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ICD-10 O03
ICD-9 634
OMIM [1]
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This is a background article. see Psychological aspects of spontaneous abortion

Spontaneous abortion or Miscarriage is the natural or spontaneous end of a pregnancy at a stage where the embryo or the fetus is incapable of surviving, generally defined in humans at a gestation of prior to 20 weeks. Miscarriages are the most common complication of pregnancy. The medical term "spontaneous abortion" is used in reference to miscarriages because the medical term "abortion" refers to any terminated pregnancy, deliberately induced or spontaneous, although in common parlance it refers specifically to an induced abortion an active termination of pregnancy.


Very early miscarriages - those which occur before the sixth week LMP (since the woman's Last Menstrual Period) are medically termed early pregnancy loss[1] or chemical pregnancy.[2] Miscarriages that occur after the sixth week LMP are medically termed clinical spontaneous abortion.[1]

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."[3]

Labour resulting in live birth before the 37th week of pregnancy is termed "premature birth," even if the infant dies shortly afterward. Although long-term survival has never been reported for infants born from pregnancy shorter than 21 weeks, infants born as early as the 16th week of pregnancy may cry and live a few minutes or hours.[4]

A fetus that dies while in the uterus after about the 20th week of pregnancy is termed a "stillbirth". Premature births or stillbirths are not generally considered miscarriages, though usage of the terms and causes of these events may overlap.

Forms and types

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.[5]

An empty sac is a condition where the gestational sac develops normally, while the embryonal part of the pregnancy is either absent or stops growing very early. Other terms for this condition are blighted ovum and anembryonic pregnancy.

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 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 3 consecutive miscarriages. A large majority (85%) of women who have had two miscarriages will conceive and carry normally afterwards, so statistically the occurrence of three abortions at 0.34% is regarded as "habitual".[6]


Miscarriages can occur for many reasons, not all of which can be identified.

First trimester

Most miscarriages (more than three-quarters) occur during the first trimester.[7]

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.[8] Genetic problems are more likely to occur with older parents; this may account for the higher miscarriage rates observed in older women.[9]

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.[8]

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.[8] These conditions may also contribute to premature birth.[7]

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.[10]

General risk factors

Pregnancies involving more than one fetus are at increased risk of miscarriage.[8]

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. High blood pressure and certain illnesses (such as rubella and chlamydia) increase the risk of miscarriage.[8]

Tobacco (cigarette) smokers have an increased risk of miscarriage.[11] An increase in miscarriage is also associated with the father being a cigarette smoker.[1] 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.[8]

Cocaine use increases miscarriage rates.[11]

Physical trauma, exposure to certain chemicals, obesity, high caffeine intake (> 300 mg/day), high levels of alcohol consumption, and use of NSAIDs have also been linked to increased risk of miscarriage.[How to reference and link to summary or text]


Determining the prevalence of miscarriage is difficult. Many miscarriages happen very early in the pregnancy, before a woman may know she is pregnant. Treatment of women with miscarriage at home means medical statistics on miscarriage miss many cases.[12] Prospective studies using very sensitive early pregnancy tests have found that 25% of pregnancies are miscarried by the sixth week LMP (since the woman's Last Menstrual Period).[13][14] The risk of miscarriage decreases sharply after the 8th week, i.e. when the fetal stage begins.[15] Clinical miscarriages (those occurring after the sixth week LMP) occur in 8% of pregnancies.[14]

The prevalence of miscarriage increases considerably with age of the parents. Pregnancies from men younger than twenty-five years are 40% less likely to end in miscarriage than pregnancies from men 25-29 years. Pregnancies from men older than forty years are 60% more likely to end in miscarriage than the 25-29 year age group.[16] The increased risk of miscarriage in pregnancies from older men is mainly seen in the first trimester.[17] In women, by the age of forty-five, 75% of pregnancies may end in miscarriage.[18]


The most common symptom of a miscarriage is bleeding;[19] 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.[12] Symptoms other than bleeding are not statistically related to miscarriage.[19]

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.


Blood loss during early pregnancy is the most common symptom of both miscarriage and of ectopic pregnancy. Pain does not strongly correlate with miscarriage, but is a common symptom of ectopic pregnancy.[19] In the case of concerning blood loss, pain, or both, transvaginal ultrasound is performed. If a viable intrauterine pregnancy is not found with ultrasound, serial βHCG tests should be performed to rule out ectopic pregnancy, which is a life-threatening situation.[20][21]

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 should 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:

  • With no treatment (watchful waiting), most of these cases (65-80%) will pass naturally within two to six weeks.[22] This path avoids the side effects and complications possible from medications and surgery.[23]
  • Medical management usually consists of using misoprostol (a prostaglandin, brand name Cytotec) to encourage completion of the miscarriage. About 95% of cases treated with misoprostol will complete within a few days.[22]
  • Surgical treatment (most commonly dilation and curettage, or D&C) is the fastest way to complete the miscarriage. It also shortens the duration and heaviness of bleeding, and is the best treatment for physical pain associated with the miscarriage.[22] In cases of repeated miscarriage or later-term pregnancy loss, D&C is also the best way to obtain tissue samples for pathology examination.


