Uterus is a pear shaped reproductive organ in a female of size 7cm in length and 4 cm in width in the reproductive age group.
Its size varies with the age and parity of the women.
Uterus has a body, cervix and two fallopian tubes one on each side.
It is either Anteverted (tilting forwards) or Retroverted (tilting backwards).
The sonographic examination of the uterus by the transvaginal approach is typically initiated at the midsagittal plane. This view is obtained by introducing the transvaginal transducer into the upper
vaginal fornix while maintaining the reference notch on the transducer at the 12 o’clock position. In this view, the uterine fundus, uterine isthmus and cervix is seen and the uterine length is measured from the fundus to the external os.
The depth (height) of the uterus (anteroposterior dimension) is measured in the same long- axis view from its anterior to posterior walls, perpendicular to the length
This midsagittal view also allows for assessment and measurement of the endometrium. The endometrium should be analyzed for thickness, focal abnormalities, and the presence of fluid in the endometrial cavity.
Measurement of the endometrium should include the anterior and posterior portions while excluding any endometrial fluids.
Accurate evaluation and measurement of the endometrium is important especially in the presence of uterine bleeding. When measuring endometrial thickness on ultrasound, it is critical to ensure that the uterus is in a mid-sagittal plane, the whole endometrial lining is seen from the fundal region to the endocervix.
The thickest portion is measured and the image is clear and magnified.
Rotating the transducer 90 degrees counterclockwise (maintains correct orientation) allows for the display of the transaxial or transverse view of the uterus. The operator should fan the probe in the superior-inferior direction until the widest transverse view of the uterus is displayed. From this widest transverse view, the maximum width of the uterus is measured.
On USG uterine relation to surrounding organs like ovaries, bladder and bowels can be assessed.
Cervix as seen on USG with a clear layer of mucus in the cervical canal is a favourable sign re-ecting good level of oestrogen production.
Important aspect of fertility scan is the examination of the endometrium in the assessment of endometrial receptivity based on the appearance like triple layer with the minimum thickness of 7mm and increased blood flow on colour doppler studies.
On the 2nd day of menstrual cycle i.e. D2 endometrial lining is thin as most of it is shed.
On the 9th day of menstrual cycle i.e. D9 the triple layer pattern is seen due to gradual increase in thickness of the endometrium due to the effect of the hormone called oestrogen. (This is the best time to asses endometrial polyp).
On the 21st day of the menstrual cycle i.e. D21 the endometrial lining is homogenous and thick due to the effect of the hormone called progesterone.