The majority of miscarriages are triggered by outside events over which the lady has no control. Genetic problems are a major cause of miscarriage early in pregnancy. Around 80% of miscarriages happen during the first trimester, which lasts from 0 and 13 weeks. The remaining 20% occur after the first trimester. Many factors can increase a woman's risk of miscarriage including age, weight, health issues like diabetes and heart disease, smoking, alcohol use, unplanned pregnancy, and poverty. Genetic problems also play a role. A family history of miscarriage increases your risk as well. About half of all miscarriages are due to genetic problems with embryo development. For example, you may be born with an abnormal number of chromosomes (called a syndrome) that can lead to miscarriage. A better term for these types of syndromes is "genetic disorders." Other causes of genetic miscarriage include thalidomide exposure, certain infections, and certain medications. Women who have had a previous miscarriage are often advised to have their reproductive organs scanned to look for any problems with their fallopian tubes or ovaries. If problems are found, treatment may be recommended to try and prevent future losses. Women should not worry about losing a pregnancy too soon. The vast majority of pregnancies last until at least 22 weeks. Only 1 in 100 babies dies before reaching week 22. The most common reason for early loss is unknown.