11.3: Nomogram (which plane, where, in tables)

P. Reginald Wesley

Nomograms in female reproductive system

The imaging appearance of the uterus and ovaries depend on age and sexual maturation of the individual as they are under hormonal influence. Furthermore, the endometrium and ovaries vary their appearance depending on the time of imaging during the menstrual cycle.

Uterus and cervix

How to measure the uterus?

Fig. 11.3.1 shows the technique of measuring the uterus. Uterine length is more accurately measured with transabdominal ultrasound compared to transvaginal scan where the cervix may not be included within the field of view. Table 11.3.1 shows the normal uterine length and size ratio between the uterus and cervix in various age groups.

Fig. 11.3.1 First, the sagittal image of the uterus is taken. Length is measured from the outer margin of the fundus up to the external os of the cervix. Depth (anteroposterior diameter) is measured from the most anterior to the posterior margin of the uterine walls perpendicular to the length. The probe is then rotated 90 degrees to the sagittal plane. In transverse image, the maximum width of the uterus is measured.

TABLE 11.3.1

Normal Uterine Length and Size Ratio Between the Uterine Body and Cervix

Stage	Uterine Length (cm)	Uterine Body to Cervix Ratio
Neonatal	3.5	2:1
Paediatric	1–3	1:1
Prepubertal	3–4.5	1–1.5:1
Pubertal	5–8	1.5–2:1
Reproductive	8–9	2:1
Postmenopausal	3.5–7.5	1–1.5:1

How to measure the endometrium?

Optimally assessed by transvaginal ultrasound. It represents the sum of the thickness of the two endometrial layers. To measure the endometrium, first the midline longitudinal image of the uterus is taken. Then place the cursor at the interface between the endometrium and the myometrium at the anterior and posterior walls of the uterus. Fig. 11.3.2 shows the appearance of the endometrium in various stages of menstrual cycle. The measurement is preferably taken at the fundal region with widest endometrium (Fig. 11.3.3).

Fig. 11.3.2 Transvaginal ultrasound images showing the endometrium in various stages of menstrual cycle. (A) Menstrual phase, (B) proliferative phase, (C) LH and ovulatory phase, (D) secretary phase and (E) postmenopausal endometrium.

Fig. 11.3.3 Transvaginal ultrasound showing the technique of measuring the endometrium.

The echogenic line at the centre denotes the interface where the anterior endometrial layer opposes the posterior endometrial layer.

The hypoechoic layer peripheral to the endometrium represents the inner layer of myometrium and should not be included while measuring the endometrial thickness. Table 11.3.2 shows the endometrial thickness and appearance in different stages of menstrual cycle.

TABLE 11.3.2

Endometrial Thickness and Appearance

Stage	Endometrial Thickness (mm)	Appearance
Menstrual phase (days 1–4)	4.6	Mildly echogenic
Proliferative phase (days 5–13)	4.6–12.4	Mildly echogenic
Luteinizing hormone (LH) surge (12–48 h before ovulation)	12.4	Striated with an inner hypoehoic and a peripheral more hyperechoic layer
Ovulatory phase (days 13–16)	Decreases slightly	Striated with an inner hypoehoic and a peripheral more hyperechoic layer
Secretary phase (days 16–28)	Increases by 2 mm	Thick and hyperechoic
Postmenopausal	1–2	Thin hyperechoic line or band

Ovaries

Technique of scanning

Ideally, transvaginal ultrasound is better because of its higher resolution especially in the assessment of polycystic ovaries. However, transabdominal scan has its use in adolescent girls and virginal women. It is also useful in cases of displaced ovaries. Fig. 11.3.4 shows the technique of measuring the ovarian volume.

Fig. 11.3.4 Ovarian volume measurement is performed using the simplified formula for a prolate ellipsoid: Ovarian volume = length × width × thickness × 0.5.

While measuring the volume in transabdominal scan, urinary bladder should be adequately distended. However, care should be taken not to over distend the bladder as it may compress the ovaries leading to incorrect measurement of the size. Bladder distension is not required for transvaginal ultrasound. Table 11.3.3 shows the appearance and size of ovaries in various age groups.

TABLE 11.3.3

Normal Ovarian Volume and Appearance

Stage	Ovarian Volume (cc)	Appearance
Neonatal	1–3.5	Follicles and cyst common
Paediatric	0.5–1.5	Fewer than six follicles, cysts uncommon
Prepubertal	1–4	Follicles and cysts common
Pubertal	2–6	Follicles and cysts common
Reproductive	4–16	Follicles and cysts common
Postmenopausal	1.2–5.8	Follicles and cysts in about 15%–20%

Polycystic ovarian syndrome

According to the technical recommendation for the assessment of polycystic ovaries as per 2003 Rotterdam PCOS consensus:

Time of performing ultrasound:

Women who have regular menstrual cycles – early follicular phase between days 3 and 5.

Women who are oligomenorrheic or amenorrheic – random or between 3 and 5 days after inducing withdrawal bleeding following progestin administration.

Estimation of the number of follicles – done in both longitudinal and anteroposterior planes of the ovaries. The follicles which measure less than 10 mm, their size should be given as the average of the two diameters measured in each plane.

Criteria for diagnosis of PCOS

Presence of 12 or more follicles in each ovary measuring 2–9 mm in size and/or ovarian volume of more than 10 mL.

Ovarian volume is a surrogate measurement for stromal hypertrophy.

The presence of a single polycystic ovary is sufficient for the diagnosis of polycystic ovary syndrome (PCOS).

How to measure antral follicle count and size?

Measurement of the number of follicles (antral follicle count) should be done in longitudinal plane.

Measurement of the size and distribution of the antral follicles should be done in orthogonal plane.

Average of two orthogonal measurements is used for antral follicle diameter.

Ovarian and stromal areas

In PCOS, there is ovarian androgenic dysfunction, which leads to stromal hypertrophy. This is called hyperthecosis where there is enlarged ovaries with increased stromal thickness and echogenicity without mature follicles. This is indicated by the stromal area.

How to measure the stromal and ovarian areas?

To measure the areas, first the stroma is identified which is represented by the central echogenic area of the ovary. Using the callipers, this central area is measured along with its outer margin. Then the total area of the ovary is measured by placing the callipers along with the outer margin of the ovary (Fig. 11.3.5).