Chances of Miscarriage After a Normal Pregnancy

It is common for a pregnant woman to worry about miscarriage, at least in the beginning.

This is understandable, considering the startling statistics floating around out there—that first-trimester miscarriages occur in approximately 10% of confirmed pregnancies and that 30% to 40% of all conceptions end in a miscarriage.

The Risk of Miscarriage

That all being said, if you have one or more living children, you may not need to worry quite that much, claims an older study in the British Medical Journal. In this study, British researchers examined the effects of women's previous pregnancy history on the risk of miscarriage in the next pregnancy.

They found that in women whose previous pregnancy had ended in a live birth, the risk of miscarriage the next time around was only 5% (1 in 20). With all previous pregnancies ending in a live birth, the risk was even lower still at 4% (1 in 25). Obviously, the risk of miscarriage will never be zero. But, it can be reassuring to know when you fall in a lower-risk group.

Main Causes of Miscarriage

Various risk factors for miscarriage exist, many of which have yet to be elucidated. Miscarriages during the first trimester of pregnancy are due to chromosomal abnormalities, about 50% of the time.

Chromosomes are like hard drives that contain all the information your body needs for development. They are blocks of genetic information that serve as the seeds of life. During conception, when the gametes (or egg and sperm which contain chromosomes) meet, sometimes either too many or too few chromosomes result.

Often when the number of chromosomes is off, the pregnancy is nonviable and can't survive, resulting in a miscarriage. Of note, not all pregnancies that involve abnormal chromosome counts go on to miscarry. For example, Edward's syndrome is caused by trisomy 18, or triplicate copies of chromosome 18, and Down's syndrome is caused by trisomy 21, or triplicate copies of chromosome 21.

Nevertheless, babies with abnormal chromosome counts may experience profound complications which can result in early death. For instance, whereas people with Down's syndrome can go on to live to middle age, the majority of babies with Edward's syndrome that makes it to birth die within the first few days of life.

Other Causes of Miscarriage

Although chromosomal problems are the most common cause of miscarriage, there are other things that can result in miscarriage including the following:

• Abnormalities in the shape of the womb
• Drug abuse
• Infections (for example, rubella, parvovirus B19, cytomegalovirus)
• Maternal health conditions like obesity, high blood pressure, diabetes, or autoimmune diseases
• Medications (for example, NSAIDs, retinoids, and methotrexate)
• Placental problems
• Smoking 

Miscarriages due to chromosomal problems occur during the first trimester. However, the infections and chronic medical conditions listed above can result in miscarriage during the second trimester—which is much less common (about 1% to 5% of pregnancies).

In addition, according to the American College of Obstetricians and Gynecologists, two of the most common risk factors for miscarriage (in the first trimester) include a prior first-trimester miscarriage and advanced maternal age (age 35 years or older).

Factors Unrelated to Miscarriage

Often there's nothing that you can do to prevent a miscarriage, as in the case of chromosomal abnormalities. However, some miscarriage risk factors are modifiable, such as smoking, drug, and alcohol cessation during pregnancy.

In addition to these non-modifiable and modifiable risk factors, there's a lot of buzz about things that have nothing to do with miscarriage, including the following:

• Depression
• Emotional stress
• Exercise
• Lifting or straining
• Sex
• Shock or fright
• Spicy foods

A Word From Verywell

If you (or your partner) find yourself worrying about a miscarriage, especially if your anxiety is overwhelming or distressing, please talk with your doctor. You deserve to feel good and calm during your pregnancy.