Miscarriage is the loss of a pregnancy before 20 weeks of gestation, and it happens because something prevents the pregnancy from continuing—most often a genetic abnormality in the embryo that makes survival impossible. About one in four pregnancies end in miscarriage, though many occur so early that a person may not know they were pregnant. Understanding the actual causes helps parents move past blame and fear, and move toward planning for what comes next.
Miscarriage is not caused by exercise, sex, stress, or most of the things pregnant people worry about. It is a biological event, usually unpreventable, that reflects a problem with the pregnancy itself rather than a failure on your part. Knowing what actually raises the risk—and what does not—helps you make informed decisions about your health and your next pregnancy.
Table of Contents
- The Most Common Cause: Chromosomal Abnormalities
- Maternal Age and How It Affects Miscarriage Risk
- Uterine Structure and Reproductive Health Problems
- Infections and How They Affect Pregnancy
- Medication, Substance Use, and Chemical Exposure
- What Does Not Cause Miscarriage
- When to Seek Care—Warning Signs and Red Flags
- What Happens After Miscarriage—Physical Recovery
- The Emotional Impact and When to Seek Support
- After Miscarriage—Testing, Investigation, and Moving Forward
- Frequently Asked Questions
The Most Common Cause: Chromosomal Abnormalities
Chromosomal problems account for about half of all early miscarriages. Chromosomes carry the genes that tell a developing embryo how to form, and when a sperm and egg combine, errors can happen during the copying process. A missing, extra, or scrambled chromosome makes it impossible for the embryo to develop properly, and the body terminates the pregnancy naturally.
The most common chromosomal problem is trisomy—an extra copy of one chromosome instead of the normal pair. Down syndrome (trisomy 21) can result in a live birth, but many trisomies are lethal and cause early loss. Monosomy X (Turner syndrome) and triploidy (three full sets of chromosomes instead of two) are also frequent causes of early miscarriage.
These errors happen by chance during egg or sperm formation, not because of anything you did before or during pregnancy. They are not inherited from parents and cannot be prevented by lifestyle changes, prenatal vitamins, or medical treatment. They reflect the randomness of cell division, which becomes slightly more common as maternal age increases. A miscarriage caused by chromosomal abnormality does not mean future pregnancies will have the same problem.
Each pregnancy is independent, and most parents who miscarry once go on to have healthy pregnancies. Testing the miscarried tissue can confirm whether a chromosomal issue caused the loss, which helps guide decisions about future monitoring. Genetic counseling may be useful if miscarriages are recurrent or if testing reveals a pattern. A counselor can review your family history, explain inheritance risks, and discuss which tests or monitoring might be relevant in future pregnancies. Most recurrent miscarriages are still random events, not a sign of an inherited disorder.
Maternal Age and How It Affects Miscarriage Risk
Miscarriage risk increases with maternal age, primarily because egg quality declines over time. At age 20, the miscarriage rate is around 10%, at age 35 it rises to about 20%, and at age 45 it reaches approximately 50%. This shift is almost entirely driven by chromosome errors in older eggs, not by maternal health problems.
The risk increase is real but gradual, and many people over 35 have healthy pregnancies. Age is one factor among many, and age alone does not mean you cannot carry a pregnancy safely. Regular prenatal screening and early ultrasounds can detect many chromosome problems, allowing informed decision-making. Paternal age (the father's age) has a much smaller effect on miscarriage risk than maternal age.
Some research suggests that advanced paternal age may slightly increase the risk of certain genetic conditions, but this is not a major miscarriage driver. The quality of sperm does decline with age, but not to the degree that egg quality does. Medical conditions like diabetes or thyroid disease can also raise miscarriage risk, but this is separate from age.
A 40-year-old with well-controlled health conditions may have lower risk than a 25-year-old with unmanaged diabetes. Focusing on health optimization before pregnancy can reduce some risks, regardless of age. If you are over 35 and planning pregnancy, early prenatal care, carrier screening, and early ultrasound can help identify potential problems and inform your choices. Testing options like cell-free DNA screening or detailed ultrasound can detect chromosomal issues that would have caused miscarriage.
Uterine Structure and Reproductive Health Problems
Structural problems in the uterus or cervix cause some miscarriages, most often in the second trimester. A septate uterus (a wall dividing the uterine cavity) or an incompetent cervix (one that opens prematurely) can interrupt pregnancy. Fibroids, adhesions, or scarring from prior procedures can also interfere with implantation or fetal development. Uterine problems are diagnosed by ultrasound or MRI and account for about 10-15% of recurrent miscarriages.
