It is very unlikely that you will ever know the actual cause of a single miscarriage, but most are due to the following problems:
• ABNORMAL FETUS
The most common cause of early miscarriages is a temporary abnormal development of the fetus, often due to chromosomal abnormalities. “It’s not like the baby is fine one minute and suddenly dead the next,” says Professor James Walker, professor of obstetrics and gynaecology at the University of Leeds.
“These pregnancies fail from the start and were never meant to succeed.” Most such miscarriages occur by eight weeks, although bleeding may not start until three or four weeks later – something worth remembering in subsequent pregnancies. “If an ultrasound at eight weeks shows a healthy heart rhythm, there is a 95 per cent chance of a successful pregnancy,” says Professor Walker.
• HORMONAL FACTORS
A hormonal change may cause a sporadic miscarriage and not cause a problem again. However, a small number of women who have long cycles and irregular periods may experience recurrent miscarriages because the lining of the uterus is too thin, making implantation difficult.
Unfortunately, hormonal treatment is not very successful.
“Progesterone treatment used to be used, but clinical trials show that it doesn’t work,” warns Professor Walker. “There is evidence that HCG (human chorionic gonadotrophin, a hormone released in early pregnancy) injections can help, but it’s not the solution for everyone.” Treatment should be started as soon as pregnancy is confirmed, around the fourth or fifth week.
• AGE
For women over 40, one in four women who become pregnant will miscarry. (One in four women of all ages miscarry, but these numbers include women who don’t know they are pregnant. For women who do know they are pregnant, the number is one in six. Once you reach age 40 and know you are pregnant, the number rises to one in four.)
• AUTOIMMUNE BLOOD DISORDERS
About 20 percent of recurrent miscarriages suffer from lupus or a similar autoimmune disorder that causes blood clots to form in the developing placenta.
A simple blood test, which may need to be repeated several times, can reveal whether this is the problem or not. “A negative result does not mean a woman is okay,” warns Roy Farquharson, a consultant gynaecologist who runs an early pregnancy unit at Liverpool Women’s Hospital.
“Pregnancy can often be a trigger for these disorders, so it’s worth testing as soon as possible,” he adds. But it can be easily treated with low-dose aspirin or heparin injections, which help thin the blood and prevent clots from forming; a recent trial also showed that women respond equally well to either. “We have a 70 per cent live birth rate in women treated for these disorders,” says Dr Farquharson, “which is excellent.”
• OTHER CAUSES
While uterine abnormalities such as fibroids can cause miscarriage, many women have no trouble carrying a pregnancy to term. An incompetent cervix can also cause miscarriage around 20 weeks.
While this can be treated with a special suture in the cervix, trials suggest it is not particularly successful, although it may delay labour by a few weeks. Genetic and chromosomal abnormalities, which can be detected by blood tests, can also cause recurrent miscarriages in a small number of couples.
A procedure known as preimplantation genetic diagnosis may help. After in vitro fertilization (IVF), a single cell is removed from the developing embryo and tested for the genetic defect. Only healthy embryos are then placed back into the uterus.
It is an expensive and stressful procedure (and pregnancy rates tend to be quite low), but for some people it is preferable to suffering repeated miscarriages or having a genetically abnormal baby.
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