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What is actually meant by miscarriage?

| Part 2 of our topic series »Trying to conceive after a miscarriage«

[← article overview of the topic-series »Trying to conceive after a miscarriage«]

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If a pregnancy cannot be brought to term but instead ends in spontaneous abortion or miscarriage, this could be a devastating experience, especially for those couples who had long been trying in vain to get pregnant and have decided to finally undergo fertility treatment. In order to be able to cope with this traumatic event and find out what exactly happened, a sound medical explanation or diagnosis could be very helpful. The prerequisite for this, however, is the clear determination of the gestational age at the time of miscarriage and the type of pregnancy loss.

In general, spontaneous abortion or miscarriage refers to any pregnancy loss before 20-24 weeks of gestation. A distinction is made between early abortion and late abortion. In addition to this, a blighted ovum, also known as anembryonic pregnancy or an ectopic pregnancy may occur.

Types of pregnancy loss (miscarriage/spontaneous abortion) and their definition

  • Spontaneous abortion or miscarriage
  • Spontaneous abortion or miscarriage refers to any pregnancy loss before 20-24 weeks of pregnancy (depending on the definition).

  • Early abortion
  • This refers to the loss of pregnancy (depending on the definition) within the first 10-12 weeks of gestation (chemical pregnancy diagnosed by serum ß-hCG).

  • Late abortion
  • This refers to the spontaneous termination of pregnancy (depending on the definition) after the first trimester (10-12 weeks pregnant) but before 20-24 weeks (confirmed ultrasonically or histologically).

  • Blighted ovum
  • A fertilized egg implants into the uterus but the embryo does not develop (anembryonic pregnancy). The embryonic (gestational) sac can be detected via ultrasound, but it remains empty. A blighted ovum leads to spontaneous abortion, typically up to the 12th week of pregnancy.

  • Ectopic pregnancy
  • Ectopic pregnancy is when a pregnancy grows outside of the uterine cavity. In about 95% of cases, the embryo implants in one of the fallopian tubes. In very rare cases, implantation can also occur within the abdomen, on the ovaries or the cervix. Ectopic pregnancy can be life-threatening for the mother, if left untreated.

The risk of miscarriage increases with age

The risk of miscarriage clearly increases with advanced maternal age. However, as a general rule, the following shall apply: The more advanced the pregnancy, the lower is the risk of miscarriage. Thus, after ultrasound documentation of fetal cardiac activity, the risk of spontaneous abortion is on average at about 10%. As from the 15th week of pregnancy, the risk amounts to only 1-3%. The risk level decreases gradually from one week to the next.

On the other hand, the risk of spontaneous abortion ranges from 15-20%. Over 80% of miscarriages occur before 12 weeks and must therefore be classified as early abortion.

Different causes for miscarriage require an individual analysis

Experts assume that about one third of all embryos do not implant in the first place. An additional one-third does not develop any further (or does not develop properly) during the first implantation phase. So far, the exact causes are still not known completely.

According to estimates, more than 50% of miscarriages can, however, be associated to the maldistribution of chromosomes in the embryo, thus affecting subsequent embryonic development. This phenomenon is also in line with an age-related increase in the number of chromosomal abnormalities in the oocytes and a higher probability of miscarriage.

Sometimes it also happens that a blastocyst (embryo capable of implantation) attaches itself to the uterine wall, but only the trophoblast (outer cell layer covering the blastocyst) continues to grow. Usually, an empty gestational sac without yolk sac and embryo is visible on ultrasound. This is referred to as a blighted ovum or anembryonic pregnancy.

Implantation problems of the embryo may also result in miscarriage. Actually, many of these miscarriages go unnoticed.

In summary: The treating doctor should look at the couple’s medical situation, analyze it in order to determine personalized fertility treatment tailored to the needs of the couple and/or to mutually consider follow-up investigations (e.g. genetics).

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