The 2D (two-dimensional) ultrasound examination is used to assess the function of the ovaries and uterus. To assess the function of the ovaries, the examination is planned for the first days of the menstrual cycle (days 3-5). On these days, all the ovarian follicles (fluid pockets where the oocytes develop and mature) are small (2-5 mm in diameter), which makes it possible to determine their number in each ovary with more precision than in the middle of the cycle, when the dominant follicle (the one that will release the oocyte during ovulation) can hide the smaller ones. It is precisely the number of small follicles that informs the doctor of the ovarian reserve of follicles, on which depends the number of oocytes that can be obtained by the ovarian puncture after hormonal stimulation.
On the other hand, for an evaluation of the endometrium (the mucosa that lines the interior of the uterus) ultrasound examination carried out just before ovulation, or a few days after it, can be more informative regarding the growth of the endometrium in the proliferative phase of the cycle and its secretory transformation, respectively. The size of the uterus, its shape and position, the thickness of the endometrium and its morphological appearance are assessed. Fibroids and cysts are searched for and, if present, their size and location are determined. This information is useful to evaluate the possibilities of treatment if it is suspected that these formations may prevent the development of a pregnancy.
In the case of morphological abnormalities of the uterus, detected or suspected during the 2D ultrasound examination, a 3D (three-dimensional) ultrasound examination can provide more accurate information and refine the diagnostic conclusion.