Why Does a Miscarriage Happen? – Causes, Symptoms & Treatment

By BSc, MSc (embryologist), MD, PhD, MSc (gynecologist), (gynecologist), MD (gynecologist) and BA, MA (fertility counselor).
Last Update: 09/24/2018

A miscarriage, also known as natural or spontaneous abortion, is an involuntary embryo loss that occurs before the 20th week of pregnancy, or the loss of a fetus that weighs 500 grams or less. If it happens later, it's considered a preterm birth with risk of stillbirth.

It's important for the pregnant woman not to blame the miscarriage on herself, as the cause behind is not usually related to the mother, but on chromosomal abnormalities in the fetus.


Acording to the Merriam-Webster Dictionary, the following is the meaning of the noun miscarriage:

Spontaneous expulsion of a human fetus before it is viable and especially between the 12th and 28th weeks of gestation.

Taking this definition into account, we should not confuse it with an abortion, which often refers to the induced expulsion of a human fetus.

Statistical data shows that most miscarriages occur during the first trimester of pregnancy. More often than not, the woman isn't even aware that she was expecting.

A miscarriage can lead to serious consequences or side effects for the health of the woman, both at the physical and psychological levels. A miscarriage is, unfortunately, a dramatic scenario that causes significant distress in prospective parents.

Recovering from a miscarriage can take several weeks or even months. Most women have their periods again within 4 to 6 weeks after having miscarried.

The most complicated after going through a miscarriage is to overcome the psychological impact and avoid depression and anxiety. Miscarrying severely affects prospective mothers not only on the emotional side, but also because the hormones levels change sharply in a short period of time.

It is estimated that about 10% of women who experience an spontaneous abortion may have acute stress disorder and up to 1% may have post-traumatic stress disorder.

There's no reason for you to be ashamed or afraid after a miscarriage. You can join a support group or get couple therapy if you need it to cope with this situation.


We distinguish several types of miscarriage or spontaneous abortion based on the following factors:

Sporadic vs. recurrent
If the pregnancy loss occurs spontaneously or repeatedly.
Clinical vs. subclinical
If it occurs at an advanced gestational age or very early, that is, after embryo implantation.
Anembryonic vs. embryonic
When the embryonic sac cannot be seen on an ultrasound yet or, on the contrary, the embryo is seen but stops developing.
Complete vs. incomplete
Depending on whether your body expels all the products of pregnancy or not.

Learn more about the different types of spontaneous abortion and their names here: What Are the Different Types of Miscarriage?


The causes of miscarriage are typically related to the fetus, but they can be associated with the mother-to-be as well. Let's see some examples of each:

Fetal causes
The presence of chromosomal abnormalities in the fetus is the leading cause of spontaneous abortion and early pregnancy loss.
Maternal causes
Uterine malformations, infections, autoimmune diseases or endocrine disorders can lead to miscarriage.

Complications during pregnancy can lead to the loss of the pregnancy as well. However, the severity of these complications is higher when the following risk factors are involved:

  • An unhealthy or incomplete diet. You should take special care with the foods you eat during pregnancy.
  • Smoking
  • Hormonal imbalances
  • Sexually Transmitted Diseases (STDs)
  • Health conditions, including congenital heart diseases, kidney diseases, diabetes, or thyroid problems.
  • Running a high fever
  • Poor IUD positioning at the time of conception
  • Uterine malformations

If you are interested in getting more insight on the causes of miscarriage, go check the following guide: What Causes a Miscarriage?


Although one can notice certain symptoms or signs directly associated with miscarriage, it is important to know that it doesn't happen in all cases. Having symptoms of miscarriage is just a warning sign.

The following are the most common symptoms associated with miscarriage:

  • Heavy vaginal bleeding
  • Moderate-to-severe pain of unknown origin
  • Abdominal pain
  • Fever
  • General weakness or lethargy

When a woman has signs of miscarriage, she should contact her doctor at once to look for the best solution and prevent the risk of miscarriage from becoming an actual miscarriage.


When a woman is at risk of miscarrying, rest in bed is crucial. Also, your doctor may prescribe you progesterone capsules, although the effectiveness of this practice has been questioned in several scientific studies.

If miscarriage finally occurs, no specific treatment is necessary. Your body will expel the fetus naturally in the form of bleeding. If this doesn't happen, the remaining tissue will be removed by means of D&C (Dilation & Curettage).

Using an anesthetic, D&C involves the dilation of the cervix and subsequent removal of the remaining tissue that may still be in the uterus.

