what causes miscarriage

Common Causes and Signs of Miscarriage

Dr. Jolene BrightenPublished: Last Reviewed: Pregnancy Leave a Comment

Miscarriages are common, which is why it is important for women to know the signs of a miscarriage and when to call their provider. In this article, I’m going to go through the possible causes and types of miscarriage, ways to help minimize risk, and lab tests to request from your doctor if you’ve experienced more than one miscarriage. 

If you’re coming to this post searching for answers about a recent miscarriage, please know that I am so very sorry for your loss. Losing a pregnancy is devastating, emotionally and physically. For a lot of women, however, a miscarriage is typically a temporary stop on the road to a full-term pregnancy, and I understand that may be of little comfort to you at this moment. The most important thing right now is to give yourself space to fully grieve. 

What Is a Miscarriage?

A miscarriage is the spontaneous end of pregnancy and loss of a fetus that occurs before the 20th week of gestation. 

How Common Are Miscarriages? 

Miscarriage is still somewhat taboo in our culture, which can make it seem much more rare than it actually is. 

Most doctors will tell you that one in five pregnancies end in miscarriage. When you include pregnancies that were undetected, or mistaken for a late period, that number increases to 1 in 3. Some experts estimate that the number is even higher than that, but since not every miscarriage is counted, it’s hard to know for sure. Bottom line – miscarriage is common.  

Knowing that a lot of pregnancies end in miscarriage doesn’t make your experience any easier, and it doesn’t mean that you “should” feel any better about your situation. Loss is loss, and it takes time to process the emotions around it. 

But sometimes, knowing just how common miscarriage is can shift your mindset from “what’s wrong with me?” to “this is something that happens sometimes.” Processing grief is much easier if you don’t have feelings of guilt on top of it.  

That said, if you do feel you need extra support in the grieving process, please do not hesitate to reach out to a mental health provider.

What Causes Miscarriage?

For many miscarriages that happen early in pregnancy, we may not know the exact cause. 

Some of the causes of miscarriage include:

  • Chromosomal abnormalities
  • Blighted ovum
  • Molar pregnancy
  • Illness or infection
  • Problems with sperm
  • Autoimmune disease
  • PCOS
  • Luteal phase defect
  • Ectopic pregnancy
  • Uterine fibroids 
  • Uterine abnormalities
  • Cervical incompetence
  • Placenta difficulties
  • Environmental exposure
  • Diabetes

Chromosomal Abnormalities 

The most common reason that an embryo (<10 weeks) or fetus doesn’t survive is that it is not viable, due to genetic abnormalities. This means that the fetus is developing with a genetic issue that would mean it is unable to survive outside the womb or further along in pregnancy. 

Scientists believe that sometimes, certain genes in a developing baby may be missing or causing abnormal growth of the baby or placenta. The baby has the wrong number of chromosomes. This results in miscarriage. It is possible that the mother’s body recognizes that the fetus is unable to survive and ends the pregnancy.

Blighted Ovum

A blighted ovum is also called anembryonic pregnancy. This means that there is no embryo, only a sac, and a placenta. This condition shows up as a positive pregnancy test because pregnancy hormones are being created. Often, women with a blighted ovum will exhibit symptoms of pregnancy as well. They may feel breast tenderness, have nausea and become bloated. If this condition is discovered by your doctor before you have a miscarriage, you may have to choose between waiting for the pregnancy to terminate on its own or having a surgical procedure to remove the ovum.

Molar Pregnancy

Molar pregnancy, or hydatidiform mole, is a condition that causes miscarriage. There are two kinds of molar pregnancy:

  • Complete molar pregnancy. This occurs because the chromosomes from the mother are missing and both sets of chromosomes are from the father.
  • Incomplete or partial molar pregnancy. The mother’s chromosomes are present, but two sets of chromosomes from the father are, too. 

Symptoms of a molar pregnancy include vaginal bleeding, nausea, vomiting, pelvic pain, and cysts that pass through the vagina.

Illness Or Infection

If a mother has an illness or infection, it can cause her to lose her pregnancy. Illnesses like the Zika virus, measles, or sexually transmitted infections can prevent a baby from developing to full term. 

Problems With Sperm

While traditional narratives typically focus on the mother’s role in miscarriage and infertility, there is evidence to suggest that the quality of the father’s sperm can have an impact on miscarriage. In a recent study, researchers found a link between the quality of a man’s sperm and the incidence of recurrent miscarriage in their partner. 

