
There are a number of reasons a fetal heartbeat may not be detected using a fetal Doppler, and it isn’t always a bad sign. These reasons may include:
- You’re checking before 12 weeks in the pregnancy
- The baby is not big enough yet
- Even if parents wait until 12 weeks, the baby may not be big enough at this stage and the heartbeat can be difficult to detect
- The baby may be in a position that makes it difficult to detect a heartbeat
- The mother may not be in the correct position
- The mother should be lying back in a reclined position that props up the uterus
- The mother’s bladder is empty (the heartbeat is sometimes easier to detect when women have a full bladder)
- Incorrect use of the Doppler
- Too much gel
If there is no heartbeat detected, and you are also noticing an absence of activity in the baby or symptoms of a miscarriage, see your doctor immediately.
What Is a Fetal Doppler?
What’s the Difference Between a Fetal Doppler and an Ultrasound from a Doctor?
The over-the-counter handheld fetal Doppler units are for sale to expectant parents to use at home, while a medical professional uses a more sophisticated machine that is more accurate.
There are several types of professional ultrasound used to produce images of the fetus (sonogram):
- Transvaginal
- Standard ultrasound
- Traditional exam
- Uses a transducer over the abdomen to generate 2-D images of the developing fetus
- Advanced ultrasound
- Similar to a standard ultrasound, but the exam is specially targeted to a suspected problem and uses more sophisticated equipment
- Doppler ultrasound
- Used to measure slight changes in the frequency of ultrasound waves as they bounce off moving objects
- 3-D ultrasound
- Uses specially designed probes and software to generate 3-D images of the developing fetus
- 4-D or dynamic 3-D ultrasound
- Uses specially designed scanners to look at the face and movements of the baby prior to delivery
- Fetal echocardiography
- Used to assess the baby’s heart anatomy and function
- Can help evaluate suspected congenital heart defects
From 
Pregnancy and Parenting Resources
References
https://www.fda.gov/consumers/consumer-updates/avoid-fetal-keepsake-images-heartbeat-monitors
https://www.babydoppler.com/blog/cant-find-heartbeat-with-fetal-doppler-8-things-to-do/
https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/ultrasound-720/
https://www.babydoppler.com/blog/cant-find-heartbeat-with-fetal-doppler-8-things-to-do/
https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/ultrasound-720/