If necessary, your doctor may prescribe you medications such as Misoprostol, which can cause uterine contractions that help expel the remaining tissue. Misoprostol has, however, a series of side effects that one should not overlook:

  • Nausea
  • Vomiting
  • Diarrhea
  • Shivering
  • Headache
  • Vaginal bleeding

The materials expelled spontaneously or as a consequence of scratching the uterine cavity is sent to the laboratory so that a specialist can evaluate it. The goal is to find the cause of the miscarriage and prevent it from happening again.

If you need to undergo IVF to become a mother, we recommend that you generate your Fertility Report now. In 3 simple steps, it will show you a list of clinics that fit your preferences and meet our strict quality criteria. Moreover, you will receive a report via email with useful tips to visit a fertility clinic for the first time.


The first prevention measure for miscarriage is to take care of yourself from the very beginning of your pregnancy. We have mentioned the main risk factors for miscarriage above, so we recommend that you avoid these habits at all costs to reduce the chances of miscarriage.

If you are planning a pregnancy, we strongly recommend that you treat first any disease or health problem that is directly associated to miscarriage or can be a risk factor.

High blood pressure, obesity, and diabetes can increase the risk of miscarriage if untreated. Examining whether the intended mother has had an infection such as toxoplasmosis or rubeola, which can cause severe fetal alterations leading to pregnancy loss.

Other disorders that should be taken into account when trying to conceive, due to its direct relation with spontaneous abortions, are uterine malformations and immunological diseases.

Leading a healthy lifestyle, including a balanced diet and moderate exercise, is crucial as well. Moreover, regular prenatal care, attending every prenatal visit, and following the doctor's instructions strictly, is the best way to avoid potential pregnancy complications.

FAQs from users

What are the causes of recurrent chemical pregnancies?

By Dr. Joel G. Brasch (gynecologist).

A chemical pregnancy is an early pregnancy loss that occurs shortly after implantation.

The exact cause of a chemical pregnancy is unknown. But in most cases the miscarriage is due to problems with the embryo, possibly caused by a low quality of sperm or egg.

Other causes may include:

  • abnormal hormone levels
  • uterine abnormalities
  • implantation outside the uterus
  • Sexually transmitted infections
  • Being over the age of 35 increases the risk of a chemical pregnancy
  • blood clotting and thyroid disorder

Read more

What is a therapeutic abortion?

By Óscar Oviedo Moreno MD (gynecologist).

A therapeutic abortion is a type of abortion that is performed for medical reasons. Common basic medical causes include:

  • In case a pregnancy is a life-threatening condition for the mother.
  • To protect the physical and/or mental health of the mother.
  • When there exists risk of birth defects or genetic disease.
  • In multiple pregnancies, it is possible to perform a selective reduction or multifetal pregnancy reduction (MFPR) to a number of fetuses that removes serious risks and makes the pregnancy a viable one.
  • When there is a serious risk for the life of the developing baby, either because there exists a malformation, or because there is a high risk of being born dead (stillbirth) or death right after being born

Is there an increased risk of miscarriage in pregnancies achieved using reproductive technologies?

By Carmen Ochoa Marieta MD, PhD, MSc (gynecologist).

No, the risk of miscarriage once a woman achieves pregnancy, whether naturally or through assisted conception, is exactly the same.

How do you calculate your fertile days after a miscarriage?

By Andrea Rodrigo BSc, MSc (embryologist).

Ovulation can occur again as early as two weeks after a miscarriage. To calculate your fertile days, we recommend that you take your temperature each morning before you get out of bed using a basal body thermometer.

How much does a miscarriage hurt?

By Andrea Rodrigo BSc, MSc (embryologist).

It varies from woman to woman. It is often described as a period-like pain that is accompanied by cramps of a varying intensity. In some cases, it doesn't hurt, but for others it can become extremely painful.

What week in pregnancy do miscarriages usually happen?

By Andrea Rodrigo BSc, MSc (embryologist).

We cannot mention a particular week, but we can say that they occur within the first 20 weeks of pregnancy, and most of them in the first 12 weeks.

What types of autoimmune diseases cause miscarriage?

By Andrea Rodrigo BSc, MSc (embryologist).

Some of the most common are listed below:

  • Crohn's disease
  • Celiac disease (gluten intolerance)
  • Type I diabetes
  • Reactive arthritis
  • Multiple sclerosis
  • Grave's disease
  • Scleroderma
  • Addison's disease
  • Hashimoto’s thyroiditis

What are normal hCG levels after miscarriage?

By Andrea Rodrigo BSc, MSc (embryologist).

After a miscarriage, hCG levels may vary depending on the week of pregnancy in which it happens. For example, if it happened on week 6, hCG levels would be expected to range between 1.080 mUI/ml and 56.500 mUI/ml.

See also: hCG Levels After a Miscarriage or a Medical Abortion.

Why do miscarriages keep happening?

