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Specialties : Obstetrics & Gynecology : Spontaneous Abortion (Miscarriage)
Spontaneous Abortion (Miscarriage)

A spontaneous abortion means that a pregnancy is lost naturally before the baby reaches a point of development where the fetus (baby) can survive. This typically means any pregnancy lost before 23 weeks.

Spontaneous abortion and miscarriage mean the same thing. Spontaneous abortion has nothing to do with the usual topic of abortion (also called a medical abortion, therapeutic abortion or voluntary interruption of pregnancy) that is often discussed in our society.

Incidence Signs and Symptoms
Common Causes Diagnosis and Treatment
Rare Causes After a Spontaneous Abortion

Doctors classify spontaneous abortions (miscarriages) into different categories. This helps doctors communicate about the circumstances of a patient's situation.

  • A complete spontaneous abortion means that all pregnancy tissue, the fetus (baby), placenta (after-birth), and membranes (sac), has passed out of the uterus.
  • An incomplete spontaneous abortion means that some of the pregnancy tissue has passed out of the uterus, but some of the tissue has remained inside of the uterus. An inevitable spontaneous abortion means that a miscarriage is happening or is going to happen, but the pregnancy tissue is still inside of the uterus.
  • A threatened spontaneous abortion simply means a patient has signs and/or symptoms of a possible miscarriage. It does not mean that a miscarriage will definitely happen. A blighted ovum and empty sac generally mean the same thing. The placenta and a pregnancy sac can be seen on ultrasound, but a fetus cannot be seen. This occurs because a fetus never formed.

Recurrent spontaneous abortion means that a woman miscarries three or more times.


Most spontaneous abortions occur in the first 14 weeks of the pregnancy. In fact, 15 percent to 20 percent of all first trimester pregnancies will miscarry. The earlier a patient is in the pregnancy, the greater the chance of a miscarriage. Studies have shown that only 50 percent of pregnancies will be successful. This means it is very possible to have a positive pregnancy test before it is time to have your period and yet your period occurs like it should (or it is only a few days late). The chance of a spontaneous abortion is less if the fetus has a heart beat after the tenth week of the pregnancy. The chance of a miscarriage is much less between 14 and 23 weeks of a pregnancy.

Common Causes

Chromosome Problems: The most common reason pregnancies miscarry is because the fetus has abnormal chromosomes. Chromosome problems typically do not allow the fetus to develop (form) normally. Abnormal development means the fetus cannot survive. A miscarriage occurs because the body recognizes that a pregnancy is not successful. It is nature's way of assuring we develop normally.

Abnormal Physical Development: Even if the chromosomes are normal, a fetus may not develop normally. Many things have to occur for normal development to occur. A message has to be created. The message has to be sent and received. Finally, the message has to be acted on. A mistake at any point can lead to abnormal development. We usually do not know if the fetus developed abnormally, because the fetus is too tiny. We do know that this stage of development is beyond our control in the vast majority of cases. There is rarely anything a person does that causes abnormal development and there is nothing a person can do to prevent abnormal development.

Abnormal Placental Development: Sometimes the problem occurs with the placenta. The placenta may not attach to the uterine lining like it should. At other times, the cells of the placenta do not form like they should. Eventually, the fetus is not able to receive the oxygen and nutrients (food) it needs. This means the fetus cannot survive. Once again, there is rarely anything a person does that causes a placenta to develop abnormally.

Rare Causes

Medications and Other Substances: There are very few medications that will affect the development of a fetus, the chromosomes or the placenta. This is also true of most things a person eats or drinks. If a woman becomes pregnant while she is using birth control pills, she is not at risk of a miscarriage. There are a few medicines and substances that can affect the pregnancy. It has been shown that spontaneous abortion is more likely in women who smoke. The use of alcohol and illegal drugs also increase the chance of miscarriage.

Infections: On rare occasions, an infection with certain viruses or bacteria can cause the fetus to develop abnormally and /or the pregnancy to miscarry.

Diseases of the Mother: Some conditions that a person develops can increase the chance of a miscarriage. Such diseases include diabetes, thyroid disease, systemic lupus and other autoimmune diseases.

Uterine Problems: Some women are born with a uterus that did not develop normally. There can be tissue inside the uterus that divides the cavity of the uterus. At other times, a benign tumor called a fibroid or leiomyoma can form in the uterus. These can occasionally interfere with implantation of the egg or development of the pregnancy and it makes a miscarriage more likely.

Abnormal Chromosomes in the Parents: It is possible for a person to have abnormal chromosomes (genes), yet they develop normally. All of the person's chromosome material is present, but it has been rearranged. The rearranged chromosome material means that a person's eggs or sperm will not have normal amounts of chromosome material. This leads to abnormal development of the fetus.

Abnormal Hormone Levels in the Mother: Hormones in the mother help support an early pregnancy until the pregnancy can support itself. On rare occasions, a mother does not produce enough of the hormones that are needed.