When looking for gross or microscopic pathologic symptoms of miscarriage, one looks for the products of conception. Microscopically, these include villi, trophoblast, fetal parts, and background gestational changes in the endometrium. Genetic tests may also be performed to look for abnormal chromosome arrangements.

ICD10 codes

  • Habitual abortion
  • Incomplete abortion
  • Missed abortion
  • Threatened abortion


See also


  1. 1.0 1.1 1.2 Venners S, Wang X, Chen C, Wang L, Chen D, Guang W, Huang A, Ryan L, O'Connor J, Lasley B, Overstreet J, Wilcox A, Xu X (2004). Paternal smoking and pregnancy loss: a prospective study using a biomarker of pregnancy.. Am J Epidemiol 159 (10): 993-1001. PMID 15128612.
  2. What is a chemical pregnancy?. Baby Hopes. URL accessed on 2007-04-27.
  3. Hutchon D, Cooper S (1998). Terminology for early pregnancy loss must be changed. BMJ 317 (7165): 1081.
    Hutchon D (1998). Understanding miscarriage or insensitive abortion: time for more defined terminology?. Am. J. Obstet. Gynecol. 179 (2): 397-8.
  4. Patricia Lee June (November 2001). "A Pediatrician Looks at Babies Late in Pregnancy and Late Term Abortion". Presbyterians Pro-Life. Retrieved on 2006-12-24.
  5. MedlinePlus. Abortion - incomplete. Medical Encyclopedia. URL accessed on 2006-05-24.
  6. Royal College of Obstetricians and Gynaecologists (May 2003). The Investigation and Treatment of Couple with Recurrent Miscarriage. Guideline No 17.
  7. 7.0 7.1 Rosenthal, M. Sara The Second Trimester. The Gynecological Sourcebook. WebMD. URL accessed on 2006-12-18.
  8. 8.0 8.1 8.2 8.3 8.4 8.5 Miscarriage: Causes of Miscarriage. Physician's Desk Reference Family Guide to Women's Health. URL accessed on 2006-12-18.
  9. Pregnancy Over Age 30. MUSC Children's Hospital. URL accessed on 2006-12-18.
  10. Peng H, Levitin-Smith M, Rochelson B, Kahn E. Umbilical cord stricture and overcoiling are common causes of fetal demise.. Pediatr Dev Pathol 9 (1): 14-9. PMID 16808633.
  11. 11.0 11.1 Ness R, Grisso J, Hirschinger N, Markovic N, Shaw L, Day N, Kline J (1999). Cocaine and tobacco use and the risk of spontaneous abortion.. N Engl J Med 340 (5): 333-9. PMID 9929522.
  12. 12.0 12.1 Everett C (1997). Incidence and outcome of bleeding before the 20th week of pregnancy: prospective study from general practice.. BMJ 315 (7099): 32-4. PMID 9233324.
  13. Wilcox AJ, Baird DD, Weinberg CR (1999). Time of implantation of the conceptus and loss of pregnancy.. New England Journal of Medicine 340 (23): 1796-1799. PMID 10362823.
  14. 14.0 14.1 Wang X, Chen C, Wang L, Chen D, Guang W, French J (2003). Conception, early pregnancy loss, and time to clinical pregnancy: a population-based prospective study.. Fertil Steril 79 (3): 577-84. PMID 12620443.
  15. Q&A: Miscarriage. (August 6 , 2002). BBC News. Retrieved January 17, 2007. Also see Lennart Nilsson, A Child is Born 91 (1990)(At eight weeks, "the danger of a miscarriage . . . diminishes sharply.")
  16. Kleinhaus K, Perrin M, Friedlander Y, Paltiel O, Malaspina D, Harlap S (2006). Paternal age and spontaneous abortion. Obstet Gynecol 108 (2): 369-77. PMID 16880308.
  17. Slama R, Bouyer J, Windham G, Fenster L, Werwatz A, Swan S (2005). Influence of paternal age on the risk of spontaneous abortion.. Am J Epidemiol 161 (9): 816-23. PMID 15840613.
  18. Nybo Andersen A, Wohlfahrt J, Christens P, Olsen J, Melbye M (2000). Maternal age and fetal loss: population based register linkage study. BMJ 320 (7251): 1708-12. PMID 10864550.
  19. 19.0 19.1 19.2 Gracia C, Sammel M, Chittams J, Hummel A, Shaunik A, Barnhart K (2005). Risk factors for spontaneous abortion in early symptomatic first-trimester pregnancies. Obstet Gynecol 106 (5 Pt 1): 993-9. PMID 16260517.
  20. Yip S, Sahota D, Cheung L, Lam P, Haines C, Chung T (2003). Accuracy of clinical diagnostic methods of threatened abortion. Gynecol Obstet Invest 56 (1): 38-42. PMID 12876423.
  21. Condous G, Okaro E, Khalid A, Bourne T (2005). Do we need to follow up complete miscarriages with serum human chorionic gonadotrophin levels?. BJOG 112 (6): 827-9. PMID 15924545.
  22. 22.0 22.1 22.2 Kripke C (2006). Expectant management vs. surgical treatment for miscarriage. Am Fam Physician 74 (7): 1125-6. PMID 17039747.
  23. Tang O, Ho P (2006). The use of misoprostol for early pregnancy failure.. Curr Opin Obstet Gynecol 18 (6): 581-6. PMID 17099326.

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