The evaluation of the uterine cavity consists of a basic step in the investigation of all subfertile women since the uterine cavity and its inner layer, the endometrium, are important for the implantation of the human embryo. Nevertheless, the complex mechanisms leading to successful implantation are still not entirely understood. Despite the huge investment in research and developments of the technologies and biology involved in medically assisted reproduction (MAR), the maximum implantation rate per embryo transferred remains only around 30%. The different phases of the implantation process are established by the complex interchange between the blastocyst and the endometrium.
Intrauterine abnormalities have been detected in 19-62% of infertile women in several studies, while major uterine cavity abnormalities can be found in 10% to 15% of women seeking treatment for subfertility; they usually consist of the presence of excessive normal uterine tissue. The most common acquired uterine cavity abnormality is an endometrial polyp. This benign, endometrial stalk‐like mass protrudes into the uterine cavity and has its own vascular supply. Depending on the population under study and the applied diagnostic test, endometrial polyps can be found in 1% to 41% of the subfertile population. A fibroid is an excessive growth originating from the muscular part of the uterine cavity. Fibroids are present in 2.4% of subfertile women without any other obvious cause of subfertility. A submucous fibroid is located underneath the endometrium and is thought to interfere with fertility by deforming the uterine cavity. Intrauterine adhesions are fibrous tissue strings connecting parts of the uterine wall. They are commonly caused by inflammation or iatrogenic tissue damage (meaning involuntarily caused by a physician's intervention, for example an aspiration curettage after miscarriage) and are present in 0.3% to 14% of subfertile women.
A septate uterus is a congenital malformation in which the longitudinal band separating the left and right Müllerian ducts, which form the uterus in the human female fetus, has not been entirely resorbed. A uterine septum is present in 1% to 3.6% of women with otherwise unexplained subfertility.
The complete list of uterine cavity pathology that can be associated with reduced fertility is long, and except the above mentioned presence of endometrial polyp, submucosal and intramural fibroid, and septum includes endometrial synechiae (adhesions), scar tissue, localized or generalized infection of the endometrium (endometritis), adenomyosis, endometrial atrophy, endometrial hyperplasia, arteriovenous malformations, retained products of conception, incomplete abortion, gestational trophoblastic disease, and caesarean scar defects.
Ultrasonography (US), preferably transvaginal (TVS), is used to screen for possible endometrium or uterine cavity abnormalities in the work‐up of subfertile women. This evaluation can be expanded with hysterosalpingography (HSG), saline infusion/gel instillation sonography (SIS/GIS) and ultimately by diagnostic hysteroscopy. Diagnostic hysteroscopy is generally considered as the gold standard procedure for the assessment of the uterine cavity since it enables direct visualization; moreover, treatment of intrauterine pathology can be done in the same setting. Nevertheless, even for experienced gynecologists, the hysteroscopic diagnosis and management of the major uterine cavity abnormalities may sometimes be problematic.
How Hysteroscopy Works
It is assumed that major uterine cavity abnormalities may interfere with factors that regulate the blastocyst‐endometrium interplay, for example hormones and cytokines, precluding the possibility of pregnancy. Many hypotheses have been formulated in the literature of how endometrial polyps, submucous fibroids, intrauterine adhesions, and uterine septum are likely to disturb the implantation of the human embryo; nevertheless, the precise mechanisms of action through which each one of these major uterine cavity abnormalities affects this essential reproductive process are only partially understood. The fetal‐maternal conflict hypothesis tries to explain how a successful pregnancy may establish itself despite the intrinsic genomic instability of human embryos through the specialist functions of the endometrium, in particular its capacity for cyclic spontaneous decidualization, shedding and regeneration.
For endometrial polyps, submucous fibroids, intrauterine adhesions and uterine septum, observational studies have shown a clear improvement in the spontaneous pregnancy rate after the hysteroscopic removal of the abnormality. Also observational studies suggested a better reproductive outcome following hysteroscopic polypectomy in women prior to intrauterine insemination (IUI). The chance for pregnancy is significantly lower in subfertile women with submucous fibroids compared to other causes of subfertility according to one systematic review and meta‐analysis of 11 observational studies. Finally, three observational studies found a major benefit for removing a uterine septum by hysteroscopic metroplasty in subfertile women with a uterine septum.
For intrauterine synechiae (adhesions), hysteroscopic cutting (adhesiolysis) has shown to improve endometrial implantation potential both due to anatomical and patho-physiological reasons, with overall restoration of normal menstruation observed in 75%–100% and pregnancy rate ranges between 31.9 and 81.3%.
