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  4. Causes of Miscarriage

Causes of Miscarriage

  1. What are the causes of miscarriage?
  2. Age and miscarriage
  3. Chemical pregnancy
  4. Chromosomal abnormalities
  5. Placental problems
  6. Medications
  7. Diseases and infections
  8. Environmental and lifestyle factors
  9. Womb or cervical dysfunction
  10. Long-term health conditions and immune disorders
  11. Other causes
  12. Diagnosis
  13. FAQ

What are the causes of miscarriage?

A miscarriage is a fairly common complication of early pregnancy, in which the developing embryo or fetus dies in the womb of natural causes, or due to exposure to substances, i.e. in certain medications, which are unsuitable for use during pregnancy. The term miscarriage is used to describe this process when it happens during the first 20 weeks of pregnancy:

  • A miscarriage which occurs in the first trimester (weeks 1-12 of pregnancy) is known as an early miscarriage
  • A miscarriage which occurs in the second trimester (during weeks 13-20 of the pregnancy) is known as a late miscarriage

Loss of the fetus which occurs after week 20 of pregnancy is known as a stillbirth, or fetal death.

Most miscarriages are early miscarriages, and are caused by factors including:[1][2]

  • Chemical pregnancy, when the fertilized egg fails to implant in the uterine (womb) lining, and the pregnancy can only be evidenced by measuring levels of the pregnancy hormone, hCG, which will be detectable in blood or urine pregnancy tests. The embryo does not develop sufficiently to be visible on an ultrasound scan.
  • Chromosomal (DNA) abnormalities, which are present in the fetus.
  • Problems with the placenta, the organ responsible for the exchange of nutrients and gases between the pregnant person and the fetus.

Certain long-term health conditions, particularly immunological disorders, such as diabetes or systemic lupus erythematosus, may cause early or late miscarriage. (See the section on miscarriage caused by long-term health conditions and immune disorders.)

The typical causes of late miscarriages tend to be different from the causes of early miscarriages. The leading causes of late miscarriage include:[2]

  • Adverse reactions to medications
  • Diseases and infections, such as toxoplasmosis or rubella
  • Food poisoning
  • Environmental factors, such as exposure to radiation
  • Womb or cervical dysfunction

More rarely, miscarriage can be caused by other factors, including histamine intolerance, fibroids or psychological stress.

It is also possible for a miscarriage to be caused by treatable conditions; for example, fertility issues affecting one or both parents. (See the section on diagnosing and treating causes of miscarriage.)

Age and miscarriage

Being older increases the likelihood of miscarrying, in both the first and second trimesters. The older a person is, the more likely it becomes that their pregnancy will result in a miscarriage:[2]

  • In women under 30, only 1 in 10 pregnancies end in miscarriage
  • In women over 45, more than half of all pregnancies end in miscarriage

The older either parent is, the more likely it is that the developing fetus will be vulnerable to other causes of miscarriage, which renders age the leading cause of miscarriage overall. In particular, the risk of conceiving an embryo with chromosomal abnormalities, which may lead to miscarriage, increases with age.

The risk of miscarriage increases after the approximate age of 35 for women, and 40 for men. Notwithstanding the increased risk of miscarriage, it is possible to have a healthy pregnancy after these ages.

Chemical pregnancy

In a chemical pregnancy, the fertilized egg fails to implant properly in the uterine (womb) lining and/or survive in the uterus. Miscarriages caused by chemical pregnancy occur very early in pregnancy, usually at around week five of pregnancy, before the fetal heartbeat would be detectable via an ultrasound scan.

It is possible for a person to be unaware of their chemical pregnancy and of miscarrying. Many early miscarriages go unnoticed because the symptoms of early miscarriage, such as abdominal pain and/or vaginal blood loss, are not usually severe. They may therefore be perceived as normal menstruation.

Good to know: Many forms of birth control (contraception), such as the combined pill or progesterone-only mini pill work to thin the lining of the womb. These medications are usually taken intentionally to prevent pregnancy. One way in which they do this is by stopping the fertilized egg from implanting. When a fertilized egg does not implant due to the effective use of birth control, this is not considered a chemical pregnancy.

