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Cycle Monitoring & Follicle Tracking

Cycle Monitoring & Follicle Tracking

Follicles are fluid-filled sacs found in the ovary, each of which usually contains a single oocyte – an immature ovum or egg. A follicle tracking scan is a gynaecological ultrasound examination to measure the size of any active follicles which are producing an egg.

The scan is useful to estimate when ovulation is likely to occur and normally done at 1-2 day intervals from around day 9 of a woman’s menstrual cycle, day 1 being the first day of menstrual bleeding.For maximum clarity and accuracy follicle tracking scans are performed internally. A long, narrow probe is inserted a short distance into the vagina and the ultrasound signal is focussed on the ovaries to measure the size of the follicles growing inside them.

The size of a follicle can be used to calculate the time a woman is most likely to ovulate and therefore the most accurate time for sexual intercourse or fertility treatment to take place for fertilisation to occur. There will usually be three scans in one menstrual cycle. Follicular tracking can be used in conjunction with a number of treatments such as ovulation induction, super ovulation induction or IUI (intra-uterine insemination).

As with any fertility investigation or treatment a baseline ultrasound scan will be performed. This is to check the position of the uterus and to determine if there are any polyps or fibroids present that could interfere with an embryo implanting into the lining of the womb.

The ovaries are also scanned and measured. Human eggs cannot be seen by ultrasound so the size of a woman’s ovary is used to determine the number of eggs a woman still has left, her ovarian reserve. This will also indicate how she might respond to the drugs used in fertility treatment.

Antral follicles are small follicles that react to the production of follicle stimulating hormone (FSH) produced during the first week of the cycle. Only one or two antral follicles will grow to become dominant follicles so the number of antral follicles present at the start of the cycle act as another indicator of an ovarian reserve.

3D Transvaginal Sonography

During the later stages of controlled ovarian stimulation the ovaries may contain many egg follicles making it hard to make an accurate count of the number of antra follicles that can be retrieved for IVF.  3D Transvaginal Sonography enables accurate measurement of an antral follicle and therefore the best time for collecting mature eggs.

The image opposite (right) is a 3D transvaginal sonograph showing the antral follicles being measured before collection.

Transvaginal Egg Collection

Under conscious sedation or general anaesthetic, mature eggs are usually retrieved with a very thin needle which pierces the vaginal wall to reach the ovaries using transvaginal ultrasound for guidance.   The follicles are then drained (aspirated) and handed to the IVF scientist to identify ova (eggs). The procedure usually takes about 15-30 minutes.