A3. Classification of abortions, etiology, therapy options

Page created on November 22, 2021. Last updated on January 17, 2022 at 18:18

An abortion is the termination of a pregnancy before a life birth is possible (< 24th week of gestation). We distinguish spontaneous (uninduced) and induced abortions. Some use the term “abortion” to refer to induced abortions only, while leaving the term “miscarriage” for spontaneous abortion.

Transvaginal ultrasound is essential in evaluating these conditions, as the foetus is too small to be visualised with transabdominal ultrasound.

Spontaneous abortion

Spontaneous abortion usually occurs before week 12. It occurs 50% more commonly in male foetuses than female.

Spontaneous abortions are unfortunately not uncommon. 31% of pregnancies are lost, but many times it’s clinically silent, meaning that there are no clinical signs of the pregnancy ever existing. They are more common in older women.

If a couple has experienced multiple spontaneous abortions an underlying etiology should be sought. Unfortunately, in up to 30% of cases the cause is not found or an irreversible cause is found.


The majority of single spontaneous abortions occur due to foetal chromosomal abnormalities, especially abnormalities of the number of chromosomes. However, recurrent abortions are mostly due to maternal factors.

  • Foetal factors
    • Chromosomal abnormalities (especially of the number of chromosomes)
  • Maternal factors
    • Infection (bacterial vaginosis, chorioamnionitis)
    • Parental chromosomal abnormalities
    • Endocrine disorders (DM, PCOS)
    • Uterine malformations or defects
    • Immunological diseases (antiphospholipid syndrome, etc.)
    • Thrombophilia
    • Cervical incompetence
    • Environmental factors (tobacco, alcohol, caffeine, radiation)


Haemorrhage into the decidua causes adjacent tissue necrosis. This causes the embryo to detach, which stimulates uterine contractions, causing the gestational sac and all its contents to be rejected.

In case of spontaneous abortion at early gestational ages, the foetus dies before the rejection. However, spontaneous abortion occurring at later gestational ages may be accompanied by the foetus not dying before the rejection.


We can distinguish multiple clinical scenarios (“types”) of spontaneous abortion.

A threatened abortion is a situation where abortion may occur in the future. The patient experiences vaginal bleeding and abdominal pain, but the cervical os is closed and there is still foetal heart activity. We can try to administer progesterone and administer drugs which inhibit uterine contractions (drotaverine, magnesium). Unfortunately, no known management options decrease the risk of abortion. However, in most cases the pregnancy continues as normal.

An inevitable abortion is a situation where abortion definitely will occur, due to the membranes having ruptured and so the situation is no longer liveable for the foetus. Infection may occur. The uterus must be manually evacuated (see topic B13 for how).

A missed abortion is a situation where the foetus has died, but no parts of the foetus have been expelled. The cervical os is still closed, and ultrasound shows a gestational sac with contents but no foetal heart activity. The uterus must be manually evacuated.

An incomplete abortion is a situation where abortion has occurred, and some parts have been expelled but not all. The uterus must be manually evacuated.

A complete abortion is a situation where abortion has occurred, and the uterus has evacuated itself completely. The uterus is empty on ultrasonography. No manual evacuation is necessary.

Induced abortion

Pregnancy may be terminated at the woman’s will, although the exact terms for who this is possible for and when this can occur varies wildly from country to country. Induced abortion is covered in topic B13.

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