Chromosomal abnormalities

Chromosomal abnormalities are the most common cause of early miscarriage. They are detected in 50 to 85 percent of miscarried pregnancy tissue, which, as standard practice, is usually analyzed after a miscarriage takes place, to help determine the cause.[3]

Most people have 23 pairs of chromosomes. Chromosomes are basically blocks of DNA; the mechanism by which parents pass their genes onto their offspring, determining characteristics like hair and eye color and the possibility of carrying – or being affected by – hereditary diseases like sickle cell disease.

The male sex cell (sperm) and the female sex cell (egg) each carry 23 chromosomes. A normal fertilized egg (zygote) has 23 pairs of chromosomes and is equipped to develop into a healthy embryo, which in turn develops into a fetus as the pregnancy progresses. An embryo becomes a fetus at around eight weeks into the pregnancy, at which point all major body parts are present.

If an embryo has more or fewer than 23 pairs of chromosomes, this is a chromosomal abnormality and the zygote will be vulnerable to miscarriage, either during its embryo stage or when it develops into a fetus.

A multitude of potential problems stemming from chromosomal abnormalities can affect the embryo or fetus. It can take an unpredictable amount of time for an embryo or fetus to develop enough for it to become clear that, due to its chromosomal makeup, it would be unlikely to survive after birth. It is at this point, usually in the first trimester, that miscarriage will occur.

Types of chromosomal abnormalities which commonly lead to miscarriage include:[4]

Blighted ovum

Blighted ovum is a very common type of miscarriage which occurs early in pregnancy, usually in week 5-6. This is before the developing fetus would be visible on an ultrasound scan.

A blighted ovum miscarriage is caused by high levels of chromosome abnormalities in the fetus which would prevent any resultant baby from developing healthily. As a result, the fertilized egg does not develop into an embryo. Instead, a cluster of cells forms in the uterus to make an empty pregnancy sac. A blighted ovum often results in miscarriage before a person is aware that they had become pregnant.

Trisomy

The fetus will contain one extra chromosome, so 47 chromosomes will be present in total, rather than the usual 46 (23 pairs). The chances of miscarriage in a case of trisomy are high. Trisomies that do not result in miscarriage are usually born with congenital conditions such as Down syndrome.

Nullisomy

The embryo will be missing a pair of chromosomes. Embryos with missing chromosomes cannot develop healthily and will result in miscarriage.

Monosomy

A monosomy is a fetus in which one chromosome is missing. The fetus will contain 45 chromosomes: 22 pairs and a half. Monosomies almost always result in miscarriage. If a monosomy comes to term, the baby usually has a congenital condition and/or can only survive outside the womb for a short time.

Placental problems

Problems with the placenta are frequently found to be the cause of miscarriage or stillbirth, especially early miscarriage. The placenta is an organ which develops in the uterus during pregnancy. It is pancake-shaped and should be positioned at the top of the uterus, as far away as possible from the cervix, i.e. the part connecting the womb to the vagina. After the baby is born, further contractions will typically push the placenta out through the vagina.

In its correct position, a healthy placenta performs important functions including:[5]

  • Providing the developing fetus with oxygen and nutrients
  • Removing waste products from the fetus’ blood through the umbilical cord
  • Secreting the hormones necessary to maintain pregnancy
  • Passing on antibodies to protect the fetus from infection

If the placenta does not form or function correctly throughout pregnancy, this is likely to negatively affect the development of the fetus, causing a miscarriage. Ways in which the placenta may cause miscarriage include:[6][7][8]

  • Passing on toxins from alcohol, excess caffeine, unsuitable environments, medications that are unsuitable for use in pregnancy and illicit substances from the pregnant person to the pregnancy tissue and/or fetus.
  • Passing on harmful cells related to infections or inadequately managed long-term health conditions from the pregnant person to the pregnancy tissue and/or fetus.
  • Placental insufficiency, in which the placenta fails to pass sufficient hormones, antibodies, oxygen and nutrients to the developing baby. Placental insufficiency is particularly common when the placenta does not grow big enough to sustain the fetus. For example, this sometimes happens when it is sustaining twins rather than a single fetus.

Medications which can cause miscarriage

People who become pregnant may have an ongoing health condition, or develop a new condition, which requires continual treatment and/or management using certain over-the-counter (OTC) or prescription medications. Before using any medication, pregnant women should always confirm with a doctor that it is safe for use in pregnancy.

