Fetal Heart Rate and Miscarriage: Is There a Link?
The steady thump-thump of your baby's heartbeat is one of the most rewarding and reassuring parts of every ultrasound because it's proof that your pregnancy is going well. So when the fetal heart rate is slower than expected, it's only natural to think the worst.
But are fetal heart rate and miscarriage linked? It's important to note that your baby's heart rate is anything but consistent in the early weeks of gestation. Around 6 to 9 weeks, it can range from 160 to 180 beats per minute. Then, as baby's brain grows, the heart rate gradually drops to 110 to 160 beats per minute until term, says Erika Nichelson, D.O., a board-certified ob-gyn at the Family Childbirth and Children's Center at Mercy Medical Center in Baltimore.
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 sustainable and a miscarriage is imminent. (Most miscarriages occur in the first seven weeks of pregnancy, and chromosomal abnormalities are generally to blame.) In fact, studies have found that the chance of a miscarriage increases when the baby's heart rate is less than 100 beats per minute at 6.2 weeks gestation or less than 120 beats per minute at 6.3-7 weeks.
Still, most doctors avoid declaring a miscarriage based on one fetal heart rate taken during one ultrasound. Instead, your ob-gyn will likely keep a close eye on how your baby is developing. She 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 make sure they're increasing properly. She may also repeat 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 and hCG levels rise normally, your doctor will likely give you the "all clear" signal.
Though the wait between tests can feel like an eternity for concerned moms-to-be, it's precious time for your health care provider to figure out exactly what's going on with your baby. Rest assured that chances are your pregnancy will continue to progress normally. In fact, in pregnancies where the fetal heartbeat is detected, there's only a 1 percent chance of miscarriage between weeks 6 and 11.
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