Miscarriage rates by week vary between women. However, the odds of having a miscarriage, or pregnancy loss, start to drop as the pregnancy progresses.
The risk figures for pregnancy loss are just averages, so each woman's risk may be higher or lower depending on a range of factors.
A pregnancy loss can occur before a woman even knows she is pregnant. After an ultrasound detects a healthy heartbeat, the risk of pregnancy loss is significantly lower.
If a woman knows about the pregnancy, the risk of loss is about 10 to 15 percent.
A pregnancy loss is the loss of a fetus that occurs before 20 weeks of gestation. A stillbirth is pregnancy loss that happens any time after 20 weeks.
Most pregnancy losses are due to factors the woman cannot control. Early in pregnancy, genetic issues are a major cause of miscarriage.
Around 80 percent of miscarriages occur in the first trimester, which is between 0 and 13 weeks.
While the loss can be devastating, these genetic issues mean that the baby could not have survived outside the womb. Even if a woman has this type of pregnancy loss, she is generally able to go on to have a healthy pregnancy.
Fetuses are most vulnerable early in development, so other factors — such as exposure to alcohol — can have the most damaging effects at this time. This is why most miscarriages occur early in pregnancy.
As the fetus gets stronger, it may be less vulnerable to harm. Also, women may change any potentially damaging lifestyle habits once they know they are pregnant.
A general estimate of miscarriage risk by week is as follows:
Implantation usually occurs around 3 weeks after a woman's last period, and about a week after ovulation. By week 4, a woman may be able to get a positive result on a home pregnancy test.
As many as 50 to 75 percent of pregnancies end before getting a positive result on a pregnancy test. Most women will never know they were pregnant, though some may suspect they were because of pregnancy loss symptoms.
The rate of miscarriage at this point varies significantly. A 2013 study found that the overall risk of losing a pregnancy after week 5 was 21.3 percent.
The same study suggested that after week 6, the rate of loss was just 5 percent. In most cases, it is possible to detect a heartbeat on an ultrasound around week 6.
In the second half of the first trimester, the rate of miscarriage was between 2 and 4 percent.
Between weeks 13 and 20, the risk of experiencing a miscarriage is less than 1 percent.
By week 20, a miscarriage is known as a stillbirth and may still cause a woman to go into labor.
Stillbirth is relatively rare and is getting rarer because very young babies may be able to survive outside of the womb thanks to modern technology.
According to a research group based in the United Kingdom, there is a minimal chance that a baby born at 22 weeks will survive. That chance increases each week.
In high-income countries, 77 percent of premature babies born at 26 weeks will survive, while almost all premature babies born at 30 weeks or later survive.
Will I experience a pregnancy loss?
A 2012 study looked at the overall risk of pregnancy loss during the first and second trimesters and found it to be between 11–22 percent in weeks 5 through 20.
However, other research puts the percentage between 10–15 percent.
These statistics suggest that the risk of miscarriage varies from woman to woman, depending on a variety of factors, including age and overall health.
Age is a major risk factor for pregnancy loss. This is because egg quality tends to decline over time.
The average risk of miscarriage by the age of the mother is as follows:
- Under 35 years old: 15 percent chance of pregnancy loss
- Between 35–45 years old: Between 20 and 35 percent chance of pregnancy loss
- Over 45 years old: About a 50 percent chance of pregnancy loss
It is essential to note that these are average figures and do not take any other factors into account.
The effects of lifestyle issues, such as smoking or a sedentary lifestyle, can also accumulate with age, worsening underlying health issues and further increasing the risk of a pregnancy loss.
However, some women have healthy pregnancies in their 40s, and a few do so in their 50s.
Most women who experience a pregnancy loss go on to have healthy pregnancies. A single miscarriage does not mean a woman will have trouble getting or staying pregnant in the future.
In fact, a 2016 study found that women are more likely to get pregnant again immediately after experiencing a pregnancy loss.
Some women ask for genetic testing following one or more pregnancy losses. Genetic testing may help a doctor understand the cause of pregnancy loss.
Some risk factors for a miscarriage include:
Most of the time, the earliest sign of a miscarriage is bleeding. However, not all bleeding is due to a pregnancy loss.
About 20–30 percent of women experience some spotting during pregnancy. Bleeding is more likely to indicate a miscarriage when it is heavy, getting heavier with time, or occurs with intense cramps.
A miscarriage can also happen without bleeding.
Some other symptoms of a miscarriage include:
- a sudden reduction in pregnancy symptoms, though symptoms can decrease even without a miscarriage due to fluctuating hormones
- a decrease in the baby's movements in the second trimester
- intense cramps
- passing blood clots
A woman should speak to a doctor about any bleeding during pregnancy. If the bleeding is heavy or painful, it is best to go to the emergency room.
Some other signs to watch for include:
- loss of pregnancy symptoms
- not feeling the baby move after regularly experiencing movement
Most pregnancies end with a healthy birth, even if the mother has a previous history of or has risk factors for a miscarriage.
There is no right or wrong way to react to a pregnancy loss. The experience can be emotional or spur doubts about future pregnancies. Conversely, some women are surprised that they do not have a strong reaction to a pregnancy loss.
A pregnancy loss is not anyone's fault. Most women can have a healthy pregnancy following a miscarriage.
Quality medical care, support from friends and family, and taking time to heal can help women manage the process more successfully.