What Causes A Miscarriage?

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A miscarriage, also known as a pregnancy loss, is the spontaneous ending of a pregnancy before the fetus is able to survive outside the womb. It typically occurs within the first 20 weeks of gestation, with the majority happening in the first trimester (0-13 weeks). Miscarriages can happen for various reasons and may involve the natural termination of a pregnancy due to internal factors, such as anatomical or genetic problems or external factors such as alcohol or drug use. The loss of a pregnancy can be emotionally and physically challenging for individuals and couples, and it is important to seek support and medical care during this difficult time.

Internal Causes Of Miscarriages

After conception and fertilisation, a few factors may affect the possibility of a successful pregnancy. These causes may be seen in the female anatomical structure, the fetus’s genetics, the female’s health condition, clotting disorders, and infections.

Anatomical Problems

The uterus might have defects and may not be able to support the pregnancy. The uterus might not have formed in the correct manner and may pose a risk to the unborn child in the long term, then a miscarriage could be the result. A weakened cervix may cause a miscarriage as the cervix may dilate (open) too early during the pregnancy due to weakened muscles around the cervix area.


Fibroids are benign (non-cancerous) growths seen within the uterus. These growths are made up of muscle and fibrous tissue. They may cause a miscarriage of the unborn child as the fetus and the fibroids will be competing for space in the uterine cavity. Ultimately, the fibroids might only be discovered when symptoms have developed.

Fetus’s Chromosomes

When a child is conceived, they receive 23 chromosomes from the mother and 23 chromosomes from the father. The child will then have 46 chromosomes, just like the mother and the father. There may be a problem during the diving phase of the chromosome and the chromosome might be repeated, duplicated, or missed.  Resulting in a child that has a total of 45 or 47 chromosomes. This is usually not compatible with life and around 50% of miscarriages are due to chromosomal abnormalities.


Infections that are located in the uterus, cervix or placenta can be detrimental to the unborn child. These infections include but are not limited to, listeria, rubella (German measles), herpes simplex, malaria, chlamydia, gonorrhoea, bacterial vaginosis, cytomegalovirus, toxoplasmosis, and parvovirus B19.

Clotting Disorders

A clotting disorder is when the body's blood clotting process is disrupted, resulting in abnormal clot formation. Blood clots in the placenta may impair its proper development and functioning. A compromised placenta may not adequately support the growing fetus, leading to insufficient nourishment and oxygen supply.

Autoimmune Response

Antiphospholipid syndrome is an autoimmune disease that causes the body’s immune system to make antibodies against normal substances in the body, specifically against substances involved in the blood clotting process. These antibodies can affect blood flow and increase the risk of blood clots forming in the placenta, leading to complications such as poor fetal development, placental insufficiency, and miscarriage.

Systemic Lupus Erythematosus is an autoimmune disease that can affect multiple organs and tissues in the body. In pregnancy, it can increase the risk of miscarriage due to the production of autoantibodies that can harm the placenta and disrupt proper fetal development. Certain medications used to manage Lupus may also pose risks during pregnancy.

Conditions like Hashimoto's thyroiditis and Graves' disease, which involve autoimmune responses against the thyroid gland, can increase the risk of miscarriage. Imbalances in thyroid hormones caused by these conditions can negatively impact pregnancy outcomes and fetal development.

Chronic Health Conditions Of The Mother

Certain health conditions of the mother may increase the risk of having a miscarriage. Diabetes, hypertension (severe high blood pressure), kidney disease, thyroid conditions (hyperthyroidism and hypothyroidism - overproduction and underproduction of thyroid hormones) and polycystic ovary syndrome may all increase the risk of miscarriage. It is important to ensure that chronic conditions are properly treated and monitored during the pregnancy.

External Causes Of Miscarriages

Understanding these external factors that might increase the risk of miscarriage can help expecting mothers take the necessary precautions to help minimise the risks and promote a healthier pregnancy.


The use of alcohol during pregnancy can increase the risk of miscarriage, preterm birth, low birth weight, and developmental issues such as Fetal Alcohol syndrome. No amount of alcohol is safe during pregnancy (not even one glass of wine), but overconsumption of alcohol may lead to alcohol poisoning and physical harm to mother and baby due to loss of coordination.


Certain medications may cause a miscarriage. It is important to confirm with your doctor, to see if medication is safe to take or not during pregnancy. Medications like misoprostol (for stomach ulcers), retinoids (for acne), methotrexate (used for certain autoimmune diseases), and non-steroidal anti-inflammatory drugs (such as ibuprofen and pain or inflammation tablets) are not safe.

Food Poisoning

Contaminated food may cause food poisoning and may increase the risk of a miscarriage. Listeriosis can be found in contaminated dairy products, toxoplasmosis can be found in raw meat or undercooked meat, and salmonella can be found in raw eggs or undercooked chicken.

Radiation And Toxic Substances

Radiation and toxic substances from the environment may cause harm to the fetus and also to the mother. Radiation that occurs during the early gestation of the fetus may cause malformation. Toxic substances may cause chemical abortions. Substances to look out for include ethylene oxide, anaesthetic gases, heavy metal poisoning, and bromopropane.

Causes Of Miscarriage

Miscarriages can be caused by various internal and external factors. Internal causes include anatomical problems, genetic abnormalities, infections, clotting disorders, autoimmune responses, and chronic health conditions. External causes include alcohol and drug misuse, contaminated food, radiation, and exposure to toxic substances. Taking precautions, seeking prenatal care, maintaining a healthy lifestyle, and following medical advice can help reduce the risk of miscarriage.

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