However, there is no clear evidence that has shown live vaccinations to increase the risk for miscarriage or fetal abnormalities.Some live vaccinations include: MMR, varicella, certain types of the influenza vaccine, and rotavirus. Treatments for cancer
Ionizing radiation levels given to a woman during cancer treatment cause miscarriage. Exposure can also impact fertility. The use of chemotherapeutic drugs used to treat childhood cancer increases the risk of future miscarriage. Pre-existing diseases
Several pre-existing diseases in pregnancy can potentially increase the risk of miscarriage, including diabetes, polycystic ovary syndrome (PCOS), hypothyroidism, certain infectious diseases, and autoimmune diseases. PCOS may increase the risk of miscarriage. Two studies suggested treatment with the drug metformin significantly lowers the rate of miscarriage in women with PCOS, but the quality of these studies has been questioned. Metformin treatment in pregnancy has not been shown to be safe. In 2007 the Royal College of Obstetricians and Gynaecologists also recommended against use of the drug to prevent miscarriage. Thrombophilias or defects in coagulation and bleeding were once thought to be a risk in miscarriage but have been subsequently questioned. Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. A condition called luteal phase defect (LPD) is a failure of the uterine lining to be fully prepared for pregnancy.
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.