Causes
What is Recurrent Miscarriage (also known as recurrent pregnancy loss) and how common is it?
A miscarriage or pregnancy loss is when you lose a pregnancy at some point in the first 23 weeks. When this happens two or more times it is called recurrent miscarriage. Around one woman in every 100 experiences recurrent miscarriage. This is about three times more than you would expect to happen just by chance.
While for some women there are specific causes why this may happen, no underlying problems can be identified for others and repeated pregnancy loss may be due to chance alone. Most couples who have suffered from recurrent miscarriage still have a good chance of a successful birth in future, although the rate of pregnancy loss increases gradually with age.
Genetic Factors
In about 5 in every 100 women who have experienced recurrent miscarriage, they or their partner have an abnormality on one of their chromosomes (the genetic structures within our cells that contain our DNA). Although such abnormalities may cause no problem for you or your partner, they may sometimes cause problems if passed on to your baby.
Abnormalities in the embryo
An embryo is a fertilised egg. An abnormality in the embryo is the most common reason for single pregnancy loss. The chances of such abnormalities increase with advancing age of the mother.
AUTO-IMMUNE FACTORS
Antibodies are substances produced in our blood in order to fight off infections.
Some people produce antibodies that react against the body’s own tissues - this is known as an autoimmune response. About 15 in every 100 women who have
recurrent miscarriage have particular antibodies called antiphospholipid antibodies in their blood and these can increase the chance of having further miscarriages. Another type of antibody that is associated with pregnancy loss is the antinuclear antibody. The condition that we typically associate with antinuclear antibodies is Systemic Lupus Erythematosus (SLE). The pregnancy loss rate in women with SLE patients is much higher than that of the general population.
Thyroid antibodies are also a marker for ‘at-risk’ pregnancies. The two antibodies
studied, anti-thyroid peroxidase and anti-thyroglobulin antibodies, are collectively
referred to as anti-thyroid antibodies.
INFECTIONS
If you suffer from a serious infection during pregnancy, it can lead to miscarriage. It is not entirely clear though, whether infections cause recurrent miscarriage.
WEAK CERVIX
In some women the neck of the womb (the cervix) may open (or give way) too early in pregnancy and cause miscarriage. This typically happens between 12-24 weeks of pregnancy. This condition is known as ‘cervical weakness’.
Womb Structure
Women who have serious anatomical abnormalities of the shape and/or size of the womb cavity seem to be more likely to miscarry or give birth early. Minor variations in the structure or shape of your womb do not cause repeated pregnancy loss.
Blood
Conditions
The inherited ‘Thrombophilias’ are a group of genetic disorders of the blood-clotting pathway which cause abnormal or excessive blood clot formation (thrombosis). These conditions are associated with increased risk of pregnancy loss, intrauterine fetal death and high blood pressure/pre-eclampsia during pregnancy.
Following are the major thrombophilias -
Factor V Leiden mutation
Factor II (Prothrombin) G20210 gene mutation
Methylene-tetrahydrofolate reductase (MTHFR) mutation, leading to hyperhomocytseinemia
Protein C deficiency
Protein S deficiency
Hormonal Inbalace
Uncontrolled diabetes and thyroid abnormalities can cause repeated pregnancy loss. Also, Polycystic Ovary Syndrome (PCOS) causes an imbalance of hormones. Just under half of women with recurrent early pregnancy loss have polycystic ovaries; this is about twice the number of women in the general population. It is however unclear
whether PCOS on its own can cause recurrent miscarriage and what the possible mechanism is.