Miscarriage explained: how common it is, the warning signs and what happens next

What counts as a miscarriage

In the UK, a miscarriage is the loss of a pregnancy before 24 weeks. The NHS distinguishes an early miscarriage, before 14 weeks, from a late miscarriage, between 14 and 23 weeks (NHS, Miscarriage). The distinction matters because the way a miscarriage is managed changes with the stage of pregnancy. A loss from 24 weeks onwards is called a stillbirth and is covered by different guidance.

The NHS also describes a missed miscarriage: a pregnancy that has stopped developing without causing any symptoms, which is found at a routine scan. For many people this is the hardest form to take in, because nothing seemed wrong.

How common it is

The most complete recent estimate comes from a 2021 series in The Lancet, led by Siobhan Quenby and colleagues at Tommy's National Centre for Miscarriage Research (Quenby et al., The Lancet, 2021). Pooling studies from several countries, the authors estimated that:

• the pooled risk of miscarriage is 15.3% of all recognised pregnancies, about one in seven;
• about 23 million miscarriages occur worldwide every year;
• 10.8% of women have had one miscarriage, 1.9% two, and 0.7% three or more.

"Recognised" is the key word. Many very early losses happen before a pregnancy is known, so the true share of conceptions that end in miscarriage is higher than any figure based on known pregnancies. This is one reason why different sources quote different numbers: they are often measuring different things.

Why it happens

The NHS is candid that the cause of an individual miscarriage is often not known, but that it is usually linked to a problem with the way the pregnancy develops. Some factors are associated with a higher chance of miscarriage. The NHS lists:

• being aged 35 or over, and the baby's father being aged 45 or over;
• being from a Black African or Black Caribbean background;
• long-term conditions such as diabetes, a blood clotting condition or a thyroid condition, and a hormonal ovarian condition the page now lists as polyendocrine metabolic ovarian syndrome (PMOS), long known as polycystic ovary syndrome (see PCOS explained);
• a problem with the womb, low levels of the hormone progesterone and vitamin D deficiency;
• smoking, drinking alcohol or a lot of caffeine, obesity or being underweight;
• exposure to harmful chemicals or high levels of air pollution.

The Lancet review adds previous miscarriages, very young maternal age (under 20), stress and night-shift work to the list. These are associations seen across populations, not a verdict on any one pregnancy: most people with one or more of these factors do not miscarry, and many miscarriages happen with none of them. Several of the factors that can be changed are the same ones covered in our guide to what the official guidance recommends before trying for a baby.

Symptoms, and when to get help

The main symptom is vaginal bleeding before 24 weeks, which can range from spotting to heavy bleeding. Others include cramping and pain in the lower tummy, fluid suddenly leaking from the vagina, and the passing of tissue. Bleeding in early pregnancy is common and does not always mean a miscarriage, but it should always be checked.

The NHS advice is in two tiers:

• Get urgent medical help for light bleeding or spotting with no pain or only mild pain, or for unusual discharge or leaking fluid. Call your maternity unit if you have its number. Before 20 weeks, an early pregnancy unit may be able to help; if you cannot reach either, call NHS 111.
• Call 999 if you are pregnant, have vaginal bleeding and also have severe tummy pain, pain in the shoulder, feel sick, faint or dizzy, or the bleeding is heavy (soaking a pad soon after putting it on). These can be signs of an emergency, including an ectopic pregnancy.

How a miscarriage is diagnosed and managed

Doctors usually ask about the pregnancy and general health, and may offer blood or urine tests and an internal (transvaginal) ultrasound scan. A miscarriage cannot be stopped once it has started, so care focuses on managing it safely. For an early miscarriage, the NHS describes three options:

1. Waiting for the pregnancy to pass naturally, which usually takes about two weeks but can take longer;
2. Medicine to help the pregnancy pass, sometimes at home and sometimes with monitoring in hospital;
3. A short procedure that removes the pregnancy with gentle suction, under general or local anaesthetic, often with discharge the same day.

For a late miscarriage, the care team discusses options individually, and the person may need to give birth, with medicines to start labour if it does not begin by itself. Anyone whose blood type is D-negative (rhesus negative) and who was at least 12 weeks pregnant may be offered an anti-D injection, which helps protect future pregnancies from haemolytic disease of the fetus and newborn.

In England, the care that NHS services should offer is set out in the NICE guideline on ectopic pregnancy and miscarriage (NG126), which covers early pregnancy assessment services, the choice between these options and the information people should be given.

Can progesterone prevent a miscarriage?

Progesterone helps maintain a pregnancy, and it has long been suggested as a treatment for bleeding in early pregnancy. The largest trial, PRISM, randomised 4,153 women with early pregnancy bleeding at 48 UK hospitals to vaginal progesterone or a placebo (Coomarasamy et al., NEJM, 2019). Live births after at least 34 weeks were 75% with progesterone and 72% with placebo, a difference that was not statistically significant overall. The trial's analysis of women who had previously miscarried pointed to a possible benefit in that group, and NICE updated NG126 in 2021 to recommend offering vaginal micronised progesterone to women with bleeding in early pregnancy, a pregnancy in the womb confirmed by scan, and a previous miscarriage. It is a decision to make with a clinician, not a supplement to buy.

After a miscarriage

Physical recovery usually takes days to weeks: tummy pain may last a few days and bleeding or spotting up to two weeks. The NHS advises resting as needed, taking paracetamol for pain, and avoiding sex until symptoms have gone because of the risk of infection. A period can take up to eight weeks to return, and a few months to settle into its usual pattern. There is no set waiting time before trying again: the NHS advice is to try when you feel ready, once symptoms have gone. Most women who have had a miscarriage go on to have a successful pregnancy.

Emotional recovery can take much longer. The Lancet review found that miscarriage increases the risk of anxiety, depression and post-traumatic stress, and partners can be affected too. GP surgeries and pregnancy units can refer to counselling, and the NHS points to two national charities: Miscarriage UK (helpline 0303 003 6464) and Tommy's (helpline 0800 0147 800).

Recurrent miscarriage

Three or more miscarriages are described as recurrent miscarriage. It is uncommon, affecting fewer than 1 in 100 women on the Lancet estimate, and the NHS advises talking to a GP, who will usually refer for tests to look for a treatable cause, together with support. The Lancet authors also stress that recurrent miscarriage is a marker of higher risk in later pregnancies, including preterm birth and stillbirth, and recommend that women who have experienced it are cared for in clinics that specialise in higher-risk pregnancies.

This article summarises official UK guidance and published research. It is not personal medical advice. If you are pregnant and bleeding, contact your maternity unit, early pregnancy unit or NHS 111, and call 999 in an emergency.