Miscarriage Risk by Week: How the Chance Falls as Pregnancy Goes On

What is the risk of miscarriage by week?

The risk of miscarriage is highest in the first weeks of pregnancy, and Cleveland Clinic says it goes down with each week that passes. ACOG says loss in the first 13 weeks, which it calls early pregnancy loss, happens in about 10 in 100 known pregnancies, and March of Dimes estimates that 10 to 20 in 100 known pregnancies end in miscarriage. March of Dimes adds that 8 out of 10 miscarriages happen in the first trimester, before the 12th week.

A 2012 systematic review in Birth Defects Research Part A worked out miscarriage rates for each week from 5 to 20. In each week before week 13, the highest rate among the studies it pooled was more than 20 miscarriages per 1,000 women. By week 14 the rate was below 10 per 1,000, and it fell lower still through week 20. Across weeks 5 to 20 combined, the risk ranged from 11 to 22 in 100.

Some losses happen before a pregnancy is known. March of Dimes says some research suggests that more than 30% of pregnancies end in miscarriage, many of them before the person knows they are pregnant.

The cut-off for the word differs by country. March of Dimes and Cleveland Clinic define miscarriage as a pregnancy loss before 20 weeks, while the NHS uses before 24 weeks.

What is the risk of miscarriage after seeing a heartbeat?

For women with no symptoms, the risk of miscarriage after a heartbeat is seen on ultrasound is low, and it is lower the later that scan happens, according to a 2008 study in Obstetrics & Gynecology. The study followed 697 women in Australia carrying one baby, whose heartbeat was seen at a first prenatal visit between 6 and 11 weeks. Overall, 11 of 696 women followed to the end, or 1.6%, went on to miscarry.

The risk was 9.4% when the heartbeat was seen at 6 weeks, 4.2% at 7 weeks, 1.5% at 8 weeks, 0.5% at 9 weeks and 0.7% at 10 weeks. The authors concluded that for women without symptoms the risk is low, especially from 8 weeks onward, and that the chance of the pregnancy continuing past 20 weeks is very good.

What is the risk of miscarriage after 12 weeks?

After 12 weeks the risk is much lower: Cleveland Clinic puts the risk of pregnancy loss in the second trimester at around 1 in 100, compared with about 1 in 10 in the first trimester. The 2012 systematic review found weekly rates below 10 per 1,000 by week 14, falling further through week 20.

March of Dimes says problems with the uterus and cervix can cause miscarriage after 12 weeks but before 20 weeks, and that a provider usually recommends tests after a second-trimester miscarriage to look for the cause. The NHS calls a loss between 14 and 23 weeks a late miscarriage.

What raises the risk of miscarriage?

The risk of miscarriage rises with age, ACOG says, and for women over 40 about 1 in 3 pregnancies end in miscarriage. A 2019 study in the BMJ of 421,201 pregnancies in Norway found the risk was lowest at ages 25 to 29, at 9.8%, and rose to 16.7% at 35 to 39, 32.2% at 40 to 44 and 53.6% at 45 and over.

The same study found the risk rose with each previous miscarriage in a row. ACOG says most women who have an early pregnancy loss go on to have successful pregnancies, and that repeated miscarriages are rare.

ACOG says about half of early miscarriages happen when the embryo does not develop properly, often because of an abnormal number of chromosomes. The NHS lists other things that may increase the chance, including diabetes, a thyroid condition, smoking, drinking alcohol and drinking a lot of caffeine.

In almost every case a miscarriage is not your fault, ACOG says, and it is usually a random event. ACOG says working, exercising, stress, arguments, having sex, or having used birth control pills before getting pregnant do not cause miscarriage, and neither does morning sickness.

What are the signs of a miscarriage?

Vaginal bleeding is the most common sign of miscarriage, according to ACOG, which also lists a gush of fluid from the vagina and passing tissue. Cleveland Clinic adds cramping or pain in the lower belly that is stronger than a period, and low back pain. The NHS says tissue may come out as pink, grey or white lumps.

March of Dimes says many pregnant people have these signs in early pregnancy and don't have a miscarriage. ACOG says a small amount of bleeding early in pregnancy is common and does not necessarily mean you will miscarry; spotting during pregnancy and cramping in early pregnancy cover the other causes.

A miscarriage can also happen with no symptoms. The NHS says you may only find out at a scan, which is called a missed miscarriage. If you do have bleeding or cramping, ACOG says your OB-GYN may do an ultrasound and a blood test for hCG, and that several of each may be needed to confirm a loss.

When should you call your doctor or midwife?

Call your doctor or midwife if you have any sign of miscarriage, as ACOG and the NHS advise; Cleveland Clinic says to contact your provider right away. In the UK the NHS suggests your maternity unit, an early pregnancy unit if you are less than 20 weeks pregnant, or NHS 111. Call about:

• Vaginal spotting or bleeding, with or without pain. ACOG says to contact your OB-GYN right away if the bleeding is heavy or comes with pain like period cramps.
• Cramping or pain in your lower belly that is stronger than a period, or low back pain (Cleveland Clinic).
• A gush of fluid from your vagina, even without pain or bleeding (ACOG).
• Passing tissue from your vagina (ACOG).
• Vaginal discharge that is unusual for you (NHS) or smells bad, or a fever (March of Dimes).