The most common cause of miscarriage at 5 weeks is a chromosomal abnormality in the embryo. Roughly 50% of all first-trimester miscarriages happen because the embryo received too many or too few chromosomes during fertilization, making normal development impossible. At 5 weeks, the pregnancy is so early that many losses fall into a category called “chemical pregnancy,” where a positive test is followed by bleeding before anything can be seen on ultrasound. In most cases, nothing the mother did or didn’t do caused the loss.
Chromosomal Problems Are the Leading Cause
When a sperm and egg combine, each contributes a set of chromosomes. If either the egg or sperm carries an abnormal number, the resulting embryo will too. As that embryo’s cells begin dividing and multiplying in the first weeks, errors in this process can also derail development entirely. The embryo simply cannot grow into a viable pregnancy, and the body ends it.
This type of loss is essentially random. It becomes more common with age because egg quality declines over time, increasing the odds of chromosomal errors during fertilization. But it happens to people of all ages, and having one chromosomally abnormal pregnancy does not mean the next one will be.
Low Progesterone and Hormonal Factors
Progesterone plays a critical role in early pregnancy by thickening the uterine lining so a fertilized egg can implant and grow. Once the egg attaches, progesterone levels need to keep rising to support the developing embryo. During the first trimester, levels can climb as high as 90 ng/mL. If progesterone is too low, the lining may not be thick or stable enough to sustain the pregnancy.
This is sometimes called a luteal phase defect. The ovary produces progesterone after ovulation, and if that production falls short, the environment inside the uterus becomes inhospitable before the pregnancy can establish itself. Some people with recurrent losses are treated with supplemental progesterone, though its effectiveness depends on whether low levels are actually the underlying issue.
Blood Clotting and Immune Conditions
Certain autoimmune conditions can interfere with the blood supply to a developing pregnancy. Antiphospholipid syndrome is the most well-known example. In this condition, antibodies in the blood trigger inflammation and abnormal clotting, which can damage the tiny blood vessels forming in the early placenta. The result is poor blood flow to the pregnancy, sometimes visible later as widespread tissue damage in the placental lining.
These conditions are relatively uncommon causes of a single early loss but become an important consideration for people who experience repeated miscarriages. Testing is typically recommended after two or three consecutive losses rather than after a first one.
Thyroid Disease and Chronic Health Conditions
Uncontrolled thyroid disease, particularly an underactive thyroid, raises the risk of early pregnancy loss. Thyroid hormones help regulate metabolism and development at the cellular level, so significant imbalances can disrupt the hormonal environment a pregnancy needs. Poorly managed diabetes and uncontrolled high blood pressure can also contribute, though these are more commonly associated with losses later in the first trimester or beyond.
Chemical Pregnancy vs. Clinical Miscarriage
At 5 weeks, many losses are technically chemical pregnancies. The term refers to a pregnancy detected only through a positive test (which picks up the hormone hCG) but that ends before a gestational sac or heartbeat can be seen on ultrasound. A positive test turns negative within days, and bleeding begins around the time a period would have been expected or shortly after.
A clinical miscarriage, by contrast, involves a pregnancy that has progressed far enough to be visible on ultrasound. Most clinical miscarriages happen after the sixth week. The distinction matters medically because it affects how the loss is monitored and managed, but for the person going through it, a chemical pregnancy can feel just as real and just as painful. The causes are the same: chromosomal problems, hormonal insufficiency, or implantation failure.
What Doesn’t Cause Miscarriage at 5 Weeks
Exercise, sex, and everyday stress do not cause early miscarriage. The Mayo Clinic notes that short-term, ordinary stress does not appear to raise the risk. Severe, prolonged stress (ongoing financial crisis, homelessness, the death of a loved one) may elevate risk through sustained high cortisol levels and immune system changes, but that is a different category from the normal anxieties of early pregnancy.
Working, lifting moderate weight, eating a food you later worried about, or not knowing you were pregnant and having a glass of wine are not causes. Caffeine consumption under 200 mg per day (roughly one 12-ounce cup of coffee) has not been shown to significantly increase miscarriage risk. The guilt many people feel after a loss is understandable but almost never supported by the evidence.
Recognizing the Signs
Light spotting in early pregnancy is common and does not automatically mean a miscarriage is happening. Implantation bleeding and small amounts of brown discharge (old blood leaving the uterus slowly) can occur in healthy pregnancies. The signs that suggest an actual miscarriage include bright red bleeding or clots, cramping in the lower abdomen, a gush of clear or pink fluid, or passing tissue. Some people describe the bleeding as heavier than a normal period, while others initially mistake it for one.
If you experience these symptoms, an ultrasound is the primary tool used to determine what’s happening. At 5 weeks it may be too early to see much on ultrasound, so your doctor may also track hCG levels with blood draws 48 to 72 hours apart. In a healthy pregnancy, hCG should at least double in that window. Levels that plateau or drop suggest the pregnancy is not progressing.
What Happens After a 5-Week Loss
Because a 5-week pregnancy involves very little tissue, many people pass everything on their own without medical intervention. This is called expectant management. Bleeding and cramping typically resolve within two weeks, though it can take longer. For some, it feels similar to a heavy period.
If the body doesn’t pass the tissue completely, medication can help start the process. Cramping and bleeding usually begin within a few hours of taking it, and most people pass the remaining tissue within 48 hours. A surgical procedure (a brief uterine aspiration) is rarely needed at this stage but may be recommended if tissue remains after other approaches.
Heavy bleeding that soaks through more than two large pads per hour for two hours or more, fever, or feeling very unwell are signs of a complication that needs immediate attention. These problems are rare but possible with any type of miscarriage management.
Recurrence and Next Steps
A single miscarriage at 5 weeks, while difficult, is very common and usually does not indicate a fertility problem. Most people go on to have a healthy pregnancy afterward. Doctors typically do not recommend extensive testing after one loss. After two or three consecutive miscarriages, blood work to check for clotting disorders, thyroid function, and hormonal imbalances becomes standard. Chromosomal testing of both partners may also be suggested to look for structural rearrangements that increase the odds of producing embryos with abnormal chromosomes.