A miscarriage is the natural loss of a fetus, which occurs before a pregnancy has reached its midway point of twenty weeks. When a woman has a miscarriage, her fetus and placenta can be expelled naturally from the body through her vagina. This manifests as vaginal bleeding, spotting, or blood clots, and as abdominal pain or cramping. For those women unable to expel the tissue naturally, a surgical procedure may be required to extract the fetus from the womb. Miscarriages are devastating, but they usually occur when there is something very wrong with the baby or the pregnancy. There are three common causes of a miscarriage, which can be subdivided into chromosomal abnormalities, internal difficulties, and substance abuse. Chromosomes are strands of DNA which carry a person's genes and help to the pass on hereditary traits from parent to child. Humans have 23 pairs of chromosomes, or 46 total, which are with them from their first day in the womb. Occasionally though, a developing fetus will not have the proper number of chromosomes. For example, in a trisomy, a baby receives three chromosomes of one type rather than a standard pair. With one extra chromosome, the pregnancy will often not carry to term. Conversely, a fetus with a condition known as monosomy is missing one chromosome. This is also a common cause of a miscarriage. Sometimes, a mother may have internal difficulties of her own that can lead to an interrupted pregnancy. One example is a misshapen uterus, in which a woman's uterus is not large enough to accommodate the needs of a growing baby. Some women experience miscarriages (or even infertility), due to non-cancerous tumors in the uterine cavity, which are called submucous fibroids. Others have adhesions, or scar tissue, inside the womb, which can restrict the implantation of the fetus and stunt its growth, leading to a miscarriage. Cervical incompetence is a problem that occurs less frequently, when a weakened cervix shortens and widens, expelling the fetus prematurely. On a rare occasion, a chronic condition present in the mother...such as diabetes, kidney disease, high blood pressure, or lupus...can also provoke a miscarriage. But don't worry: with careful monitoring, women with these conditions usually deliver perfectly healthy babies! Rarely, outside toxins like high-dose radiation, insecticides, and lead, may lead to a miscarriage. Miscarriages are devastating, but there can be ways to reduce the chances of having one. If you are attempting to conceive, make sure that you speak with your doctor about preconception care and your own health risks.