Estradiol

Estradiol is the most powerful natural oestrogen in men. It regulates reproduction in women and, together with progesterone, helps maintain pregnancy.

Most estradiol is secreted by the ovaries (non-pregnant women). The testicles and adrenal cortex (in both men and women) secrete small amounts. 

During pregnancy, the placenta produces most of the circulating estradiol.

Oestradiol levels are lowest at the time of menstruation and at the start of the follicular phase. They rise during the late follicular phase to reach a peak just before the rise in LH (human luteinising hormone), which triggers ovulation. When LH reaches its peak, estradiol levels fall before rising again during the luteal phase.

The growth of the endometrium is stimulated by oestradiol and progesterone (secreted by the corpus luteum) with a view to the implementation of a fertilised egg. If conception does not occur, the secretion of oestradiol and progesterone by the corpus luteum decreases, triggering menstruation.

During in vitro fertilisation, oestradiol levels are systematically measured after stimulation with gonadotropins in order to determine the follicular state. 

Falling oestradiol levels are a feature of the perimenopause and menopause. Measurement of oestradiol can confirm the onset of menopause and help assess associated symptoms such as hot flashes, mood changes and loss of bone density.

Estradiol levels are used to diagnose conditions such as polycystic ovary syndrome (PCOS), ovarian failure and other ovarian dysfunctions. Abnormally high or low estradiol levels can be indicative of these conditions.

In men, high estradiol levels can cause gynecomastia (enlarged breast tissue).