Evaluation of three-dimensional SonoAVC ultrasound for antral follicle count in infertile women: its agreement with conventional two-dimensional ultrasound and serum levels of anti-Müllerian hormone

One of the biggest challenges in the management of infertile patients is the loss of reproductive potential with increasing age. The postponement of pregnancy in the modern world is due to several factors, including the pursuit of careers by women, widespread use of contraception, and the development of assisted reproduction techniques. Maternal age is a major factor for decrease in fertility and increase in abortion rates [1‐3]. Decreased ovarian reserve with the loss of oocyte quality and depletion of the number of available oocytes with increased age is reflected in the decline in oocyte recovery rate and the decrease in embryo quality and pregnancy rates by in vitro fertilization [1, 2]. The use of follicle - stimulating hormone (FSH), oestradiol (E2), inhibin B, and, more recently, anti-Müllerian hormone (AMH) to evaluate reproductive potential have been described as good markers [4].

Antral follicle count (AFC) has been assessed by two-dimensional (2D) transvaginal ultrasound for several years with good resolution and accuracy. Some authors evaluated the applicability of three-dimensional (3D) technology in comparison with conventional 2D ultrasound to assess the accuracy of this new image management software and did not find any advantage [5]. Furthermore, recently, some authors validated a new mathematical tool to predict ovarian age, using some hormonal and ultrasonographic parameters. Using multiplanar and inversion mode 3D, they showed that AFC is a reliable marker for ovarian reserve, but did not compared to 2D; in addition, the sample was composed mainly by fertile patients [6].

Although few studies had evaluated this new technology in infertile women, there is a need for consensus on a parameter of follicle diameter that represents ovarian functional’s reserve and the usefulness of this emerging technology (3D) compared to 2D. There is also the need to analyze these two different technologies along with serum AMH levels to evaluate ovarian reserve. In this context, it is imperative to evaluate and validate new imaging tools, such as 3D SonoAVC, to explore its potential and define its liabilities.

Therefore, the aim of this study was to identify the agreement between AFCs measured by transvaginal ultrasound (2D and 3D SonoAVC) and serum AMH levels in infertile women.

The results regarding the women that underwent the study are presented in the Table 1. The causes of infertility found in this study were sterility without apparent cause (n = 8), anatomical factors (n = 11), hormonal factors (n = 1), endometriosis (n = 11), polycystic ovarian syndrome (PCOS; n = 6), ovarian factors (n = 3) and male factors (2). Considering that 42 women represent 100% that were studied, the causes of infertility represent 19.0%, 26.2%, 2.4%, 26.2%, 14.3%, 7.1% and 4.8%, respectively.

The same researcher performed both ultrasounds’ techniques, therefore intra-observer correlation was calculated at 0.68 (0.942–0.983) through Spearman’s correlation test. Measurements from the left, right and both ovaries were considered to perform volume analysis. The mean volume of left ovary follicles was 7.46 ± 3.90 for 2D US and 7.18 ± 3.75 for 3D. For the right ovary follicles volume, the mean was 7.18 ± 3.80 and 7.06 and 3.76 for 2D and 3D ultrasounds, respectively. Considering the total volume (left and right ovaries), the mean for 2D US was 7.28 ± 3.50 and the mean for 3D US was 7.10 ± 3.54 (Fig. 3). When comparing the two ultrasounds’ techniques and the follicular volume, there is no statistical difference (p ≥ 0.05; p ≥ 0.05; p ≥ 0.05 for left, right and both ovaries, respectively) (Fig. 4).

When comparing both ultrasounds’ techniques regarding AFC, there was statistical difference in left and right ovaries. This data characteristic can also be verified when comparing 2D and 3D techniques and AFC regarding the total AFC, which is represented as mean from both ovaries. The median of total AFC was 13.50 with 10.00 and 21.25 as percentile 25 and 75, respectively for 2D ultrasound. Considering 3D technique, the median number of total antral follicle count was 14.50 with 10.00 and 22.00 as 25 and 75 percentiles respectively, showing statistical difference between both ultrasounds’ techniques. According to Wilcoxon’s signed-rank test, the 3D ultrasound AFC was significantly higher than 2D ultrasound (p < 0.001) (Fig. 5). The agreement between both ultrasounds’ techniques regarding AFCs can be found in Fig. 6. The mean time taken to perform manual 2D ultrasound was significantly longer than that taken to perform 3D SonoAVC (275 ± 109 and 103 ± 57 s, respectively; p < 0.05; Mann Whitney’s test).

The results presented no correlation between s-AMH levels and BMI (p ≥ 0.05). The absence of correlation was observed between AFC and BMI comparing 2D and 3D techniques (p ≥ 0.05, for 2D and 3D US; Spearman’s correlation test).