Physicians can advise on making changes to long-term medications which are needed and/or recommend appropriate new medications to use, to minimise the risks to both mother and baby.

In addition to needing medications for possible ongoing conditions and/or new conditions unrelated to the pregnancy itself, pregnancy can cause a person to be affected by certain related conditions such as severe morning sickness or headaches, mainly in the first trimester. These can usually be treated effectively and safely with appropriate OTC or prescription medications as recommended by a doctor.[9]

However, particular medications are unsuitable for pregnant women and using them can cause miscarriage or (teratogenic) abnormalities and/or malformations. The reason that certain medications may cause miscarriage is that, like food and drink consumed by the pregnant person, their components are transmitted by the placenta to the developing fetus. Pregnant women are not usually included in safety trials for new compounds, and therefore only a limited amount is known about whether medications are wholly safe for use during pregnancy.

To minimize the risk of a medication-induced miscarriage, doctors will:

  • Prescribe only medications which are widely accepted to be safe for pregnant women and the developing fetus
  • Advise people to avoid medications which have been linked to pregnancy or birth complications and miscarriage

Medications which are commonly linked to miscarriage include:[10][11]

Ibuprofen

An over-the-counter or prescription painkiller commonly used to treat fever inflammation and pain, ibuprofen is not recommended for use during pregnancy and can cause congenital defects as well as increase the risk of miscarriage.

Read more about Ibuprofen »

Isotretinoin

Used to treat severe acne, this medication can cause congenital defects, most often affecting the baby’s heart and face, as well as increase the risk of miscarriage. People who take this medication regularly and are trying to conceive should discuss the issue, and the possibility of a change in medication with their doctor, in advance of becoming pregnant.

Vitamins and herbal supplements

Although vitamins and herbal supplements may contain only natural ingredients and thus may appear to be a healthier alternative to pharmaceutical medications, many are unsuitable for use in pregnancy and can cause birth defects or increase the likelihood of miscarriage and other complications. For example, consuming too much vitamin A can cause congenital defects; supplements containing a maximum of 5,000 IU are recommended. Normal quantities of garlic and fenugreek (as used in cooking) pose no health risks, but larger quantities, found in supplements, may cause miscarriage or preterm birth.

Ergotamine and methysergide

Used to treat migraine headaches, these medications are associated with an increased risk of premature birth and miscarriage.

Read more about Migraine Headache »

Natalizumab

This medication, which is used to treat multiple sclerosis (MS), may cause miscarriage. To avoid this outcome, people affected by MS who are using natalizumab and wish to become pregnant should stop taking it and devise an alternative treatment plan for the course of their pregnancy with their doctor, in advance of trying to conceive.

Read more about Multiple Sclerosis »

Antithyroid medication

People who are taking medications to regulate the activity of the thyroid may need to adjust their prescription in consultation with their doctor to ensure that their treatment routine is safe for pregnancy. In the first trimester, propylthiouracil is usually prescribed. In the second and third trimesters, the medication may be changed to methimazole or carbimazole to minimize the risk of toxicity.

Read more about Thyroid and Pregnancy »

The Centers for Disease Control and Prevention recommend always consulting a licensed healthcare provider before using any over-the-counter or prescription medication during pregnancy. Consult a medical professional about which products are safe for pregnancy, including prenatal vitamins and herbal supplements. Doctors can advise against the use of medications that are not suitable for pregnancy, reducing the risk of miscarriage.

Diseases and infections

The exact mechanisms by which diseases and infections cause miscarriage is not yet fully understood. It is believed to vary between different conditions and may affect a person’s pregnancy differently in each case. In general, when a pregnant person contracts an infection, this is believed to set off a cascade of possible events within the maternal body. This may eventually affect the fetus or uterine area, potentially causing miscarriage.[12] Feeling unwell? You can get a free symptom assessment at any time by downloading the Ada app.

Not all cases of disease or infection lead to miscarriage, but it is important to seek medical attention promptly if an infection is suspected, as effective treatment can significantly reduce the likelihood of this outcome. Preventable infections are believed to account for up to 15 percent of early miscarriages and up to 66 percent of late miscarriages.[12]

TORCH panel test

Pregnant women are often offered TORCH panel test on their first pregnancy screening visit. The TORCH test is a single test which screens for the a group of infections which are likely to cause pregnancy complications, including miscarriage.

