Fetal Heart Rate

I learned to worry about fetal heart rate with my first pregnancy, when I hurried to the computer after each visit with my reproductive endocrinologist, anxious to see if my pregnancy was progressing normally. We were able to hear a heartbeat as early as at the end of week 5, which was a milestone we were happy to reach, but once we were able to measure the heart rate, I began to feel apprehensive.

Many websites list ranges of fetal heart rates for each week of early pregnancy, and most present fairly consistent information. Each time, however, I kept searching for more obscure web pages, which might indicate that my baby’s heart rate—which appears to be on the high end of the spectrum according to the popular sites—might be normal.

At each bi-weekly office visit, I asked my doctor if the heart rate we measured was within the expected range. He did not want to alarm me and reminded me that it was too early to make any conclusions. I had found a scientific article on the Web, though, which had assigned a high probability for chromosomal abnormalities (trisomy 13 being one of the top aneuploidies) to fetuses with heart rate in the top 95 percentile, so—naturally—I continued to be worried.

Thus, at the end of the first trimester, when my blood test results arrived, I wasn’t completely shocked to learn that an aneuploidy had been detected. (In fact, it was trisomy 13, just like the article had predicted.) The findings were confirmed on a fetal ultrasound by a perinatologist, who specialized in detecting chromosomal disorders during the second trimester.

For my third pregnancy, which was achieved via frozen embryo transfer (FET), I had made sure the embryo we implanted was fully tested and chromosomally normal. When we detected a heartbeat at week 6, I was happy. When we were able to measure it the week after, I was even happier—this time it was right in the middle of the fetal heart rate range.

Then all of a sudden, a couple of days late, the heartbeat had suddenly stopped.

This is now my fourth pregnancy, and now, at week 19, I am barely able to relax and not think of the baby’s heart rate. We had again implanted a genetically tested embryo, and at each week of testing, the fetal heartbeat has been within norms. My OB-GYN tells me this is unlikely to change in the next few months.

If you are like me and worry about what your baby’s heart rate should be as the pregnancy progresses, here are some average values (measured in beats per minute) you could use as guidelines:

• ~ 110 bpm by 5–6 weeks
• ~ 170 bpm by 9-10 weeks
• ~ 150 bpm by 14 weeks
• ~ 140 bpm by 20 weeks
• ~ 130 bpm by term

If you want to compare your baby’s heart rate with that of my baby, here are the values my doctor had recorded:

• 161 bpm at 7 weeks 5 days 
• 171 bpm at 9 weeks 5 days 
• 150 bpm at 13 weeks 3 day
• 140 bpm at 18 weeks 2 days