Causes of Miscarriage in the First Trimester
Experiencing a miscarriage in the first trimester can be deeply distressing and confusing. Many people are left asking “Why did this happen?” or “Was it something I did?”
The reality is that most first-trimester miscarriages happen for medical reasons completely outside a person’s control. Understanding the causes can help reduce guilt, fear, and misinformation—and support emotional healing.
👉 For a full overview of miscarriage care, symptoms, treatment options, and recovery, read our Miscarriage Care: A Comprehensive Guide.
How Common Is First-Trimester Miscarriage?
Around 80% of miscarriages occur within the first 12 weeks of pregnancy. Many happen before someone even realises they are pregnant. While this does not reduce the emotional impact, it highlights how common early pregnancy loss is.
Chromosomal Issues (Explained Simply)
The most common cause of first-trimester miscarriage is a chromosomal abnormality.
What does that mean?
A healthy pregnancy usually has 46 chromosomes, which carry genetic instructions. Sometimes, when the egg and sperm join:
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There are too many chromosomes
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Too few chromosomes
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Or chromosomes are arranged incorrectly
When this happens, the embryo cannot develop normally, and the pregnancy ends naturally.
Important to know
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This is not inherited in most cases
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It is not caused by lifestyle, stress, or actions
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It is the body’s natural way of stopping a pregnancy that cannot develop safely
🔗 Related emotional support reading:
👉 Coping with Pregnancy Loss and Grief – TodaysWomen.uk
👉 How to Talk About Miscarriage Without Shame – TodaysWomen.uk
Lifestyle Myths (What Does NOT Cause Miscarriage)
One of the most harmful aspects of miscarriage is self-blame, often driven by myths. Let’s clear them up.
❌ Stress
Everyday stress, work pressure, or emotional upset does not cause miscarriage. Severe physical trauma may increase risk, but normal life stress does not.
❌ Exercise
Moderate exercise—including walking, yoga, or prenatal workouts—is safe in early pregnancy. Normal movement does not cause miscarriage.
❌ Sex
Sex during early pregnancy does not cause miscarriage unless a doctor has advised otherwise due to specific complications.
❌ Lifting or bending
Routine physical activity and household tasks do not lead to miscarriage.
💡 If a miscarriage happens, it would have happened regardless of these activities.
🔗 Helpful reassurance article:
👉 Miscarriage Myths That Harm Women’s Mental Health – TodaysWomen.uk
Age-Related Risks
Age plays a role in miscarriage risk—but it is not a fault, and many people go on to have healthy pregnancies later.
Approximate miscarriage risk by age:
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Under 30: 10–15%
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30–34: ~15%
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35–39: 20–30%
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40+: 40% or higher
This increase is mainly due to age-related chromosomal changes in eggs, not lifestyle choices.
🔗 Emotional perspective:
👉 Pregnancy After 35: Managing Fear and Expectations – TodaysWomen.uk
Other Medical Factors That May Contribute
Although less common, these can also increase first-trimester miscarriage risk:
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Hormonal conditions (e.g. untreated thyroid disorders)
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Uncontrolled diabetes
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Certain infections
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Structural issues of the uterus
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Autoimmune conditions (in rare cases)
If miscarriages happen repeatedly, further medical investigations may be recommended.
👉 Learn more about testing and support in our Miscarriage Care: A Comprehensive Guide.
Most common gynaecological problems
Emotional Impact: It’s Not “Just Physical”
Even an early miscarriage can cause profound grief. Feelings of sadness, guilt, anger, or numbness are all normal.
🔗 Support-focused reading:
👉 The Emotional Impact of Early Pregnancy Loss – TodaysWomen.uk
👉 Supporting a Partner After Miscarriage – TodaysWomen.uk
Key Takeaways
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Most first trimester miscarriage causes are chromosomal
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Lifestyle activities like stress, sex, or exercise do not cause miscarriage
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Age increases risk, but healthy pregnancies are still common
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Medical support and emotional care are equally important
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You are not to blame
For complete guidance on symptoms, diagnosis, treatment options, recovery, and future fertility, read our main resource:
👉 Miscarriage Care: A Comprehensive Guide
Do You Have Any Questions?
Frequently Asked Questions About First Trimester Miscarriage Causes
What are the most common first trimester miscarriage causes?
The most common cause of miscarriage in the first trimester is chromosomal abnormalities. This means the embryo has missing, extra, or incorrectly formed chromosomes, which prevents normal development.
Can stress cause a miscarriage in the first trimester?
Everyday stress, anxiety, or work pressure does not cause miscarriage. Most early miscarriages happen due to medical reasons beyond anyone’s control, especially chromosomal issues.
Can sex or exercise cause a first trimester miscarriage?
Sex and gentle to moderate exercise do not cause miscarriage in early pregnancy unless a healthcare professional has advised avoiding them for specific medical reasons.
Does age increase the risk of miscarriage?
Yes, miscarriage risk increases with age, mainly because chromosomal abnormalities become more common as eggs get older. Many people over 35 still go on to have healthy pregnancies.
Is miscarriage usually preventable in early pregnancy?
Most first trimester miscarriages are not preventable. They usually occur because the pregnancy could not develop normally, not because of something the person did or didn’t do.
When should someone seek medical help after early pregnancy bleeding?
Medical advice should be sought urgently if bleeding is heavy, lasts several days, or is accompanied by severe pain, fever, dizziness, or unusual discharge.