Read more information about undergoing the TORCH panel test »

Known by the acronym TORCH, the infections screened for in this test are:

Toxoplasmosis

This infection is caused by a parasite called Toxoplasma gondii. The infection is often symptomless, but may cause flu-like symptoms such as fever, fatigue and muscle aches. It is usually harmless, but increases the likelihood of miscarriage in pregnant women, particularly in early pregnancy.

Toxoplasmosis can be found in raw meat, unpasteurized milks and untreated water, as well as soil and cat feces. Pregnant women may want to take particular care while gardening or in having contact with animals, including cleaning pet litter boxes, to reduce the risk of infection.

Other infections, including syphilis

Sexually transmitted infections (STI) such as syphilis, gonorrhea and chlamydia are associated with an increased risk of miscarriage.

In addition to the TORCH screen, pregnant women are advised to undergo regular sexual health screenings so that any STIs that develop can be diagnosed and treated promptly to minimize this risk.

Rubella (German measles)

Rubella can cause miscarriage, stillbirth or congenital defects; health problems which affect the baby from birth. It is especially likely to cause problems with the pregnancy, including miscarriage, if a pregnant person contracts rubella in the first 20 weeks.

Read more about Rubella »

Cytomegalovirus infection

Cytomegalovirus (CMV) infection is a condition which usually affects the respiratory tract, and significantly increases the risk of miscarriage. It is a member of the Herpes virus family, and is sometimes also called Human Herpes Virus 5 (HHV-5). The virus can spread through blood, saliva, or sexual contact. It can also be spread through cervical mucus and breast milk.

People who have been affected may shed the virus in their feces and urine for some time after infection.

Read more abou Cytomegalovirus Infection »

Herpes simplex virus (HSV)

Herpes simplex typically referred to as “herpes” or HSV, is a viral infection caused by the herpes simplex virus. The virus comes in two varieties: Herpes type one (HSV-1) and herpes type two (HSV-2). Although it can occasionally cause genital herpes, herpes type one (also called herpes labialis) generally leads to sores around the mouth, whereas herpes type two generally leads to genital sores.

Genital herpes is linked to pregnancy complications, including miscarriage and the development of genital conditions, but rarely causes miscarriage. It is, however, vital to treat herpes in pregnant women to reduce these risks, as neonatal herpes, in which the baby is born with the condition as a result of catching the infection from the mother during pregnancy or birth, can pose serious complications.

Read more about Herpes Simplex » Read more about Herpes Labialis » Read more about Genital Herpes »

Other diseases and infections which can cause miscarriage

Good to know: Many of the diseases and infections which can cause miscarriage can also cause other complications in pregnancy, such as congenital defects or preterm birth. Feeling unwell? You can get a free symoptom assessment by downloading the [Ada a]](https://app.adjust.com/e8ex7r4?redirect_macos=https%3A%2F%2Fappstore.com%2Fadapersonalhealthcompanion).

Read more about Pregnancy Complications »

Conditions which are linked to the development of pregnancy complications that can cause a miscarriage include:[13][14][15][16][17]

Human immunodeficiency virus (HIV)

The risk of miscarriage is believed to be significantly higher among those affected by HIV than within the general population. However, undergoing antiretroviral therapy (ART) is believed to reduce the likelihood of this outcome, as well as other risks such as that of transmitting HIV to the unborn child.

Dengue fever

A mosquito-borne infection, dengue fever can be passed from the mother to the fetus via the placenta. Dengue fever is most likely to cause miscarriage when the pregnant person is severely rather than mildly affected. Severe infections are much more likely to occur in people with multiple medical conditions, weakened immune systems, or in those who have had a previous dengue infection, than in the general population.

Read more about Dengue Fever »

Bacterial vaginosis (BV)

This is a common infection of the vagina involving discharge which may be foul-smelling, resulting from an imbalance of the types of bacteria found within the vagina. This can cause itching and foul-smelling vaginal discharge. In people who are not pregnant, BV is typically harmless and easily treatable with antibiotics.

In pregnant women, BV is associated with a significantly increased risk of miscarriage, particularly in the first trimester, equivalent to one extra miscarriage for every six pregnant women with BV. Seeking medical attention if BV is suspected, so that it can be treated early with antibiotics, can help prevent adverse outcomes.

