What Causes Miscarriage?
- Renee Grandi
- Apr 29
- 4 min read
Miscarriage is one of the most heartbreaking experiences a couple can face. It affects approximately one in four pregnancies — a devastating statistic that is often brushed over without enough investigation or understanding. Many couples are told, "These things just happen," or given no real answers. However, current science reveals that miscarriage is often not random. There are usually deeper biochemical, hormonal, immunological, or cellular factors involved, both in women and men.
Understanding the causes of miscarriage is critical not only for emotional closure but also for future fertility and pregnancy outcomes.
The Complex Biology Behind a Healthy Pregnancy
Successful conception and pregnancy rely on a synchronised, finely tuned biological system involving:
Hormonal precision (progesterone, oestrogen, thyroid hormones)
Immune tolerance (acceptance of the embryo)
Optimal cellular and mitochondrial function
Healthy uterine environment
Adequate nutrient availability
Minimal oxidative stress and inflammation
When any one of these systems is disrupted, the risk of miscarriage increases.
Causes of Miscarriage: Female Factors
1. Hormonal Imbalances
Hormones are essential for pregnancy maintenance. Even slight imbalances can create an environment that is hostile to implantation and foetal growth.
Low progesterone (Luteal Phase Defect): Progesterone prepares the uterine lining for implantation and maintains early pregnancy. Low levels can cause early pregnancy loss.
Thyroid Dysfunction: Even subclinical hypothyroidism (TSH > 2.5 mIU/L) has been linked to increased miscarriage risk.
Thyroid Antibodies (TPO, TgAb): The Presence of thyroid autoantibodies, even with normal thyroid function, doubles the risk of miscarriage.
Polycystic Ovary Syndrome (PCOS): Hyperinsulinemia and androgen excess impair ovulation quality and endometrial receptivity.
✅ Optimal fertility target for TSH is 1.0–2.0 mIU/L.
2. Immune Dysregulation
The immune system must "tolerate" the embryo, which is genetically distinct from the mother. Disruptions in immune tolerance can trigger miscarriage:
Antinuclear Antibodies (ANA): Linked to implantation failure and early pregnancy loss.
Antiphospholipid Antibodies: Can trigger clot formation, impairing placental blood flow.
Elevated Inflammatory Cytokines: IL-6 and TNF-α are associated with early miscarriage.
Natural Killer (NK) Cell Overactivity: Excess NK cells may attack the embryo at the implantation site.
✅ Testing includes ANA panels, antiphospholipid profiles, NK cell activity, and cytokine panels.
3. Chronic Inflammation and High CRP
Low-grade inflammation can damage the uterine lining and the embryo. High-sensitivity CRP levels above 1.5–2 mg/L are associated with infertility and pregnancy complications.
4. Gut Health and Microbiome Disruptions
The gut is a foundational component of immune regulation. Dysbiosis, intestinal permeability ("leaky gut"), and chronic gastrointestinal inflammation can indirectly trigger miscarriage by fuelling systemic inflammation and immune dysregulation.
Key factors include dysbiosis, small intestinal bacterial overgrowth (SIBO), and undiagnosed coeliac disease.
5. Uterine and Structural Factors
Thin Endometrial Lining (<7mm): Insufficient for implantation.
Fibroids, Polyps, and Adhesions: Physical barriers to embryo development.
Chronic Endometritis: A low-grade infection of the uterine lining can reduce implantation success.
✅ Pelvic ultrasound, saline infusion sonohysterography (SIS), and endometrial biopsy are essential diagnostics.
6. Nutrient Deficiencies
Nutrient status directly influences egg quality, implantation, placental development, and foetal growth:
Nutrient | Role | Impact |
Folate (MTHFR polymorphisms) | DNA methylation, embryo development | Poor DNA replication, miscarriage |
Vitamin D | Immune modulation, implantation | Deficiency linked to recurrent loss |
Zinc and Selenium | Antioxidant protection | Oocyte quality, placental function |
Coenzyme Q10 | Mitochondrial energy for egg division | Lowers embryo viability |
✅ Vitamin D optimal range for fertility: 100–150 nmol/L.
7. Oxidative Stress and Mitochondrial Damage
Eggs are mitochondria-dense cells.
Oxidative stress impairs mitochondrial ATP production, leading to poor chromosomal segregation and increased miscarriage risk.
Contributors to oxidative stress:
Environmental toxins (plastics, pesticides)
Smoking, alcohol
Inflammatory diets
Chronic infections
✅ Antioxidants like CoQ10, NAC, and vitamin E are critical.
Causes of Miscarriage: Male Factors
1. Poor Sperm DNA Integrity
Male sperm quality is half the equation, yet it is often neglected. Even when sperm count and motility are normal, DNA fragmentation inside sperm can cause early embryo loss.
✅ Ideal DNA Fragmentation Index (DFI): <15%.
2. Sperm Morphology
WHO standards only require 4% normal morphology to be considered ""normal".
However, actual optimal fertility requires much higher morphology rates (ideally 15–20% or higher).
Poor morphology impacts:
Fertilisation success
Placental development
Early embryo cleavage
Chromosomal integrity
3. Oxidative Stress
Men are highly vulnerable to oxidative stress due to minimal antioxidant defences in sperm.
Contributors:
Smoking
Alcohol
Environmental toxins
Infections (chlamydia, mycoplasma)
A poor diet low in antioxidants
✅ Semen oxidative stress testing (e.g., ROS assays) can reveal hidden sperm vulnerabilities.
4. Hormonal Imbalances
Low free testosterone
High oestradiol (due to obesity)
Low FSH
All impair spermatogenesis and reduce embryo viability.
✅ Optimal male fertility testing should include total testosterone, free testosterone, SHBG, LH, FSH, and oestradiol. The GOLD-STANDARD test for hormones is a DUTCH test. This will provide you with exact information about your hormones.
Other Contributing Factors to Miscarriage
Homocysteine elevation (>8 µmol/L): Associated with vascular issues, clotting, and placental dysfunction.
Alcohol: Increases oxidative stress, alters DNA methylation.
Heavy metal exposure (mercury, cadmium, lead): Direct DNA toxicity in eggs and sperm.
Chronic infections: Hidden bacterial, viral, or fungal infections.
High stress levels: Cortisol stealing from progesterone, reducing implantation chances.
Endocrine Disrupting Chemicals (EDCs): BPA, phthalates, pesticides impacting egg/sperm quality.
Why Most Miscarriages Are Under-Investigated
Couples are often told miscarriage is "bad luck" after one loss, yet science shows that even a single loss warrants comprehensive evaluation when:
Maternal age is over 35
There are risk factors (thyroid disease, PCOS, autoimmunity)
There is a strong emotional drive to find answers
Proper miscarriage investigation should involve both partners, including:
Full hormone mapping
Thyroid antibodies
Autoimmune screening
CRP, homocysteine, vitamin D
Advanced semen analysis
Oxidative stress and DNA fragmentation testing
Final Thoughts: Miscarriage Is a Biological Signal
Miscarriage, while emotionally devastating, is not random in most cases. It is the body's way of communicating that something, such as immune function, nutrient status, hormonal balance, or mitochondrial integrity, needs to be strengthened. By moving beyond superficial testing and addressing the deeper biochemical, immunological, and environmental factors that influence pregnancy, it is often possible to dramatically improve future outcomes.
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