Anatomical differences are common and can be congenital. In some women, cervical incompetence or cervical insufficiency occurs with the inability of the cervix to stay closed during the entire pregnancy. It does not cause first trimester miscarriages. In the second trimester, it is associated with an increased risk of miscarriage. It is identified after a premature birth has occurred at about 16–18 weeks into the pregnancy. During the second trimester, major trauma can result in a miscarriage. Smoking
Tobacco (cigarette) smokers have an increased risk of miscarriage. There is an increased risk regardless of which parent smokes, though the risk is higher when the gestational mother smokes. Morning sickness
Nausea and vomiting of pregnancy (NVP, or morning sickness) is associated with a decreased risk. Several possible causes have been suggested for morning sickness but there is still no agreement. NVP may represent a defense mechanism which discourages the mothers ingestion of foods that are harmful to the fetus; according to this model, a lower frequency of miscarriage would be an expected consequence of the different food choices made by women experiencing NVP. Chemicals and occupational exposure
Chemical and occupational exposures may have some effect in pregnancy outcomes. A cause and effect relationship almost can never be established. Those chemicals that are implicated in increasing the risk for miscarriage are DDT, lead, formaldehyde, arsenic, benzene and ethylene oxide. Video display terminals and ultrasound have not been found to have an effect on the rates of miscarriage.
Paternal age is associated with increased risk. Obesity, eating disorders and caffeine
Not only is obesity associated with miscarriage; it can result in sub-fertility and other adverse pregnancy outcomes. Recurrent miscarriage is also related to obesity. Women with bulimia nervosa and anorexia nervosa may have a greater risk for miscarriage. Nutrient deficiencies have not been found to impact miscarriage rates but hyperemesis gravidarum sometimes precedes a miscarriage.Caffeine consumption also has been correlated to miscarriage rates, at least at higher levels of intake. However, such higher rates are statistically significant only in certain circumstances. Vitamin supplementation has generally not shown to be effective in preventing miscarriage. Chinese traditional medicine has not been found to prevent miscarriage. Endocrine disorders
Disorders of the thyroid may affect pregnancy outcomes. Related to this, iodine deficiency is strongly associated with an increased risk of miscarriage. The risk of miscarriage is increased in those with poorly controlled insulin-dependent diabetes mellitus. Women with well-controlled diabetes have the same risk of miscarriage as those without diabetes. Food poisoning
Ingesting food that has been contaminated with listeriosis, toxoplasmosis, and salmonella is associated with an increased risk of miscarriage. Amniocentesis and chorionic villus sampling
Amniocentesis and chorionic villus sampling (CVS) are procedures conducted to assess the fetus. A sample of amniotic fluid is obtained by the insertion of a needle through the abdomen and into the uterus. Chorionic villus sampling is a similar procedure with a sample of tissue removed rather than fluid.