3. Assessing development of the eggs
We time egg collection to within two or three hours of when
we expect you to ovulate. If eggs are not collected fairly close
to this time they may not fertilize properly. This is why we
invest in so many tests to confirm the progress of your hormone
results and the development of your eggs.
Each egg grows in a fluid-filled follicle (a small balloon-like structure) in the ovary. The follicle grows in size during the first few days after your period. Normally, ovulation (when an egg escapes from its follicle) occurs when the follicle is just under one inch across - usually around the twelfth to fourteenth day of your cycle.
There are basically three ways by which we try to make sure that we collect mature eggs. None is wholly accurate and a good deal of experience is used to pinpoint the moment before ovulation. There are two tests and a drug treatment.
Hormone tests: During IVF treatment, the hormones oestrogen and progesterone are produced in increasing amounts. Regular blood tests ( usually tests of oestrogen levels ) detect the increase
Firstly, measurement of oestrogen can help predict whether or not the ovaries are responding sufficiently well to justify proceeding to the next stage, egg collection. This is particularly helpful in some difficult cases, particulary those women who do not respond well to stimulation of the ovaries. We would obviously prefer to abandon egg collection if there is no chance of pregnancy, rather than cause patients unnecessary distress, and the extra expense of a complete (albeit destined to fail) IVF treatment cycle.
Secondly, oestrogen measurerement may give an indication that the ovaries are responding to the fertility drugs too vigorously. This early sign seems to be helpful sometimes in avoiding some of the more serious complications of ovarian over-stimulation.
Thirdly, and often most important, the results of hormone tests
are very useful indeed when trying to decide after the event
why a particular treatment cycle has failed, and sometimes whether
or not a repeated treatment cycle is realy worthwhile. This
alone seems to us to be the key reason why we continue to put
patients to the added inconvenience of repeated blood tests,
and to justify the extra money they have to spend.
Ultrasound: the swelling follicle can be directly measured using
ultrasound. Ultrasound works like a ship-sonar, used to detect
objects under sea-water. In this case the object being detected
is the ovary containing the follicle and the "sea-water" is
either urine in the bladder or the body fat, which is almost
liquid! Ultrasound is usually done daily - we know from experience
that when the follicle is about 20 millimeters across, ovulation
is fairly imminent. In recent years, ultrasound has become more
and more accurate and sophisticated, and our machines are regularly
upgraded in order with the advancing technology.
Ultrasound measurements are also indirectly useful in timing egg collection because with ultrasound we can assess the thickness of the uterine lining - the endometrium. A reasonably thick endometrium tends to argue that the uterus is fairly "ripe" and will be shortly ready to receive an egg or an embryo.
One further way of ensuring that we collect mature eggs is by
giving an injection of hCG shortly before we expect ovulation.
This drug is very similar to your own luteinising hormone and
can give a message to the ovary to ovulate. It is only used
if your own pituitary gland has not yet started to produce LH
or if you are taking Buserelin.
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