What you might read as “fact” in one place could be called a “myth” in another. For example, one article may claim that stress causes miscarriages, while another says there is no evidence it does. Here’s what you need to know about the risk factors and causes of miscarriage, how they are different, and how you can sort through the myths to get to the truth.
Overview
You might be confused about the difference between miscarriage causes and miscarriage risk factors. When you are interpreting information on the Internet about miscarriage, it’s important that you understand how the two are different.
Correlation vs. Causation
You might have heard the phrase, “correlation is not causation.” It means that just because two factors are associated with each other, one didn’t necessarily cause the other. To understand why correlation does not equal causation in terms of miscarriage causes, consider the following study. In 2017, researchers found that women who have tooth problems (periodontal disease) are more likely to give birth prematurely and have babies with low birth weight, and might even be more likely to miscarry. There is a strong correlation between eating ice cream cones and drowning in a lake—but that doesn’t mean that eating an ice cream cone causes someone to drown. Eating ice cream and drowning are related because they are both much more likely to happen during the summer. Does that mean that tooth problems cause pregnancy complications? It’s plausible: Tooth decay bacteria could secrete some as-yet-undiscovered substance that triggers preterm labor. However, there are also other equally plausible reasons for the link, and it might be that the miscarriage didn’t have to do with a woman’s dental health at all. Instead, it could be that there was something that made them more vulnerable to both miscarriage and poor dental health. For example, smoking increases the risk of both tooth decay and premature birth, as does having diabetes. There could also be socioeconomic factors. A woman with tooth decay might not visit the dentist because they don’t have insurance. If they don’t have insurance, they might also be less likely to receive prenatal care that could have helped prevent premature birth. As these alternate explanations demonstrate, having tooth decay could mean that a woman has an increased risk for premature birth—not that her tooth decay caused premature birth. In this case, tooth decay would be considered a risk factor, not a cause.
Miscarriage Research
The same mechanism applies to several theories about miscarriage causes. Many factors have been linked to the risk of miscarriage, but very few of them have been proven to cause miscarriages. Again, the two could be related through correlation rather than causation: if a woman has high levels of stress, they might be more likely to drink alcohol or engage in other behaviors that independently increase the risk of miscarriage.
Research Challenges: What Causes Miscarriage?
Using the example of stress as a possible contributor to miscarriage, it’s important to understand why so little is known. The main reason is that it’s difficult—if not impossible—to study the impact of stress on pregnancy and pregnancy loss. It would be unethical to “stress” one group of pregnant people to see if they had more miscarriages than a similar group of pregnant people who were not stressed. Instead, researchers conduct studies on topics like miscarriage by looking at groups of people and trying to sort out statistically which factors are linked with a higher or lower risk (such as how the risk of miscarriage changes during an economic downturn). However, studies like these have many variables that are difficult to control. Another example is the theory that low progesterone causes miscarriages. Pregnant people who miscarry are likely to have low progesterone. However, there is controversy over whether low progesterone is the actual cause of the miscarriage or whether it’s merely a sign that miscarriage is impending.
Making Sense of Causes and Risk Factors
Ultimately, for the pregnant person concerned about pregnancy loss, the distinction is mostly academic. The more important thing to focus on is which factors you can change vs. which you cannot. For example, things like your genetics and certain health conditions are not necessarily avoidable. However, there are also certain lifestyle risk factors that have been linked to miscarriage, which you do have some control over. Factors that are associated with miscarriage—but are not necessarily causes of miscarriage—include:
Age over 35 Certain medical conditions (such as antiphospholipid syndrome and endocrine disorders) Chromosomal and other genetic abnormalities (including MTHFR gene mutations) Elevated natural killer cells Environmental exposures High intake of trans fats Immune disorders (including some autoimmune diseases) Infections (such as bacterial vaginosis) Large quantities of caffeine during pregnancy Lifestyle factors (including exposure to cigarette smoke and alcohol use) Obesity Previous elective abortion Stress Strenuous activity (including exercise or work-related activity) during pregnancy Structural factors (such as adhesions or malformation of the uterus or cervix) Thyroid disease
If you are actively trying to get pregnant, you might make certain changes to your lifestyle that can reduce your risk of having a miscarriage. For example, you might decide to quit smoking. However, if you don’t realize that you’re pregnant, you might not make changes to modifiable risk factors soon enough to prevent their effects. In the end, all you can do is try to control the things that are actually in your control.
Handling Feelings of Blame and Guilt
If you’ve experienced a miscarriage, you might wonder if there is a specific risk factor that you can “blame.” You might even blame yourself. You should know that treatments that are considered experimental can be risky and are unlikely to be covered by insurance. The first thing you should know is that spontaneous miscarriage is quite common—while the exact numbers are hard to estimate because they vary between age groups, it’s thought that it occurs in about 15% of pregnancies. Even if you have recurrent miscarriages—which are less common than a single, spontaneous miscarriage—the reason is not always identifiable. In most cases—unless a provider performs very specific tests—the cause of the miscarriage is not known. Often, even if tests are done, the cause is still unclear. Even if you think there was a specific risk factor that led to your miscarriage, it probably wasn’t the only thing that caused it to happen. Experts believe that it’s more likely that most miscarriages happen because of multiple factors, or simply random chance.
A Word From Verywell
When you’re trying to parse out the facts from myths and sort through proven vs. unproven science, it can be overwhelming—especially when there is no shortage of information available on the Internet. Know that there are many risk factors and causes of miscarriage—but these are not necessarily one and the same. If you’ve had a miscarriage, you might feel guilty and wonder if there are certain risk factors that are to blame. In most cases, it’s not clear what caused a miscarriage— it might well have happened by chance. If you are worried that you did something wrong, know that as there are different risk factors, there are likely different causes—and scientists are still trying to figure out how they work.
