Polyps could impact on fertility rates by distorting the endometrial cavity, having a detrimental effect on endometrial receptivity and increasing the risk of implantation failure [3]. Some authors conclude that the impact of the polyp depends mainly on the number of polyps, their size and location [4, 5].

Regarding the fibroids, only those that are submucosal or those intramural that distort the endometrial cavity are considered to interfere with fertility by deforming the uterine cavity. Although this is a widely accepted theory, there are some authors who do not agree. A systematic review about observational studies showed that the presence of non-cavity-distorting intramural fibroids could be associated with adverse pregnancy outcomes in women undergoing IVF treatment [6]. In order to avoid confusion, we should confirm this data with better designed studies. In other words, nowadays, only those fibroids that impact on the endometrium are suggested to be resected. The American Society for Reproductive Medicine (ASRM) states that (a) effects of fibroids on infertility are not well established, (b) those that distort the uterine cavity and those that are large could have some impact on the fertility outcomes, and (c) myomectomy should be considered after a thorough evaluation is completed [7].

Synechiae are fibrous tissue strings in the uterine wall that could impact embryo implantation or development. They are commonly caused by inflammation (sometimes, after a D&C procedure) and are present in 0.3–14 % of subfertile women [8].

The origin of most of the abnormalities in the uterus result from a defect in the development of the Mullerian ducts, usually due to polygenic mechanisms.

Septate uterus is the most common structural anomaly, present in 1–3.6 % of women with otherwise unexplained subfertility [9, 10]. Although it can be seen using hysterosalpingography, it is not easy to distinguish from a bicornuate uterus. Therefore, the accurate diagnosis is better obtained using ultrasonography and magnetic resonance imaging (MRI). Septate uterus is associated with recurrent miscarriage and with high rates of infertility, mainly as a result of poor blood supply at the septum, which is not good enough for the implanting embryo.

Partial failures in development or fusion of the Mullerian ducts result in unicornuate and bicornuate uterus. The first of these two abnormalities, although less common, is associated with a higher incidence of urinary tract anomalies and with poor reproductive outcomes. The second one is the most common uterine anomaly and is usually present in women with recurrent miscarriages. However, most women with bicornuate abnormalities have no reproductive problems.

Uterus didelphys is the abnormality that results from a complete failure of fusion of the Mullerian ducts. These patients have a duplication of the uterus. Although women with uterus didelphys have higher incidence of miscarriage and preterm deliveries, they usually have good prognosis in terms of difficulty to achieve a pregnancy. Nowadays, surgery is not usually indicated in these cases.

No good-quality studies have evaluated the association between subclinical chronic endometritis and infertility. Although bacterial vaginosis is associated with histological endometritis and some studies observed that bacterial vaginosis is more prevalent among patients undergoing IVF and, especially, in those with unexplained infertility, there is no good-quality data supporting the evaluation of endometritis and its treatment [11, 12]. Nowadays, there are no scarce data focused on the evaluation and treatment of chronic endometritis and IVF outcomes.

The incidence of the presence of endometrial cavity fluid on the day of oocyte retrieval in an IVF cycle is around 2–3 % [13]. The presence of fluid has a negative impact on the cycle outcome, as it is published in several studies. One study showed that the presence of fluid higher than 3.5 mm is associated with lower pregnancy rates [13]. Another study showed that the presence of fluid is associated with a lower implantation rate and suggested cancelling the embryo transfer. Nowadays, as vitrification has shown excellent results, postponing the embryo transfer seems to be a good option, when fluid is present in the endometrial cavity [14].

Hysterosalpingography (HSG) is a test that uses X-rays to define the shape and size of the uterine cavity, revealing developmental anomalies (unicornuate, septate, bicornuate uteri) or other acquired abnormalities (endometrial polyps, submucous myomas, synechiae) which could have potential reproductive consequences. This test has been used for a long time. However, its diagnostic profile is not always considered by health providers, and therefore, diagnosis may sometimes be inaccurate. At the same time, we should also say that it is not so easy to perform a serious, non-biased research on diagnostic tools in the infertility field. Although in the case of the HSG, the most obvious reference test could be the hysteroscopy and/or laparoscopy (depending on if we are evaluating the uterine cavity or tubes), in an ideal research world, we would like to assess the HSG in a work-up model, where live birth rate (or at least pregnancy rate) is the outcome that says what is a true positive and what is a true negative. Real world that shows that such kinds of studies are not easy and, therefore, they are not available. Then, what do we have to evaluate the performance of HSG?