Autoimmune Disorders: Antibodies are proteins we make that help fight off infection. It is possible for a person to develop antibodies that fight (attack) their own tissue. This can sometimes occur in pregnancy. A mother's antibodies can interfere with blood flow in the uterus or they can attack the cells of the placenta. Eventually, the fetus cannot get enough oxygen to survive.

Signs and Symptoms

The most common sign of a miscarriage is vaginal bleeding. This will often start as spotting. The bleeding will continue and it will get heavier. Most women who have spotting or light bleeding in pregnancy will have normal pregnancies and normal babies.

The most common symptom is cramping. The cramping of a miscarriage can start off mild, but it will become worse over time. As with bleeding, most mild cramping in pregnancy is normal. Mild cramping can be due to the uterus growing or it can be due to the bladder or the bowel.

Some women will notice they no longer have morning sickness or that their breasts are no longer tender. However, it is totally normal for morning sickness and breast tenderness to go away.

A pregnancy usually does not miscarry if any sign or symptom is mild and/or if it does not continue. For example, spotting that occurs once and then goes away is usually not a sign of miscarriage. Spotting that becomes bleeding and cramps that are getting worse indicate that a miscarriage may happen. You should notify your doctor if you experience vaginal bleeding and cramping. If you should pass tissue at home, place the tissue in a container (if possible). Your doctor may want to examine the tissue.

Diagnosis and Treatment

The diagnosis of a miscarriage is usually made by a combination of your physical exam, ultrasound findings and by measuring your human chorionic gonadotropin (HCG, pregnancy hormone) level. On examination, there will be blood coming from the cervix and the cervix may be opening up. Your uterus may be smaller than it should be. This is because the pregnancy stopped growing weeks before your signs and symptoms occurred. The ultrasound will show that there is no fetus or that the fetus no longer has a heart beat. The ultrasound may also show bleeding between the placenta and the wall of the uterus. The pregnancy hormone level will not increase as it should, it will not increase at all, or it will be falling.

If the pregnancy appears to be fine, you may be asked to stay off your feet for a day or two and to avoid sex. This will not prevent a miscarriage, but it may help decrease spotting and/or cramping. If the pregnancy is not successful and the pregnancy is less than 14 weeks, you will be told what to expect during a miscarriage. A spontaneous abortion can be treated by allowing the miscarriage to occur naturally or by performing a surgical procedure known as a D&C (dilatation and curettage). A D&C is performed by passing smooth metal rods through the cervix (birth canal) to open it up. A plastic tube is then placed into the uterus and gentle suction is used to remove the pregnancy tissue. This procedure can be performed using medicines to cause sedation, regional nerve blocks, or general anesthesia (going to sleep). Risks of a D&C include infection, putting a hole in the uterus (uterine perforation), and side effects of medications. Risks of a natural miscarriage include excess bleeding and infection.

A very early unsuccessful pregnancy (4-7 weeks) is often best treated by allowing the miscarriage to occur naturally. Miscarriages that occur at 8-14 weeks are often best treated by a D&C. Miscarriages that occur 14-23 weeks are managed in the hospital similar to other delivery situations. Other factors to consider are the amount of bleeding, pain, risks of infection and risks associated with a D&C. If you are Rh negative, you will receive a shot of Rhogam to prevent you from forming antibodies that attack a baby's red blood cells. Your doctor will help you decide which treatment is best for you.

After a Spontaneous Abortion

After a first trimester miscarriage, you may want to take it easy for a day or two. You should avoid sex for at least two weeks and you should not have sex until you stop bleeding. You should not use tampons until your next normal period. Your doctor may prescribe medicine for cramping or you may use over the counter ibuprofen or naproxen sodium. Your doctor may want to see you in a few weeks or in six to eight weeks depending on your circumstances. You can expect a normal period in four to eight weeks.

You will need birth control if you do not intend to get pregnant. If this is not your first miscarriage, your doctor may order lab work to see if one of the rare causes of recurrent spontaneous abortion is present. If you experience a miscarriage at 14-23 weeks, it is a good idea to give yourself a week to recover. You may experience leaking from your breasts. You should wait a couple of weeks before exercising heavily. You should also talk to your doctor before trying to get pregnant again. It is important to remember that grieving is common after any pregnancy loss. You may experience mild depression, mood swings, anger or anxiety. This can also be true for your spouse or your partner. If you experience difficulty during your grieving process, you should talk to a professional counselor and/or your doctor.

Finally, it is important to remember there is nothing anyone does to cause a miscarriage in the vast majority of cases. Miscarriage does not happen due to lifting, exercise, sex or stress. In rare cases, spontaneous abortions can happen repeatedly. These cases can be diagnosed and there is treatment available for many of these women. Miscarriage is a natural process of cleaning out the uterus and preparing the woman for a normal pregnancy.

Ferrell-Duncan Clinic, Springfield, Missouri | (417) 875-3000