Hearing the baby's heart beat for the first time is often the first bonding experience for many parents. The sound of the "galloping" heart of your family's newest addition forming inside of the new mother can be enough to put many parents to tears. For doctors, monitoring the fetal heart is one of the easiest ways to determine the health of your unborn baby and there is no known risk to listening.
The embryonic heart starts beating 22 days after conception, during the fifth week of pregnancy. It is too small to hear at this early stage but sometimes can be viewed as a flicker on an ultrasound as early as four weeks. If the doctor can’t see a heartbeat, it could just mean that the dating of the pregnancy is incorrect and he might suggest you come back at a later date. At 9-10 weeks you might be able to hear the heartbeat using Doppler but it depends on your weight, the position of your uterus and the instrument. By week 12-14, you should be able to hear it consistently with Doppler.
The technician will assess the fetal heartbeat, sometimes referred to as fetal heart tones, by counting how many beats are in a minute. They might listen for a full minute, for 15 seconds and then multiply by four, or just be attuned enough to listen for a normal rate. Some instruments are already equipped to provide a reading so that the technician doesn’t need to count. It’s not uncommon for the Doppler to pick up the mother’s heart beat instead of the fetus. A medical professional might check the mother’s heartbeat to see if it matches what they are hearing. The mother’s heartbeat should be under 100 bpm (beats per minute) but the baby’s will be between 120-180 bpm. The fetal heart typically starts beating at 80-85 bpm, then spikes up to180 bpm and then gradually slows to 120-160 bpm by 12 weeks gestation. It typically slows again before birth to a range of 120-140 bpm. Some fetal heartbeats past term might drop to 110 bpm. The male and female heartbeats exhibit no differences, contrary to the popular myth.
When listening to the heartbeat using a Doppler ultrasound fetal heartbeat detector, it won’t be the actual heartbeat that you are hearing. What you hear is an amplified “beat frequency”; that is the interaction between the response and the frequency used by the Doppler. As the outgoing frequency (sent by the Doppler) runs into the physical movements of the heart, the closer the heart is, the higher the frequency is and the further the heart is the lower. The beating heart thus creates an alternating frequency that creates the sound of the heart beat. A quiet or loud heartbeat is not an indicator of abnormalities; it just depends on the distance between the fetus and the instrument.
Twin heartbeats can be hard to distinguish. Placing the instrument at two different places over the uterus can usually allow a technician to hear the two different beats; however an ultrasound might be required to be sure.
Once you reach 20 weeks, Doppler is no longer necessary to hear the heartbeat. A fetoscope can be placed on the uterus - much like a stethoscope is used to hear the heart at a routine doctor’s appointment. It might be hard to hear though if you are overweight or if the placenta lies in the way. Sometimes a fetoscope can be used to hear the heartbeat as early as 16 weeks. As the pregnancy progresses, it will be easier to hear using this instrument.
Some parents purchase Doppler to use in the home. If you decide to purchase one of these, be aware that the heartbeat can often be hard to find, or picking up the mother’s heartbeat is not uncommon. In other words, if you don’t find the heartbeat right away, it is not a cause for panic.
The fetal heartbeat may react to chronic anxiety of the mother and other heart rate changes in the mother. A wide-range study revealed that hearing the voices of strangers can decelerate the heart rate and hearing the mother’s voice can accelerate it. If the fetal heart rate does not change, is too low or too high (outside a range of 110-180 bpm) it could indicate a problem. When giving birth, the fetal heart rate will respond to the contractions with a pattern. Deviance from this established pattern could indicate a problem as well. However, fetal heart beat changes do not always indicate a problem. About 14% of normal babies have irregular heartbeats (a skipped beat or extra beat) during their time in the womb and there is only a 1-2% chance of finding something wrong, according to a
study. If fetal heart rate variances present themselves during labor you may be asked to change positions, take medication to relax the uterus, be given an IV or oxygen through a mask. Yale University
Listening to a baby’s heart beat can be a heart-warming experience. Conversely, when problems present themselves it can be difficult to not panic. Hopefully, fueled with the knowledge of how the fetal heartbeat develops and knowing how rare the incidence of problems due to fetal heart rate abnormalities are, you will be prepared for whatever a Doppler or fetoscope reveals and be able to enjoy it as the miraculous sound of life that it is.
Have you heard the heartbeat yet?
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