A cervical problem may cause loss later in pregnancy, often announced by heavy bleeding or discharge. If structural abnormality is found after miscarriage, surgical repair or cervical support (a cerclage stitch) in future pregnancies may help. Polycystic ovary syndrome (PCOS) increases miscarriage risk through multiple pathways: insulin resistance, inflammation, and sometimes progesterone deficiency. Managing PCOS before and during pregnancy—through diet, weight management, and sometimes medication like metformin—may lower risk.
If you have PCOS, early ultrasound and hormone monitoring in pregnancy can catch problems earlier. Thyroid disease, especially untreated hypothyroidism, raises miscarriage risk. The thyroid regulates metabolism and is critical to fetal development. If you have hypothyroidism, maintaining good thyroid control before and during pregnancy reduces miscarriage risk significantly.
Antiphospholipid antibody syndrome is an autoimmune condition that causes blood clots and raises miscarriage risk dramatically. It is diagnosed by blood tests and is highly treatable with anticoagulation therapy in pregnancy. If recurrent miscarriage occurs and other causes are ruled out, testing for antiphospholipid syndrome is warranted.
Infections and How They Affect Pregnancy
Some infections increase miscarriage risk, though the risk varies by infection type, timing, and maternal immunity. Rubella (German measles), cytomegalovirus, toxoplasmosis, and listeria can cross the placenta and harm the fetus, especially in early pregnancy. Most people are immune to rubella from childhood vaccination, and other infections are rare with ordinary hygiene. Untreated urinary tract infections or bacterial vaginosis do not typically cause miscarriage, but severe or ascending infections can increase risk slightly.
These are easily treated with antibiotics, and treatment before pregnancy or early in pregnancy reduces risk. Routine screening for asymptomatic bacteriuria is recommended in early pregnancy. Sexually transmitted infections like chlamydia or gonorrhea can cause infection and inflammation that may increase miscarriage risk, though the absolute risk remains low. They are detected by routine screening in early pregnancy and treated with antibiotics.
Untreated infections are a reason to treat promptly, but past infections do not raise future risk. Zika virus, acquired in specific geographic areas, has been linked to birth defects and possibly miscarriage. If you are pregnant or planning pregnancy and live in or travel to an area with Zika transmission, consult your doctor about risk.
The geographic range of Zika transmission changes seasonally and geographically, so current local information matters. COVID-19 in pregnancy has not been shown to cause miscarriage directly, though infection during early pregnancy may slightly raise risk of poor outcomes. Vaccination against COVID-19 before or during pregnancy is safe and reduces severe illness. If you have been infected with COVID, this does not mean future pregnancies are at risk.
Medication, Substance Use, and Chemical Exposure
Most medications are safe in pregnancy, but a few increase miscarriage risk and should be avoided when trying to conceive or early in pregnancy. Certain blood pressure medications (ACE inhibitors), retinoids (high-dose vitamin A), some arthritis drugs, and a few others carry documented risk. If you take medication regularly, discuss pregnancy planning with your prescriber to make informed choices.
Smoking increases miscarriage risk through multiple mechanisms: reduced oxygen delivery to the fetus, increased inflammation, and possibly impaired placental function. The risk is dose-dependent; quitting before pregnancy eliminates most of the excess risk. If you smoke, a fertility specialist or primary care doctor can discuss cessation strategies before you try to become pregnant. Alcohol use, especially heavy drinking, raises miscarriage risk.
The exact threshold for safe consumption in early pregnancy is debated, but the safest approach is to avoid alcohol entirely if you know or suspect you are pregnant. Light drinking before pregnancy confirmation carries minimal risk, but stopping once pregnancy is confirmed is prudent. Cocaine, methamphetamine, and other recreational drugs increase miscarriage risk and cause other serious complications.
If substance use is part of your life, discussing this with a counselor or addiction specialist before pregnancy planning can help you access support and stabilize your situation. Pregnancy is a time when many people are motivated to change, and resources exist to help. Environmental chemical exposure—including lead, pesticides, and certain industrial solvents—may increase miscarriage risk at high exposure levels.
If you work in a potentially hazardous environment (farming, manufacturing, laboratory), discussing reproductive safety with your employer or occupational health provider before pregnancy is reasonable. Most everyday exposures do not significantly raise risk.
