Is There a Link Between High Fetal Heart Rate and Miscarriage?

The steady thump-thump of your baby's heartbeat is often one of the most rewarding and reassuring parts of every prenatal ultrasound. But, if the fetal heart rate climbs to 190 at nine weeks, is that normal or cause for concern?

Read on to learn about normal and abnormal fetal heart rates, the link to miscarriage, and the causes and treatment of fetal tachyarrhythmia.

What Is a Normal Fetal Heart Rate?

The following is how the average fetal heart rate breaks down throughout pregnancy.

The averages above provide a starting point for reference, but it's important to note that they are just that: averages. This means that many healthy fetuses will have heart rates that are faster or slower. It's also important to note that an embryo's cardiac activity is anything but consistent in the early weeks of pregnancy.

Around six to nine weeks, a healthy heart rate can range from 160 to 180 beats per minute. Then, as the fetus's brain grows, the heart rate gradually drops somewhere between 110 to 160 beats per minute until term, says Erika Nichelson, D.O., a board-certified OB-GYN at the UPMC Pinnacle Obstetrics and Gynecology Specialists in Gettysburg, Pennsylvania.

Are Fetal Heart Rate and Miscarriage Linked?

A fetal heart rate that's a week or more behind where it should be based on gestational age could be a temporary blip, but it may also be a sign that the pregnancy isn't viable and miscarriage is imminent. High fetal heart rate can also be cause for concern, but only when the high rate is sustained. (That is to say that a single scan showing a higher-than-normal fetal heart rate isn't usually a cause for concern.)

Low fetal heart rate

Studies have found that the chance of a miscarriage increases when the fetus's heart rate is low for its gestational age.

For example, one study found that when an embryo had a low fetal heart rate (considered 122–158 beats per minute for embryos between six and eight weeks) and a small crown-to-rump length (that is, the measurement from the top of the head to the bottom of the buttocks), there was a 21% probability of pregnancy loss. This pregnancy loss risk was 15% higher than those with neither characteristic.

High fetal heart rate

Alternatively, research shows that when higher-than-expected fetal heart rates (fetal tachyarrhythmia) endure, there is a high risk of fetal death. Experts suggest these situations be closely monitored.

Causes of High Fetal Heart Rate

According to researchers, common causes of fetal tachyarrhythmia (abnormally fast fetal heart rate) include:

• Infection
• Low blood oxygen levels
• Hyperthyroidism in the gestational parent

Since sustained fast fetal heart rate can lead to fetal heart failure and fetal and maternal fluid buildup—complications that can lead to miscarriage, premature birth, and other negative outcomes—it is essential to monitor pregnancies with consistently fast fetal heart rates closely.

Treatment for High Fetal Heart Rate

Whether the fetal heart rate is higher or lower than expected, most doctors won't declare a miscarriage based on one fetal heart rate taken during one ultrasound. Instead, the health care provider will likely want to follow up and closely monitor how your baby is developing over time.

In early pregnancy, this monitoring is usually done through ultrasound and blood work. In later pregnancy, monitoring might include other procedures such as fetal echocardiogram, a type of ultrasound that looks at the chambers of the heart.

In most cases of abnormal fetal heart rate, health care providers may do a follow-up ultrasound or, if it's early in the first trimester, check your human chorionic gonadotropin (hCG) levels within 48 to 72 hours to ensure they're increasing as expected.

They may also do another ultrasound a week or so later. "Usually, you have an idea where things are headed at that point," Dr. Nichelson says. If the fetal heart rate bounces back to healthy levels and hCG levels rise normally, the doctor will likely give you the "all clear" signal.

Monitoring and treatment options will also vary depending on the type of tachyarrhythmia and the age of the fetus. Fortunately, most cases of high embryonic or fetal heart rate resolve on their own, especially when they are found in early pregnancy. Medication is generally reserved for situations that occur in late pregnancy, not those found in the first trimester.