Genetic abnormality
The body detects that the future baby will have genetic problems due to abnormal chromosomes and therefore triggers a miscarriage.
Non-viable gametes
The egg or the sperm may have defects. Just as with a genetic abnormality, the body then triggers a miscarriage.
Blighted ovum
The embryonic membranes and placenta develop, but there is no embryo. It is as though there is a container without any contents. A blighted ovum is diagnosed by ultrasound.
Age of the woman and/or the man
The older we get, the greater the likelihood of miscarriage, as fewer gametes remain viable.
To find out more, take a look at our article on age and fertility.
Luteal phase deficiency
In other words, insufficient progesterone production in the second half of the menstrual cycle (during the luteal phase). This can result in a short luteal phase, leaving insufficient time for the egg, if fertilised and becoming an embryo, to implant in the uterus and begin the pregnancy. It will then be expelled with the period.
Fibroids
They could hinder adequate blood supply and sufficient space for the foetus. However, a large 2017 study involving 5,512 participants concluded that there is no link between miscarriage and the presence of fibroids.
PCOS
Women with polycystic ovary syndrome (pcos) are in particular more susceptible to miscarriage. This is probably due to issues with insulin and inflammation.
Ectopic pregnancy
This is an embryo that develops outside the uterus, often in one of the fallopian tubes. The body may then trigger a miscarriage. If not, medical intervention will be necessary, as an ectopic pregnancy can be life-threatening.
Septate uterus
This is a malformation characterised by the presence of an intrauterine septum. It is often diagnosed by 3D ultrasound following a miscarriage or difficulties conceiving. A hysteroscopy procedure is one option to correct it.
Endometriosis
A 2017 meta-analysis and literature review concluded that "endometriosis appears to be a risk factor for spontaneous miscarriage, increased by nearly 80%".
Cervical insufficiency
When the cervix dilates during pregnancy before labour, this can trigger a miscarriage.
Problems with the placenta
If the placenta does not develop correctly, a miscarriage may occur.
MTHFR gene mutation
This is a gene encoding an enzyme required for the proper use of vitamin B9, among others. A mutation in this gene could potentially be linked to miscarriage, though the subject is still very much debated.
Diabetes
Blood sugar regulation issues can in particular increase the risk of miscarriage and complications during pregnancy.
Autoimmune disease
Autoimmune diseases (lupus, coeliac disease, Hashimoto's, Graves' disease, Sjögren's syndrome…) can also have an impact. However, having an autoimmune disease does not necessarily mean you will experience a miscarriage.
Infection
Infections such as toxoplasmosis, rubella, salmonella, cytomegalovirus, sexually transmitted infections, Zika… and/or high fever can also play a role.
Consumption of certain substances
Taking medications or herbal remedies that are contraindicated during pregnancy may also have an effect.
The use of drugs or alcohol, exposure to heavy metals, pesticides, pollution, and radiation are also problematic.
Amniocentesis
This procedure involves extracting amniotic fluid and therefore foetal cells. It can detect potential genetic abnormalities, which carry a risk of miscarriage in 0.5 to 1% of cases.