by Marjorie Greenfield, M.D.
reviewed by Marjorie Greenfield, M.D.
If you're like most parents-to-be, hearing the fetal heartbeat for the first time is an exciting moment. Even if you've already seen the embryo on an ultrasound, there's something about that steady little drumbeat that makes you realize that you really, truly are going to have a baby soon. Here is some information about when you would expect to hear the baby's heart beating and what those sounds mean.
The fetal heart
The embryonic heart starts beating 22 days after conception, or about five weeks after the last menstrual period, which by convention we call the fifth week of pregnancy. The heart at this stage is too small to hear, even with amplification, but it can sometimes be seen as a flickering in the chest if an ultrasound is done as early as four weeks after conception.
The Doppler instrument
After the 9th or 10th week after your last menstrual period, you might be able to hear your baby's heartbeat at your prenatal appointment. Your obstetrical practitioner probably uses a Doppler instrument for this purpose, which bounces harmless sound waves off the fetal heart. The way the sound comes back is affected by motion, so a beating heart creates a change in the sound that can be picked up by the receiver in the Doppler. Whether you actually hear the heartbeat at 9 or 10 weeks depends partly on luck-the instrument must be placed at just the right angle. It also depends on the position of your uterus, and if you're slim or heavy. By the 12th week, the heartbeat can usually be heard consistently, using the Doppler instrument for amplification.
Measuring the heart rate
To measure the baby's heart rate, your practitioner will count the heartbeats for a full minute, or count for 15 seconds and then multiply by four. Some of the instruments eliminate the need for this by providing a readout of the rate. And some practitioners are so attuned to the normal range that they listen carefully and only count if it seems high or low.
At times, the Doppler picks up sounds from the mother's side of the placenta and relays her heartbeat instead of the fetus'. A normal heart rate for the mother is under 100, but the baby's should be over 120, so they sound different. If there is a question, the practitioner will feel the mother's pulse and see if it's the same as what he's listening to through the Doppler instrument.
Interpreting the fetal heart rate
A normal fetal heart rate usually is between 120 and 160 beats per minute. While rumors abound, the truth is there is no difference between girls' and boys' rates, so knowing if the heart beat is fast or slow can't help you to choose baby clothes or room decor. The loudness or quietness of the heartbeat also doesn't mean anything. The sound has to do only with the volume controls on the instrument, as well as the distance and angle from the heart to the Doppler. So don't worry if it sounds quiet or far away sometimes.
In a twin pregnancy, it can be hard to distinguish the two heart rates, especially if they are similar. Your practitioner will listen at different places on the uterus, and try to identify two distinct rates. If there is a real question whether both babies were heard, ultrasound can be used to see each twin's heart.
Listening for the heartbeat without amplification
Starting at about 20 weeks, the heartbeat can be heard without Doppler amplification. A special stethoscope called a fetoscope can be used, or the bell (concave) side of a regular stethoscope can be pressed firmly onto your abdomen. The heartbeat is best heard over the baby's back, which often seems firm when you feel around on the uterus. If you are overweight or if the placenta is on the front wall of the uterus, it may be difficult to hear the fetal heart by stethoscope. It gets easier later in the pregnancy.
Listening to the heartbeat at home
Some companies now sell Doppler-like instruments to hear the baby's heartbeat at home. While this might sound like fun, keep in mind that you sometimes can have difficulty finding it, which you might find alarming. Or you might pick up your own heart, which is slower than the fetus', and worry unnecessarily about how your baby is doing.
After 20 weeks, you may be able to hear the heartbeat with a stethoscope, instead of spending money on one of the expensive Doppler-like instruments for home use (they can cost as much as $500 for a good one). And as the pregnancy progresses, you'll have the baby's daily movements to give you constant reassurance and may no longer feel any need to listen to the fetal heartbeat. But there isn't any known medical risk to listening frequently, and there's no denying that the steady beat of your baby's heart is one of the joys of pregnancy.