Interpretation of FNPO to be used in regular gynecologic practice
FNPO
Ovarian morphology
Interpretation
1–3
Oligofollicular
Menopause is more likely to occur in less than a decade
5–24
Normofollicular
Normal follicle count
≥25
Multifollicular
High risk of hyperandrogenic anovulation
Interpretation of total AFC to be used in fertility centers
Total AFC
Functional ovarian reserve
Interpretation
0–4
Very low
Very high risk of poor response to COS; reduced chance of achieving pregnancy through assisted reproduction
5–8
Low
High risk of poor response to COS
9–19
Normal
Expected normal response
≥20
High
High risk of excessive ovarian response and OHSS
1.2 How We Do It
Follicles should be counted preferentially between days 2 and 5 of a spontaneous menstrual cycle. The standardization is suggested because the number of antral follicles can vary with approximately 9 % during menstrual cycle, and there is an average reduction of 30 % in women using hormonal contraceptives [25]. In clinical practice, large reductions in follicle count can be seen with only 1 month of hormonal contraception. Follicles should be counted using transvaginal ultrasound examination using one of the three methods: real-time 2D ultrasound, cine-loop 2D ultrasound, or 3D ultrasonography.
1.2.1 Real-Time 2D Ultrasound
The follicles are counted during “live” ultrasound examination by sweeping the transducer along the entire ovary.
How to perform:
Scan the ovaries in both planes (sagittal and coronal) and decide which plane provides a better view of the ovary.
Choose the best plane and use it to count all follicles starting from one margin until the other.
Don’t measure the follicles during this step.
Consider all round anechoic structures as follicles
Don’t consider elongated structures as follicles
Scan again measuring only the follicles that could be <2.0 or >10.0 mm. The number of these follicles should be subtracted from the total follicle count.
Repeat the same procedure in another ovary.
When using this technique, it is possible to use different machine settings and apply different probe pressures to improve the image quality. Additionally, it permits to better evaluate whether the structure is ovarian (follicle) or extra-ovarian (e.g., hydrosalpinx, para-ovarian cysts) by assessing the mobility in relation to the ovary. The scan, however, takes longer time and might be uncomfortable for a patient. Another limitation of this technique is that it does not allow future analysis of the whole ovary if necessary as only one image is available.
1.2.2 Cine-Loop 2D Ultrasound
A 3–5 s cine loop can be saved by an ultrasound examiner when sweeping the transducer through the entire ovary for counting the follicles later “off-line” (Video 1.1). This technique is available in almost all modern ultrasound machines.
How to perform:
Scan the ovaries in both planes (sagittal and coronal) and decide which plane provides a better view of the ovary.
Use the best plane, place the transducer in one of the margins of the ovary, and freeze the image.
Unfreeze the image and scan quickly from one side to another, and then freeze again.
Check whether the entire sweep will be stored, i.e., if the scan time needed for the entire ovary is less than the maximum allowed to save time (this time can be adjusted in the machine settings). If not, repeat the process; if yes, store the cine loop.
Repeat the same procedure with another ovary.
Perform follicle count on the ultrasound machine as described above for real-time 2D ultrasound.
The main advantage of this technique is reducing the scan time and patient discomfort. Additionally, the saved videos can be analyzed in the future by the examiner or other persons, which might be useful for training and auditing purposes. However, some extra training is required both for learning how to scan the whole ovary in a short time and also for learning how to use cine loops. Another limitation of this method is that only saved videos can be analyzed afterward, not being possible to retrieve any missing information. Compared to automatic acquisition of 3D ultrasound volume, the manual sweep required for the cine loop is frequently more uncomfortable for the patient because the probe moves inside the vagina when using a considerable pressure.
1.2.3 3D Ultrasound
Using 3D ultrasound the aim of the acquisition is to acquire a 3D ultrasound dataset of the whole ovarian volume to be analyzed after the scan.
How to perform:
Scan the ovaries in both planes (sagittal and coronal) and decide which plane provides a better view of the ovary or the largest ovary diameter.
Using this plane, place the probe in the center of the ovary.
Select the maximum image quality (or the largest scan time) and the maximum acquisition angle (e.g., 120°). This will increase the acquisition time, but will improve image quality and reduce the risk of missing part of the ovary during acquisition
Press the button that starts the automatic acquisition of the ovarian volume and check whether it included the entire ovary. If not, repeat the process; if yes, save the 3D dataset.
Repeat the same process with the other ovary.
Release the patient.
Count the follicles either directly on the ultrasound machine or on a personal computer.
The 3D ultrasound allows data manipulation with the use of exclusive techniques as sonography-based automated volume calculation (SonoAVC), inversion mode, or volume contrast imaging (VCI). SonoAVC enables a semiautomatic calculating of both follicle size and number by automatically detecting low-echogenicity areas in a selected volume. The average diameter of the follicle is determined and all follicles are listed according to their size. Inversion mode permits identification the follicles when all hypoechoic areas are rendered. VCI enhances the contrast between the follicles and the parenchyma, and multiplanar images of the volume are presented.
The acquisition of a 3D dataset is a technique that causes less discomfort for woman and takes less time. It allows analysis of the whole ovarian volume and evaluating each follicle in the three orthogonal planes simultaneously. This technique, however, is restricted to more expensive ultrasound machines and requires examiner training for dataset acquisition and volume analysis.
1.3 Important Technical Tips
Optimize the image; apply adequate probe pressure to reduce the distance between the ovary and the transducer; reduce pressure if the ovary is too close and there is reverberation; place the focal zone at the level of ovary; use the smallest depth possible, if the ovaries are not close to the ultrasound probe (e.g., cranial to the myometrium); and magnify the image until the ovary occupies at least 50 % of the screen on its largest plane; true zoom is recommended.
When counting follicle using 2D ultrasound, prefer using harmonics. The harmonics imaging reduces the reverberation which frequently impairs the identification of follicles that are very close to the transducer (Fig. 1.1).
Fig. 1.1
Effect of the harmonics on image quality when using 2D ultrasound: same ovary without (left) and with harmonics (right)
When using 3D ultrasound, harmonics increases the acquisition time and impairs SonoAVC, and, although the basis is completely different, VCI results in similar or frequently better improvement on image quality (Fig. 1.2). Therefore, if you are using 3D ultrasound, only use harmonics if there is a large improvement on 2D image quality.
