As an expectant mom, one of your early concerns during the first trimester will be, 'When can I hear my baby's heartbeat?' In previous decades, a stethoscope-like device was the only available tool, and only the doctor could actually hear the heartbeat. Today, modern technology such as the fetal doppler and obstetrical ultrasound enable earlier detection of the heartbeat, and moms can also listen in on those exciting first heart sounds of their baby.
Initially, you need to know the terminology that your doctor uses when referring to the "age" of your growing baby. Estimated gestational age (EGA) refers to the length of pregnancy after the first day of the last menstrual period (LMP) and is usually expressed in weeks and days. Note that this does not refer to the date when your baby was actually conceived. Conceptional age (CA) is the actual fetal age and refers to the length of pregnancy from the date of conception. Although you might guess that conceptual age is the logical method for dating your baby's age, doctor's actually use the EGA method when referring to your baby's age.
Your Baby's Developing Heart
Early in the fifth week of pregnancy, your baby's heart begins to form. Your baby's heart will start beating at 22 or 23 days post-conception, which is during the fifth week of your pregnancy. At this point, your baby's heart is too small to generate enough sound waves to be audible, even when amplified by the use of medical equipment in your doctor's office.
Hearing a Heartbeat Starting at 12 Weeks
A fetal doppler is a small, handheld ultrasound instrument that transmits the sounds of your baby's heartbeat, either through a loudspeaker or into ear pieces that are attached. Fetal heart dopplers can usually detect your baby's heartbeat after about eight or nine weeks gestation, although it may be faint or inconsistent at that age. By 12 weeks into pregnancy, the doppler should consistently and audibly detect your baby's heartbeat, allowing you to hear it sooner than you otherwise would.
Hearing Your Baby's Heartbeat at 20 Weeks
A fetoscope is an instrument your OB may use to listen to your baby's heartbeat. It is basically a reconfigured stethoscope that works by amplifying the sound of your baby's heartbeat. It's noninvasive and allows your doctor to monitor your baby's heart, causing no harm to your baby. Your doctor will press the "bell" side of the fetoscope firmly onto your abdomen and attempt to locate your baby's back—which is the ideal site to hear your baby's heartbeat. With the fetoscope, the OB/GYN should be able to hear your baby's heartbeat at about 20 weeks.
Hearing and Seeing the Heartbeat
The obstetrical ultrasound, or sonogram, is the most accurate and commonly used method that your physician will use to check your baby's heartbeat. Every OB/GYN's office has one. In addition to checking for your baby's heartbeat, your obstetrician may use the sonogram to confirm pregnancy at six weeks; determine fetal age and size; rule out problems with your pregnancy; or check for twins.
As a general rule, 5.5 to 6.5 weeks is the earliest time that your doctor will be able to detect a fetal heart beat by trans-vaginal ultrasound. In other words, about six weeks is the earliest stage where you can hear your tiny baby's heartbeat with an ultrasound. At that early phase, your baby's heart rate should be about 100 beats per minute. Sometimes the baby's heartbeat will not be clearly audible until seven or even eight weeks.