The fetal heart rate is measured with the help of an ultrasound Doppler. Expectant women can themselves measure the heart beats as well as feel them. Women who hear the heart beats of their baby for the first time will find the experience to be exhilarating and fascinating.
Unfortunately, after getting to know about the presence of a low or high FHR or fetal heart rate, some pregnant women begin worrying unnecessarily. Such women can follow the below available fetal heart rate chart and put their worries to rest.
A normal fetal heart rate chart
| Size of the fetus or fetal age | Normal fetal heart rate |
| 2 mm embryo along with a 20 mm gestational sac diameter | 75 beats per minute or bpm |
| 5 mm embryo along with a 30 mm gestational sac diameter | 100 bpm |
| 10 mm embryo | 120 bpm |
| 15 mm embryo | 130 bpm |
| The beginning of 5 weeks | 80 to 85 bpm |
| 5 weeks | Begins at 80 bpm and ends at 103 bpm |
| 6 weeks | Begins at 103bpm and ends at 126 bpm |
| 7 weeks | Begins at 126bpm and ends at 149 bpm |
| 8 weeks | Begins at 149bpm and ends at 172 bpm |
| 9 weeks | Between 155 bpm to 195 bpm with the average being 175 bpm |
| 12 weeks | Between 120 bpm to 180 bpm with the average being 150 bpm |
| Post 12 weeks | Between 120 bpm to 160 bpm with the average being 140 bpm |
The chart presented above elucidates the manner in which fetal heart rate changes during the 1st and second trimesters. The fetal heart rate is relatively stable in the third trimester, while it tends to slightly slow down in the third/last trimester just before labor. The FHR still continues to be nearly two times an adult heartbeat rate. Doctors will monitor the fetal heart rate at the time of labor in pregnancies with high risk. With regards to a full-term pregnancy the average FHR at the time of labor is around 140 bpm, while it may be about 155 bpm during labor with regards to a preterm delivery.
It is important to remember that the fetal heart rate audibility is dependent on varied factors such as the nature and position of the mother’s abdominal tissues, the position of the unborn baby, etc. The risk to a miscarriage is minimal when the fetal heart rate is normal. It may be noted that an FHR falling between 100 and 160 is deemed as normal.
The risk to miscarriage greatly increases if the fetal heartbeat remains inaudible for a week or more. An abnormally high or low fetal heart rate is one of the key fetal distress signs. High or low FHR during early or latter part of a pregnancy usually occurs due to increased physical exertion by the expectant woman, certain umbilical cord or placental anomalies, genetic abnormalities, mental stress, or other kinds of complications.
The average FHR differs from one fetus to another; it also keeps rising or dropping during the course of pregnancy. Hence, a fetal heart rate that is as low as 100 or as high as 180 is deemed normal. The rate of fetal growth may differ somewhat as per some genetic factors. Therefore mothers of varied races may see different FHR. Measurement of fetal heart rate may also alter from one country to another.
Fetal age and the heart rate
A fetal heartbeat is also called FHT or fetal heart tone.All of us know that pregnancy is categorized into 3 trimesters. Depending on the position of the baby, the mother’s weight, and the location of the placenta, it is possible to hear the heartbeats of the fetus via a fetoscope or a stethoscope at around 18 to 20 weeks, or even during/after 12 weeks.
It is also possible to hear a baby’s heartbeat at around 8 weeks with the help of ultrasound technology. Occasionally, fetal heartbeats cannot be heard till the 12th to 14th week of pregnancy, even via a Doppler ultrasound. Fortunately, this is normal and nothing to fret about.
A baby’s heart begins beating during the fifth week. The fetal heart rate is a lot faster than an adult heart rate. At around the fifth week, the fetal heart rate is initially similar to the heart rate of the mother, i.e. 80 to 85 bpm. It later increases at a rapid rate, at nearly three beats a minute per day till the early part of the ninth week.Then around the 12th week, the FHR will stabilize to around 150 bpm. The normal fetal heart rate post 12 weeks ranges between 120 to 160 bpm. The pattern of FHR increases remain fixed. Hence, fetal heart rate is used approximate the fetal age.
It may also be noted that FHR tends to vary as per the mother’s movements. It can be different when the mother is physically active and vary when she is resting. Pregnant women should always consult a doctor if they have any questions about abnormal FHR.