By Andrea Rodrigo BSc, MSc (embryologist).

The truth is, sometimes the cause of recurrent pregnancy loss (RPL) cannot be found. The good news in these cases is that there's always a chance that a successful pregnancy happens next time.

There are, however, some health conditions that are known to increase a woman's chances of miscarrying. Although they are uncommon, the following are some conditions that are known to lead to RPL:

  • Antiphospholipid syndrome (APS)
  • Thrombophilia
  • Genetic problems
  • Problems with your womb
  • Bacterial vaginosis
  • Polycystic ovaries
  • Some lifestyle factors

I want to get pregnant fast after a miscarriage, is it possible?

By Andrea Rodrigo BSc, MSc (embryologist).

As explained earlier, you can expect to ovulate again and therefore be able to get pregnant again as early as two weeks after a miscarriage.

Suggested for you

A miscarriage is a devastating situation for most women, but our advice is that you keep on trying unless otherwise indicated by your doctor. Do you know what is the best time to start to conceive again? Learn more here: Pregnancy After a Miscarriage or Abortion.

A few days or even weeks after a miscarriage, it is likely that a pregnancy test still shows a positive result. How is it possible? It is related to hCG, the pregnancy hormone, and you can discover the details of this phenomenon here: hCG Levels After a Miscarriage or a Medical Abortion.

Finally, we recommend that you have a look at the following guide should you need further information about the most common causes of miscarriage: Why Does a Miscarriage Happen?

Our editors have made great efforts to create this content for you. By sharing this post, you are helping us to keep ourselves motivated to work even harder.


Chung et al. Spontaneous abortion: a randomized, controlled trial comparing surgical management with conservative management using misoprostol; Fertility and Sterility 1999; 71:1054 – 9.

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Verdú LI, Santamaría R. (2003). Aborto: concepto y clasificación. Etiología, anatomía patológica clínica y tratamiento. En: Cabero L. editor. Tratado de Obstetricia, Ginecología y Medicina de la Reproducción. 1ª Ed. Madrid: Editorial Médica Panamericana; pp. 500-508

Wang JX, Norman RJ,Wilcox AL. Incidence of spontaneous abortion among pregnancies produced by assisted reproductive technology. Hum Reprod 2004;19:272 – 227.

Wilcox AJ, Weinberg CR, O’Connor JF, Baird DD, Schlatterer JP, Canfield RE, Armstrong EG, Nisula BC. Incidence of early loss of pregnancy. N Engl J Med 1988;319:189 – 194.

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FAQs from users: 'What are the causes of recurrent chemical pregnancies?', 'What is a therapeutic abortion?', 'Is there an increased risk of miscarriage in pregnancies achieved using reproductive technologies?', 'How do you calculate your fertile days after a miscarriage?', 'How much does a miscarriage hurt?', 'What week in pregnancy do miscarriages usually happen?', 'What types of autoimmune diseases cause miscarriage?', 'What are normal hCG levels after miscarriage?', 'Why do miscarriages keep happening?' and 'I want to get pregnant fast after a miscarriage, is it possible?'.

Read more

Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
BSc, MSc
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Carmen Ochoa Marieta
Carmen Ochoa Marieta
MD, PhD, MSc
Bachelor's Degree in Medicine from the Basque Country University. PhD in Medicine & Surgery from the University of Murcia. Currently, she is the director of the Assisted Reproduction Unit of Centro de Estudios para la Reproducción (CER SANTANDER) in Santander, Spain, as well as the director of the Diagnostic Unit of Human Assisted Reproduction in Bilbao. More information about Carmen Ochoa Marieta
License: 484805626
Dr. Joel G. Brasch
Dr. Joel G. Brasch
Dr. Joel Brasch is the Medical Director of Chicago IVF, founded in 2005. He is board certified by the American Board of Obstetrics and Gynecology, and has over 25 years of direct experience in fertility treatment and reproductive care. He is also the Director of Mount Sinai Medical Center’s Division of Reproductive Endocrinology and Infertility. More information about Dr. Joel G. Brasch
 Óscar Oviedo Moreno
Óscar Oviedo Moreno
Bachelor's Degree in Medicine & Surgery from the University of Caldas (Colombia). Specialist in Internal Medicine by the Pontificia Universidad Javeriana of Bogotá. Degree standardized in Spain in 2003. Specialist in Gynecology & Obstetrics from the Complutense University of Madrid, with residence at Hospital Clínico Universitario San Carlos de Madrid. Expert in Reproductive Medicine and Certification in Obstetric-Gynecologic Ultrasound (levels I, II and III). More information about Óscar Oviedo Moreno
License: 282858310
Adapted into english by:
 Sandra Fernández
Sandra Fernández
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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