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What causes a miscarriage in the first trimester?

What causes a miscarriage in the first trimester?

Kindara | June 15, 2021 | priya_app
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Let's get three things straight about miscarriage before we start. First, there are a number of causes of miscarriage in the first trimester. Two, a miscarriage is not your fault. (Write this second one down and put it where you will see it often.) Three, just because it's not your fault and it's extremely common, doesn't mean it still isn’t devastating.

According to the Mayo Clinic, a miscarriage is a spontaneous loss of pregnancy before the 20th week. Miscarriage is incredibly common — they occur in between 10 and 20 percent of pregnancies, and that number may be actually be higher, since some miscarriages take place before the person even knows she's pregnant. When a pregnancy ends very early (around the 5th week of gestation), it's known as a chemical pregnancy (1). 

What can cause an early miscarriage? Read on for the information you've been looking for. 

Fetal chromosomal abnormalities 

Eighty percent of miscarriages occur in the first trimester, and of those, 50% are the result of fetal chromosomal abnormalities (2). When the fetus is developing, it may have an extra chromosome or be missing a chromosome, and both of these situations can result in the end of the pregnancy (3). Why does this happen? There are a couple of possibilities. One is that the immune system of the pregnant person recognizes that something is up with the fetus and causes the miscarriage (4). Another is that the chromosomal abnormality doesn't allow for the continued development of the fetus, so it stops growing (5). Not every chromosomal abnormality leads to miscarriage, and unfortunately, exactly why some do and others don't isn't known. 

A lot of research is being done to figure out what leads to chromosomal abnormalities in the first place. One contributing factor is maternal age — if you're in your late 30s, possibility of miscarriage and chromosomal problems increases, but it's important to remember that many people who have children after 35 give birth to healthy children (6). Exposure to certain toxins, such as teratogens, substances that produce foundational defects in embryos and fetuses, can also lead to chromosomal abnormalities. Examples of teratogens range from radiation and cocaine, to agents that raise the body temperature (think saunas and hot tubs) (7).  These don't all carry the same level of risk.  It's not a great idea to use a hot tub or sauna during pregnancy because pregnant people are at an increased risk for dehydration or a dangerously overheated body. You can minimize risk to your fetus by avoiding hot tubs and saunas, and if you do use them, keeping your time brief (less than 10 minutes) and not submerging your whole body (8). 

Bacterial infections 

Listeriosis is a type of bacterial infection that occurs when one ingests food contaminated with Listeria monocytogenes. Pregnant people are 10 times more likely to get listeriosis (you're 24 times likely to get it if you're a Hispanic pregnant person) (8). The good news is listeriosis can be avoided! Listeriosis is the reason pregnant folks are advised to avoid raw seafood, unpasteurized milk, soft and Mexican-style cheeses, deli meat, hot dogs, unwashed fruits, vegetables or sprouts, cold salads from delis or salad bars, as well as refrigerated patés, meat spreads, and smoked seafood (9). Symptoms of listeriosis, like fever, stiff neck, chills, and upset stomach, can take a while to show up, and those who contract it don't always feel sick, but it can still result in miscarriage or stillbirth. The U.S. Food and Drug Administration (FDA) emphasizes preventing listeriosis by avoiding the aforementioned foods, keeping your refrigerator and kitchen surfaces clean, making sure you're throwing out expired foods, and maintaining good hygiene (wash those hands!) (10). If you experience symptoms of listeriosis, you should contact your health care provider immediately. 


Have you ever heard that pregnant people shouldn't clean up after the cat litter? It turns out that it's not just a wild rumor! Toxoplasma gondii is a bacteria found in cat feces, raw or uncooked meat, unwashed vegetables, and unpasteurized milk, that can result in the development of toxoplasmosis, a condition that for many people, has no symptoms and they aren't even aware that they have it. In the US, it's estimated that 11% of the population 6 years and older has been infected with toxoplasmosis (11). You can't catch it from person-to-person contact (or from touching a cat), but it can be passed from mother to unborn child, and it does  pose a risk of miscarriage and birth defects if the mother has it during pregnancy (12).  Avoid raw and cured meats, wash your vegetables, and if you are cleaning your cat's litter, make sure you're wearing gloves and wash your hands afterwards. There is a blood test for toxoplasmosis that can be done at any stage in pregnancy, so if you're concerned about exposure, talk to your doctor. 

Certain medical conditions 

Uncontrolled diabetes, clotting disorders, uterine fibroids, weak cervical tissue, untreated chlamydia and gonorrhea as well as bacterial infections (see above) may result in miscarriage (13, 14). Thyroid issues also impact your hormones, and both untreated hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) interfere with the development of an embryo and have been linked to increased risk of miscarriage (15, 16). "It is recommended for women who are already diagnosed with thyroid disease or women who have clinical signs of thyroid disease to be screened for thyroid-stimulating hormone (TSH) and TPO antibodies on a thyroid blood test," says Dr. Sapna Shah, an endocrinologist with Paloma Health. "It is further recommended to have normal thyroid function prior to attempting to conceive or as soon as a positive pregnancy test is confirmed. Treatment of thyroid disease early on may help reduce the risk of further miscarriage in some patients."

"Although there is no specific way to prevent a miscarriage, receiving prenatal care during the early stages of pregnancy promotes the best possible pregnancy outcome," says Dr. Leah Alexander, MD, FAAP, Medical Consultant at Mom Loves Best. And when you do visit your healthcare provider, bring all your questions (write them down beforehand so you don't forget) — you're the one who can best advocate for your health and that of your pregnancy. 

If you've experienced a miscarriage or if you’re anxious about having one,  don't be afraid to seek support. You definitely aren't alone.

About the author

Chanel Dubofsky's writing on gender, reproductive health, popular culture, and religion can be found in New York Magazine, Lilith, Rewire, Modern Fertility, Cosmopolitan, and others. She lives in Brooklyn, New York. Follow her on Instagram at cdubofsky.

References +

What is a Chemical Pregnancy? (2020, May 22). Retrieved  February 8, 2021, from https://www.whattoexpect.com/pregnancy/chemical-pregnancy/


Medical Genetics: How Chromosome Abnormalities Happen. (n.d.). Retrieved February 8, 2021, from https://www.stanfordchildrens.org/en/topic/default?id=medical-genetics-how-chromosome-abnormalities-happen-90-P02126


Tantibanchachai, Chanapa, "Teratogens". Embryo Project Encyclopedia (2014-01-22). ISSN: 1940-5030 http://embryo.asu.edu/handle/10776/7510.


Pregnancy  Week by Week. (2020, November 21). Retrieved February 22, 2021, from https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/expert-answers/pregnancy-and-hot-tubs/faq-20057844


People at Risk - Pregnant Women and Newborns. (2016, December 22.) Retrieved February 8, 2021, from https://www.cdc.gov/listeria/risk-groups/pregnant-women.html


Food Poisoning During Pregnancy. (2016, May). Retrieved February 8, 2021, from https://www.marchofdimes.org/complications/food-poisoning-during-pregnancy.aspx


Toxoplasmosis in Pregnancy. (2019, October 3). Retrieved February 12, 2021, from https://www.tommys.org/pregnancy-information/pregnancy-complications/infections/toxoplasmosis-pregnancy


Miscarriage: Symptoms and Causes. (n.d.) Retrieved February 8, 2021, from https://www.mayoclinic.org/diseases-conditions/pregnancy-loss-miscarriage/symptoms-causes/syc-20354298

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