Ovarian Stimulation
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| Under the influence of stimulation treatment, several follicles ripen together |
Hormone preparations and anti hormones
Possible side effects
In
theory, we learned that during the natural cycle, usually only one follicle matures fully into a fertile egg cell.
Medically assisted conception techniques involve hormonal stimulation of the ovaries, in order to allow a larger number of follicles to ripen and many more eggs to be available at the moment of collection. Which stimulation method is applied depends on the type of treatment, therefore we will discuss the stimulation methods for each treatment apart. The following is a summary of the general principles of stimulation.
Hormone preparations and anti hormones
The hormones used to stimulate the ovaries are either hormones which occur naturally in the womans' body at other times (see
female hormones), or else the hormonal table of the womans' body is synthetically influenced and stimulated in this way.
The preparations below can all be used as part of a stimulation course. Only hCG is used to trigger ovulation.
- anti-oestrogens: a synthetic substance used to lightly stimulate the ovaries. To read precisely how it works, see clomifeen citrate.
- aromatase-inhibitors: this synthetic product inhibits the transformation of testosterone into oestrogen within the ovary. This fools the brain into thinking that there are insufficient levels of oestrogen present and more FSH is produced, thus stimulating the ovaries.
- hMG (human menopausal gonadotrophin) is a combination of FSH and LH. The levels of both these hormones are high during the menopause. In IVF a purified form obtained from human urine is used. It has the same effect as FSH.
- FSH (follicle stimulating hormone) is one of the two sex hormones produced in the hypofyse. It ensures the growth and development of follicle in the ovaries. In IVF, a purified form obtained from human urine is used.
- rec-FSH, a synthetic version of the naturally occurring FSH. Made in a lab without using any natural products.
- LH, the sex hormone which stimulates ovulation is not produced medically, because it can be substituted by hCG, which has the same effect. There is a synthetic product available; rec-LH, which is not currently on the market in Belgium.
- hCG (human chorion gonadotrophin) or pregnancy hormone. It can be obtained from the urine of pregnant women and when administered at the correct moment of a stimulation course, it has the same effect as LH: it causes ovulation after 36-42 hours.
Possible side effects
Multiple pregnancies
A significant undesirable side effect of hormone stimulation treatment is the increased risk of multiple pregnancy. Because many eggs ripen at once, more than one could be fertilized.
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Ultrasound scan showing triplets |
The risk of miscarriage increases with multiple pregnancy, along with the chance of premature birth and other complications. Perinatal morbidity (the number of babies which die between the 28th week of pregnancy and the 7th day after birth) is also significantly higher. The chance of having a multiple pregnancy depends on several factors.
The medication used:
- the GnRH pump (see ovulation induction) increases levels of the hormone in the blood which stimulates production of FSH and LH (see hormones and what they do). It regulates rather than stimulates. In women who become pregnant via this method, the incidence of multiple pregnancies is less than 5%.
- the use of FSH and LH (or the synthetic variant rec-FSH) can increase the risk of twins to 25%. These gonadotrophins directly affect the reproductive organs and stimulate the ovaries to produce many follicles at the same time.
- a 'lighter' stimulation, as is used in artificial insemination and timed intercourse techniques, is usually obtained via the administration of clomifeen citrate, an anti-oestrogen. This method carries a 10% risk of resulting in twins.
But fertility treatment itself plays a decisive role
- During both artificial insemination and timed intercourse stimulation phases, regular ultrasound techniques are performed to see that not more than three ripe follicles (>17mm) have developed. If there are too many, the chance of a multiple pregnancy is too great. The decision then has to be made whether to stop the treatment, or to reduce the number of follicles, by puncturing them until there are only a maximum of two remaining. Another possibility would be to switch over to IVF, harvest the eggs and fertilize them in the laboratory.
- The CRG adheres to valid legislation when performing IVF (see also financial aspects):
- in women under 36, only one embryo may be transferred during the first and second treatments. Only in exceptional circumstances may two embryos be replaced on the second attempt. A maximum of two embryos may be replaced during the third and fourth treatment cycles.
- in women over 36, two embryos may be transferred during the first two treatments. Three may be transferred during the third attempt.
- over the age of 40, the number of embryos which may be replaced is at your doctors' discretion.
Possible treatments afterwards
If a triplet should result from the treatment, the pregnancy can be reduced to twins via selective embryo reduction.
Ovarian hyperstimulation syndrome This side effect only effects IVF patients (after embryo transfer) and is addressed in the
embryo transfer section.
Two important questions
Of all the questions asked in connection with fertility treatment, two are specific to the stimulation phase. Click on the question to read the answer.