Autoimmune Disease

Sometimes, women who suffer from autoimmune diseases are at risk for miscarriage. While many, many women with autoimmune disease have healthy babies, sometimes it can be a contributing factor to miscarriage.

Some of the autoimmune conditions that researchers have linked to miscarriage include:

  • Lupus
  • Autoimmune thyroid disease
  • Antiphospholipid antibody syndrome
  • Scleroderma
  • Sjogren’s syndrome


Women with Polycystic Ovarian Syndrome (PCOS) are at 3 times higher risk for miscarriage. Researchers believe that elevated levels of insulin and inflammation in women with PCOS may cause this unfortunate phenomenon. Many women with PCOS can and do have full-term pregnancies. Please do not despair if you are trying to get pregnant with PCOS.  

Luteal Phase Defect

Luteal phase defect occurs when the lining of the uterus doesn’t develop properly. It is characterized by low levels of progesterone. Your doctor may recommend progesterone treatment if you experience miscarriage and have a luteal phase defect. 

Ectopic Pregnancy

An ectopic pregnancy happens when a fertilized egg begins to develop outside of the womb. Typically, this occurs in one of the fallopian tubes. Ectopic pregnancy is considered a life-threatening emergency, and requires immediate medical attention. If the pregnancy isn’t miscarried, the egg continues to grow outside of the womb and is very serious for the mother. Ectopic pregnancy can be accompanied by abdominal pain and vaginal bleeding.

Uterine Fibroids

Since they can hinder the baby’s blood supply and room for growth, uterine fibroids have been a suspected cause of miscarriage. However, a large, high-quality, recent study appeared to refute this commonly held belief, stating there is no association between fibroids and miscarriage. Still, if you have fibroids and plan on getting pregnant, it’s an important thing to mention to your healthcare provider. 

Uterine Abnormalities

Some women are born with a uterus that is divided into sections by muscles. This condition is called a septate uterus. Unfortunately, this condition often remains undiagnosed until a woman experiences a loss of pregnancy. Once the septate uterus is discovered, surgery can be performed to correct it in most cases.

Other uterine issues such as endometriosis and Asherman syndrome – which causes scar tissue to form in the uterus – can also lead to a higher incidence of miscarriage. Endometriosis has been linked to an 80% increased chance of miscarriage. 

Cervical Incompetence

When the cervix dilates early in pregnancy (it’s not supposed to open until you give birth) miscarriage can occur. This is called cervical incompetence or cervical insufficiency. Sometimes, the cervix can be stitched closed in a procedure called a cerclage to prevent miscarriage if cervical incompetence is discovered before a miscarriage occurs. 

Placenta Difficulties

When the placenta does not develop properly, miscarriage can result. The placenta is the organ that develops during pregnancy to sustain the baby’s growth. The placenta provides nutrients to the baby and removes waste from the baby through the umbilical cord. It helps to pass on the necessary antibodies to the baby from the mother and emits the hormones that help keep a pregnancy viable. If the placenta doesn’t grow properly or grow large enough to do its job, miscarriage can result. 

Environmental Exposure

Smoking, alcohol, heavy metals, endocrine-disrupting chemicals, solvents, pesticides, pollution, and radiation have all been linked to miscarriage, preterm delivery, low birth weight, and birth defects. If a mother is exposed to high levels of any of these chemicals, loss of pregnancy may result. 


Experts recommend getting a good handle on your blood sugar levels before trying to become pregnant if you have diabetes. High blood sugar levels early in pregnancy have been shown to increase the risk of miscarriage. Women with diabetes often have full-term pregnancies and healthy babies, but they do need to plan for extra complications that pregnancy can bring to a woman’s body. 

MTHFR Gene Mutation

Methyltetrahydrofolate reductase is a gene involved in the utilization of folate. Folate is necessary for DNA synthesis, which as you can imagine, is happening quite rapidly in a developing baby. Some studies have pointed to MTHFR being a cause of miscarriage due to clotting disorders. There’s also been observations that women who experience miscarriage have a mutation in this gene.

At this time, the data to support this idea is highly debated. When considering the intervention would be taking a quality prenatal with active folate and perhaps beginning aspirin under a doctor’s supervision, many experts agree the benefits outweigh the risks while we await more studies to be produced.

I have an article on folate vs folic acid if you’d like to learn more on the topic.