Read more about Bacterial Vaginosis »

Malaria

Malaria is caused by a parasite known as Plasmodium, which is normally spread through the bite of an infected mosquito. Sometimes malaria does not show up immediately in a blood test. This happens especially in pregnant women, where the parasite can be present in high numbers in the placenta, without being apparent in the rest of the body.

For this reason, it is important that all pregnant women who have reason to suspect they may have been infected consult a doctor as soon as possible.

Read more about Malaria »

Parvovirus B19

This is a common virus which causes a non-serious condition known as fifth disease or slapped cheek syndrome, most often in children. It is most likely to cause miscarriage if it occurs during the first trimester of pregnancy; however, fewer than five percent of all cases of parvovirus B19 in pregnancy result in miscarriage. A doctor will be able to screen for the virus using a blood test and recommend treatment options thereafter if necessary.

Food poisoning

Eating food which has been contaminated by parasites, bacteria, viruses or certain chemicals is a common way for people to catch infections during pregnancy which can increase the risk of miscarriage.

A pregnant person’s immune system is somewhat weaker than that of a healthy, non-pregnant person, which makes getting food poisoning from contaminated food more likely. The most common types of infection associated with miscarriage are:[18][19][20]

Listeriosis

This infection is caused by Listeria monocytogenes bacteria. The infection involves flu-like symptoms such as fever, fatigue and muscle aches. In pregnant women, listeriosis can lead to miscarriage, premature birth or the newborn being born with a life-threatening form of the infection.

Listeria can be found in many foods, including soft cheeses, sprouts, melons, raw and reheated meats and unpasteurized milks.

Salmonella

This infection is caused by bacteria called Salmonella that can attack the intestinal tract.

Salmonella is not a common cause of miscarriage, but medical attention should be sought if it is suspected. It usually involves diarrhea, vomiting and stomach cramps and lasts for 4-7 days. It is generally caught from contaminated food, especially meat, eggs, poultry and milk.

Foods to avoid during pregnancy

Foods which are associated with a heightened risk of catching infections that can cause miscarriage include:[21]

  • Unpasteurised dairy products
  • Mold-ripened soft cheeses such as brie and camembert - these are more prone to growths of harmful bacteria
  • Raw or partially-cooked, unpasteurized eggs
  • Raw meat and fish; such as sushi
  • Paté made with meat
  • Cured meats
  • Undercooked meat - lamb, pork and venison in particular should be avoided
  • Meats which have been cooked and reheated, unless heated until steaming hot

Seek medical attention promptly at the first sign of food poisoning during pregnancy. In some cases, antibiotics and other medications may need to be prescribed, and no self-medication should be carried out without seeking medical advice. These can limit the potential impact of the infection on the developing embryo or fetus, reducing the likelihood of having a miscarriage.

Read more about Foods to Eat during Pregnancy » Read more about Foods to Avoid during Pregnancy »

Environmental and lifestyle factors

Many environmental conditions have been linked to decreased levels of fertility and an increased risk of miscarriage.

These include:[22]

  • Using tobacco products and/or being in regular proximity to secondhand smoke, or vapour from e-cigarettes
  • Metals, including lead, found in some types of fish; and nickel; found in jewelry and some foods
  • High levels of air pollution
  • Organic solvents; chemicals which vaporize at room temperature and are used to dissolve certain plastics and varnishes
  • Pesticides; chemicals sprayed on plants/crops to kill pests
  • Inhalational anesthetics, such as nitrous oxide and xenon, as used in healthcare professions
  • Ionising radiation above safe limits.

Read more about working safely with ionising radiation »

It is strongly recommended that all women who are trying to conceive or are pregnant adapt their lifestyle and day-to-day or work routine in order to avoid these factors, to minimize the risk of miscarriage.

Stopping using tobacco products is very important, as this is a primary cause of pregnancy complications.

Certain types of jobs in sites such as radiology departments, factories or farms may be associated with an increased risk of miscarriage. Pregnant women should discuss any concerns related to their work or home environment with their doctors and employers, so that adequate precautions against miscarriage can be taken where necessary.

