Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation. Miscarriage is the most common complication of early pregnancy.
Very early miscarriages—those that 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 (and veterinary) contexts, the technical term "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, because in everyday English the word is strongly 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". In 2005 the European Society for Human Reproduction and Embryology (ESHRE) published a paper aiming to facilitate an update and revision of nomenclature used to describe early pregnancy events.
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, fetuses 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.
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.
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 a condition in which the cervix has already dilated open, but the fetus has yet to be expelled. This usually will progress to a complete abortion. The fetal heart beat may have been shown to have stopped, but this is not part of the criteria.
* 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.
Signs and symptoms
The most common symptom of a miscarriage is bleeding; bleeding during pregnancy may be referred to as a threatened abortion. Of women who seek clinical treatment for bleeding during pregnancy, about half will go on to have a miscarriage. Symptoms other than bleeding are not statistically related to 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.
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