Introduction

The female reproductive system comprises the vagina, uterus, ovaries and fallopian tubes. The appearances of these structures on ultrasound depend on the age of the patient and menstrual state and stage at the time of the scan. Throughout the woman's life, particularly during the functional cycle, the organs are subject to physiological changes brought about by the influence of the hormones.

While the main object of the scan in most situations is to examine the reproductive organs, it is also essential to know and recognise other structures within the pelvis, including muscles, blood vessels, ligaments, rectum and sigmoid colon and the bladder and ureters (Figs. 3.1 and 3.2).

Vagina

The vagina is a midline, thin-walled, muscular structure approximately 8–9 cm in length, extending from the uterus to the vestibule (Fig. 3.3). It is H-shaped in cross-section, constructed of longitudinal folds and transverse ridges (rugae) which give it the ability to distend to accommodate the fetus during parturition. In its upper portion, it is contiguous with the uterine cervix and it divides into the fornices – anterior, posterior and right/left lateral.

During transabdominal (TA) scanning the distended bladder, which acts as an acoustic window, does not affect vaginal position. The vagina can therefore be used as an effective landmark, even if the uterus does not occupy its familiar position in the pelvis. The bladder also compresses the vagina, producing the hyperechoic midline echo (Fig. 3.4).