A woman’s menstrual cycle is measured from the first day of her period (blood flow, not spotting), so Cycle Day 3 is the third day of her period. When a woman is undergoing a fertility work-up, Cycle Day 3 is the day she has blood work performed to check the levels of three important levels: follicle stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E2).
FSH is secreted by the pituitary gland. It stimulates the production of estradiol (estrogen) and eggs (oocytes) during the first half of the menstrual cycle. The eggs begin to grow in their individual fluid sacs, or follicles, which is the first step in the ovulation process. High levels of FSH are an indication of poor ovarian reserves; in other words, the quality and quantity of eggs is low. This does not necessarily mean that pregnancy is impossible, but it may be more difficult to achieve.
The FSH blood test is used to help diagnose problems with sexual development, menstruation, and fertility. It can be used to diagnose or evaluate polycystic ovary disease, ovarian cysts, irregular vaginal bleeding and infertility.
The LH blood test measures the amount of luteinizing hormone, which is also secreted by the pituitary gland. In women, LH levels rise at mid-cycle; within 24 to 36 hours, ovulation occurs. Higher-than-normal levels of LH indicate several disorders, including ovarian failure and polycystic ovary disease.
Estradiol is the most important form of estrogen. It is primarily made in and released from the ovaries, adrenal cortex and the placenta, and it is responsible for the growth of the breasts, outer genitals, uterus, fallopian tubes and vagina.
These three hormones can all be checked with a simple performed on Cycle Day 3. Normal value ranges for the FSH, LH and E2 tests may vary among different laboratories, so it's imporant to get an accurate interpretation of the results from your fertility specialist.