reproductive hormones

Follicle stimulating hormone (FSH) and luteinising hormone (LH)

Luteinising hormone (LH) and follicle stimulating hormone (FSH) are important pituitary hormones, required for reproductive processes in both males and females. LH and FSH are released by the anterior pituitary in response to pulsatile gonadotropin-releasing hormone (GnRH) stimulation by the hypothalamus, and the negative feedback of oestrogen or testosterone.

In females, the combined action of FSH and LH stimulates growth of ovarian follicles and steroidogenesis, with the production of androgens, which are then converted to oestrogens by the action of the enzyme aromatase. A mid-cycle surge in LH also triggers ovulation. FSH levels usually increase during menopause, because the ovaries become less responsive to FSH, which causes the pituitary gland to increase FSH production. However, fluctuating ovarian activity, especially early in perimenopause, means that FSH and oestradiol levels are not reliable predictors of menopause, as they are sometimes at pre-menopausal levels.

In males, FSH stimulates the Sertoli cells resulting in spermatogenesis and LH causes the interstitial Leydig cells of the testes to produce testosterone.

Reference range

The reference range for FSH in adult males is 2 – 12 IU/L and for LH is 2 – 9 IU/L.

The reference range for FSH and LH in adult females is: 

Phase	FSH (IU/L)	LH (IU/L)
Early follicular	3 - 10	2 - 8
Mid-cycle peak	4 - 25	10 - 75
Post-menopausal	> 20	> 15
Pregnancy	< 1	2 - 9

Oestradiol

Oestradiol is the principal oestrogen in females who are ovulating and the dominant 
ovarian hormone during the follicular (first) phase of the menstrual cycle.
The concentration of oestradiol varies throughout the menstrual cycle. Oestradiol is
released in parallel to follicular growth and is highest when the follicle matures
(prior to ovulation). Oestradiol production gradually reduces if the oocyte released
by the follicle is unfertilised. Laboratory testing routinely measures E2 forms of 
oestradiol, most of which is bound to sex hormone-binding globulin (SHBG).
Oestradiol levels decrease significantly during menopause.

In males, oestrogen is an essential part of the reproductive system, and is required for
maturation of sperm. Primary hypogonadism (impaired response to gonadotropins including
 LH and FSH) can result in increased testicular secretion of oestradiol and
increased conversion of testosterone to oestradiol. Obesity may also increase oestrogen
levels in males. An increase in the ratio of oestrogen to androgens in males is associated
with gynaecomastia (the development of breast tissue).

Reference range
The adult female reference range for oestradiol is:

Phase	Oestradiol (pmol/L)
Early follicular	< 300
Ovulatory surge	< 500 - 3000
Luteal surge	100 - 1400
Post-menopausal	< 200

N.B. Oestradiol levels are usually undetectable in females using oestrogen-containing oral contraception as this suppresses oestradiol production from the ovary. Oestradiol levels in females taking some forms of HRT (e.g. oestrogen valerate) will be high.

The adult male reference range for oestradiol is assay dependent, so it is recommended to consult the local laboratory. An example of an adult male reference range for oestradiol is 0 – 200 pmol/L.

Progesterone

Progesterone is the dominant ovarian hormone secreted during the luteal (second) phase of the menstrual cycle. Its main function is to prepare the uterus for implantation of an embryo, in the event that fertilisation occurs during that cycle. If pregnancy occurs, human chorionic gonadotropin (hCG) is released which maintains the corpus luteum, which in turn allows progesterone levels to remain raised. At approximately twelve weeks gestation, the placenta begins to produce progesterone in place of the corpus luteum. Progesterone levels decrease after delivery and during breastfeeding. Progesterone levels are low in women after menopause. In males almost all progesterone is converted to testosterone in the testes.

There are no indications, other than fertility investigation in females (in some circumstances), which requires progesterone measurement in a general practice setting.

Reference range
Detecting ovulation – measured on day 20 – 23 of a normal 28 day cycle: 
The reference range for progesterone in adult males is < 1 nmol/L. 

0 – 6 nmol/L	ovulation unlikely
7 – 25 nmol/L	ovulation possible
> 25 nmol/L	ovulation likely

Prolactin

In females, prolactin stimulates the breasts to produce milk, after oestrogen priming. During pregnancy, prolactin concentrations begin to increase at approximately six weeks gestation, peaking during late pregnancy.

In males and non-pregnant females, the secretion of prolactin from the pituitary gland is inhibited by the hypothalamic release of dopamine. Tumours or masses that result in compression of the pituitary stalk or drugs that block dopamine receptors, e.g. psychotropics, opiates and dopamine agonists, can cause hyperprolactinemia by reducing dopamine delivery to the pituitary. Hypothyroidism can also be associated with hyperprolactinaemia if levels of thyrotropin-releasing hormone (TRH) are raised, which stimulates prolactin production.

