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  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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