Discussion
Evaluating the shape and size of the uterine cavity is helpful for us to understand and make a correct judgement in our clinical work. For instance, it has been reported that small uterine cavity size was beneficial in LNG-IUS users, as they reported less bleeding and pain compared with women with larger measurements (17) and transverse dimensions of uterine cavity far less than the length the transverse arm of IUD resulted in distortion, displacement, and expulsion of the IUD (18). So, it is especially important and necessary to have a detailed understanding of the shape of the uterus cavity of the patients. The present study was original in that we presented data of uterine cavity measurements of adult women on a 3D coronal view of uterine cavity.
The length and internal os width of uterine cavity do not seem to be important Clinically, but the importance of the cavity width has been studied a lot, especially in the field of application of intrauterine device (18, 19, 20). In our study the measurements of uterine cavity width (fundal transverse diameter) obtained using 3D-US ranged from 24 mm to 44 mm. This result was consistent with Jia-guang Wang’s results (19), who measured 8217 transverse diameter of the uterine cavity of the normal fertile women in Liao-Ning district of China and reported that normal transverse diameter of the uterine cavity was 23-39mm. In another research it was reported that the more usual transfundal endometrial cavity width was 22–34 mm depending on parity (20). According to these researches, we propose that if the width of the uterine cavity measured on the coronal plane is less than 22mm it can be judged to be narrow.
One can now use three measurements with cut-offs (lateral indentation depth ≥ 7 mm, lateral indentation angle ≤ 130° and T-angle ≤ 40°), which have good accuracy and moderate reliability to confirm the diagnosis when there is any suspicious of T-shape uterus by subjective assessment of the uterine cavity on the coronal plane (16). Our research showed the consistent results with this consensus. In our study an adult female with normal uterus had lateral indentation depth ≤ 7mm (the maximum was 7mm), lateral indentation angle ≥130° (the minimum was 130° and the mean was 151°) and cornual angle ≥40° (the minimum was 40° and the mean was 63 °). Our research shows that these three indexes and the thresholds we currently apply can well distinguish between normal uterus and T-shape uterus.
So far, we have not found any report on the uterine cavity area on the coronal section by 3D ultrasound in adult women( only one publication reported the uterine cavity area21 but used different calculating method without comparability). We found the uterine cavity surface area on the coronal section ranged from 3.4 to 10.5cm2, the mean was 5.5cm2, which was a relatively large range of floats. We speculate that this is due to many factors, such as the width, length, and angles of the uterus cavity, can affect the area of uterine cavity. Further multivariate analysis confirmed this point. We think that measuring the area of uterine cavity is helpful to diagnose uterine adhesion. For uterine adhesion, the commonly used diagnostic methods are hysterosalpingography and hysteroscopy, but they are invasive procedures that cause pain and have certain complications (22). With the development of ultrasonography resolution, transvaginal three-dimensional ultrasonography (3D TVS) has been more frequently used in the diagnosis of IUA (4). 3D ultrasound can provide a more accurate depiction of adhesions and extent of cavity damage than hysterosalpingography in patients with suspected Asherman’s syndrome(23). In another article we have published, we found that using uterine cavity area 4.23cm2 on the coronal section as the diagnostic threshold to distinguish uterine adhesion, it could reach 86% sensitivity and 74% specificity, and for every 1 cm2 reduction in the area of the uterine cavity, the risk of uterine adhesion increased by 18.9%(14). In the present data, about 10% adult females had uterine cavity areas less than 4cm2 and about 2% less than 3.5cm2. The mean uterine cavity area was 5.5cm2 and 95% reference interval was 3-8cm2. Maybe uterine cavity area less than 3cm2 can be considered “small uterine cavity”. We believe Data from present study may be useful in screening cases of uterine adhesion and other disorders that may need further evaluation.
In conclusion, our research showed that a normal uterine cavity in adult women of childbearing age had lateral indentation depth ≤7mm, lateral indentation angle ≥130° and cornual angle ≥40°. The width of the uterine cavity measured on the coronal plane less than 22mm and the uterine cavity area less than 3cm2 can be considered smaller than normal.
Our study is limited by the lack of data concerning gravity and parity of the subjects in the study. So, we cannot analyze the relationship between uterine cavity measurements and the number of pregnancies and parturient. It was reported that nulligravid and nulliparous women have smaller uterine dimensions than parous women(24,25). But considering that our purpose of this study is to provide data for clinical work, the results of this study are still of practical significance.