Hyperprolactinaemia is the most common endocrine disorder of the hypothalamic-pituitary axis and causes infertility in both sexes. Prolactin-secreting tumours (prolactinomas) are the most common type of pituitary tumour. These are usually small tumours (microprolactinomas) and are characterised by anovulation or other menstrual disturbances, galactorrhoea (milk secretion from the breast) and sexual dysfunction. Rarely, tumours may be large (macroprolactinomas) and present with symptoms such as headaches and bitemporal hemianopia (missing vision in the outer halves of the visual field).

N.B. Galactorrhoea can occur in males, but is a much less common symptom of high prolactin in males.

Reference range
There is a diurnal variation in prolactin levels and serum levels are lowest approximately three hours after waking. Samples are best collected in the afternoon.  Stress or illness can also elevate prolactin levels, so ideally patients should be well and not taking medicines that can interfere with prolactin levels such as psychotropics, opiates or dopamine agonists.

Reference ranges are assay-specific so it is recommended to consult the local laboratory for their reference range. An example of a reference range for prolactin is 50 – 650 mU/L for adult females and 50 – 450 mU/L for adult males. Increased prolactin levels are usually associated with decreased oestrogen or testosterone levels.

Testosterone

Testosterone is the primary androgen responsible for the development and maintenance of male sexual characteristics. It also stimulates anabolic processes in non-sexual tissues. In males, LH stimulates the Leydig cells in the testes to produce testosterone. A small amount of testosterone in males is produced by the adrenal glands.

In females, the majority of testosterone is produced by peripheral conversion of androgen precursor steroids to testosterone, with the remainder produced in the ovaries and adrenal glands. Circulating levels of testosterone fluctuate with the menstrual cycle, and increase during pregnancy. Serum levels of testosterone remain relatively stable during and after menopause.  Polycystic ovary syndrome is the most common cause of hyperandrogenism (increased testosterone levels) in females. Rarer causes include Cushing’s syndrome, congenital adrenal hyperplasia and androgen-secreting tumours.

Reference range
The reference range for total testosterone in adult males differs between laboratories. An approximate range is 8 – 35 nmol/L. If a single early morning testosterone level is clearly within the reference range (e.g. >15 nmol/L) then no further testing is required. If a low or borderline result is obtained, a confirmatory early morning test (when the patient is well) should be conducted.

Testosterone reference ranges for females are also assay-specific. An example of an adult female reference range for total testosterone is 0.5 – 2.5 nmol/L.  Modern second generation testosterone assays generally have lower ranges in females, due to less interference from other steroids such as DHEAS

Free testosterone can be calculated from total testosterone and sex hormone-binding globulin (SHBG). However, SHBG testing is only ever rarely required, such as when abnormalities of sex hormone binding (e.g. hyperthyroidism, anticonvulsant use, severe obesity) can cause total testosterone levels to be misleading. Discussion with an endocrinologist or chemical pathologist is recommended before requesting SHBG.

Human chorionic gonadotrophin (hCG)

hCG is structurally and functionally identical to LH, apart from its beta chain, therefore it is often referred to as beta-hCG (or β-hCG).

hCG is released by trophoblast cells during pregnancy. These cells form the outer layer of the developing blastocyst following conception and embryonic implantation. hCG stimulates progesterone production by the corpus luteum and increases vascularity between the trophoblast and the uterus wall. It is detectable approximately three days after implantation of the embryo, which occurs approximately six to twelve days following ovulation and fertilisation. During a normal pregnancy hCG levels usually double approximately every two days, then plateau and begin to decrease at eight to ten weeks, but will remain elevated throughout pregnancy.  Women pregnant with twins generally produce higher levels of hCG than those with single embryos, but hCG levels cannot be reliably used to predict this. 

Urine or serum hCG measurement can be used to confirm early pregnancy (urine hCG is adequate in most cases). Serum hCG can also be useful as an initial investigation in women who have symptoms that may suggest ectopic pregnancy, miscarriage or trophoblastic disease. Transvaginal ultrasound can be used after approximately five weeks gestation, or hCG levels > 1000 – 2000 IU/L, to detect signs of pregnancy. ⁷

A non-viable pregnancy may be indicated by a decrease or plateau in hCG levels in early pregnancy (remembering that hCG decreases in normal pregnancies after approximately nine to ten weeks gestation). However hCG alone is not a reliable predictor of ectopic pregnancy as there is no particular pattern of decrease or increase.8 Following miscarriage it may take three or four weeks for hCG levels to return to non-pregnant levels (< 5 IU/L).  In incomplete miscarriage, hCG levels can remain raised and surgical intervention may be required.

In males, hCG is produced by some testicular tumours, and it is therefore used as a serum tumour marker for some forms of testicular cancer.

Reference range
There is a wide range of variability of hCG levels during early pregnancy. The rate of increase, i.e. doubling time, gives more useful information than the actual levels. Most urine tests turn positive with hCG levels > 20 – 25 IU/L. Serum hCG < 5 IU/L is considered negative for pregnancy. 

Excessively high hCG levels, e.g. > 100 000 IU/L may be suggestive of gestational trophoblastic disease, e.g. molar pregnancy.