Can Prolactin Cause Recurrent Miscarriages?

The mammalian pituitary gland, showing the anterior lobe (adenohypophysis) and posterior lobe
The mammalian pituitary gland, showing the anterior lobe (adenohypophysis) and posterior lobe.

Getty Images/Encyclopaedia Britannica/UIG

If you are researching miscarriage causes or have experienced one or more miscarriages, you may have learned that doctors cannot always explain why they happen. Recurrent miscarriages have an identifiable cause only about 25% to 50% of the time.

There are many as yet unproven theories about what causes the remaining recurrent miscarriage cases. One of them is that high levels of a hormone called prolactin may contribute to pregnancy loss. When a high blood prolactin concentration interferes with the function of the ovaries, secretion of estradiol, the main estrogen, decreases.

What Is Prolactin?

Prolactin is a hormone produced primarily by the anterior pituitary gland, a pea-sized gland at the base of the brain. Prolactin gets its name because it plays a major role in inducing milk production in the lactation process. 

Prolactin levels normally increase throughout pregnancy, although the levels can vary widely. Prolactin levels reach their highest point at the time of delivery and then go back to normal around six weeks after delivery (even if the parent is breastfeeding).

When prolactin levels are elevated, the condition is called hyperprolactinemia. These high levels can interfere with how the ovaries function. This can lead to menstrual irregularities, infertility, and sometimes milk release from the breasts, even in someone who is not breastfeeding.

The most common cause of hyperprolactinemia is a non-cancerous pituitary tumor called an adenoma, but the condition can also occur in some people with hypothyroidism. Prolactin can also be elevated in response to environmental triggers, such as strenuous exercise or stress, and in people who take medications that affect the brain chemical dopamine.

Prolactin's Role in Fertility

Because menstruation and the normal ovulatory cycle often ceases during lactation, prolactin acts as a natural contraceptive that protects against back-to-back pregnancies. However, your body's prolactin levels should not be relied upon as proper contraception. Be sure to discuss postpartum contraception with your healthcare provider.

According to the widely accepted theory that high prolactin levels can impair ovarian function, people with elevated prolactin levels may experience menstrual and/or ovulatory cycles that are irregular, making it more difficult to become pregnant.

When it comes to prolactin and recurrent miscarriages, however, the jury is still out. A few studies have found elevated prolactin levels in people who experienced recurrent miscarriages. What this finding means, however, is controversial. Some experts feel that elevated prolactin may cause miscarriages, while others feel that it is too early to say so definitively.

In Support of the Theory

Given the interworking of so many different hormones in the human body, it's feasible that an imbalance could cause numerous problems. Since hyperprolactinemia may contribute to miscarriages, some doctors check a woman's prolactin level and give medication to lower the level if it is elevated. 

In the case of recurrent miscarriages and prolactin, one older study found elevated prolactin levels in women who had two or pregnancy losses.

When these women were treated with a medication called bromocriptine (which works to lower prolactin levels) in their next pregnancy, there was an 86% live-born rate compared to untreated women who had a 52% live-born rate. 

These findings have not been verified in a large-scale study. But because the treatment is thought to be safe, some doctors test for and treat elevated prolactin when investigating the causes of recurrent miscarriages.

In Opposition to the Theory

The studies that have found a link between high prolactin levels and miscarriage are not large enough to be conclusive.

In addition, researchers still do not fully understand the functioning of prolactin in the body, and many feel that it is too early to say whether or not the elevated prolactin levels in people experiencing recurrent miscarriages have any clinical relevance.

Other factors could theoretically account for higher prolactin levels associated with recurrent miscarriages. For example, in people with significantly abnormal thyroid glands, an elevated thyroid-stimulating hormone (TSH) can be associated with a mildly elevated prolactin level. Elevated TSH is clearly linked to miscarriage.

Current Thinking

Some doctors regularly test prolactin in people with recurrent miscarriages and prescribe medications to reduce prolactin levels. These medications appear to be safe to use during pregnancy and are commonly used for people with infertility resulting from hyperprolactinemia. Still, there are no formal recommendations to test for and treat prolactin levels in people who experience recurrent miscarriages.

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4 Sources
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