What Are The Types Of Miscarriage?

Miscarriages are divided into several different types, depending on the cause. 

Early Miscarriage

A miscarriage is considered an early miscarriage if it occurs during the first 12 weeks of pregnancy. This is when the majority of miscarriages happen. Some women do not even know they are pregnant yet when a miscarriage occurs since many happen in the first two weeks of pregnancy. 

Late Miscarriage

Late miscarriage is when pregnancy is lost between 14 and 24 weeks of gestation. Only about 1-2% of miscarriages occur during this second trimester. That is why you’ll often hear to wait on  announcing and celebrating a pregnancy until after 12 weeks have passed. It is much more likely that once a fetus reaches the 12-week mark it will make it to full term. 

However, you need to do what is best for you and your family. If announcing and celebrating feels good to you then go for it. Yes, there is a risk off loss, but you’re going to need support if it does, which will likely come from those who you’d share the news with in the first place.

Threatened Miscarriage

When you are experiencing signs and symptoms like bleeding or abdominal pain, this is what’s called a threatened miscarriage. A lot of the time, women that experience these signs and symptoms go on to have full-term pregnancies. Other times, these symptoms can be a symptom that the pregnancy may end prematurely. 

Inevitable Miscarriage

An inevitable miscarriage is when a miscarriage happens without any preceding symptoms – meaning, the pregnancy has ended before the mother has any symptoms. Inevitable miscarriage typically is accompanied by severe cramping and vaginal bleeding. During this type of miscarriage the cervix usually opens and the contents of the womb are expelled. Sometimes, women may need to have a procedure to make sure the uterus is clear. 

Complete Miscarriage

Complete miscarriage is characterized by a complete voiding of the pregnancy tissues from the uterus. In these situations, women may bleed for several days and/or experience cramping, or even labor-like pains. 

Incomplete Miscarriage

As the name implies, incomplete miscarriage means that the body doesn’t completely expel all of the pregnancy-related tissues. The uterus may contract and try to empty, but not everything comes out. Sometimes, women who experience an incomplete miscarriage will need a medical procedure called a dilation and curettage (D&C) in order to remove the remainder of the tissues inside the uterus. During this process, the cervix is dilated and the uterine lining is scraped out. Although this is considered an outpatient procedure, it is a surgery and requires anesthesia.

Missed Miscarriage

When a baby passes away but remains in the womb, this is considered a missed miscarriage. This is sometimes discovered during a routine checkup appointment. Sometimes, women notice that their pregnancy symptoms have subsided but not always. When missed miscarriage occurs, women may be given the choice to wait and see if the miscarriage will happen on its own, or have a D&C procedure done.

What’s the Difference Between a Spontaneous Abortion and Miscarriage?

A spontaneous abortion is the medical term for miscarriage. Miscarriage is the term often used with patients because most people associate the word “abortion” with an elective procedure.

Abortion is a term that refers to the end of a pregnancy due to expulsion or removal of the tissue from the body. In the case of a spontaneous abortion, this is an involuntary event.

Do not be alarmed if you see the diagnosis of spontaneous abortion in your chart notes following a miscarriage. This is the accurate medical diagnosis of this event and does not imply  that you had the option to end your pregnancy or not.

What Are The Signs Of Miscarriage?

It’s important to note that sometimes, women have the signs and symptoms of miscarriage but do not actually lose the pregnancy. Sometimes, women have normal spotting around 3-5 weeks into their pregnancy. However, if you experience any of the following symptoms, it’s important to contact your doctor right away.

Some of the signs of miscarriage include: 

  • Brown or bright red vaginal bleeding
  • Vaginal bleeding with clots
  • Heavy vaginal bleeding
  • Painful cramping
  • Abnormal discharge
  • Sudden disappearance of pregnancy symptoms like nausea, vomiting or breast tenderness
  • Back pain

What Does Tissue Look Like When You Miscarry?

For the most part, when you miscarry, the vaginal discharge won’t look too different from a regular period. This is particularly true if you miscarry very early in the pregnancy. Sometimes, rather large blood clots can be expelled. 

Bleeding from a miscarriage can take up to two weeks. During a miscarriage, heavy bleeding may occur for several hours as the tissues and fetus pass from the body.   

How Common Is Miscarriage?

