Miscarriage is response of female body to unfavorable conditions of its external or internal environment. There may be one or more causes of miscarriage:
Genetic abnormalities of the embrio are the most common reason of early (in the 1st trimester) miscarriages. The abnormalities include wrong quantity or structure of chromosomes in the embrio cells leading to wrong development of the embrio. It becomes non-viable, dies and is taken away from the womb. The “wrong” chromosomes can be inherited by the embrio from the parents (who can be healthy) but seldom. More often chromosome abnormalities occur due to intrauterine growth failures. Such failures may be caused by different environmental factors, such as radiation, chemicals etc. but in most cases the reason is unknown.
Infections, especially of the genitals, are the 2nd common reason of miscarriage. Microbes cause inflammation of womb mucosa, fetal membranes, placenta that often leads to miscarriage. Chronic inflammations are particularly dangerous. Infections may cause miscarriages at any stage of pregnancy.
The age of a pregnant woman can also influence the pregnancy development. The best age for pregnancy and labor is between 20 and 35 years, the first child should be better born before 28-30 years. Too young and too old female age may be one of miscarriage reason.
Endocrine disorders in pregnant women also often lead to miscarriages. Nevertheless the modern medicine correct such states so timely diagnostics and treatment makes carriage and delivery of a healthy baby possible.
Inborn or acquired maternal anatomical abnormalities (e.g. one-horned uterus), tumors (ovarial miomas and cysts); endometrial trauma (e.g. due to repetitive abortions) etc. can cause miscarriage in the 2nd trimester.
Pregnancy complications (e.g. toxicosis, abnormal fetus position in the womb) can cause miscarriage in the 3rd trimester.
Environmental factors: exposure to chemicals or drugs, occupational hazards or smoking, drinking alcohol etc.
Physical stress, minor falling down etc. are seldom real reasons of miscarriage despite of the common opinion. They can (and often they do) induce miscarriage if there is one of the above mentioned problems. But if the maternal body is healthy and genetic program of the fetus is correct, than fall down or stress should be really enormous to cause any harm to the fetus.