Miscarriage is defined as the loss of a pregnancy before 24 weeks of gestation. It is a common event, affecting up to 20% of all pregnancies. In the majority of cases, no cause for the miscarriage is discovered; it is believed, however, that most first-trimester miscarriages are secondary to chromosomal abnormalities. The risk of miscarriage increases with age, lifestyle factors such as smoking and some maternal disease such as diabetes.

There are several different types of miscarriage, which can be classified based on the stage of pregnancy at which they occur and how they present. The definitions and details surrounding these different types of miscarriage are commonly encountered in both undergraduate and postgraduate medical exams.

Threatened miscarriage

This is the most common type of miscarriage and occurs when there is bleeding in the first trimester of pregnancy, but no products of conception have been passed, and the cervical os is closed.

The features of a threatened miscarriage include:

  • Vaginal bleeding (often brown discharge or spotting)
  • Minimal abdominal pain
  • No products of conception passed
  • Cervical os closed
  • Pregnancy test positive

In most cases, the pregnancy continues to term, but in some cases, it may progress to a more serious type of miscarriage. Stable patients more than six weeks pregnant with bleeding in early pregnancy without features suggestive of an ectopic pregnancy are usually followed-up in an early pregnancy assessment unit (EPAU).

Inevitable miscarriage

A threatened miscarriage progresses to become an inevitable miscarriage if cervical dilatation occurs. The pain and bleeding are generally more severe, and the cervical os will be found to be open on examination.

Many women with an inevitable miscarriage are managed by ‘expectant management’, where the miscarriage is expected to happen naturally without any intervention. This approach is sometimes referred to as ‘watchful waiting’. It may be recommended for women who are experiencing an inevitable miscarriage but who are not experiencing any complications such as infection or heavy bleeding. During expectant management, the woman will be monitored closely for signs of infection, heavy bleeding, or other complications.

In some cases, for example, where there is heavy bleeding, medical or surgical intervention may be required. It may be appropriate to give drugs such as ergometrine, syntometrine or misoprostol or even perform an emergency surgical evacuation of retained products of conception (ERPC).

Incomplete miscarriage

An incomplete miscarriage occurs when a miscarriage has happened, but the products of conception have not been completely lost from the uterus. This most commonly occurs between weeks 8 and 14 gestation.

Pain and bleeding are commonly present, and the cervical os is typically open. The diagnosis is confirmed by ultrasound scan that will reveal an absent foetal heartbeat and retained products. Incomplete miscarriages can be managed medically (e.g. misoprostol treatment) or surgically (e.g. ERPC).

Potential complications of an incomplete miscarriage include:

  • Endometritis
  • Myometritis
  • Septic shock
  • Disseminated intravascular coagulation (DIC)

Complete miscarriage

This type of miscarriage occurs when all of the pregnancy tissues have been passed out of the uterus. It is characterised by vaginal bleeding, cramping, and the passage of blood clots and pregnancy tissues. This type of miscarriage is usually not associated with any long-term complications.

Missed miscarriage

This type of miscarriage occurs when the pregnancy has stopped growing but the woman does not experience any symptoms of miscarriage. The pregnancy may have stopped growing weeks or even months before it is diagnosed.

This type of miscarriage is usually diagnosed by ultrasound, which shows an empty gestational sac. Treatment may include observation, medical management, or surgical evacuation of the remaining pregnancy tissues.

Recurrent miscarriage

This is defined as three or more consecutive pregnancy losses before the 20th week of gestation. Recurrent miscarriage is usually associated with underlying medical or genetic factors that need to be addressed before attempting another pregnancy. Miscarriage is not labelled as ‘recurrent’ unless two consecutive miscarriages occur with the same partner.

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