What does this study actually say?
The headline “Women with long-term illnesses face a higher risk of miscarriage during pregnancy” needs a little clarification. The study did not find that every woman with a chronic illness has a high risk of miscarriage. Instead, the increased risk was mainly seen with certain chronic conditions, particularly those affecting metabolic and cardiovascular health.
1. What is a miscarriage?
A miscarriage is the loss of a pregnancy before the fetus is able to survive outside the womb. Early pregnancy loss is relatively common, and the causes can include genetic abnormalities in the embryo, hormonal or metabolic problems, immune factors, maternal age and other factors.
Importantly, having a miscarriage does not necessarily mean that a woman has a health problem.
2. What did researchers study?
Researchers in Norway examined 593,009 pregnancies recorded between 2010 and 2016. They linked information from three national health registries and looked at 25 chronic diseases that had been diagnosed before pregnancy.
The women were around 29.7 years old on average.
Among these pregnancies:
- 409,952 (69.1%) ended in live birth.
- 85,676 (14.5%) ended in miscarriage.
- 1,740 (0.3%) resulted in stillbirth.
- 95,641 (16.1%) were induced abortions.
3. Which illnesses were associated with higher miscarriage risk?
The strongest overall association was seen with cardiometabolic diseases—conditions affecting the heart, blood vessels, blood pressure or metabolism.
| Condition | Approximate increase in odds of miscarriage |
|---|---|
| Atherosclerosis | 122% higher |
| Type 2 diabetes | 38% higher |
| Crohn’s disease | 31% higher |
| Endometriosis | 22% higher |
| Hypertensive disorders | 19% higher |
| Type 1 diabetes | 11% higher |
The study also found associations with some less common conditions, including hypoparathyroidism and Cushing syndrome.
4. Why might these conditions matter?
Researchers believe that conditions affecting blood vessels, metabolism, hormones or inflammation could potentially interfere with the processes needed for a healthy pregnancy.
For example, diabetes can affect blood-sugar regulation, while hypertension can affect the cardiovascular system. These factors may influence the placenta and the environment in which the pregnancy develops.
However, this particular study did not prove exactly why these conditions were associated with miscarriage. The researchers specifically said that further investigation is needed to understand the biological mechanisms.
5. What about having multiple chronic illnesses?
An interesting finding was that the association became stronger when women had more than one chronic condition.
Compared with women without a recorded chronic disease:
- 1 chronic disease: OR 1.01 — essentially no meaningful increase
- 2 chronic diseases: OR 1.14 — about 14% higher odds
- 3 or more: OR 1.49 — about 49% higher odds
This is one reason the headline can be misleading: having one chronic illness does not automatically mean a woman is at substantially greater risk.
6. What does “38% higher risk” actually mean?
This is very important.
The study reported odds ratios (ORs). For example, the OR for type 2 diabetes was 1.38, which means the odds of miscarriage were about 38% higher compared with women without that condition, after accounting for age.
It does not mean:
“38% of women with diabetes will miscarry.”
And it does not mean that diabetes directly causes 38% of miscarriages.
It describes an association between the condition and miscarriage odds.
7. Does chronic illness cause miscarriage?
Not necessarily.
This was a registry-based observational study. It can identify associations, but it cannot establish that a particular disease directly caused a miscarriage.
For example, the researchers did not have enough information to completely account for factors such as lifestyle and socioeconomic circumstances, and they also could not distinguish whether some associations were related to the underlying disease or to medications used to treat it.
So the correct interpretation is:
Certain chronic conditions were associated with increased miscarriage odds—not that chronic illness automatically causes miscarriage.
8. What conditions were not strongly associated?
The study looked at a broad range of conditions, including:
- Asthma
- Allergic rhinitis
- Atopic dermatitis
- Migraine
- Epilepsy
- Multiple sclerosis
- Rheumatoid arthritis/ankylosing spondylitis
- Ulcerative colitis
- Thyroid conditions
- PCOS
- Various autoimmune conditions
The researchers concluded that overall, chronic diseases were largely not associated with increased miscarriage risk, with the clearest pattern occurring among cardiometabolic conditions and a few other diseases.
9. Does this mean women with chronic illnesses shouldn’t become pregnant?
Absolutely not.
The study is not saying that women with chronic conditions should avoid pregnancy.
Rather, it highlights the importance of pre-pregnancy planning and appropriate medical care. A woman with conditions such as diabetes or high blood pressure may benefit from having those conditions well controlled before and during pregnancy.
Medication should also never be stopped on one’s own because some medicines need to be changed before or during pregnancy, while others may be important to continue.
10. What is the biggest takeaway?
The most accurate takeaway is:
Most chronic illnesses were not strongly linked to miscarriage in this large Norwegian study. However, certain conditions—particularly type 2 diabetes, hypertension and other cardiometabolic diseases, as well as some reproductive and inflammatory conditions—were associated with higher odds of miscarriage.
And importantly, an association does not mean that a woman with one of these conditions will have a miscarriage. Many women with chronic illnesses have completely healthy pregnancies.
Study: Maria C. Magnus et al., Risk of miscarriage in women with chronic diseases in Norway: A registry linkage study, PLOS Medicine, 2021.
