One of the most significant decisions while doing the IVF treatment is to decide when to make the embryo transfer to the uterus. In order to grow multiple eggs while undergoing in vitro fertilization the ovaries must be stimulated using medication. A trans-vaginal sonogram can be used to visualize the eggs as “follicles”. At the time the follicles grow to a particular size and they are considered to be mature enough then additional medicine called the “trigger shot” is given. This medication is administered in order to cause the release of the eggs into the follicular fluid. In the next 36 hours the eggs are being aspirated. Next just after the retrieval the eggs are fertilized with the sperm of either the partner’s or donor’s sperm. The created embryos are then cultured in the laboratory up to the day of the embryo transfer.
The embryo develops in the laboratory initially consisting only of a few cells which with time keep dividing and multiplying. The shape of the embryo is also changing when accumulating the cells and the embryo goes to the “cleavage stage” and later to a more developed form of a blastocyst. A blastocyst development makes it more differentiated with the different sections. One section for example is the fundament of the subsequent placenta while another will develop into a fetus.
The stage of transfer
While undergoing IVF there are a few different stages of development in which the embryos can be transferred into the uterus. In some cases the embryo transfer is made at an early stage on the second or even the first day. However usually the embryos are transferred in two specific stages:
- The cleavage stage: Which is on the third day of the embryo’s life – it is usually called the “day 3 transfer”;
- The blastocyst stage: This is the fifth day of the embryo’s life and is usually called the “day 5 transfer”.
The scientific and medical world still debates which time is the best for transferring the embryos. Various clinics have different policies on the day of the transfer, some do it in the cleavage stage some in the blastocyst stage. Sometimes the decisions on the stage is different for each patient after the diagnosis and is specially chosen for his individual needs.
Day 5 embryo transfer benefits
The most significant benefit of doing the transfer on the blastocyst stage is the fact you can choose the strongest embryos which are more like to implant and in a result get pregnant.
Waiting for the embryo to develop to the blastocyst stage is a kind of selection itself. In fact some embryos which are of poor quality or have genetic abnormalities or disorders have a lower chance to survive 5 days to become a blastocyst. Which means that in a way the low quality embryos eliminate themselves leaving you to select among the strongest. Studies show that women which produce many embryos can benefit from doing “day 5 transfer”. Those of the patients which responded well to the medication and had multiple embryos had higher pregnancy rates. However among the older women and women which produced lower amounts of eggs or embryos this benefits were not visible. In case of these women there are no obvious benefits of to do a 5 day transfer over a 3 day transfer.
Blastocyst stage disadvantages compared to 3 day transfer
- Like it was said earlier sometimes embryos are too weak to survive 5 days to develop to into a blastocyst. This however is a bit of a risk at the same time because it might result in cycle cancellation due to lack of embryos to be transferred. If an older woman wants to do a 5 day transfer and she only has few embryos then the chance that none of the embryos will survive to the fifth day is higher and unfortunately the patient is left with no embryo to be transferred.
- There is also a risk that fewer embryos or even no embryos will be available for freezing to be transferred in the future.
- There is a bit higher risk of getting pregnant with identical twins.
- There is a slight higher chance of the child being male.
To sum up doing a 5 day blastocyst stage transfer has clear benefits for younger women which are able to produce multiple embryos increasing their pregnancy rate and giving them the option to choose the best quality embryos. However women of older age and with reduced possibilities of producing embryos and embryos of high quality have no clear advantages for using the 5 day transfer.