What Does Not Cause Miscarriage
Many commonly feared activities do not cause miscarriage in a healthy pregnancy. Exercise, including running, weightlifting, and sports, does not cause miscarriage; in fact, staying physically active in pregnancy is recommended. The exception is contact sports with collision risk, which should be modified later in pregnancy to protect your belly. Sexual intercourse does not cause miscarriage in uncomplicated pregnancies, even late in pregnancy.
If bleeding, fluid leakage, or severe pain occurs, those are reasons to contact your doctor regardless, but intercourse itself is not a risk. Orgasm triggers uterine contractions, which are normal and not harmful in early to mid-pregnancy. Emotional stress, anxiety, and grief do not cause miscarriage, though they are painful experiences alongside miscarriage. A demanding job, a family crisis, or depression does not terminate a healthy pregnancy.
This distinction matters: feeling that stress "caused" your miscarriage adds guilt to an already difficult loss, and guilt is not justified. Lifting, climbing stairs, or other household activities do not cause miscarriage. The notion that pregnant people must remain mostly immobile is outdated. Normal daily life, work, and activity are compatible with continuing pregnancy in the vast majority of cases.
Caffeine consumption in moderate amounts (up to 200 mg daily, roughly one to two cups of coffee) has not been shown to increase miscarriage risk in reliable studies. Very high caffeine intake has been associated with higher risk in some studies, but this is not universal or certain. Reducing caffeine is a reasonable precaution if you are anxious about it, but not necessary for safety.
When to Seek Care—Warning Signs and Red Flags
Vaginal bleeding in early pregnancy does not automatically mean miscarriage, but it is a sign to contact your doctor promptly for evaluation. Bleeding can indicate miscarriage, ectopic pregnancy, subchorionic hemorrhage, or other conditions. An ultrasound can determine the status of the pregnancy and guide next steps. Severe abdominal pain, especially if one-sided, can signal ectopic pregnancy (implantation outside the uterus) or other emergencies requiring immediate evaluation.
Sharp, steady pain is different from the mild cramping that accompanies normal pregnancy or early miscarriage. If pain is severe or accompanied by dizziness or heavy bleeding, seek emergency care. Passage of tissue or clots during early pregnancy bleeding suggests miscarriage. Tissue can be collected and tested to determine whether a pregnancy was present and whether chromosomal abnormalities caused the loss.
This information can be reassuring and sometimes guides decisions about future monitoring. Lack of pregnancy symptoms (nausea, breast tenderness, fatigue) after weeks of symptoms can indicate miscarriage, though symptoms naturally wax and wane. An ultrasound confirms whether a heartbeat is present. Absence of symptoms alone is not definitive and may simply reflect normal variation. If you had a positive pregnancy test and then bleeding heavy enough to soak through pads or accompanied by clots, contact your doctor to confirm whether miscarriage occurred.
Bleeding patterns help determine the stage of pregnancy and whether all tissue has passed. Medical evaluation ensures nothing is left behind that could cause infection.
What Happens After Miscarriage—Physical Recovery
After miscarriage, the body passes fetal tissue and blood over hours to weeks, depending on how far the pregnancy advanced. This process is painful and heavy, sometimes resembling a difficult period. Over-the-counter pain relief (ibuprofen or acetaminophen) helps, and heating pads provide comfort. Infection is a risk after miscarriage if tissue remains in the uterus.
Fever, foul-smelling discharge, severe cramping, or heavy bleeding days after the initial miscarriage should be evaluated by a doctor. Antibiotics or a procedure to remove retained tissue may be necessary to prevent serious infection. Some miscarriages are complete (all tissue passes naturally), while others are incomplete (some tissue remains and requires medical intervention). Ultrasound determines this, and if tissue remains, options include medication to complete the process or surgical removal.
Rhesus-negative blood type requires an injection (RhoGAM) after miscarriage to prevent problems in future pregnancies. Bleeding after miscarriage typically lasts two to six weeks but can extend longer. Gradual lightening of flow, not all at once, is normal. Heavy bleeding that suddenly returns after light flow, or bleeding lasting beyond six weeks, warrants follow-up. The uterus returns to its non-pregnant state within weeks, and menstrual periods usually resume within four to six weeks.
