Miscarriage Risk Factors
Defining Miscarriage
Miscarriage is defined as the loss of a pregnancy in the first 20 weeks. After 20 weeks, a pregnancy loss is considered a stillbirth. Between 15 and 20 percent of pregnancies that are known, that is the woman is aware she is pregnant, end in miscarriage and nearly 80 percent of these losses happen within the first trimester. These numbers do not reflect the missed pregnancies that happen when a fertilized egg is lost before a positive pregnancy test. Studies show that 30 to 50 percent of fertilized eggs are lost before a woman even knows she is pregnant, since the loss is so early that her menstrual period arrives on time.
Causes Of Miscarriage
The cause of most early miscarriages is thought to be due to chromosomal abnormalities in the fertilized eggs. Most frequently the egg or the sperm had the wrong number of chromosomes and the fertilized egg is not able to develop normally. It is estimated that between 50 and 70 percent of first trimester losses are due to this situation.
Other factors that cause early miscarriage include improper implantation of the egg in the uterus or structural defects in the embryo that affect its ability to grow and develop. Most health care providers do not do a full investigation into the miscarriage if it is a single episode, so it is difficult to determine why a pregnancy was lost. Multiple miscarriages require investigation because it can be a signal of some fertility problems. However, even with detailed evaluations after two or three consecutive miscarriages, it is still difficult to determine the cause in about half of the cases.
Once the baby has a heartbeat, which is discernible on ultrasound at about six weeks, the chances of miscarriage drop significantly.
Risk Factors For Miscarriage
Even though miscarriage can happen to any woman, there are some situations which make for higher risk. Women over the age of 40 are more than twice as likely to miscarry than women in their 20s. Women, who have a history of miscarriages, having had two or more in a row, are at greater risk for pregnancy loss. Certain chronic diseases and conditions increase the chance of miscarriage in many women. PCOS and uncontrolled diabetes are common causes of miscarriage. Structural problems in the uterus or a weak cervix can also make carrying a pregnancy difficult.
Genetic problems or a history of birth defects predisposes a woman to risk of pregnancy loss, as does having certain infections like listeria, mumps, rubella, measles, and exposure to STDs. Medications can be a cause of miscarriage and lifestyle choices like smoking, drinking and use of drugs all increase the risk. Some studies indicate that consuming more than four cups of coffee a day is associated with higher rates of miscarriage.
Preconception Preparedness
A woman who is thinking about pregnancy is wise to check in with a health care professional for a preconception visit to ensure as healthy a setting as possible before conception. Good lifestyle choices and proper care are also important. However, even women who have "done everything right" may suffer pregnancy loss.
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