FSH, LH & Prolactin

Follicle-stimulating hormone (FSH) is a hormone which is associated with reproduction and the development of eggs in women and sperm in men. This test measures FSH in the blood.

FSH is produced by the pituitary gland, and its production is controlled by a feedback system involving the hypothalamus in the brain, the pituitary gland, and the hormones produced by the ovaries or testicles. The Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the pituitary gland to release FSH and luteinizing hormone (LH; another closely-related hormone also involved in reproduction). FSH affects the growth and maturation of egg follicles in the ovaries during the follicular phase of the menstrual cycle. The menstrual cycle is divided into follicular and luteal phases, each phase lasting for 14 days. During the follicular phase, FSH initiates the production of estradiol by the follicle, and the two hormones work together in the further development of the egg follicle. Near the end of the follicular phase, the production of FSH and luteinizing hormone increases. The release of the egg from the ovary (ovulation) occurs shortly after this increased production of hormones. The hormone inhibin as well as estradiol and progesterone help control the amount of FSH released by the pituitary gland. FSH also facilitates the ability of the ovary to respond to LH. At menopause, ovarian function decreases and eventually ceases which results in increased levels of FSH and LH.

In males, the role of FSH is to stimulate the testicles to produce mature sperms and also promotes the production of androgen binding proteins. FSH levels are relatively constant in men after puberty than in women.

In infants and children, FSH levels rise shortly after birth and then fall to very low levels by 6 months in boys and 1-2 years in girls. Concentrations begin to rise again before the beginning of puberty and the development of secondary sexual characteristics.

 Disorders affecting the hypothalamus, pituitary, and/or the ovaries or testicles can cause the production of too much or too little FSH, resulting in a variety of conditions such as infertility, abnormal menstrual cycles, or early (precocious) or delayed sexual maturation (puberty).

Luteinizing hormone is associated with reproduction and ovulation. In females, it stimulates the release of an egg from the ovary. However, in males, testosterone production is dependent on LH. This test helps in measuring the amount of LH present in the blood.

 LH is produced by the pituitary gland, and its production is controlled by the hypothalamus, pituitary gland, and the hormones produced by the ovaries (in women) or testicles (in men).

 In premenopausal women, LH stimulates ovulation and the production of other hormones, estradiol, and progesterone. The menstrual cycle is divided into 2 phases, follicular and luteal phases, each of these last for about 14 days. Near the end of the follicular phase, there is a mid-cycle increase in follicle-stimulating hormone (FSH) and LH. This triggers ovulation. During the luteal phase, LH secretion stimulates the corpus luteum to start producing progesterone. At this point, FSH and LH levels get reduced, while progesterone and estradiol concentrations rise. If the egg is not fertilized, then the levels of these hormones fall after several days followed by the beginning of the next menstrual cycle. With the onset of menopause ovarian function reduces and eventually discontinues, which results in increased levels of FSH and LH.

 In men, LH stimulates Leydig cells in the testicles to produce testosterone. However, LH levels remain relatively constant in men after puberty. A high testosterone level provides negative feedback to the pituitary gland and the hypothalamus, thus decreasing the amount of LH secreted.

 In infants and children, LH levels rise shortly after birth and then fall to very low levels (by 6 months in boys and 1-2 years in girls). At about 6-8 years of age, levels again rise before the beginning of puberty and secondary sexual characteristics development.