Fertility returns quickly after miscarriage; the next menstrual cycle can bring ovulation and pregnancy is possible within weeks. This surprises many people, but it is normal physiology.
The Emotional Impact and When to Seek Support
Grief after miscarriage is real and legitimate, regardless of how early the loss occurred. The loss of hopes, plans, and identity as a pregnant person is profound, even if the pregnancy was newly discovered. Naming this loss and allowing yourself to grieve is important and does not mean something was wrong with you. Depression and anxiety after miscarriage are common and treatable.
Persistent sadness, loss of interest in activities, sleep disturbance, or obsessive worry can be addressed with counseling, medication, or both. If these symptoms develop, reaching out to your doctor or a mental health professional is a sign of strength, not weakness. Grief after miscarriage does not follow a timeline, and everyone's experience is different. Some people feel ready to try again quickly; others need months or years.
Neither response is wrong, and expecting yours to match someone else's can add pain to loss. Your timeline is yours. Partners, family members, and friends often do not know what to say or how to help after miscarriage. Telling people directly what you need—whether it is to talk, to be left alone, to avoid baby-related events, or to plan a memorial—can reduce secondary pain.
Some people find meaning in naming their loss or marking it somehow. Support groups, whether in-person or online, connect you with others who have experienced miscarriage. Hearing that your feelings are shared and normal can be profoundly validating. Many hospitals and fertility clinics offer resources or referrals to counseling specifically for miscarriage loss.
After Miscarriage—Testing, Investigation, and Moving Forward
After a single miscarriage, extensive testing is not usually recommended, since most are due to one-time chromosomal errors. However, if miscarriage tissue is available, testing (products of conception analysis) can identify chromosomal abnormality and provide closure. This information sometimes informs decisions about monitoring in future pregnancies. Recurrent miscarriage (three or more consecutive losses) warrants investigation.
Testing includes blood work to check clotting disorders, uterine imaging to detect structural problems, and sometimes genetic testing of parents. Many couples with recurrent loss have no identified cause, yet go on to have successful pregnancies. If testing reveals a treatable cause (thyroid disease, blood clotting disorder, uterine problem, or autoimmune condition), treatment before the next pregnancy can lower miscarriage risk.
Communication with your doctor about what testing was done and what it showed shapes the plan for next time. Trying again after miscarriage is a personal decision with no single right answer. Some people feel ready immediately; others prefer to wait. Medically, pregnancy can be attempted in the next cycle after miscarriage, though some doctors recommend waiting one to two cycles.
The choice depends on your readiness and your doctor's recommendation. When you do attempt pregnancy again, early ultrasound can provide reassurance and allow monitoring for potential problems. If you have risk factors (age, recurrent loss, structural problem), your doctor may recommend closer follow-up or specific interventions. Most people who have one or even several miscarriages go on to have healthy, full-term pregnancies.
Frequently Asked Questions
Can I prevent miscarriage?
No. Early miscarriages caused by chromosomal abnormalities cannot be prevented. You can manage risks from treatable causes (thyroid disease, blood clotting, PCOS) by working with your doctor before pregnancy, but most miscarriages reflect chance events, not preventable mistakes.
Does stress cause miscarriage?
No. Emotional stress, grief, and anxiety do not cause miscarriage in healthy pregnancies. If you experience miscarriage alongside stress, the stress did not cause it—this distinction matters for your healing.
Is bleeding always a sign of miscarriage?
No. Up to one in four pregnant people bleed in early pregnancy without miscarrying. Only ultrasound can confirm whether a pregnancy continues. Any bleeding warrants a call to your doctor for evaluation, but bleeding alone does not mean the pregnancy is lost.
Can I have sex during pregnancy after a previous miscarriage?
Yes. Sexual intercourse does not cause miscarriage in uncomplicated pregnancies, including after a prior loss. If you have specific risk factors (placenta previa, incompetent cervix, or bleeding), your doctor may recommend limits.
When can I try to become pregnant again after miscarriage?
Physically, you can become pregnant in the next cycle after miscarriage. Emotionally, the timeline is yours—some people are ready immediately; others need more time. Discuss timing with your doctor, especially if recurrent loss or specific risk factors apply.
Do I need testing after one miscarriage?
Testing is not usually recommended after a single loss, since most are random chromosomal events that will not repeat. If miscarriage tissue is available, it can be tested to check for chromosomal abnormality. After three or more consecutive losses, investigation is recommended.
