An Overview of Miscarriage Causes By Andrea Chisholm, MD | Reviewed by a board-certified physician Updated December 13, 2016 Print After having a miscarriage, you may question whether you did something wrong in the early weeks of your pregnancy. Most of the time, the answer to your question is no. Most miscarriages happen for reasons that you can't control. Typically, it is an isolated occurrence though some women can experience recurrent miscarriages.However, certain underlying medical and gynecologic conditions and/or lifestyle choices can increase your risk of having a miscarriage. Chromosomal AbnormalitiesChromosomal abnormalities in the developing fetus are the cause of about 50 percent of miscarriages before 13 weeks of pregnancy and about 24 percent of miscarriages between 13 to 27 weeks of pregnancy. A chromosomal abnormality can be the result of a structural change or a change in the number of chromosomes. The risk of a chromosomal abnormality complicating your pregnancy increases with your age. Article Can Sperm Be the Cause of First or Second Trimester Miscarriages? Article Can Constipation or Diarrhea Cause Miscarriage? Congenital AbnormalitiesCongenital abnormalities are birth defects that happen when a body part of the growing fetus does not develop normally. Environmental factors such as infections or exposure to toxins as well as genetic factors can result in congenital abnormalities.ObesityObesity is defined as a BMI greater than 30 and we all know that obesity is a serious health problem. But obesity in pregnancy can also increase your risk of pregnancy-related complications including birth defects and miscarriage. Studies have shown that miscarriage is more common in obese women than in age-matched women with a normal range BMI. If your BMI is over 30, losing weight before getting pregnant can reduce your risk.DiabetesWomen with preexisting diabetes are at an increased risk of complications throughout their pregnancy. These complications include an increase in certain birth defects and miscarriage. The better your glycemic control when you conceive, the less likely you are to have an early pregnancy loss or severe birth defect. If you have diabetes and you are thinking of getting pregnant, first make sure that your diabetes is in good control. Ideally, your hemoglobin A1C should be six percent or less when you are planning a pregnancy.InfectionGetting sick while you're pregnant can be very stressful. The good news is that most common infections during pregnancy do increase your risk of miscarriage. However, there are some infections like listeria that can cause a miscarriage. Autoimmune DisordersAutoimmune disorders are conditions when your immune system does not function properly and begins to attack your own tissues. Article Can Progesterone Administration Prevent Miscarriages? Article Are MTHFR Mutations a Factor in Miscarriages? Autoimmune disorders are common in reproductive-aged women. Antiphospholipid antibody syndrome and Hashimoto's thyroiditis are two examples of autoimmune disorders that can increase your risk of miscarriage.Uterine FibroidsUterine fibroids are benign smooth muscle tumors that can develop in the wall, on the surface, or in the lining of your uterus. Fibroids are relatively common in reproductive-aged women and it is possible to have an uncomplicated pregnancy if you have fibroids. However, extensive fibroids or having a fibroid that distorts the uterine cavity can increase your risk of a miscarriage. Uterine Septum/Intrauterine AdhesionsIn the early days of your pregnancy, the embryo attaches to the lining of your uterus or your endometrium and begins to grow. A condition that interferes with the uterine lining or with the cavity of your uterus can increase your risk of a miscarriage. A uterine septum is a developmental abnormality in your uterus and intrauterine adhesions are a type of scar tissue that can happen after a surgery or an infection. Both of these conditions interfere with the shape of your uterine cavity and the endometrial lining and can increase your risk of a miscarriage. Incompetent CervixYour uterus expands over the months of your pregnancy to accommodate the growing fetus. It is the job of your cervix to keep the developing fetus inside your uterus for approximately nine months. Sometimes the cervix begins to dilate or open earlier than it is supposed to. If this happens in the second trimester, typically between 13 to 24 weeks, you likely have an incompetent cervix. Your doctor may suggest a cerclage in your next pregnancy to reduce your risk of a miscarriage.SmokingThere is little doubt that smoking cigarettes are bad for your health. It is generally accepted that smoking increases your risk of miscarriage although some studies have failed to show an increased risk. That being said, if you are planning a pregnancy you should work to stop smoking as it is linked to other pregnancy complications in addition to miscarriage. Article What Is a Bicornuate Uterus? Article What Are the Primary Causes Second Trimester Miscarriages? Substance AbuseSubstance abuse during pregnancy is associated with multiple complications and potential for poor pregnancy and neonatal outcomes. Like smoking, alcohol consumption in pregnancy has conflicting evidence for its role in causing miscarriages specifically. But because it is so potentially harmful to the developing fetus, it is recommended that you consume no alcohol when you are pregnant. The same is true for all illicit drugs including (but not limited to) cocaine, heroin, and marijuana.Excessive Caffeine It is important to say that caffeine in moderation appears to be safe in pregnancy. There is evidence to suggest that excessive caffeine intake can increase your risk of a miscarriage. A good rule to follow when you are pregnant or trying to get pregnant is to limit your caffeine intake to less than 200mg a day—which is roughly two cups of coffee. A Word From VerywellHaving a miscarriage is very upsetting. But it is important to remember that a miscarriage is not your fault and that it is usually an isolated occurrence. That means you are more likely to have a successful pregnancy rather than another miscarriage the next time you conceive.However, if you have had a miscarriage or if you are planning to get pregnant, it is important to determine whether you have any conditions that increase your risk of a miscarriage. Making lifestyle changes and talking with your doctor about your health may very well reduce your risk of a miscarriage. Sources:American College Of Obstetricians and Gynecologists. (2015). ACOG practice bulletin no.150: Early Pregnancy Loss. Obstet Gynecology. 125(5) 258-67.Michels,T. (2007). Second Trimester Pregnancy Loss. American Family Physician, 76(9),1341-46.