Recurrent miscarriage is diagnosed when a woman miscarries consecutively 3 times, before 20 weeks gestation. It is true that some women miscarry more often than chance alone would expect. When considering how common recurrent miscarriage actually is, we need to consider some numbers.
How common is recurrent miscarriage?
It is well known that overall 15% of all clinically recognised pregnancies end in miscarriage. The main cause is a problem with the gene cross-over at time of conception. This is due to chance alone, and nothing can be done to prevent it. The miscarriage is nature's way of ensuring health throughout the whole of your offspring's life. When pregnancy is diagnosed much earlier, with very sensitive hormone tests, it is found in fact that up to 60% of pregnancies end in miscarriage - most would just present as a heavier late period if undiagnosed. So 2 early miscarriages is really likely to be no more than just bad luck.
Considering this figure of 15%, we would expect only 0.4% of women to miscarry 3 times consecutively, and it be due to nothing more than chance. In fact, 0.8-1.0% of women do so, suggesting other factors may be involved.
What is important to remember through all of this, is that 60-75% of women who have recurrent miscarriage (RM) will go on to have a successful pregnancy the next time - without any kind of tests or treatment. When a woman is investigated for RM, the majority of the time, no cause is found.
What are the things which can make one prone to recurrent miscarriage?
Remembering that most often no cause is found, below are some of the things which are thought to be associated with RM:
General disease - eg. Systemic Lupus Erythematosus (SLE) which is a disease affecting many systems of the body. People affected often have a butterfly-rash over the cheeks and bridge of the nose.
Antiphospholipid antibody syndrome - this is an immune disease where
the main problems are RM, clots in the veins or arteries and often a low count
of one of the blood components, the platelets. If pregnancy is successful,
it can be complicated by poor growth of the baby and a disease of pregnancy
called preeclampsia.
Chromosome problems - ie Mum & Dad are fine, but when put together an unusual gene mismatch occurs (only 3% of RM).
Uterine (womb) abnormality - eg. double-womb or a septum down the middle.
This is only associated in about 4% of RM and is found in 1.8-3.6% of the
normal population. Whether this type of problem actual is to blame hasn't
been proven, and the risks of surgery to correct the problem must be weighed
against any potential benefit. In most women with these findings they don't
cause miscarriage, hence the uncertainty.
Fibroids - whorls of normal uterus tissue growing in the muscle, sometimes
causing misshaping of the womb cavity.
Cervical incompetence (weakness) - may cause miscarriage in
2nd trimester. Only likely to be a cause if there is clear history of severe
or recurrent trauma to the cervix (not, for example, just a one D&C or
cone biopsy) with RM. Some women are just born with a weak cervix. This is
not as common as some people report, and the diagnosis is very difficult to
make.
Polycystic ovary syndrome - often this disease causes infertility or
trouble even getting pregnant. It has also been found when this is present
with a raised hormone level (LH) there is an increased risk of miscarriage.
Hormonal treatment for this is being looked into presently, but there is minimal
evidence available at the moment on who might benefit. It does appear that
women with very irregular periods and a raised LH may do so.
Immune problems - couples with RM may have some similar components
of the immune system. This can make it difficult for Mum to make the appropriate
response to pregnancy. This is a controversial finding, and no immune therapy
has been found to improve chances above and over the 60-75% seen without intervention.
Hormone 'deficiency' - in pregnancies which end in miscarriage, sometimes
the levels of a hormone called progesterone are found to be low. This is thought
to reflect an early pregnancy failure, and is probably the RESULT rather than
the cause of the miscarriage. Certainly progesterone supplements do not increase
the likelihood of an ongoing pregnancy.
Things unlikely to cause recurrent miscarriage
Retroversion - or backward tilting of the uterus.
Infection - such as toxoplasmosis, listeria, brucella, chlamydia, herpes
simplex and cytomegalovirus.
Endocrine or metabolic disease - hypothyroidism (underactive thyroid),
diabetes mellitus, Crohn's disease, sickle cell or endometriosis.
Occupational exposures - very little reliable evidence exists for things
such as herbicide spraying, electromagnetic fields, chemical inhalation, anaesthetic
gases or VDU usage.
Not resting enough - bedrest doesn't alter whether you miscarry or
not. Nor does working when you're pregnant, exercise, making love or flying.
Is there any treatment?
Progesterone supplements have been evaluated in clinical trials and have not been shown to be of any benefit. A few people still use them, but it must be realised that they are not any better than placebo (no treatment). There will be women who had miscarriage 3 times then went on to deliver the following 2 times with progesterone supplements - most doctors certainly wouldn't deny the treatment again, but the fact remains that properly conducted studies (as opposed to anecdotal reports) have not found them to be of benefit. Surrogacy is becoming a likely choice for people suffering from recurrent miscarriages.
