A miscarriage is the spontaneous end of a pregnancy before the fetus has grown enough to be able to survive independently. The limit of viability is set at the 24th week of pregnancy with a total duration of pregnancy set at 40 weeks counting from the 1st day of the woman's menstrual cycle.
Recurrent Miscarriages or habitual abortions are called recurrent, consecutive miscarriages of three or more clinically identified pregnancies. Their occurrence is 1% - 3.5% of all couples.
Many different opinions are suggested concerning their definition, as there are many who believe that monitoring and treatment must start after the second consecutive miscarriage, especially if aggravating risk factors co-exist, such as age (women over 35 years) or infertility history.
Recurrent miscarriages are classified as primary and secondary.
Primary miscarriages refer to women with three or more consecutive spontaneous abortions, with the same partner and without any pregnancy after the 20th week. Almost 80% of couples with recurrent miscarriages fall in this category.
Secondary miscarriage refers to women who have had three recurrent miscarriages, with the same partner after they had already given birth to a child or after an intra-uterine death. This case applies to almost 20% of couples with a recurrent miscarriages history.
Recurrent miscarriages may be caused due to genetic, anatomic, infectious, hormonal and immunologic reasons described below in detail:
1) Genetic factors
Chromosomal abnormalities are the most common causes of sporadic miscarriages, but they occur less often to women with recurrent miscarriages.
In 3-5% of couples, one of the parents carries a balanced chromosomal abnormality (translocation of genetic material between chromosomes or gene inversions in the same chromosome) with the most common being reciprocal or Robertsonian translocations. When one of the parents carries a balanced chromosomal translocation, the risk for miscarriage is almost double and, therefore, statistically important. Such couples need genetic consulting in order to plan for future pregnancies.
2) Anatomic Factors
Anatomical abnormalities of the uterus include many different pathological cases that their significance for recurrent miscarriages differs depending on the specific abnormality.
3) Infectious Factors
(bacteria, viruses, parasites, mycoplasma, chlamydia) The role of infections in etiology of recurrent miscarriages is still unclear. There is no clear relation with infections of toxoplasmosis, rubella, herpes, CMV or mycoplasma.
4) Hormonal Factors
5) Immunological Factors (autoimmune, alloimmune)
6) Unknown Reasons
Almost 25% of couples with recurrent miscarriage history do not know the reasons for miscarriage. In such cases, empirical treatment is used combined with psychological support