IVF is an infertility treatment where there is a problem with the passage of the sperm to the egg (such as blocked fallopian tubes, endometriosis, anti-sperm antibodies), impaired sperm function (low count or motility), some cases of "unexplained" infertility and sometimes there are problems with ovulation.
In a normal cycle, it is usual to produce one egg that is released from the developing follicle two weeks before the next period starts. The follicle is a fluid filled cyst that grows to about 16 - 22mm before releasing its egg. One follicle will usually contain one egg.
The general aim in IVF treatment is to produce a reasonable number of eggs for fertilisation through stimulation of follicles in the ovary. This is known as ‘super ovulation’. With infertility treatment it is accepted that not every egg will fertilise and not every embryo will progress to a placenta and baby. Super ovulation improves the chance of identifying the eggs and embryos with the best chance to progress.
Once fertilisation has taken place, the best embryos can be selected and replaced into the uterus. In IVF treatment the average number of eggs collected is 10 to 12 and 2 embryos are usually replaced. It is possible for remaining embryos of sufficiently good quality to be frozen for future use, and this should be discussed on an individual basis with the embryologist.
When the ovaries are stimulated by fertility drugs it is usual for several follicles to grow. However, the rate of growth of individual follicles varies and it is important that the egg collection is undertaken when, as many eggs as possible are appropriately mature. In order to achieve this, IVF clinics routinely use a combination of drugs that takes over from the body's natural hormone cycle.
The hormones that stimulate ovulation are luteinising hormone (LH) and follicle stimulating hormone (FSH), both produced by the pituitary gland in the brain. FSH and LH stimulate the growth of follicles that in turn produce Oestradiol before ovulation and oestrogen and progesterone after ovulation. Oestradiol promotes growth of the lining of the womb (endometrium) and progesterone maintains the endometrium in a favourable state for the implantation of the embryo(s).
Number of embryos:
The HFEA code of practice stipulates that not more than two embryos can be transferred. The only exception is the patient over the age of forty undergoing treatment with their own eggs. Transferring two embryos is recommended, as the pregnancy rate is usually the same for 2 or 3. In exceptional circumstances three will be considered. However, there is a well-documented increase in the multiple pregnancy rate following IVF assisted conception with 3 embryos.
Multiple pregnancies are associated with an increased risk of miscarriage and complications during pregnancy. These include premature birth of very small babies, which may be handicapped or may not survive. In addition to these risks, a multiple birth can create enormous strains for the parents, including financial difficulties, emotional and physical exhaustion.
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