The majority of miscarriages are from causes that cannot be identified. A large number are caused by chromosomal abnormalities, hormones, and lifestyle choices. There are often problems with implantation, or the age of the mother may be a factor. Sometimes, tissue rejection or infection is cited as a cause. There are many reasons for miscarriage, and while chromosomal abnormalities are likely the most common, various characteristics about the parents of the child can make other factors more probable.
Chromosomal abnormalities are one of the most common reasons for miscarriage. Problems with chromosomes are almost entirely random, although the genes of the parents can cause a miscarriage. It is much more likely for loss of the fetus to be caused by a faulty egg or sperm, which may not represent the overall quality of the parents’ reproductive potential. If repeated miscarriages occur, then it becomes more likely that the genetic issue lies within one of the parents.
Maternal health problems are also common reasons for miscarriage. Progesterone deficiency is a particularly common health problem for mothers that sometimes results in spontaneous abortion. Infection may cause abortion, but this is a problem that is sometimes avoidable. Certain diseases such as untreated diabetes or polycystic ovary syndrome put women at a higher risk of having a miscarriage, but this is not a particularly common problem across the population because it is usually known before attempting pregnancy. The age of the mother, while not a health problem, is also correlated with higher miscarriage rates.
Usually, lifestyles that affect the fetus negatively are discontinued once pregnancy is discovered, so behavioral issues are relatively uncommon reasons for miscarriage. Women who continue to engage in activities such as smoking, excessive drinking, and use of caffeine during pregnancy may experience miscarriages at a higher rate. Certain drugs may also have an effect on pregnancy. Most women take great care to ensure the safety of the fetus, which makes these decreasingly frequent reasons for miscarriage.
Many activities that are commonly held to cause miscarriages are actually quite safe. Women can continue to work, exercise, and engage in intercourse without posing any additional risk to the fetus. Even reasons such as maternal trauma are unlikely to cause a miscarriage, as during the early stages of pregnancy, the fetus is highly protected by the mother's body. Only serious trauma and extreme activities are likely to cause miscarriage.
While certain reasons for miscarriage are more common in the world, when looking at specific groups, different reasons rise to the top of the list. For instance, among groups that commonly engage in risky activities without access to medical treatment, such as drug addicts, lifestyle choices are one of the more common reasons for miscarriage. In fact, different groups have greatly different rates of miscarriage, which can give a mother a false estimate of her risk. If parents feel concerned about the possibility of miscarriage, a consultation with a doctor can usually provide a reasonable estimate of safety.