A practical guide to count ovarian antral follicles by ultrasound

A consensus opinion highlighting the main techniques of ovarian antral follicle count (AFC), and providing recommendations for future research is published in special issue on Reproductive Medicine of the journal Ultrasound in Obstetrics and Gynecology.

The consensus makes several recommendations for varied methods used in counting the antral follicles, but no single method is superior over others and the choice should make best use of resources available in a particular setting.

Ultrasound imaging of ovary with several follicles: (a) two-dimensional (2D) ultrasound (US) without harmonics; (b) 2D-US with harmonics; (c) multiplanar view without volume contrast imaging (VCI); (d) three-dimensional inversion mode; (e) multiplanar view with VCI; (f) sonography-based automated volume calculation (SonoAVC).
courtesy: Ultrasound in Obstetrics and Gynecology

In the absence of a single reliable test for predicting ovarian reserve, ovarian antral follicle count serves as a good surrogate marker for it.

AFC is most often carried out in women more than 35yrs of age and already tried to become pregnant since last 6 months, diminished ovarian reserve, ovarian surgery for endometrioma, prediction of risk of fetal aneuploidy and to predict age at menopause.

AFC count is used most often in obstetric practice while ‘follicle number per ovary’ (FNPO), is often more useful in gynecological clinical practice.

The main recommendations in the consensus include:

The AFC usually include follicles with a mean diameter between 2 to 10 mm. AFC less than 5-7 indicates small oocytes will be retrieved and AFC more than 20, predicts a higher risk of ovarian hyperstimulation syndrome. AFC less than 4 indicates an increased risk of menopause in next 7 years.

The sonography for performing AFC can be carried out anytime during menstrual cycle and is not limited to menstrual period.

AFC should be performed using a transvaginal ultrasound (US) probe with frequency ≥ 7 MHz. Transabdominal route should only be employed when ovaries are situated cranially and anteriorly in pelvic cavity or transvaginal procedure is not possible.

The sonographer should undergo 20-40 supervised examination to get trained in the technique.

AFC can be performed using real-time two-dimensional (2D) US, stored 2D-US cine-loops and stored three-dimensional (3D) US datasets. The most common method using 2D-US either in real-time or stored cine-loops.

Using 3D-US, requires special machines and software and follicles are counted manually in multiplaner mode, however, rendered mode can be used particularly inversion mode or semi-automatically, using sonography-based automated volume calculation (SonoAVC™).

Standardized report consists of:

The technique used for evaluation of the follicles.

Day of the cycle and use of hormones, especially hormonal contraception.

Mention the number of follicles between 2 to 10 mm in each ovary and the total number of follicles.

Presence of dominant follicles and cysts or tumor.

It is always good to mention the accessibility of the ovaries for egg collection.

The future research might focus on reproducibility of studies that consists of storage and later evaluation of 3D datasets.

The consensus is based on expert opinions as there are very few studies focusing on AFC. There are limitations and scarcity of studies about semi-automated techniques, and an inattentive observer may report a totally different AFC. Hence, the consensus recommends manual counting of follicles in clinical practice, using any of the following techniques: real-time 2D-US, pre-acquired 2D-US cine-loops or 3D-US datasets.

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