Day 3 Fertility Blood Test Kit

Follicle Stimulating Hormone (FSH) is produced by the pituitary gland in the brain and plays a central role in reproduction. In women, FSH stimulates the growth and maturation of ovarian follicles—the fluid-filled sacs in the ovaries that each contain an egg. During the early follicular phase of your menstrual cycle (days 1-5), FSH levels rise to recruit a cohort of follicles, one of which will become dominant and eventually release a mature egg at ovulation. As the follicles grow, they produce oestradiol, which provides negative feedback to the pituitary to reduce FSH secretion—this is how one dominant follicle is selected while others regress.

Day 3 FSH is one of the most important markers of ovarian reserve—the quantity and quality of eggs remaining in your ovaries. The key principle is that if your ovaries have good reserve (plenty of responsive follicles), relatively little FSH is needed to stimulate follicle growth, so baseline FSH remains low. If ovarian reserve is diminished (fewer remaining follicles or less responsive ovaries), the pituitary must produce more FSH to achieve the same effect, resulting in elevated day 3 FSH. Higher FSH levels on day 3 therefore suggest reduced ovarian reserve. However, FSH alone doesn't tell the whole story—oestradiol levels on the same day help validate the result, and AMH (Anti-Müllerian Hormone, tested separately) provides additional complementary information about ovarian reserve. FSH levels naturally rise as women approach menopause. Results outside the normal range may need a follow-up with your GP or fertility specialist.

Luteinising Hormone (LH) is produced by the pituitary gland alongside FSH and works in concert with FSH to regulate the menstrual cycle and ovulation. During the early follicular phase, LH levels are relatively low and stable. As oestradiol rises from the growing dominant follicle, it eventually triggers a dramatic surge in LH (the 'LH surge') which causes the mature follicle to rupture and release its egg—this is ovulation. After ovulation, LH helps support the corpus luteum (the remnant of the follicle) to produce progesterone during the luteal phase.

On day 3 of your cycle, LH should be at its baseline level. The relationship between LH and FSH on day 3 provides additional diagnostic information. In most women, FSH is slightly higher than LH in the early follicular phase, giving an LH:FSH ratio below 1. An elevated LH:FSH ratio (LH higher than FSH, or ratio above 2-3) on day 3 is one of the hormonal features of Polycystic Ovary Syndrome (PCOS), a common condition affecting ovulation and fertility. Women with PCOS often have tonically elevated LH which contributes to the hormonal imbalances and ovulatory dysfunction characteristic of the condition. However, not all women with PCOS show this pattern, and an abnormal ratio alone isn't sufficient for diagnosis—PCOS diagnosis requires additional criteria. Results outside the normal range may need a follow-up with your GP or fertility specialist.

Oestradiol (also spelled estradiol, abbreviated E2) is the most potent and abundant form of oestrogen in premenopausal women. It's primarily produced by the growing follicles in the ovaries, with small amounts also produced by the adrenal glands and fat tissue. Oestradiol has wide-ranging effects throughout the body: it maintains the uterine lining, supports bone health, influences cholesterol metabolism, affects mood and cognition, and maintains vaginal and skin health. During the menstrual cycle, oestradiol levels are low at the start, rise steadily as follicles grow (peaking just before ovulation), drop briefly after ovulation, then rise again during the luteal phase before falling if pregnancy doesn't occur.

On day 3, oestradiol should be at a relatively low baseline level (typically below 200 pmol/L or 50 pg/mL). Day 3 oestradiol serves an important role in validating your FSH result. If oestradiol is elevated on day 3 (suggesting you may have tested at the wrong time, or that a follicle has already started growing early), it can suppress FSH through negative feedback—giving a falsely reassuring low FSH even if ovarian reserve is actually reduced. This is why interpreting FSH in isolation can be misleading; the oestradiol provides a quality check. An elevated day 3 oestradiol with a 'normal' FSH should be interpreted with caution. Low day 3 oestradiol combined with high FSH is consistent with diminished ovarian reserve or approaching menopause. Results outside the normal range may need a follow-up with your GP or fertility specialist.