Spontaneous abortion or miscarriage is the spontaneous termination of pregnancy before 20 weeks of gestation or delivery of a fetus weighing 500 grams or less (a non-viable fetus). Spontaneous abortion encompasses threatened, incomplete, inevitable, complete, missed and septic abortions and is the most common cause of vaginal bleeding in the first trimester (first 12 weeks) of pregnancy.
It is estimated that more than 20% of pregnancies terminate in spontaneous abortion but the figures may actually be much higher since many early miscarriages are undiagnosed and are taken as unusually heavy periods. A miscarriage occurring before 12 weeks of pregnancy is known as early abortion, while one occurring between 12 and 20 weeks of pregnancy is called late abortion.
The terms threatened, inevitable, incomplete and complete abortion may be taken as four stages of spontaneous abortion or miscarriage, where one stage may progress into the other.
Types of Abortion
In threatened abortion, the pregnancy may be at risk of being terminated but in more than half the cases, the pregnancy can be saved. It is most common in the first trimester of pregnancy and usually presents as vaginal bleeding in early pregnancy with little or no pain, although slight abdominal cramping may be present.
There is no cervical dilatation and the most significant finding on examination is a closed cervical os (opening of the cervix). Ultrasonography may show a continuing intrauterine pregnancy. A threatened abortion needs to be differentiated from an ectopic pregnancy (a more dangerous situation) by assessing the beta-human chorionic gonadotropin level (Quantitative HCG Blood Test) in conjunction with the ultrasonography report.
In this case, conditions are such that the pregnancy cannot be saved. In addition to vaginal bleeding in early pregnancy (which may be more severe than that seen in threatened abortion), low back pain and severe abdominal cramps are more likely to be present. There is cervical dilatation and on examination the os is found to be open, with or without protrusion of the products of conception (fetal tissue, placenta and membranes). Ultrasonography may show the products of conception in the lower uterine segment or the cervical canal.
In an incomplete abortion, there is usually persistent and severe vaginal bleeding with abdominal cramps. Some, though not all, of the products of conception are expelled from the uterus through the dilated cervix. Some of the tissues may be seen in the vagina during examination or the patient may give a history of passing some products. Ultrasonography will confirm the presence of some products of conception still retained within the uterus.
In a complete abortion, all the products of conception have been expelled from the uterus. In the initial stage of the abortion or miscarriage, there is severe abdominal pain and vaginal bleeding, but after the passage of all the products, the pain and bleeding diminishes. On examination, the os will be found to be closed. Ultrasonography will show an empty uterus.
This is a type of abortion where the fetus is dead but the products of conception are retained within the uterus. There may be no symptoms at all or a brownish vaginal discharge or brown vaginal bleeding may occasionally be seen. Pain is unlikely and os will be closed.
Since no symptoms may be present, the patient is usually unaware that a miscarriage has occurred. Loss of pregnancy symptoms following a period of amenorrhea (cessation of periods), a decrease in size of the uterus, or inability to detect a fetal heart beat at the expected stage of pregnancy may raise a suspicion of missed abortion, which can be confirmed by ultrasonography.
Septic or Infected Abortion
Infection within the uterus or the products of conception (usually a bacterial infection) may occur if any tissue from the placenta or fetus remains in the uterus after an abortion. Fever, chills, foul-smelling vaginal discharge, persistent vaginal bleeding, abdominal cramping, and pelvic pain or discomfort are common findings.
Recurrent or Habitual Abortion
Sometimes, a woman may have miscarriages in successive pregnancies. When three consecutive pregnancies end in spontaneous abortion, it is known as habitual or recurrent abortion.