Womb or cervical dysfunction

Problems with the womb or cervix structure or function can increase the likelihood of miscarrying. Many womb or cervical dysfunctions make miscarriage particularly likely to occur in the second trimester as the developing fetus grows in size. A weakened cervix, known as an impotent cervix, commonly causes miscarriage, as the cervical muscles dilate too early in the pregnancy. This often results in the early expulsion of the fetus from the womb, before it would be able to survive on its own.

Good to know: If medical professionals are aware that a pregnant person has a weakened cervix; e.g. because they have previously experienced a miscarriage for this reason, a temporary stitch may be put around the cervix to keep it closed. This procedure is usually performed during the first 12 weeks of pregnancy to prevent miscarriage, and is removed around week 37 in preparation for the birth.[2]

Other problems which may affect the pelvic area and cause miscarriage include the presence of non-cancerous growths in the womb (fibroids) and having a uterine form variation (an abnormally-shaped womb). This is normally diagnosed using imaging tests. If a person is aware that they have an abnormal womb structure they should discuss the possibility of miscarriage with their doctor in advance of trying to get pregnant. Additional check-ups may be scheduled in order to detect any possible complications as early as possible in the pregnancy.

Uterine abnormalities commonly linked to miscarriage include:[23]

Arcuate womb

The uterus has a dip at the top, but otherwise looks very much like a regularly-shaped womb. This dip makes a second-trimester miscarriage more likely. Additionally, while it does not usually cause difficulties in conceiving or premature birth, an arcuate womb may cause difficulties during the birth itself. Many people with an arcuate womb opt for a Cesarean birth (C-section) as a result.

Bicornuate womb

Also called a heart-shaped womb, this abnormality increases a person’s chances of a second-trimester miscarriage or premature birth. Additionally, while it does not usually cause any difficulties in conceiving or during early pregnancy, having a bicornuate womb may cause difficulties during the birth itself. These may be overcome by opting for a Cesarean.

Septate womb

In a septate womb, a wall of muscle from the top to the bottom of the womb separates the womb into two vertical chambers. The wall of muscle may extend all or part of the way down the womb, creating a partial or total division. People with a septate womb will often have difficulty conceiving and are at greater risk of a first-trimester miscarriage or premature birth. A septate womb may cause the developing fetus to lie in an unusual position, resulting in birthing difficulties.

Unicornuate womb

A unicornuate womb is a rare abnormality in which only one side of the uterus develops. The womb chamber is therefore smaller than usual and only has one functional ovary and fallopian tube. It is usually difficult for people with a unicornuate womb to conceive and, in pregnant women, it increases the likelihood of ectopic pregnancy, miscarriage and premature birth.

Long-term health conditions and immune disorders

Long-term, or chronic, health conditions which are associated with pregnancy complications and have the potential to cause a miscarriage in the second trimester include:[2][24]

The likelihood of a miscarriage is increased if a long-term health condition is undiagnosed or poorly managed. If you think you may be affected by an undiagnosed condition, you can get a free symptom assessment at any time by downloading the Ada app. If a person has any ongoing medical conditions, they should ask the doctor if their normal treatment or management plan – and use of certain medications – needs adapting during pregnancy.

Many of the long-term health conditions which are associated with miscarriage are immune disorders, conditions which can prevent the fetus and placenta from being properly protected from the body’s regular immune response. This can leave the fetus and placenta vulnerable to attack from the mother’s immune cells.

Good to know: The immune system works to protect the body from foreign cells (antigens) by destroying them in order to prevent the development or spread of disease or infection. Both the developing embryo and placenta contain antigens. In a healthy pregnancy, the genes that are responsible for recruiting immune cells are turned off within the decidua – the lining inside the uterus which forms during pregnancy.[25] The developing embryo and placenta are therefore protected from being destroyed by the immune system in the usual way, despite containing foreign cells.

Immunological abnormalities which may cause miscarriage can stem from the pregnant person being affected by factors including:[26]

  • Chronic health conditions that affect the immune cells in the pelvic area, such as polycystic ovary syndrome (PCOS)
  • An immune response to proteins in sperm
  • Failure to generate protective cells inside the womb
  • A greater than usual number of active immune cells
  • Stress or dietary choices which affect a person’s immune tolerance during pregnancy

If a person who wishes to become pregnant knows that they are affected by any condition associated with an improper immune response to pregnancy, they should seek medical attention before trying to conceive. An ongoing antenatal management plan will be devised, in order to help prevent their condition from causing miscarriage.

