A particularly important part of assisted reproduction are the ultrasound exams. Extensive knowledge and experience are required in this area to accurately establish the number and size of follicles, correlate the findings with the thickness of endometrium, assess potential complications, and determine the most favorable time to complete the cycle. Sometimes, apart from a regular ultrasound exam, Color Doppler, 3D or 4D ultrasound exams are required.
In a natural cycle and when a patient is suggested only a timed intercourse, serial ultrasound scans are usually sufficient for the monitoring. They are to be started between days 10 and 12 of the cycle. After the ovulation is established sometimes serum progesterone is measured on 21st day of the cycle (in women with regular 28-day cycles), that will confirm the quality of ovulation.
Due to variability in different treatment responses, every patient should be monitored when any treatment is used for the first time. A development of follicles is monitored to adjust patient’s drugs dosage, and to establish the optimal time to trigger ovulation with the hCG injection. The first exam is scheduled between days 6 and 8 of the cycle, when estradiol levels are sometimes checked, as well levels of other hormones, if required.
During the ultrasound exam number and size of follicles are determined. The measuring is performed at two perpendicular planes since follicles are often of irregular shapes due to ovarian capsule pressure. Therefore, measuring at just one plane cannot produce the real values. When measuring in two planes, resulting values are summed up and divided by two which gives us an average diameter of an observed follicle. Also the thickness of endometrium is measured at its widest part at longitudinal section along the midaxis, and its quality is assessed.
Ovulation induction usually lasts for 10-12 days. When follicles reach 12-14 mm, they keep growing at the rate of 2-3 mm daily. When the size of the dominant follicle measures over 18 mm, the quality and thickness of endometrium is satisfactory and estradiol level is compliant with the size and number of follicles, all hormonal stimulation is terminated and hCG injection is given. This prompts LH increase in a woman and induces ovulation itself, which is about to occur 34-36 hours later.
Sometimes the cycle is cancelled, either due to the hyperstimulation when OHSS is suspected, or poor response when further stimulation fails to produce eggs. Hyperstimulation is frequent in women whose ovaries seem polycystic at ultrasound scan, whereas poor response is frequent in older women and women with low ovarian reserve and/or elevated FSH. If only 1-2 follicles develop, Fallopian tubes are patent and the semen is of required quality, the patient may be suggested to give up aspiration procedure and switch to intrauterine insemination.
Figure 9. Color Doppler of follicular blood flow