How Anatomic Abnomalities in the Uterus related with Pregnancy Loss

Congenital Uterine Malformations

Congenital uterine malformations are the result of disturbances in müllerian duct, from where genitor urinary tract develops. The contribution of congenital uterine anomalies to recurrent pregnancy loss is not very clear due to lack of data. The reported frequency of uterine anomalies varies widely, from 1.8% to 37.6% with patients with recurrent miscarriage.
The prevalence of uterine anomalies is highest in women with a history of late miscarriages, which probably reflects the greater prevalence of cervical incompetence (discussed later) in women with uterine malformation. Most researches suggest that congenital uterine anomalies
may contribute to pregnancy loss in a small proportion of women with recurrent miscarriage.

The Major anatomical abnormalities, which may cause abortions, are:


Cervical Incompetence

Cervical incompetence is a well-recognized cause of recurrent midtrimester miscarriage. It is defined as the inability to support a term pregnancy because of a functional or structural defect of the cervix. Cervical incompetence occurs along a spectrum of severity. Severe incompetence leads to midtrimester miscarriage, and lesser degrees underlie some cases of preterm delivery. Although some form of incompetence are the result of mechanical incompetence, such as congenital hypoplastic cervix, previous cervical surgery, and extensive trauma.

The cervix is the main mechanical barrier separating the pregnancy from the vaginal bacterial flora. Many patients who have asymptomatic midtrimester cervical dilation have evidence of subclinical intrauterine infection. It is unclear whether this high rate of microbial invasion is the result or the cause of premature cervical dilation. When premature cervical ripening occurs, the mechanical barrier is disrupted, which may further stimulate processes (e.g., colonization of the upper genital tract) that culminate in spontaneous preterm birth. When cervical incompetence is associated with mechanical weakness, supportive measures such as cerclage operation may prevent ascending infection and hence may prolong pregnancy. In contrast, if cervical changes result from non mechanical processes, then cerclage would be less effective, and even harmful in some cases, because of possible inflammatory and infectious complications.

Fibroids

Uterine fibroids have long been associated with a variety of reproductive problems, including pregnancy loss. The extent of the association is affected by the size and location of the fibroids. Although the exact mechanisms are unclear, the presumed theories of pathophysiology include mechanical distortion of the uterine cavity, abnormal vascularization, abnormal endometrial development, endometrial inflammation, abnormal endocrine milieu, and structural and contractile myometrial abnormalities. Study report from patients with infertility suggest that only fibroids with a submucosal or an intra cavitary component are associated with a reduced implantation rate and an increased rate of miscarriage. Subserous fibroids have no deleterious effect, and the role of intramural fibroids that do not distort the cavity is controversial


Intrauterine Adhesions

Intrauterine adhesions (Asherman's syndrome, an acquired uterine defect of varying severity) result from intrauterine trauma after vigorous endometrial curettage or evacuation of retained products of conception. Intrauterine adhesions are associated with recurrent miscarriage. The presumed mechanisms are decreased uterine cavity volume and fibrosis and inflammation of the endometrium that predispose the patient to abnormal placentation and pregnancy loss.