Miscarriage: symptoms, causes, types, risk factors

Learning that you are pregnant often comes with a lot of emotions. Once you get that positive pregnancy test, you start thinking about how your life may change. You might even begin preparing for a new baby and telling family and friends. And then, amid all that thinking and planning, you learn your pregnancy is no longer viable. 

A miscarriage can occur for several reasons. No matter when it happens or why it happens, it's normal to grieve following a pregnancy loss—even if your emotions surrounding the pregnancy were complicated. 

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Miscarriages are pregnancy losses that occur before 20 weeks of pregnancy. While miscarriages often feel like isolating experiences, the truth is they are quite common. Up to 26% of all pregnancies end in loss, and about 10% of all clinically recognized pregnancies—pregnancies with a detectable heartbeat—end in miscarriage (Dugas, 2021). 

About 80% of those pregnancy losses happen during the first trimester (the first 12 weeks of pregnancy). After 20 weeks, the loss is usually considered a stillbirth. Fortunately, the risk of miscarriage drops the further along you are (Prine, 2011; Dugas, 2021). 

There are a few causes of miscarriage, but about 50% of early losses are due to fetal chromosomal abnormalities. Chromosomal abnormalities are common and occur when either the sperm, egg, or both sex cells have an irregular number of chromosomes, DNA molecules that carry genetic material (American Society for Reproductive Medicine, 2012). 

Healthy sperm and egg cells have 23 chromosomes each and join to create an embryo with 46 chromosomes. The older you are, the higher your risk of chromosomal abnormalities and miscarriage becomes (American Society for Reproductive Medicine, 2012). 

Some medical conditions can increase your risk of miscarriage. If you have lost multiple pregnancies, speak to your healthcare provider about your concerns. You can also see a reproductive endocrinologist, an infertility specialist, who can help diagnose what's causing your miscarriages and help you plan for future pregnancies (Garcıa-Enguıdanos, 2002). 

Risk factors that can lead to pregnancy loss include (Garcıa-Enguıdanos, 2002): 

• Thrombophilia, a condition that causes increased blood clots

• Antiphospholipid syndrome, an immune disorder that causes increased blood clots

• Thyroid disorders, such as an underactive thyroid  

• Uterine malformations, changes to the normal size and structure of the uterus 

• Uterine fibroids, non-cancerous masses that grow in the uterus

• Hypertension, also known as high blood pressure

You may also have a higher risk of miscarriage if you smoke tobacco or use illicit drugs like cocaine or methamphetamines. Alcohol use in excessive quantities can also cause an increased risk of miscarriage; however, drinking alcohol is associated more with congenital disabilities than miscarriage (Garcıa-Enguıdanos, 2002; Pineles, 2014;). 

Some studies have found that cannabis itself is not linked to miscarriage but can negatively affect a growing fetus (Conner, 2016). Although studies on this have not been conclusive, research suggests drinking lots of caffeine is linked to a higher likelihood of miscarriage (Chen, 2016). Moderate caffeine consumption does not appear to play a role in miscarriage (ACOG, 2020). 

Many people who miscarry go on to have healthy pregnancies; however, some face an increased risk of recurrent miscarriage. You have a 20% risk of miscarriage following one previous miscarriage. After two consecutive losses, the risk is 28%. More than three losses in a row, and the risk jumps to 43% (Dugas, 2021; Regan, 1989). 

Heavy bleeding following a positive pregnancy test is the most common sign of a miscarriage. However, bleeding doesn't always signify miscarriage, so be sure to follow up with your healthcare provider if you start bleeding  (American College of Obstetricians and Gynecologists, 2018). 

Medical professionals typically rely on two tests when assessing the health of a pregnancy: a blood test checking quantitative human chorionic gonadotropin (hCG) levels and a transvaginal ultrasound, a thin probe inserted in the vagina to get images of the reproductive organs. Depending on how far along you are, your provider will likely perform both of these tests at routine visits and if you start bleeding. For the blood test, your healthcare provider will want to see your hCG levels doubling every 48 hours to confirm the pregnancy is developing normally. 

They will also use a transvaginal ultrasound to measure the gestational sac, cardiac activity, and the length of the fetus. The measurements they look for will depend on how far along you are. If it is very early in your pregnancy, your doctor may not be able to see anything via ultrasound and will instead rely on blood tests (American College of Obstetricians and Gynecologists, 2018). 