Other causes of miscarriage

Compared with the causes discussed above, miscarriage may be caused fairly rarely by additional factors including:[27][28]

  • Histamine intolerance
  • Fibroids; non-cancerous growths in the womb
  • Asherman’s syndrome; adhesions or scarring on the uterus
  • Physical trauma, such as a knock or fall
  • Being overweight or underweight
  • Consuming tobacco products, alcohol, or illicit drugs

Diagnosing causes of miscarriage

A miscarriage may be caused by one or more changeable or unchangeable factors. It may be possible to find out the causes of a miscarriage by performing an autopsy on the pregnancy tissue and/or a placental exam (an analysis of the placenta). However, it is not always possible to discern the cause(s) of a miscarriage. This is not necessarily bad news: many people whose causal factors for a miscarriage are unknown go on to have a healthy pregnancy resulting in a live birth in future.

Unchangeable factors

If the miscarriage is caused by unchangeable factors such as a person’s age or an underlying health condition which is already being managed effectively to ensure the best chance of a healthy pregnancy, it may not be possible to take preventive measures to reduce the likelihood of miscarrying in future.

Changeable factors

If the miscarriage is caused by changeable factors such as eating an unsuitable pregnancy diet, taking medications which are unsuitable for use in pregnancy, or a treatable, underlying condition, doctors can provide guidance on treating and managing these problems and help devise the best healthcare plan to follow before trying to conceive again.

Methods for diagnosing causes of miscarriage

A 2015 survey across the U.S. of people who have experienced a miscarriage, found that over 75 percent of people strongly wish to know the cause of their miscarriage.[29] To help identify any possible causes for a miscarriage, it is usual for doctors to perform:[30]

An autopsy on the pregnancy tissue

This is usually carried out by performing a whole-body radiograph, magnetic resonance imaging (MRI), a full-body examination and DNA tests to detect the presence of infectious agents and pathogens.

A placental exam

Laboratory analysis of the placenta, which may detect the presence of causal agents of miscarriage, such as infectious bacteria.

Fertility testing

After three consecutive miscarriages (recurrent miscarriage), one or both partners will be offered fertility tests in order to discern whether fertility treatments, such as in vitro fertilization (IVF) or fertility medications, may be necessary in order to increase the chances of a future healthy pregnancy.

Good to know: Fertility testing is not usually carried out except in cases of recurrent miscarriage, because it is very common to go on to have a healthy pregnancy in future after one, or even two miscarriages.

Causes of miscarriage FAQs

Q: What is male-factor miscarriage?
A: Male-factor miscarriage is more common in pregnancies where the male partner is over 40. It is a term used to describe miscarriage that is due to depleted sperm health. Semen analysis can be performed to determine the possible causes.[31] Causes of male-factor miscarriage may include:

  • Abnormal sperm shape; morphology
  • Defective or fragmented DNA; although conception may be possible, defected of fragmented DNA can lead to chromosomal abnormalities of the fetus, which may ultimately result in miscarriage

Q: What are the most common misconceptions about the causes of miscarriage?
A: There are many factors which are reputed to cause miscarriage, but which are not scientifically linked to it. These factors do not, therefore, need to be avoided with the aim of miscarriage prevention. They include:[2]

  • Eating spicy food
  • Airplane travel; always discuss air travel plans with a doctor in advance, as the risks posed can depend on the month of pregnancy
  • Sexual intercourse
  • Low mood
  • Exercise and heavy lifting, although consulting a doctor is advised to make sure that your exercise plan is suitable for pregnancy

Q: How can I tell if I am having a miscarriage?
A: The most common signs of miscarriage are vaginal bleeding, cramping, and sudden loss of pregnancy symptoms. However, these symptoms can all occur as natural features of a healthy pregnancy, and are not always a cause for concern.

Seek immediate medical attention if a miscarriage is suspected. Doctors will be able to establish whether there is a pregnancy complication, such as miscarriage or will be able to reassure you that the pregnancy is progressing normally.

Read more about the Signs of Miscarriage »


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  4. Chromosomal abnormalities in first-trimester miscarriages.” Acta Obstetricia et Gynecologica Scandinavica. November 2005. Accessed: 24 January 2018.

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