When a pregnancy ends without explanation prior to 20 weeks, it is known as a “miscarriage.” While this word can bring anxiety to women who are planning a pregnancy or already expecting, the numbers show that only 10 to 20% of pregnancies end this way for healthy women. Looking at the risk of miscarriage can help you see possible complications that may arise during the first 20 weeks of pregnancy.

Risk of Miscarriage by Week 

Losing a baby to miscarriage can be an upsetting event. The truth is that miscarriage are most common up to the 13th week of pregnancy. This means that most of them happen before a women even knows she is pregnant or shortly thereafter. Many pregnancies fail to even implant in the uterine wall and fail to raise the hormone levels that cause a positive pregnancy test. Some miscarriages happen on or around the time the next period is due so a woman may think she is just having a “normal period.”

Regardless of when it occurs, prior to the 13th or the 20th week, the reasons are almost always unknown. A miscarriage that occurs before 13 weeks is usually a problem with the baby’s chromosomes. This is often because of a problem with either the sperm or the egg being damaged or unhealthy. There also may have been an issue with cell division in the zygote during conception. Miscarriage is also caused by the following:

  • Advanced age of the mother
  • Issues with hormones, chronic health conditions in the mother or an infection
  • The egg fails to implant in the uterine lining
  • Poor health practices such as poor diet, too much caffeine, smoking, drugs or chemical exposure
  • Trauma to the mother i.e. accidents, falls and physical abuse

The overall average of miscarriages evens out to about 20% of all pregnancies during the first trimester or 12 weeks. Depending on the above factors, the numbers for miscarriages can vary. Here is a ballpark average for miscarriage by week of pregnancy:

Pregnancy Weeks

Risk of Miscarriage (Percent)

Week One and Two

75% (You may not even know your are pregnant)

Week Three to Six


Week Six to Twelve


Week Twelve to Twenty


The one thing that raises your chance of miscarriage, is the history of a previous miscarriage. Take a look at the following statistics:


Risk of Miscarriage in Future

Miscarriage during first Pregnancy

10 to 13%

One live birth/One Miscarriage


Two pregnancies/Two miscarriages


One or more live births


Three pregnancies/Three miscarriages


No live birth/Four miscarriages

95 to 100%

What About Recurrent Miscarriages?

For only one miscarriage, there usually is no more risk for another miscarriage in your next pregnancy. If you have had more than one miscarriages during your first 12 weeks of pregnancy or one pregnancy loss between 12 and twenty weeks, you need to be worked up by your doctor to find the cause. There are certain conditions that can be treated early on to reduce the chance of miscarriage. Things like thrombophilia (blood clots in pregnancy), auto-immune disorders, diabetes and problems with your thyroid raise your chances of miscarriage, but are highly treatable. A defect in the shape of your uterus can also prevent pregnancy implantation. Talking to your doctor about miscarriages that keep reoccurring can help you get early treatment and increase your chances of carrying a baby to term.

How Does Age Affect Chances of Miscarriage?

As women get older, their risk of miscarriage by week increases. Please see the table below for statistics according to maternal age.

Age of Mother

Risk of Miscarriage

Under 35 years old


35 to 45 years old

20 to 35%

Over 45 years old


There are options for older moms to increase the chances of carrying a pregnancy to term. If the issue is low levels of hormones, the doctor can keep you on prescription hormonal replacements in early pregnancy to help. For chromosomal abnormalities, genetic testing can be performed to rule out genetic disorders.

Advice from Another Mom

“I completely understand what you may be feeling right now……trust me. With each pregnancy, the anxieties and fears of having another miscarriage only seem to get worse. I am here to tell you that if a miscarriage is going to happen, there isn’t much you can do to save the pregnancy. My first miscarriage was at 8 weeks, my second miscarriage was at 6 weeks and 6 days, and my third was at 9 weeks of pregnancy. My first miscarriage, I was spotting for around 2 weeks and then they did a D and C, my second miscarriage there was only slight brownish discharge one day prior to severe contractions and cramping. Then I started bleeding heavily. My third miscarriage, I had brownish discharge after going to the bathroom. The doctor did an ultrasound and didn’t find a heartbeat. They had to do another D and C. Just remember that no two pregnancies are alike and no two miscarriages are alike. Just try to enjoy your pregnancy and your baby, even though you may be scared. I wish you the best of luck for a healthy pregnancy!”

Useful tips on how to have a healthy pregnancy can help a lot in reducing the risk of miscarriage by week: