Spontaneous expulsion of an embryo or fetus from the uterus before it can live outside the mother. More than 60percnt are caused by an inherited defect in the fetus, which might result in a fatal abnormality. Other causes may include acute infectious disease, especially if it reduces the fetus's oxygen supply; abnormalities of the uterus that have physical or hormonal origins; and death of the fetus from umbilical-cord knotting. The main sign of impending miscarriage is vaginal bleeding.
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In medical contexts, the word "abortion" refers to any process by which a pregnancy ends with the death and removal or expulsion of the fetus, regardless of whether it's spontaneous or intentionally induced. Many women who have had miscarriages, however, object to the term "abortion" in connection with their experience, as it is generally associated with induced abortions. In recent years there has been discussion in the medical community about avoiding the use of this term in favor of the less ambiguous term "miscarriage.
Labour resulting in live birth before the 37th week of pregnancy is termed "premature birth," even if the infant dies shortly afterward. The limit of viability at which 50% of fetus/infants survive longterm is around 24 weeks, with moderate or major neurological disability dropping to 50% only by 26 weeks. Although long-term survival has never been reported for infants born from pregnancy shorter than 21 weeks and 5 days, infants born as early as the 16th week of pregnancy may sometimes live for some minutes after birth.
A fetus that dies while in the uterus after about the 20-24th week of pregnancy is termed a "stillbirth"; the precise gestational age definition varies by country. Premature births or stillbirths are not generally considered miscarriages, though usage of the terms and causes of these events may overlap.
Alternatively the following terms are used to describe pregnancies that do not continue:
The following two terms consider wider complications or implications of a miscarriage:
Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks. A pregnancy with a genetic problem has a 95% chance of ending in miscarriage. Most chromosomal problems happen by chance, have nothing to do with the parents, and are unlikely to recur. Genetic problems are more likely to occur with older parents; this may account for the higher miscarriage rates observed in older women.
Another cause of early miscarriage may be progesterone deficiency. Women diagnosed with low progesterone levels in the second half of their menstrual cycle (luteal phase) may be prescribed progesterone supplements, to be taken for the first trimester of pregnancy. However, no study has shown that general first-trimester progesterone supplements reduce the risk of miscarriage, and even the identification of problems with the luteal phase as contributing to miscarriage has been questioned.
Uncontrolled diabetes greatly increases the risk of miscarriage. Women with controlled diabetes are not at higher risk of miscarriage. Because diabetes may develop during pregnancy (gestational diabetes), an important part of prenatal care is to monitor for signs of the disease.
Polycystic ovary syndrome is a risk factor for miscarriage, with 30-50% of pregnancies in women with PCOS being miscarried in the first trimester. Two studies have shown treatment with the drug metformin to significantly lower the rate of miscarriage in women with PCOS (the metformin-treated groups experienced approximately one-third the miscarriage rates of the control groups). However, a 2006 review of metformin treatment in pregnancy found insufficient evidence of safety and did not recommend routine treatment with the drug.
Tobacco (cigarette) smokers have an increased risk of miscarriage. An increase in miscarriage is also associated with the father being a cigarette smoker. The husband study observed a 4% increased risk for husbands who smoke less than 20 cigarettes/day, and an 81% increased risk for husbands who smoke 20 or more cigarettes/day.
Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. Certain immune conditions such as autoimmune diseases greatly increase the risk of miscarriage.
Cocaine use increases miscarriage rates. Physical trauma, exposure to environmental toxins, and use of an IUD during the time of conception have also been linked to increased risk of miscarriage.
Nausea and vomiting of pregnancy (NVP, or morning sickness) are associated with a decreased risk of miscarriage. Several mechanisms have been proposed for this relationship, but none are widely agreed on. Because NVP may alter a woman's food intake and other activities during pregnancy, it may be a confounding factor when investigating possible causes of miscarriage.
One such factor is exercise. A study of over 92,000 pregnant women found that most types of exercise (with the exception of swimming) correlated with a higher risk of miscarriage prior to 18 weeks. Increasing time spent on exercise was associated with a greater risk of miscarriage: an approximately 10% increased risk was seen with up to 1.5 hours per week of exercise, and a 200% increased risk was seen with over 7 hours per week of exercise. High-impact exercise was especially associated with the increased risk. No relationship was found between exercise and miscarriage rates after the 18th week of pregnancy. The majority of miscarriages had already occurred at the time women were recruited for the study, and no information on nausea during pregnancy or exercise habits prior to pregnancy was collected.
Caffeine consumption has also been correlated to miscarriage rates, at least at higher levels of intake. A 2007 study of over 1,000 pregnant women found that women who reported consuming 200 mg or more of caffeine per day experienced a 25% miscarriage rate, compared to 13% among women who reported no caffeine consumption. 200 mg of caffeine is present in 10 oz (300 mL) of coffee or 25 oz (740 mL) of tea. This study controlled for pregnancy-associated nausea and vomiting (NVP or morning sickness): the increased miscarriage rate for heavy caffeine users was seen regardless of how NVP affected the women. About half of the miscarriages had already occurred at the time women were recruited for the study. A second 2007 study of approximately 2,400 pregnant women found that caffeine intake up to 200 mg per day was not associated with increased miscarriage rates (the study did not include women who drank more than 200 mg per day past early pregnancy).
The risk of miscarriage decreases sharply after the 10th week LMP, i.e. when the fetal stage begins. The loss rate between 8.5 weeks LMP and birth is about two percent; loss is “virtually complete by the end of the embryonic period.
The prevalence of miscarriage increases considerably with age of the parents. One study found that pregnancies from men younger than twenty-five years are 40% less likely to end in miscarriage than pregnancies from men 25-29 years. The same study found that pregnancies from men older than forty years are 60% more likely to end in miscarriage than the 25-29 year age group. Another study found that the increased risk of miscarriage in pregnancies from older men is mainly seen in the first trimester. Yet another study found an increased risk in women, by the age of forty-five, on the order of 800% (compared to the 20-24 age group in that study), 75% of pregnancies ended in miscarriage.
Miscarriage may also be detected during an ultrasound exam, or through serial human chorionic gonadotropin (HCG) testing. Women pregnant from ART methods, and women with a history of miscarriage, may be monitored closely and so detect a miscarriage sooner than women without such monitoring.
Several medical options exist for managing documented nonviable pregnancies that have not been expelled naturally.
If the bleeding is light, making an appointment to see one's doctor is recommended. If bleeding is heavy, there is considerable pain, or there is a fever, then emergency medical attention is recommended to be sought.
No treatment is necessary for a diagnosis of complete abortion (as long as ectopic pregnancy is ruled out). In cases of an incomplete abortion, empty sac, or missed abortion there are three treatment options:
For those who do go through a process of grief, it is often as if the baby had been born but died. How short a time the fetus lived in the womb may not matter for the feeling of loss. From the moment pregnancy is discovered, the parents can start to bond with the unborn child. When the child turns out not to be viable, dreams, fantasies and plans for the future are disturbed roughly.
Besides the feeling of loss, a lack of understanding by others is often important. People who have not experienced a miscarriage themselves may find it hard to empathize with what has occurred and how upsetting it may be. This may lead to unrealistic expectations of the parents' recovery. The pregnancy and miscarriage are hardly mentioned anymore in conversation, often because the subject is too painful. This can make the woman feel particularly isolated.
Interaction with pregnant women and newborn children is often also painful for parents who have experienced miscarriage. Sometimes this makes interaction with friends, acquaintances and family very difficult.