Sometimes, tests might be inconclusive, and your healthcare provider will ask you to come back in a few days to repeat them. This time period can be incredibly stressful, but it's important to know with 100% certainty that the pregnancy is not viable, especially if you plan on taking medication or having surgery to help you pass the fetus and placenta (American College of Obstetricians and Gynecologists, 2018). 

You might hear a lot of different words thrown around when it comes to miscarriage. The medical term for a miscarriage is spontaneous abortion. Though the word "abortion" is highly politicized, in medical spaces, it simply means pregnancy termination. A spontaneous abortion is a pregnancy loss that occurs naturally (Dugas, 2021).

There are various terms your healthcare provider may use to describe a miscarriage. These include:  

Chemical pregnancy 

Chemical pregnancies are a form of early pregnancy loss where implantation occurs in the uterus, but the embryo fails to develop. These losses sometimes go unnoticed because the miscarriage-associated bleeding happens around the time of your menstrual period. So unless you test early, you might not catch that you were ever pregnant. A chemical pregnancy is also known as a biochemical loss because healthcare providers can only detect the loss chemically through a positive blood or urine pregnancy test (Chaudhry, 2021). 

Blighted ovum 

A blighted ovum happens when a fertilized egg implants in the uterus and a gestational sac grows without an embryo inside. Most miscarriages are due to blighted ovum (Chaudhry, 2021). 

Threatened miscarriage 

A threatened miscarriage doesn't mean you've lost the pregnancy. It does, however, mean you are at risk of having a miscarriage. Bleeding early in your pregnancy is a sign of threatened miscarriage, as is having a dilated cervix. However, bleeding doesn't always mean you'll lose the pregnancy, so your healthcare provider will want to keep a close eye on you to see how things progress (Kanmaz, 2019). 

Inevitable miscarriage 

During a threatened miscarriage, your cervix appears closed, and the fetus looks healthy on ultrasound despite any bleeding. An inevitable miscarriage means the threatened miscarriage has progressed to a point where the pregnancy is no longer viable. This might be because the cervix is open or the fetus has stopped developing (Dugas, 2021).

Incomplete miscarriage 

An incomplete miscarriage means some pregnancy-related tissue has passed but not all of it. In this case, an ultrasound would not visualize a viable fetus but may show some remaining tissue (Dugas, 2021). 

Missed miscarriage 

A missed miscarriage occurs when the pregnancy fails to develop as expected, the fetus might stop growing, or its heart might stop beating, but no bleeding occurs (Dugas, 2021). 

Complete miscarriage

A complete miscarriage means all pregnancy-related tissue has passed through the cervix. On ultrasound, no products of the pregnancy remain in the uterus (Dugas, 2021). 

There are other types of non-viable pregnancies, such as ectopic pregnancies, where the embryo implants in a location outside of the uterus like the fallopian tubes. Like miscarriages, these pregnancy types will not result in a live birth (Mummert, 2021).  

Losing a pregnancy can be emotionally and physically challenging. If you decide to try to conceive after your miscarriage, you can start as soon as you feel ready once all of the pregnancy-related tissue passes. Approximately 80% of people pass all products of pregnancy within eight weeks of the pregnancy ending (Luise, 2002). 

Medical assistance through medication

If you don't pass the tissue on your own or don't want to wait to pass the tissue naturally, there are medications and procedures that can speed up the process. If you and your healthcare provider choose medication, you will get a prescription for mifepristone and misoprostol. Your healthcare provider will give you one to two doses to take either orally or vaginally. After taking the medication, you will likely have significant uterine cramping, more than you would expect during a period, and vaginal bleeding for up to 16 days (Macnaughton, 2021). 

Medical assistance through D&C

The other option is a procedure most commonly known as a "D&C" or dilation and curettage. During this procedure, your healthcare provider dilates your cervix and removes the tissue with either sharp instruments or suction. Following the procedure, you may have abdominal pain and bleeding. There is no difference in long-term outcome between any of the different treatment options (Dugas, 2021) 

Miscarriages are often emotionally difficult. It’s normal to feel upset during the miscarriage and after. There is no right or wrong way to experience grief. Some people might cry, while others might feel depressed or numb. Up to 25% of women who lose their unborn child experience posttraumatic stress, making it challenging to heal emotionally (Wenzel, 2020). Speaking to a mental health professional or a trusted loved one about your grief and emotions can help you process your feelings. 

If you've had a miscarriage, know that you are not alone. If you have concerns about carrying a healthy pregnancy in the future, either physically or emotionally, speak to a trusted healthcare provider. It is possible to have a successful pregnancy following a miscarriage. 

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Current version

October 08, 2021

Written by

Jordan Davidson

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.