In vitro fertilization
In vitro fertilization (IVF) is a controlled reproductive process where conception is carried out with donor sperm and egg in a petri dish (in vitro). The fertilized eggs are then implanted in the uterus of a surrogate mother. The surrogate mother may or may not be the biological mother. It is carried out for couples that cannot conceive naturally.
The IVF Process
In order for IVF to have a chance of success, a number of eggs need to be collected from the mother and a good semen sample from the father. The gametes are then mixed together in a petri dish in the hope that fertilisation will occur. The fertilised embryos are chosen and implanted either back into the mother or into a surrogate.
The male can usually provide the semen sample in a non surgical manner but if the problems with fertility lie with the male, sometimes surgery is required in order to collect viable sperm. This is usually if there is no sperm in the semen due to a blockage of the transport system. The process carried out is called cervical sperm retrieval and this is where a needle is inserted into the testes to withdraw some sperm. Sometimes, a tissue biopsy is needed in order to get an efficient sample.
Once a male sample is retrieved, it is taken to the lab for analysis. Centrifugation is carried out in order to select the best quality sperm and the numbers of motile sperm within a sample are counted. The sample is then stored, ready for use when the eggs of the female are harvested.
Collecting female gametes is much more difficult. Females only produce one egg per month and that is not enough to have a good chance of fertilisation. Hyperstimulation is required in order to harvest as many eggs as possible. Before egg collection, the female is put on a certain dosage of oestrogen and the FSH and LH levels are tightly controlled. This allows for numerous follicles to mature. Once ready, the female undergoes a transvaginal ultrasound. This is where a needle is pushed through the vagina and into the ovary. It then acts as a vacuum and sucks the follicles out where they are put in a petri dish for observation. Support will need to be given to the prospective mother after this process as the corpus luteum will not be present so it cannot maintain the endometrium in readiness for pregnancy.
Culturing the Embryos
The two samples are then mixed and left overnight in the hope that fertilisation will occur. If it does so, the embryos need to be cultured. There is a time delay between fertilisation and the embryo entering the uterus in the natural world and therefore the embryos are left to grow in the medium until day 2-5. The further the embryos are allowed to grow before being put into the mother, the more chance of success in implantation. However, there is a risk for the longer they are left outside the body, the more chance there is of losing the embryos.
Once the embryos have been cultured, the best looking embryos are put back into the mother. These are graded in terms of number of cells and other aspects such as the shape of the cells. Only good embryos will be returned to the mother. Nowadays, legislation states that if the mother is healthy and under 35 then only one embryo should be placed back in the uterus. This is because placing multiple embryos back can lead to multiple pregnancies which are dangerous for both the mothers and the babies health as well as putting a strain on the health service.
The process of collecting the eggs and embryo transfer needs occur within a tight window. The embryos can be frozen in liquid nitrogen and stored for years but there is a lower chance of fertilisation after being frozen due to the risks of the thawing process.
Sometimes a process called Intra cytoplasmic sperm injection is needed to help the IVF procedure. This is usually where the sperm have failed in previous attempts to penetrate the egg on their own. A good quality sperm is taken and the tail is broken off. The sperm is the inserted into a needle and injected directly into the egg, thereby bypassing the binding and penetration steps of fertilisation. It needs to be injected to the left of the polar body release site because that is where the genetic machinery for division called the spindle pole is situated.
There are numerous advantages to using ICSI as they ensure that the egg will be fertilised and have a higher success rate. However, there are also a great number of risks associated with the procedure. The oocyte may become damaged during the injection and there is a chance that the risk of the baby having a congenital malformation increases. Also, sometimes the sperm do not fertilise to stop the baby developing with chromosomal aberrations and it will be aborted at a later time causing great pain for the parents. There have also been links with imprinting disorders which are based on the environment that the embryo is in. Beckwith- Wiedermanns syndrome and Angelman syndrome have both been associated with the use of ICSI.