It's every pregnant woman's nightmare -- the loss of her baby during pregnancy, known in the medical community as a "spontaneous abortion." As with preterm labor, there are a host of reasons why some women experience miscarriages, and sometimes, there's no explanation at all.
However, there have been some studies indicating a link between miscarriage and high levels of stress, especially early in the pregnancy or just before conception. In the June 2003 issue of Endocrinology, researchers suggest that CRH isn't just released in the brains of highly stressed pregnant women; it's also released elsewhere in the body. The CRH targets a type of cell called a mast cell, which secretes chemicals that cause allergic reactions.
Apparently, one of these chemicals, tryptase, "prevents the production of membranes to develop the embryo and disrupts the whole architecture of the placenta that feeds the baby" [Source: WebMD].
In short, your pregnant body's reaction to stress can lead to a miscarriage if it happens early in pregnancy. A 2006 study showed that high levels of another stress hormone, cortisol, may affect levels of progesterone, which impacts uterine growth and other aspects of pregnancy [source: National Academy of Sciences of the USA]. So, not only should you try to avoid chronic stress while pregnant, but you should also focus on it early in your pregnancy.
Some babies are just born small, but they're otherwise considered healthy. Other babies are underweight because they didn't get enough nutrients to grow properly. It's not just because their mothers didn't eat right, either. In the next section, learn about the connection between low birth weight and stress.