Everyone experiences a miscarriage differently. Whether it's early on or late in pregnancy, a shock or expected, it can be a physical and emotional ordeal. For couples who have been struggling to conceive, or have experienced miscarriages in the past, it can feel especially painful. But when should pregnancy loss be investigated? And which tests are offered to women in this situation?
Unfortunately, miscarriages are common, happening in 1 in 4 pregnancies. Many women may miscarry before they even realise they are pregnant.
But recurrent miscarriages, defined as the loss of three or more consecutive miscarriages, are less common, happening to 1 in 100 women.
When to investigate
After a miscarriage, it is understandable that couples want to know exactly why it has happened to see if it could be prevented the next time around. But if this is the first or even second miscarriage under 10 weeks of pregnancy, you probably won't be offered an investigation.
"Miscarriage at any stage of pregnancy can be a devastating loss for parents and their families. Making sense of what has happened can take time and it is a deeply personal experience that affects everyone differently," Professor Lesley Regan, a miscarriage expert and president of the Royal College of Obstetricians and Gynaecologists (RCOG), acknowledges.
"It's important that all women who suffer a late miscarriage are offered a referral to a specialist clinic for investigation. However, because early miscarriages are so common, the RCOG recommends couples are only offered investigations if they've had three or more first-trimester miscarriages."
This policy may seem frustrating, but early miscarriage is common and usually not a sign that something is wrong. Happily, most women will go on to have a successful pregnancy even after two miscarriages.
However, if you've experienced three or more consecutive early miscarriages, or a single miscarriage after 12 weeks, speak with your GP about getting investigated. They can arrange a referral to a specialist miscarriage clinic who will look into possible causes through a series of tests.
What causes miscarriage?
Most miscarriages that happen in the first trimester are due to a chromosomal abnormality in the developing fetus. The risk increases with maternal age. Chromosomal abnormalities are normally a one-off error. But in about 2-5% of couples experiencing recurrent miscarriages, one partner may carry a genetic abnormality.
Second trimester miscarriages are often related to the health of the mother. Several pre-existing health conditions can increase your risk of miscarriage, particularly if poorly controlled, including obesity, diabetes, high blood pressure, and polycystic ovary syndrome.
The shape of a woman's reproductive organs (such as a heart-shaped womb) can also sometimes lead to second-trimester miscarriages. And large fibroids (a benign growth in the womb) may distort the uterine cavity, causing pregnancy loss.
Antiphospholipid syndrome (APS), or 'sticky blood syndrome, is an autoimmune condition. It is associated with an increased risk of miscarriage and stillbirth, and is the cause of approximately 15% of recurrent miscarriages.
Natural killer cells
Natural killer cells are a type of white blood cell present in the uterus. Several studies have suggested that these cells are increased in women with recurrent miscarriage. But further research is needed before we can be sure of the association.
The placenta links the mother's blood supply to her baby's, providing oxygen and nutrients to the developing fetus. Abnormalities in placental development can lead to miscarriage.
Another theory to recurrent miscarriage is a luteal phase defect. The luteal phase is a part of the menstrual cycle - it occurs after ovulation and before your period starts. During this phase, progesterone stimulates the lining of the womb to thicken in preparation for a pregnancy. But in a luteal phase defect, the ovaries don't produce enough progesterone, or the lining of the womb doesn't respond to progesterone effectively. This can be a cause of difficulty in getting pregnant and pregnancies resulting in miscarriage.
Women who smoke or drink more than two units of alcohol a week have an increased risk of miscarriage. Drug misuse in pregnancy is also a risk. Excessive amounts of caffeine, above 200 mg a day (equivalent to two cups of instant coffee) can also lead to pregnancy loss.
What investigations are available?
If you are referred to a recurrent miscarriage clinic, there are several investigations that will be conducted to try to identify the cause. Available tests include:
- Investigation for fetal genetic abnormalities if fetal tissue is available.
- Investigations for genetic abnormalities in both partners.
- A blood test to look for APS antibodies or other immune system abnormalities.
- A blood test to look for hormonal problems.
- An ultrasound scan of the pelvis to look for any problems with the womb.
- For women who have had a second-trimester miscarriage, thrombophilia screening will be offered (factor V Leiden, factor II gene mutation and protein S deficiency).
Treating recurrent miscarriage
Treatments available for recurrent miscarriage depend on the cause.
Abnormal results after genetic screening should be further investigated by a referral to a geneticist.
For women who are found to have APS, low-dose aspirin and heparin may be offered. This treatment option may reduce recurrent miscarriage by 54%.
Women with a history of second-trimester miscarriage attributed to cervical weakness may be offered ultrasound monitoring of the cervical length throughout their pregnancy. If the length shortens to 25 mm or smaller, they may be offered a cervical stich, or 'cerclage', to help strengthen it.
Some studies have shown that giving progesterone to pregnant women may reduce the chances of miscarriage in those who have experienced several previous pregnancy losses. Larger meta-analysis studies however have failed to demonstrate a statistical difference in live birth rates. A large multicentre trial called the PROMISE study is underway to further investigate the hormone's role in miscarriage.