Miscarriage 101

Miscarriage 101

A miscarriage, or spontaneous abortion, is a pregnancy that ends by itself within the first 20 weeks, usually because the pregnancy is not developing normally. A baby is considered stillborn when it dies after the first 20 weeks. Experts estimate that about half of all fertilized eggs die and are miscarried, usually even before the woman knows she is pregnant.

Of pregnancies that the mother knows about (because she has missed her period or her pregnancy has been confirmed by a health-care provider,or both), approximately 10 percent to 20 percent end in miscarriage, making miscarriage very common. In most cases, miscarriage may be considered a natural-selection process because it is the ending of a pregnancy that would not have developed into a healthy baby. In fact, often in cases of miscarriage only placental tissue, not a fetus, had formed.

Miscarriage is usually a single occurrence, and often followed by successful pregnancy. Recurrent miscarriage is defined as the loss of three or more consecutive pregnancies. Even after 3 consecutive losses, the chance of a successful pregnancy is over 60%.

Risk Factors

The majority of miscarriages happen during the first 12 weeks of pregnancy. Miscarriages are more common in women who are older than 35 or who are carrying multiple fetuses.

Patients over 40 may have a miscarriage rate as high as 50%. Miscarriage rates for 40-year-old women are about twice that for 20-year-old women. There are numerous risk factors for miscarriage. Your risk rises if you have had a miscarriage in the past, if you have had a stillbirth between the fourth and eighth months of pregnancy, if you have had preterm labor in an earlier pregnancy, or if you have had difficulty conceiving.

Basically, there are several main reasons why women miscarry.


Fetal chromosomal abnormalities are the commonest cause of sporadic miscarriage. Fetal chromosomal abnormalities are the most common cause of miscarriage, affecting more than half of all early miscarriages. This may be due to abnormalities in the egg, sperm or both. The most common chromosomal defects are:


There are several uterine problems that may result in miscarriages. These include a misshapen uterus, fibroids, cervical impotence and adhesions. These need to be treated before a pregnancy would succeed. With an abnormally shaped uterus, the uterus may not enlarge enough to accommodate the pregnancy. The miscarriage often occurs in the second trimester, but early losses may occur as well. Uterine abnormalities are present from birth and include a septate uterus (a uterus divided by a wall) and double uterus.

Fibroids sometimes distort the uterine cavity and prevent pregnancy from implanting properly. During pregnancy, the cervix (neck of the womb) should remain closed until labor begins. Cervical incompetence is where, in some women, the cervix is weak and starts to open up quite painlessly with subsequent spontaneous rupture of membranes and expulsion of the fetus. Miscarriage caused by cervical incompetence is usually late in pregnancy, often after 16 weeks. This weakness of the cervix may be an inborn fault, or a result of a previous surgery such as cone biopsy, or previous childbirth.

Adhesions inside the womb cavity may not only cause infertility but may also be associated with miscarriage possibly by restricting the implantation and growth of the fetus.

Infective factors

Any severe maternal infection can cause sporadic miscarriage. An infection, such as rubella or toxoplasmosis, during pregnancy increases your risk of miscarriage, as does a fever higher than 100 degrees Fahrenheit.

Hormonal problems

Several different problems may fall in this category including low progesterone levels, high LH levels, or thyroid abnormalities. If too little progesterone is produced by the corpus luteum, the endometrium may not develop adequately to sustain the pregnancy. However, low progesterone levels in early pregnancy usually reflects a pregnancy that has already failed. Many physicians regularly give progesterone supplementation after fertility treatments and/or in early pregnancy as a type of -insurance.°

Elevated levels of luteinizing hormone(LH) is common in women with PCOS. High LH affects the quality of the eggs and hence the embryos, and may result in recurrent early miscarriages. Thyroid abnormalities may also cause miscarriage. Systemic maternal endocrine disorders such as diabetes mellitus and thyroid disease have been associated with miscarriage. However, when they are well-treated, there appear to far fewer risks.


As much as 40 percent of unexplained infertility may be the result of immune problems, as are as many as 80 percent of "unexplained" pregnancy losses. Unfortunately for couples with immunological problems, their chances of recurrent loss increase with each successive pregnancy. INCIID( http://www.inciid.org ) offers additional information on the types and treatments of immune problems. After two or more pregnancy losses, the full range of Autoimmune and Alloimmune Risk Tests should be considered, although they cost about $1,300.

Unexplained miscarriage

In a majority of women, the pregnancy loss will remain unexplained . New research, however, indicates that as many as 80 percent of "unexplained" losses may the attributable to immunological factors-and some new therapies are enabling up to 80 percent of those affected to carry a baby to term. Only after three or more miscarriages, will physicians carefully investigate possible causes. Any substance that result in toxicity in a pregnant woman may be implicated in miscarriage including, radiation, some insecticides,lead, toxic chemicals, smoking and alcohol.


In most cases, neither a woman nor her doctor can do anything to prevent a miscarriage. The best way to prevent a miscarriage is for both partners to be as healthy as possible before you conceive (avoid drugs, alcohol, chemicals, etc) and to get any other medical conditions under control.

However, if you think you may be having a miscarriage, it is important to contact your doctor. He or she may be able to determine that your pregnancy is proceeding normally, detect other pregnancy problems (such as a tubal pregnancy), or prevent miscarriage complications (such as heavy bleeding).

Journal Articles:

Stirrat G M. Recurrent miscarriage: definition and epidemiology. Lancet 1990; 336:673-5.
Regan L, Braude P B. Trembath P R. Influence of past reproductive performance on risk of spontaneous abortion. BMJ 1989; 299:541-5.

Alberman E. The epidemiology of repeated abortion. In: Beard R W. Sharp F. editors. Early pregnancy loss: mechanisms and treatment. London: RCOG Press; 1988; 9-17.

Rai R. Clifford K, Regan L. The modern preventative treatment of recurrent miscarriage. Br J Obstet Gynaecol 1996; 103: 106-10.

Clifford K, Rai, R. Watson H. Regan L. An informative protocol for the investigation of recurrent miscarriage: preliminary experience of 500 consecutive cases. Hum Reprod 1994; 9:1328-32.

Additional resources on internet:

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Thank you for drawing attention regarding the picture that was being used earlier. I just changed it. Webmaster.

The graphic of a broken egg with a dead baby painted on it is a terrible way to portray miscarriage. Thank you for the information on miscarriage, but please change that horrible picture.

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