Making Sense of Miscarriage Statistics

What the Conflicting Research Really Means

One common concern for many women, especially early in pregnancy, is the risk of miscarriage. If you're newly pregnant and trying to make sense of the myriad statistics about miscarriage, here's an explanation of each one that hopefully will ease your mind.

Miscarriage Rate for All Conceptions

If taking into account the number of known miscarriages and the number of unknown miscarriages, there is a greater chance of miscarriage than not. As alarming as this statement may be, what it illustrates is that pregnancy loss is a commonly occurring event, one that usually goes entirely unnoticed, often because it occurred within days of the conception and was non-viable from the start.

Studies involving in vitro fertilization (IVF) found that a very large percentage of harvested eggs harbored chromosome abnormalities, the leading cause of early-term miscarriage.

Another widely-quoted study from the National Institute of Environmental Health Sciences (NIEHS) found that around 22 percent of all conceptions never even complete implantation. Both of these anomalies explain why so many miscarriages go unnoticed.

Based on the current evidence, if you factor in fertilized eggs that fail to implant along with pregnancies that end in miscarriage, around 70 percent to 75 percent of all conceptions will end in pregnancy loss.

As sobering as this statistic may be, if you already know that you're pregnant, your odds of carrying your baby to term are good.

After Implantation

Whether failed implantations can be defined as a "miscarriage" is a matter of opinion. Most doctors consider pregnancy to begin at implantation rather than at fertilization. Within this context, the rate of miscarriage can differ considerably.

According to the NIEHS study, 31 percent of pregnancies confirmed after implantation end in miscarriage. That translates to roughly one of every three pregnancies.

But before you worry too much about those figures, note that this number came from a study of a population of women who were confirmed to be pregnant at the very earliest point that it's scientifically possible to detect a pregnancy.

In real life, most women find out they are pregnant at a later point than the participants in this study, and the risk of miscarriage drops as pregnancy progresses. That would mean that most women have a lower risk of miscarriage by the time they confirm their pregnancies.

Still, it's worth pointing out that many experts consider this statistic as an argument against taking ultra-sensitive early pregnancy tests before missing a menstrual period. Use of such tests increases the risk of detecting a nonviable pregnancy that will miscarry within a few days and otherwise would have just looked like a regular menstrual period.

Knowing about such pregnancies can be a source of stress for many women, and if this is true for you, it's worth waiting to test until your period is actually late.

After a Confirmed Pregnancy

For the general population of pregnant women, the miscarriage rate after a confirmed pregnancy is usually the most relevant statistic.

Research suggests that between 10 percent and 20 percent of women with a medically confirmed pregnancy will end in miscarriage. Eighty percent of these will occur during the first trimester.

The reason for the disparity between this statistic and the NIEHS study is simple: the further along a pregnancy is, the lower the risk of miscarriage. Since many women who get pregnant do not track their periods, they may already be a few weeks along—possibly more than halfway through the first trimester—by the time the pregnancy is confirmed.

Since the majority of miscarriages occur within the first 12 weeks of gestation, the risk of pregnancy loss after 12 weeks drops dramatically to between 3 percent and 4 percent. After 20 weeks, the risk is roughly 1 in 160.

After Fetal Heartbeat

Most doctors agree that seeing a fetal heartbeat on ultrasound means the risk of miscarriage is much lower. Confirmation of a fetal heartbeat means that the baby has passed the initial stages of development wherein the majority of first trimester miscarriages occur.

According to research from Monash University, the overall risk of miscarriage after the detection of a fetal heartbeat is around 4 percent, dropping to 1.5 percent after 8 weeks and 0.9 percent by 9 weeks.

The one thing that's safe to say, however, is that seeing the baby's heartbeat is a good sign. It means the baby is growing as it should be, and there's little reason to be concerned at this point.

Unfortunately, there is one exception to this rule: slow fetal heart rate (less than 100 beats per minute) may signal an impending miscarriage, especially as the pregnancy advances.

Recurrent Miscarriage Rate

Most first-time miscarriages are random and do not recur. With one past miscarriage, the odds of miscarrying in your next pregnancy are about 20 percent. This is not much higher than someone without a history of miscarriage.

With two previous miscarriages, the risk of another miscarriage is 28 percent, and with three previous miscarriages, the risk increases to 43 percent. It's possible that testing for recurrent miscarriage causes might help in these cases.

A Word From Verywell

As much as we might hate to think so, miscarriage is of unavoidable and the body's way of stopping a pregnancy that has no chance of success. While there's not a whole lot you can do to affect your odds of a miscarriage, you may be able to lower your risk if you avoid alcohol, don't smoke, and minimize certain occupational hazards.

When you are pregnant or hope to become pregnant, you may be anxious to ensure you are doing everything right. It's easy to become overwhelmed by the many statistics floating around. Try to focus on doing what is healthy for your body and for nurturing your pregnancy.

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