It's easy to become overwhelmed by the numerous statistics floating around out there on miscarriage rates. Depending on the context, you might find numbers saying everything from 5% to 70% of pregnancies miscarry. What's even more confusing is that most of these numbers are correct when put into context. For example, one study found that women who have given birth have a 5% risk of miscarrying the next time around, and some research has indicated that 70% of fertilized eggs may never go on to become a full-term pregnancy. But those numbers don't help you if you're just trying to determine an average person's risk of miscarriage after finding out she's pregnant.
I think the answer offered by UpToDate, an online reference source for doctors and patients, might help to clarify the confusion:
"Miscarriage in early pregnancy is common. Studies show that about 10% to 20% of women who know they are pregnant have a miscarriage some time before 20 weeks of pregnancy; 80% of these occur in the first 12 weeks. But the actual rate of miscarriage is even higher since many women have very early miscarriages without ever realizing that they are pregnant. One study that followed women's hormone levels every day to detect very early pregnancy found a total miscarriage rate of 31%."
So, if you already know you're pregnant, your risk of miscarrying before 20 weeks is probably somewhere between 10% and 20%, and the rates of miscarriage are highest in the first trimester (the first 12 weeks). But if you confirm your pregnancy when you are very early along, such as if you use early pregnancy tests before you miss your period, the overall risk of miscarrying might be a little higher, because you may detect a very early miscarriage that would have otherwise gone unnoticed (a chemical pregnancy). And if your pregnancy has already progressed beyond the first trimester, the greatest risk of miscarriage has most likely passed.
Remember that statistics on miscarriage rates are just that -- statistics. Your true risk of miscarriage may be higher or lower than average depending on risk factors that may or may not be present in your situation. For example, moms over 35 have higher miscarriage rates than moms in their twenties; women who have successfully given birth in the past have lower pregnancy loss rates than moms in their first pregnancies, and so on.
Here are some other questions you might have about miscarriage rates:
What if I had a miscarriage last time?
With one past miscarriage, the odds of miscarrying in your next pregnancy are about 20% (not much higher than someone without a history of miscarriage). With two previous miscarriages, the risk of another miscarriage is 28%, and with three previous miscarriages the risk increases to 43%. It's possible that having testing for recurrent miscarriage causes might help in these cases.
What if I've seen the heartbeat on an ultrasound?
Most research suggests that the odds of miscarrying decrease once the pregnancy has reached the point that an ultrasound can detect a heartbeat, with estimates ranging from 2% to 5%.
Can I do anything to reduce my risk of miscarrying?
There's not a whole lot you can do to affect your odds of miscarriage, but research suggests you may have a lower risk of miscarriage if you avoid alcohol, don't smoke, avoid known occupational hazards, and keep your caffeine intake at a low to moderate level (less than 200 mg of caffeine per day).
Want to learn more? See UpToDate's topic, "Patient information: Miscarriage," for additional in-depth medical information.
Tulandi, Togas. "Patient information: Miscarriage." UpToDate. Accessed: Nov 2009.