What is Prolactin?
Prolactin is one of several hormones that is produced by the pituitary gland. Prolactin has many different roles throughout the body. Perhaps the most important role of prolactin is to stimulate milk production in women after the delivery of a baby. Prolactin levels increase during pregnancy causing the mammary glands in a woman’s breast to enlarge in preparation for breastfeeding. Prolactin also helps with the release of milk when the baby is nursing.
During the first several months that a woman is breastfeeding, the high prolactin levels also serve to inhibit ovulation. This is the reason why women who are breastfeeding do not get their periods and therefore do not often become pregnant. As time goes on however, the prolactin levels do not stay as high with breastfeeding and the woman may start to ovulate.
Prolactin and Infertility
High prolactin levels may cause infertility . Another term for high prolactin levels is hyperprolactinemia. Women who are not pregnant and are not breastfeeding should have low levels of prolactin. If a non-pregnant woman has abnormally high levels of prolactin, it may cause her difficulty in becoming pregnant.
Prolactin may cause infertility in several different ways. First, prolactin may stop a woman from ovulating. If this occurs, a woman’s menstrual cycles will stop. In less severe cases, high prolactin levels may only disrupt ovulation once in a while. This would result in intermittent ovulation or ovulation that takes a long time to occur. Women in this category may experience infrequent or irregular periods. Women with the mildest cases involving high prolactin levels may ovulate regularly but not produce enough of the hormone progesterone after ovulation. This is known as a luteal phase defect. Deficiency in the amount of progesterone produced after ovulation may result in a uterine lining that is less able to have an embryo implant. some women with this problem may see their period come a short time after ovulation.
Symptoms of high prolactin levels
As noted above, some women with high prolactin levels may have no periods or have irregular periods. Another possible symptom of high prolactin levels is breast discharge. The discharge is the result of prolactin trying to stimulate the breast to produce milk. The occurrence of a milky discharge from the breast in a woman who has not recently been pregnant is called galactorrhea. Some women may see galactorrhea occur spontaneously. Others may see it only if they squeeze their nipples.
Measurement of prolactin
Prolactin can be measured with a simple blood test drawn at the fertility doctor’s office. In order to get accurate results, prolactin should be drawn first thing in the morning. The woman should have had nothing to eat from the night before and should avoid any stimulation of the breast or nipples from the day before also.
One common mistake that doctors make is to draw a prolactin blood test immediately after a patient has had a breast exam in the office. these women will have high prolactin levels because of the exam and therefore do not have truly elevated levels.
Prolactin should also be drawn early in the menstrual cycle – before ovulation. This is because prolactin levels are naturally higher after ovulation.
There are different forms of prolactin known as isoforms or isotypes. Not all of the forms cause reproductive problems though all are measure together on a typical prolactin blood test. For this reasons, if a prolactin level comes back elevated, it should be repeated with a more detailed test that looks at the different isoforms individually.
Causes of high prolactin levels
Prolactinoma (pituitary adenoma)
In some people, a small group of cells may form a cyst in the pituitary gland which produces elevated levels of prolactin. these cysts are called prolactinomas or pituitary adenomas. It is unclear exactly how these cysts get started. The adenomas can be classified based on their size. The adenomas can be seen and measured using MRI (magnetic resonance imaging).
Small adenomas are known as microadenomas. They measure less than one centimeter in diameter. This is the most common type of adenoma found. Microadenomas can even be present in healthy people who do not have high prolactin levels. Microadenomas can be treated with medication. They do not grow large and do not need to be treated if hormone levels are normal.
Adenomas larger than 1 centimeter are called macroadenomas. If untreated, macroadenomas can grow larger and start to push on nearby structures. The closest structures are the optic nerves. If a macroadenoma causes compression of the optic nerves, partial blindness can result. for this reason, it is important to treat macroadenomas whether or not a woman is interested in getting pregnant. Medication can be used to treat them but if that fails, surgery may be necessary.
Hypothyroidism
If a woman has an underactive thyroid gland, a portion of the brain called the hypothalamus will secrete hormones to try to stimulate the thyroid gland. This same hormone may also cause excess prolactin to be produced from the pituitary. Treatment with thyroid hormone supplements will result in correction of both the thyroid and the high prolactin levels.
PCOS (polycystic ovary syndrome)
PCOS is a common problem that can cause infertility by inhibiting ovulation. For unknown reasons, some women with PCOS may have slightly high prolactin levels.
Medications
Some medications can cause higher levels of prolactin to be produced. The most common medications that do this are known as anti-psychotic medications. Other medications which may increase prolactin levels:
- Some types of anti-depressants
- Some types of sedatives
- Estrogen
- Oral contraceptives (birth control pills)
- Some types of blood pressure medications (methyldopa, verapamil)
- A medication for nausea (Reglan, metoclopramide)
- Antacids (cimetidien)
Stress
A high prolactin level can sometimes be due to physical stress. Even drawing blood can by itself cause someone to produce to much prolactin.
Treatment of high prolactin levels
As noted above, prolactin levels can often be corrected by stopping or switching to a different medication. Correction of hypothyroidism is very effective also. If prolactin levels are persistently high, they can be effectively treated with a group of medications known as dopamine agonists.
Bromocriptine (Parlodel)
Parlodel is an effective and inexpensive medication for high prolactin levels. Parlodel is usually taken at bedtime with a snack. This is because Parlodel will occasionally cause dizziness or stomach upset. so taking it before sleep and with food will reduce those side effects. generally with time, the side effects stop anyway.
The prolactin levels can be rechecked in about three weeks. If the levels are still elevated the dose can be increased or a different medication can be tried. The Parlodel can be stopped upon diagnosis of pregnancy. However, if a woman has a macroadenoma, Parlodel should be continue through pregnancy and delivery.
Due to the side effects, some women cannot tolerate Parlodel. For these women, they may try inserted the pills vaginally instead of taking them orally.
Cabergoline (Dostinex)
Because it is more expensive, cabergoline is not usually the first choice for treatment of high prolactin levels. It is usually used when Parlodel is ineffective or a woman cannot tolerate the side effects. Cabergoline is a longer acting medication. It is usually given twice a week instead of every day.
