As you are probably aware if you are researching miscarriage causes, doctors cannot always explain why miscarriages happen. Even cases of recurrent miscarriages have an identifiable cause only about half the time. There are many theories about what causes the other half of recurrent miscarriage cases, but few are conclusively proven. One theory that falls in the latter category is the idea that high levels of a hormone called prolactin might cause miscarriages.
Prolactin is a hormone produced primarily by the anterior pituitary, 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 lactating women, but prolactin also plays many other roles in the body, including in the immune system.
When prolactin levels are elevated, the condition is labeled hyperprolactinemia. Symptoms of hyperprolactinemia can include menstrual problems, lactation in women who are not breastfeeding, and infertility, though not all women have symptoms.
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 exercise or stress, and in people who take medications that affect the brain chemical dopamine.
A few studies have found elevated prolactin levels in women with recurrent miscarriages. What this finding means, however, is controversial. Some people feel that elevated prolactin may cause miscarriages, while others feel that it is too early to say so definitively.