Recurrent miscarriage

What are the causes of recurrent miscarriage and who is at risk?

In most cases of recurrent miscarriage, no clear cause is ever found. Even so, a specialist assessment can sometimes uncover a factor that's contributing, and addressing it may improve your chances next time.

Where a cause is found, it's often one of the following:

• Chromosome problems. Around half of all miscarriages happen because the pregnancy has an unusual number of chromosomes, the structures that carry genetic instructions. This is usually a random, one-off event, though in a small number of couples, one partner carries a rearranged chromosome that can be passed on and cause it to happen again.
• Blood clotting conditions. Antiphospholipid syndrome (APS) makes your blood more likely to clot, which can affect blood flow to the placenta, and testing for it is recommended for anyone with recurrent miscarriage. An inherited clotting condition called thrombophilia has also been linked to miscarriage, though testing for this isn't currently recommended, as the evidence connecting it to recurrent miscarriage is unclear.
• An unusually shaped womb. Around 5 to 6 in 100 women are born with a womb that's an unusual shape, and this is more common in women who have recurrent miscarriage (around 13 in 100). Certain shapes, such as a septate or bicornuate womb, are more likely to raise your risk.
• Hormonal problems. Poorly controlled diabetes or thyroid disease, or having too much or too little of the hormone prolactin, can raise your chance of miscarriage. Polycystic ovary syndrome (PCOS) is also linked to a slightly higher risk, though it's not yet clear why.
• A weak cervix. Sometimes called cervical weakness, this can cause the cervix to open too early in a later pregnancy, usually between 14 and 23 weeks.
• Sperm quality. Abnormal DNA in a partner's sperm may play a role, although the evidence for this is limited and sperm testing isn't routinely offered.
• Immune factors. It's been suggested that some miscarriages happen because the immune system doesn't respond normally to pregnancy. This is an active area of research, but there currently isn't clear evidence to support it.

You're also more likely to have recurrent miscarriage if you're over 40, since the risk rises sharply with age for both parents. Smoking, drinking heavily, having a lot of caffeine, and having a BMI outside the 19 to 25 range are also linked to a higher risk. If you're of Black African or Black Caribbean background, your risk of early miscarriage is higher too, though this isn't yet fully understood.

Are there different types of recurrent miscarriage?

Recurrent miscarriage isn't divided into distinct types in the way some conditions are. Doctors do distinguish between recurrent miscarriage where a cause is found through testing, and unexplained recurrent miscarriage, where investigations don't reveal a clear reason. Most people fall into the unexplained group.

How is recurrent miscarriage diagnosed?

If you've had recurrent miscarriage, you should be offered investigations to look for a possible cause. In the UK, this is usually after three or more early miscarriages, though you may be offered tests sooner if your doctor suspects an underlying reason, or after just one loss in the second trimester. Your assessment will usually include a detailed discussion of your medical history and a physical examination, ideally with your partner present if you have one. You'll likely be offered:

• blood tests for antiphospholipid syndrome (APS) – you'll need two positive results at least 12 weeks apart and at least 6 weeks after a miscarriage
• thyroid tests, including tests for thyroid antibodies
• a pelvic ultrasound scan to check the shape of your womb
• genetic testing for you and your partner, particularly if a chromosome problem is suspected or has been found in pregnancy tissue.

Some clinics may also test for infection or analyse a partner's sperm, though this isn't offered everywhere.

How is recurrent miscarriage treated?

Treatment depends on whether a specific cause has been found. If investigations don't reveal a clear reason, which is common, there's currently no medical treatment shown to reduce your risk of a further miscarriage, though supportive care, such as reassurance and early scans in a future pregnancy, can still help.

Non-surgical treatment for recurrent miscarriage

If you're found to have antiphospholipid syndrome, taking low-dose aspirin alongside daily heparin injections during pregnancy can improve your chances of a successful pregnancy. You'll be monitored closely, as APS also raises your risk of complications during pregnancy.

If you have diabetes or thyroid disease, getting this well controlled before you try again can reduce your risk. For an inherited blood clotting disorder, routine treatment hasn't been shown to help, though heparin may still be offered depending on your individual risk.

Progesterone isn't generally used to prevent recurrent miscarriage, but if you bleed in early pregnancy and have had a previous loss, you may be offered progesterone pessaries, typically 400mg twice a day up to 16 weeks, once a scan confirms the pregnancy is in your womb. Taking folic acid (400 micrograms a day, ideally from three months before you conceive) and vitamin D (10 micrograms a day) may also help lower your risk.

You'll usually also be supported to reach a healthy weight, stop smoking, and cut down on alcohol and caffeine, aiming for under 200mg a day, around two cups of instant coffee, as all of these are linked to a higher chance of miscarriage.

Surgical treatment for recurrent miscarriage

If you have a septum, a wall of tissue dividing your womb, you may be offered an operation to remove it. Surgery for other womb shape problems, such as fibroids, is used less often, as it's not yet clear whether it improves your chances, so this will depend on your individual situation.

If a scan shows your cervix has become short in a later pregnancy, you may be offered a cervical stitch to help hold it closed. If a chromosome translocation is found in you or your partner, options can include IVF with genetic testing of embryos before they're transferred, or using donor eggs or sperm.

When should I see a doctor?

Speak to your GP if you've had three or more early miscarriages, so they can refer you for specialist investigations. You may also be offered a referral sooner, after two losses if your doctor suspects an underlying cause, or straight away if you've had a single second-trimester loss.

It's also important to talk to your GP or another healthcare professional if you or your partner are finding it hard to cope emotionally. Recurrent miscarriage can bring on real grief, anxiety or low mood, and support and referral for further help are available.