Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving, generally defined in humans at prior to 20 weeks of gestation. Miscarriage is the most common complication of early pregnancy.
Terminology
Very early miscarriages—those which occur before the sixth week LMP (since the woman's Last Menstrual Period)—are medically termed early pregnancy loss or chemical pregnancy . Miscarriages that occur after the sixth week LMP are medically termed clinical spontaneous abortion .
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 is 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.
Miscarriage of a fetus is also called intrauterine fetal death (IUFT).
Forms and types
The clinical presentation of a threatened abortion describes any bleeding seen during pregnancy prior to viability, that has yet to be assessed further. At investigation it may be found that the fetus remains viable and the pregnancy continues without further problems. It has been suggested that bed rest improves the chances of the pregnancy continuing when a small subchorionic hematoma has been found on ultrasound scans.
Alternatively the following terms are used to describe pregnancies that do not continue:
- An empty sac is a condition where the gestational sac develops normally, while the embryonic part of the pregnancy is either absent or stops growing very early. Other terms for this condition are blighted ovum and anembryonic pregnancy .
- An inevitable abortion describes where the fetal heart beat is shown to have stopped and the cervix has already dilated open, but the fetus has yet to be expelled. This usually will progress to a complete abortion.
- A complete abortion is when all products of conception have been expelled. Products of conception may include the trophoblast, chorionic villi, gestational sac, yolk sac, and fetal pole (embryo); or later in pregnancy the fetus, umbilical cord, placenta, amniotic fluid, and amniotic membrane.
- An incomplete abortion occurs when tissue has been passed, but some remains in utero .
- A missed abortion is when the embryo or fetus has died, but a miscarriage has not yet occurred. It is also referred to as delayed or missed miscarriage .
The following two terms consider wider complications or implications of a miscarriage:
- A septic abortion occurs when the tissue from a missed or incomplete abortion becomes infected. The infection of the womb carries risk of spreading infection (septicaemia) and is a grave risk to the life of the woman.
- Recurrent pregnancy loss (RPL) or recurrent miscarriage (medically termed habitual abortion ) is the occurrence of three consecutive miscarriages. If the proportion of pregnancies ending in miscarriage is 15%, then the probability of two consecutive miscarriages is 2.25% and the probability of three consecutive miscarriages is 0.34%. The occurrence of recurrent pregnancy loss is 1%. A large majority (85%) of women who have had two miscarriages will conceive and carry normally afterwards.
The physical symptoms of a miscarriage vary according to the length of pregnancy:
- At up to six weeks only small blood clots may be present, possibly accompanied by mild cramping or period pain.
- At 6 to 13 weeks a clot will form around the embryo or fetus, and the placenta, with many clots up to 5 cm in size being expelled prior to a completed miscarriage. The process may take a few hours or be on and off for a few days. Symptoms vary widely and can include vomiting and loose bowels, possibly due to physical discomfort.
- At over 13 weeks the fetus may be easily passed from the womb, however the placenta is more likely to be fully or partially retained in the uterus, resulting in an incomplete abortion. The physical signs of bleeding, cramping and pain can be similar to an early miscarriage, but sometimes more severe and labour-like.
Causes
Miscarriages can occur for many reasons, not all of which can be identified.
First trimester
Most clinically apparent miscarriages (two thirds to three-quarters in various studies) occur during the first trimester.
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% probability of ending in miscarriage. Most chromosomal problems happen by chance, have nothing to do with the parents, and are unlikely to recur. Chromosomal problems due to a parent's genes is, however, a possibility. This is more likely to have been the cause in the case of repeated miscarriages, or if one of the parents has a child or other relatives with birth defects. 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.
Second trimester
Up to 15% of pregnancy losses in the second trimester may be due to uterine malformation, growths in the uterus (fibroids), or cervical problems. These conditions may also contribute to premature birth.
One study found that 19% of second trimester losses were caused by problems with the umbilical cord. Problems with the placenta may also account for a significant number of later-term miscarriages.
General risk factors
Pregnancies involving more than one fetus are at increased risk of miscarriage.
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.
High blood pressure during pregnancy, known as preeclampsia, is sometimes caused by an inappropriate immune reaction to the developing fetus, and is associated with the risk of miscarriage. Similarly, women with a history of recurrent miscarriages are at risk of developing preeclampsia.
Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. The presence of certain immune conditions such as autoimmune diseases is associated with a greatly increased risk of miscarriage.
Certain illnesses (such as rubella, chlamydia and others) increase the risk of miscarriage.
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.
Cocaine use increases miscarriage r
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