Miscarriage is estimated to occur in 10-25% of known pregnancies. The risk of miscarriage increases with age. Women under 35 are least likely to have a miscarriage with a 15% chance. Women aged 35-45 are 20-35% likely to have a miscarriage. For women aged 45 and older, the risk increases to 50%. 

Having a previous miscarriage means a woman has a 14-25% chance of having another one. If she’s had two, her chances of a third increase to 24-29%. 

That said, age plus miscarriage history do not determine whether or not a woman can carry a healthy pregnancy. It’s possible for women over 40 with a history of miscarriages to have healthy babies – sometimes with medical intervention, other times with medical supervision but no intervention.

Miscarriage Prevention

Not all miscarriages can be prevented and a miscarriage does not indicate you did anything wrong. In fact, you can do everything right and a miscarriage may still occur due to issues with the embryo.

  • Take a prenatal vitamin prior to conceiving and during pregnancy to ensure your fetus has the nutrients it needs to develop.
  • Meet with your birth provider to ensure you're getting proper prenatal care.
  • Communicate with your provider and seek medical care if you have any concerns throughout your pregnancy.
  • Avoid smoking, alcohol, and drug use while pregnant.
  • Avoid infection and food borne illness. Wash your hands, avoid sick people, and ensure meals are properly prepared.
  • Maintain healthy blood sugar levels by eating a nutrient dense diet with plenty of quality protein and vegetables. You can check out a free recipe guide here.
  • Limit caffeine, whether coffee or tea, to no more than 200 milligrams daily.

How Do Doctors Test For Miscarriage? 

Most doctors won’t recommend testing until after you’ve had more than one and sometimes three miscarriages, which can seem cruel, I know. This is because most of the time, women go on to have healthy pregnancies after having a miscarriage. 

Some tests your doctor may be able to use to help determine the cause of recurrent miscarriage include:

  • Tests for autoimmune diseases
  • Chromosome testing
  • Hormone testing
  • Blood sugar testing
  • Uterine testing

Tests For Autoimmune diseases

Some women have autoimmune diseases and are unaware. Now may be the time to get to the bottom of any issues that may be affecting your immune system. Tests for antiphospholipid antibodies and lupus should be performed. 

Chromosome Testing

Certain blood tests for you and your partner may be able to reveal any chromosomal issues that may be going on. Testing the tissues of the miscarriage can also reveal if genetic abnormalities are the cause of miscarriage if a D&C was performed.

Hormone Testing

Abnormal blood levels of certain hormones can shed light on issues that may be causing miscarriage. Thyroid antibodies, and progesterone and prolactin levels should be evaluated, as well as follicle-stimulating hormone (FSH), luteinizing hormone (LH) and anti-Mullerian hormone (AMH). 

Blood Sugar Testing

Testing blood glucose levels may be appropriate as well. Some women have diabetes or prediabetes and they are unaware until they miscarry. 

Uterine Testing

Since uterine abnormalities can play a role in miscarriage, it’s sometimes warranted to evaluate uterine health. Transvaginal ultrasounds, hysteroscopy, and hysterosalpingogram can visually check for problems that may be contributing to miscarriage. Sometimes, a biopsy of the endometrium can reveal issues that may be causing miscarriage.  

There Is Always Hope

Even though you may be experiencing unimaginable pain, grief, and loss right now, there is always hope to hold on to.

Remember, the majority of women who experience a loss of pregnancy go on to have happy, healthy babies. 

Don’t forget to utilize your support system, and don’t be afraid to talk to a professional. Most of all, don’t suffer in silence. 

I hope you’re able to use this information here to find a small bit of comfort.


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About The Author

Dr. Jolene Brighten

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Dr. Jolene Brighten, NMD, is a women’s hormone expert and prominent leader in women’s medicine. As a licensed naturopathic physician who is board certified in naturopathic endocrinology, she takes an integrative approach in her clinical practice. A fierce patient advocate and completely dedicated to uncovering the root cause of hormonal imbalances, Dr. Brighten empowers women worldwide to take control of their health and their hormones. She is the best selling author of Beyond the Pill and Healing Your Body Naturally After Childbirth. Dr. Brighten is an international speaker, clinical educator, medical advisor within the tech community, and considered a leading authority on women’s health. She is a member of the MindBodyGreen Collective and a faculty member for the American Academy of Anti Aging Medicine. Her work has been featured in the New York Post, Forbes, Cosmopolitan, Huffington Post, Bustle, The Guardian, Sports Illustrated, Elle, and ABC News. Read more about me here.