed it has been argued that the objective of IVF is the conception and birth of a simple healthy baby and increasingly IVF centers are transferring single blastocysts into the uterus. However, under standard IVF conditions only 25 – 40% of human embryos will proceed to blastocysts stage after 5 days culture and a number of couples will end up with no embryos available for transfer.
Further more, it has been shown that the embryos that proceed to blastocysts are usually the ones that implant when transferred in day 2 and there is no significant improvement in pregnancy rates when we compare blastocyst stage transfer with day 2 transfers.
Pre-implantaton genetic diagnosis is a relatively recent addition to our pool of processes that attempts to improve the pregnancy rates with IVF. In this technique, a single cell is removed from the embryo and the genetic make up of this cell can be studied. Although PGD holds a lot of promise, it is currently only useful for the prevention of genetic conditions that can be identified on the chromosome. It holds promise for the management of older women where the low pregnancy rates seen are thought to be due to genetic defects in the embryos.
Two or Three Embryo Transfer
It is natural to assume that by putting more embryos back into the woman’s womb, the chance of pregnancy will be increased. This does not seem to be the case. A study conducted over the last six years at Kings College Hospital, London has shown that the chance of pregnancy after the transfer of two good quality embryos is 25%. Thus, if each embryo had an equal chance of conception (12.5%) one would expect a 37.5% chance of conception after the transfer of three good quality embryos. They have shown that this is not the case. The chance of pregnancy after the transfer of three good quality embryos is 29% which is only an increase of 4%. The disadvantage of transferring three good quality embryos is that if pregnancy occurs, there is a one in seven chance of that pregnancy being a triplet pregnancy. There is an equal chance of a pregnancy being a twin pregnancy following the transfer of 2-3 good quality embryos. Unfortunately there is a very real chance of problems developing in a triplet pregnancy. 1 in 100 singleton pregnancies end in the delivery of a baby that is dead or dies soon after birth. 1 in 27 twin pregnancies end in the delivery of a baby that is dead or dies soon after birth. 1 in 4 triplet pregnancies end in the delivery of a baby that is dead soon after birth. When deciding the number of embryos to be transferred, you have to balance the slightly increased pregnancy rate of three embryo transfer against the risks associated with multiple pregnancy.
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