A fetal heart will begin to beat at around 5-6 weeks' gestation. Although an ultrasound machine will be able to detect this by about 6 weeks, a fetal Doppler cannot detect a heartbeat until closer to 8-10 weeks. An ultrasound machine uses very powerful probes (5-10 Mhz) at a much higher output level (up to 720 Mw/cm2) whereas a fetal Doppler only uses a 2-3 Mhz probe at a much lower level of less than 20 mw/cm2. For this reason, fetal Dopplers are unable to detect a heartbeat before 8 weeks and usually not before 10-12 weeks. Dont be misled. If someone says she heard her baby's heartbeat at 6 weeks, she is probably referring to an ultrasound scan not a fetal monitor.
Type of baby Doppler being used: Be sure that your Doppler is in fact a 'fetal Doppler' and not a prenatal listener. Some of the products available do not utilize the same technology as a fetal Doppler and cannot detect a fetal heartbeat until after 30 weeks. Also, different types of fetal Dopplers vary with regards to sensitivity and durability. Not all fetal Dopplers are created equally.
The size and shape of the mother: Taller women and women who are overweight may have a more difficult time hearing the heartbeat in the early weeks. However, by 12-14 weeks, a Doppler should be able to pick up a heartbeat in women of all shapes and sizes
Required Tools:
Fetal Doppler
Ultrasound gel
Patience (especially if you are less than 10 weeks)
When to Monitor Baby’s HeartbeatYou can begin to monitor your baby’s heartbeat anytime after the 10th week of pregnancy. However, it may be difficult for you to hear the beat before the 12th week. You can continue listening to your baby’s heartbeat right up until your due date.
Quick Tips:
Have a full bladder.
Use lots of gel.
Start low and move SLOW.
Fetal heart rates
Starting at week 5 the fetal heart rate accelerates by 3.3 bpm per day for the next month.
The fetal heart begins to beat at approximately the same rate as the mother's, which is typically 80 to 85 bpm. The approximate fetal heart rate for weeks 5 to 9 (assuming a starting rate of 80):
Week 5 starts at 80 and ends at 103 bpm
Week 6 starts at 103 and ends at 126 bpm
Week 7 starts at 126 and ends at 149 bpm
Week 8 starts at 149 and ends at 172 bpm
At week 9 the fetal heartbeat tends to beat within a range of 155 to 195 bpm.
At this point, the fetal heart rate begins to decrease, and generally falls within the range of 120 to 160 bpm by week 12.[2]