Ovarian volume correlated to serum AMH concentration (correlation coefficient = 0.558; p < 0.001 for 2D US and correlation coefficient = 0.569; p < 0.001 for 3D US). Considering only follicles with less than 6 mm, they correlate to s-AMH levels (correlation coefficients = 0.537 and 0.510; p < 0.001 for 2D and 3D ultrasounds).

The aim of this study was to identify the agreement between AFCs through two ultrasounds’ techniques in infertile women. This study evaluated the results obtained by 2D conventional ultrasound and 3D SonoAVC ultrasound performed in 42 infertile women.

The study concluded that 3D technology can measure more follicles than 2D, this is particularly important and relevant in ovaries with more than 20 follicles. The better estimation of AFCs by 3D ultrasound was also detected by others investigators, regarding a different group of patients like obese PCOS patients [8]. Weenen et al. also demonstrated that 3D technology was more accurate than 2D when ovaries were submitted to histological confirmation [9].

Our findings are important and opens a new discussion concerning the usefulness of this new technology. We suggest a clinical trial to study ovarian hyperstimulation syndrome (OHSS) and the 3DSonoAVC technique. The 3D ultrasound could be implemented even during infertility investigation, as it is the first step for planning treatment. The fact that AFC was higher using 3D ultrasound did not invalidate 2D technology, both were well correlated to serum AMH levels. However, in high risk patients, such as patients that present PCOS, we should rethink the role of 2D. The positive correlation of AFC to serum AMH and a negative correlation to age observed in our study agree with those of previous studies.

There are both advantages and disadvantages of 3D SonoAVC technology when compared with 2D ultrasound. In traditional 2D follicle count, it is harder to correctly determine the number of follicles when they are presented in a large number, which could lead to over or underestimate follicles count, as described in previous studies [10, 11]. In 3D SonoAVC technology, AFC is performed automatically in a few seconds; the program recognizes anechoic areas of the follicles. The follicular diameter is plotted on three axes (x, y and z) and the follicular volume is calculated automatically, which saves considerable time in routine patient evaluation and increases the quality of the measures. However, these same measures can be performed by conventional 2D ultrasound. The downside of this new 3D SonoAVC technology is the equipment’s higher cost and the need for specialized training for correctly capture 3D images from the ovaries.

Furthermore, in 3D SonoAVC, the ovary must be appropriately placed in the region of interest to prevent the addition of vessels and/or other extraovarian pelvic structures, such as iliac vessels, hydrosalpinx, and Morgagni hydatids. This structures could affect the accuracy and result in under or overestimation of AFC, depending on the experience of the operator and appropriate interpretation of the obtained images. Nevertheless, the automatic image capture process must be evaluated and repeated if considered unsatisfactory [12].Previous studies have reported a good correlation between the results obtained by inter and intra-observer methods [13]. In this study, the same researcher, using the same technique and settings, captured all images and the intra-observer correlation was calculated.

A benefit of 3D SonoAVC observed in this study was the ease of quickly obtaining reproducible measurements, particularly for small follicles. However, after image capture, the examiner must assess image quality and verify if the automatic count matches expectations. This software’s characteristics can improve performance and workflow in fertility clinics where the number of follicles to be measured is sometimes numerous.

Another interesting possibility of this new technology is the ability to store images in a 3D virtual block for further detailed studies in case of special interest or to create a research database. The future prospects of research in this field are promising with the advent of new equipment and image management’s technologies to enhance the knowledge of ovarian folliculogenesis, particularly for AFCs when the follicle diameter is less than 2 mm.

The main limitation about our results was the fact that we cannot certify the accuracy of both methods using histology, Deb et al., 2010, already discussed this. Also, the exclusion of obese patients (BMI > 30 kg/m2) could be seen as conservative bias in favor to 2D technology. We conducted AFCs in the initial menstrual cycle’s phase to minimize the effect of intracycle variation of follicular diameters and avoid inclusion of ovarian cysts or a pre-existing corpus luteum, which were considered in the exclusion criteria in this population. The measurements performed by the same researcher in both ultrasounds’ techniques were obtained with twenty minutes of interval between them. Although we tried to minimize the bias, this observation could be assessed as one weakness of the study.

In conclusion, the results of this study suggest that 3D SonoAVC can estimate AFCs better when compared to 2D ultrasound, mainly because it can capture images of ovaries with more than 20 follicles, resulting in a more reliable counting and was found to be faster than 2D for AFC. In addition, AFCs by both technologies presented a positive correlation to serum AMH levels.