Background:

Success rates with in vitro fertilization - IVF are significantly better if the ovarian response to stimulation is "good", and poor if less than 5 mature follicles are present at the end of stimulation. Therefore, a test that accurately predicts ovarian response prior to starting the treatment cycle would be very useful for counseling patients regarding their likelihood of responding well to the drugs - and would also be a potential benefit when deciding on the starting dose of injectable gonadotropins (HMG or FSH) to use in individual women.

There are several known risk factors for poor response, such as older age of the female, obesity,  smoking, and a past history of ovarian surgery. Hormonal tests such as day 3 FSH levels and FSH after a clomiphene challenge are also used to predict "egg quantity and quality" as well as ovarian response to stimulation. In recent years, ultrasound assessment of ovarian volume and the number of antral follicles has also been used to help predict the ovarian response to stimulation.

Antral follicles are small follicles (about 2-5 mm in diameter) that we can see (and measure) on an ultrasound of the pelvis. Vaginal ultrasound is the best way to accurately assess these small structures.

More details about antral follicles

Ultrasound image of an ovary at the beginning of a menstrual cycle The ovary is outlined in blue Each antral follicle is marked with a red spot 16 antral follicles are shown here This is a high count for one ovary This woman was a "high responder" to injectable FSH medication

In our field of medicine we often refer to "ovarian reserve" - a measure of the number and the quality of the eggs remaining in the woman's ovaries - as well as the ability of the ovaries to respond to injectable FSH stimulation.

This prospective study compared several variables as predictors of the number of eggs that would be obtained from women going through their first IVF cycle. The variables evaluated were (1) the female's age , (2) her body mass index (BMI - which is a measure of how "skinny" a person is), (3) day 3 FSH levels, (4) the volume of both ovaries on ultrasound, and (5) the number of antral follicles seen with ultrasound.

Results:

The number of antral follicles was the best predictor of the number of eggs retrieved, followed by day 3 FSH, BMI, and the age of the woman. The total ovarian volume was not found to be useful in the prediction.

Women with fewer antral follicles needed longer duration and higher dosages of gonadotropins during the stimulation. Even with these higher doses of medication, the number of eggs obtained was significantly less as compared to what was obtained from women with more antral follicles.

Cycle cancellation before egg retrieval was more likely in women with £6 antral follicles.

Women with >9 antral follicles appeared to be at increased risk for developing ovarian hyperstimulation syndrome (overstimulation of the ovaries that causes abdominal pain, bloating, and other unpleasant side effects).

The total number of antral follicles was significantly correlated with age (P < 0.05), day 3 FSH (P < 0.01), total ovarian volume (P < 0.01), HMG (gonadotropin) duration and dosage (P < 0.01), estradiol level on the day of HCG (P < 0.01) and the number of eggs obtained (P < 0.01).

The 5th, 25th and 50th per centiles of the total antral follicle number were four, six and nine respectively.

When the patients were grouped according to the number of antral follicles, the pregnancy rate per cycle started or embryo transfer were similar between the groups.

Discussion

Fertility is reduced with increasing age of the female in both spontaneous conceptions and with the use of IVF and other assisted reproductive methods. The decrease in fertility with aging is related to a decreasing number of primordial follicles - and to the decreasing quality of the eggs in those remaining follicles. One study showed that over 250,000 primordial follicles were present at menarche (age of onset of menstrual periods) whereas only a few hundreds or thousands remained at the end of the reproductive life. The loss of follicles accelerates at about 37 years of age in most women. This acceleration in the loss of follicles (eggs) occurs much earlier in some women.

Antral follicle counts and other tests of ovarian reserve are useful in predicting the probability of a good ovarian stimulation for IVF purposes. The number of eggs obtained at retrieval is an important issue related to whether the cycle will be successful or not.

The total number of antral follicles was the best predictor of the ovarian response to stimulation for IVF. The next best predictor was day 3 FSH, followed by BMI, and the age of the woman.

In those women with fewer antral follicles,  a higher dosage of HMG and more days of stimulation were needed - and the number of eggs obtained was still significantly less than those with more antral follicles. 

Significantly more cycles were cancelled before egg retrieval in women with £6 antral follicles.