Anomalies of the uterus occur in 3.8% to 4.3 % of the general population, depending on the actual indication for study; the mean incidence for women with subfertility falls in the range of 3.5% and increases significantly for those who have experience recurrent pregnancy loss (˜10% to 15%). Although no classification system has been universally accepted, the American Society for Reproductive Medicine (ASRM) grouped these anomalies into seven types based on three main categories: a) agenesis/hypoplasia, c) lateral fusion defects, and c) vertical fusion defects. Although most anomalies observed fall into the ASRM classification (originally devised by Buttram and Gibbons), there are isolated anomalies that do not fit this system so easily, such as the complete (full) septum with duplicated cervices.

The uterine septum represents one of the most common müllerian anomalies encountered with a mean incidence of 1% to 3% in the general population. This particular anomaly most likely occurs as a result of varying degrees of incomplete resorption of the midline septum between the two laterally fusing müllerian ducts. Although the overwhelming majority of women with such anomalies are genotypic female (46, XX), the etiology of this disorder has not been clearly defined and it is felt to occur as a result of polygenetic and multifactorial processes.

A septate uterus is differentiated from other anomalies by its smooth fundal contour and two separate uterine cavities. The defect may range from a small midline septum to a larger defect resulting in a complete uterine septum and longitudinal vaginal septum. These anomalies are differentiated from the arcuate uterus based on the degree of intrauterine fundal defect (visualizing an imaginary line between the tubal ostia, the arcuate fundus does not generally protrude more than 2 cm into the intrauterine cavity, although there is no established distance that clearly differentiates arcuate uterus from a small septate uterus.

Continued debate exists over whether and when to proactively correct the septate uterus, since this defect may have a negative impact on reproductive outcome. The adverse impact on reproduction may arise from decreased vascularity of the septum itself, affecting the growth of an embryo implanted in the septum proper, diminished volume of the endometrial cavity, and suboptimal implantation site options. Since the incidence of septate uteri in women with and without infertility are similar, there is a large population of women with a septate uterus who will likely conceive and go on to deliver a healthy infant without complications and without the need for preconceptional surgical intervention. Overall, the negative impact of a uterine septum on the fecundability of asymptomatic women or those with primary infertility seems quite modest.

Alternatively, case series suggest that women with a septate uterus appear to have a higher rate of adverse obstetrical outcomes, including spontaneous pregnancy loss and preterm delivery. Thus, if a septum is found in a patient with untested fertility, consideration may be given to proactively correct those who have not yet demonstrated poor outcomes. Women with a septate uterus and who experience recurrent pregnancy
loss are also likely candidates for metroplasty since posttreatment obstetrical outcomes are comparable to those of unaffected women. Finally, and although the effect of this müllerian anomaly on fecundability is not clear, the higher adverse pregnancy outcomes of women undergoing in vitro fertilization (IVF), such as preterm delivery, and the high cost of the treatment, suggest that patients who are scheduled for IVF and are found to have a septate uterus would be considered appropriate surgical candidates.

Metroplasty was first described in 1953 as a procedure that involved a wedge-like resection of the midline defect (Jones metroplasty) and so it had a wider range of application for various midline anomalies. It was performed by laparotomy, involved a fundal uterine incision, and removal of the defect. These procedures carried an increase risk for morbidity, intra- and postoperative hemorrhage, and reduced intra-cavitary volume, and necessitated cesarean delivery. Alternatively, hysteroscopic metroplasty is a relatively straightforward ambulatory procedure that obviates the majority of the aforementioned risks while providing excellent outcomes. Its risks are low enough that most surgeons feel comfortable offering this procedure prophylactically to asymptomatic women.

Establishing the correct preoperative diagnosis becomes pivotal in the evaluation and treatment of women with suspected müllerian anomalies, particularly in women with prior poor reproductive or obstetrical outcomes. Historically, a combination of hysteroscopy and laparoscopy were used for diagnostic means, but the role of transvaginal ultrasound, with or without saline infusion (i.e., sonohysterography) and magnetic resonance imaging (MRI) continue to be the studies of choice.

MRI provides a comprehensive picture of the abdomen and pelvis, allowing for a single modality to be used for the diagnosis of müllerian anomalies, especially since extra-uterine anomalies (e.g., isolated uterine remnant) are not uncommon in women with unilateral müllerian defects. An MRI can also differentiate a muscular from fibrous septum and may delineate cervical duplication and the septate uterus from uterine didelphys. In turn, the experienced ultrasonographer may also be able to differentiate many of the duplicative anomalies. While hysterosalpingography (HSG) represents the gold standard for evaluating the endometrial cavity and tubal patency, it lacks the ability to establish the presence of more complex anomalies that may require assessment of the external uterine contour or extrauterine phenomena. Finally, as with any other operative hysteroscopic procedure, the procedure should be timed to occur when the endometrium is at its thinnest, whether in the immediate postmenstrual period during a natural ovulatory cycle or achieved by hormonal (e.g., progestogenic) suppression. Following are brief descriptions of the surgical procedures used (see also videos: Hysteroscopic Metroplasty (Resection of Intrauterine Septum)).

1. Instrument selection: The surgeon performing a metroplasty should be experienced in the performance of diagnostic and basic operative hysteroscopy, including understanding the instrumentation, distention media, energy sources, and risks and monitoring. The operator should use instruments with which he/she is most comfortable with, although using a hysteroscope with the smallest outer diameter is preferred in order to minimize the need for excessive cervical dilation. A 0° lens is helpful for on-axis visualization, especially when using an electrosurgical means of incising the septum; however, an angled lens (12° or 30°) may allow for greater total visualization of the uterine cavity (Figure 26.1).

Preference should be given to the use of nonelectrosurgical means, such as a 3-mm rigid scissors placed through the operating channel of an operating hysteroscope with an angled offset ocular or an operative hysteroscope with a 5 to 7 French (˜1.7 to 2.3 mm) semi-rigid scissors, in order to avoid thermal injury to the surrounding endomyometrium. An added benefit when using semi-rigid scissors is the ability to utilize a narrower hysteroscopic outer sheath, smaller than the larger electrosurgical resectoscopes, which are at least 9 mm in diameter (Figure 26.1).