Any spontaneous pregnancy loss during the first 20 weeks of pregnancy is considered a miscarriage. Once such a spontaneous pregnancy loss occurs after 20 weeks of gestation, it is considered an intrauterine demise.

Miscarriages can take various forms and have various names attached to them, such as:

Chemical Pregnancy

A chemical pregnancy and miscarriage is a very early pregnancy loss, characterised by a positive pregnancy test (hCG-level) that is not maintained. This type of pregnancy never reaches the stage where a gestational sac is seen on ultrasound examination. Most chemical pregnancies are not recognised, since most women do not have very early pregnancy tests performed. With infertility treatment we diagnose these very early pregnancy losses quite universally because every treatment cycle is followed by a very early pregnancy test.

Clinical Pregnancy

In contrast, a gestational sac seen on ultrasound examination characterises a so-called ‘clinical pregnancy’. The miscarriage of a clinical pregnancy can take place either before, or after, the pregnancy was demonstrated (usually by ultrasound) to show a fetal heart rate. In a normal pregnancy, a fetal heart should be demonstrable between 5.5 to 6 weeks from the first day of the last menstrual period. If a pregnancy stops growing before that time, or if no fetal heart is seen by the expected time, then the pregnancy is generally considered to be a ‘blighted ovum’ or ‘missed abortion’.


In an unselected population of women, the average miscarriage rate is actually not that high. Roughly 15% of all pregnancies are lost at various stages. Patients with fertility problems can have a much higher miscarriage risk. Their risk can be higher for a variety of reasons, the most obvious of which is that women with fertility problems are older than average. Miscarriage risks increase with advancing female age due to a higher risk of chromosomal problems with the embryo. Indeed, once a woman reaches the age of 42 years, her risk of miscarriage reaches 50%. As she ages, that risk increases even further.

The reason for this increasing miscarriage rate with advancing age lies in the fact that approximately 85% of all miscarriages that occur are due to genetic (i.e. chromosomal) abnormalities. Such chromosomal abnormalities increase with advancing female age.


We have already mentioned that around 85% of all pregnancy loss is genetic (or chromosomal) in nature. This leaves 15% due to other causes. Of this group, most are attributed to uterine abnormalities, general medical (ill health) or immunological (e.g. Lupus anticoagulant) causes.

Uterine abnormalities, especially fibroids, are clearly associated with an increased miscarriage risk. Certain congenital uterine abnormalities such as ‘septae’ can also be responsible. If correctly diagnosed, these problems can be treated often with minor surgery.

Medical conditions, such as diabetes mellitus, thrombophilias and thyroid disease, have been associated with increased miscarriage rates. In diabetics, this risk can be normalised if the patient’s blood sugar levels are well controlled. The risk with thyroid disease is more difficult to define.

Autoimmune disease (Antiphospholipid Antibody Syndrome) is well documented in its relation to miscarriage and treatment is available. Since miscarriages occur relatively frequently, and since immunological causes are, in an unselected patient population, relatively rare, the suspicion of immunological pregnancy loss is usually alerted by either a relevant medical history (personal, or familial), or by repeated (or habitual) pregnancy loss. Habitual pregnancy loss is used to describe the occurrence of three consecutive first-trimester losses, or two, with one in the second trimester.


The later a pregnancy loss occurs the less likely it is the pregnancy loss is genetic in nature and the more likely is it medically induced. Most medically induced pregnancy loss is immunological in nature. The same also applies to a diagnosis of multiple losses. The more miscarriages a woman has experienced, the more likely her losses are medical in nature and the less likely they are of genetic or chromosomal origin (except for a genetic condition called a translocation, which also can cause multiple, repeated miscarriages).

A history of habitual miscarriages (3 or more) should always raise the suspicion of an immunological cause for pregnancy loss. Such a suspicion should also arise if the patient or close family members report a history of autoimmune diseases or relevant symptomatology, like joint pains, unexplained rashes, etc.


One of the reasons immunological pregnancy loss has remained a controversial and divisive subject is that investigators have not been able to reach consensus on how best to treat affected patients. However, many studies have demonstrated that a variety of treatment approaches may be quite effective. These include aspirin, corticosteroids, heparin and on rare occasions, intravenous gamma globulin.



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