The nine months of pregnancy seem endless for many expectant mothers. In reality, it is amazing how much a baby grows and changes during that time. In fact, many of those changes, including the development of a heartbeat, occur before the expectant mother even knows she is pregnant, according to MayoClinic.com.

Time Frame

A baby develops a heartbeat early in the first trimester. The first trimester is the first 12 weeks of pregnancy as measured by the first day of the last period, according to MayoClinic.com. These early weeks are marked by intense hormonal changes in the woman’s body and rapid growth in the baby’s body. For this reason, it is very important for the mother-to-be to eat healthy foods and take good care of herself, according to the University of Iowa Hospitals and Clinics website.

Heartbeat

By the end of the eighth week, all of the major organs, including the brain and spinal cord are formed and functioning, according to the University of Maryland Medical Center. The baby even has arms, legs, fingers and toes. The tiny heart begins to beat between the fifth and seventh week of pregnancy, even though the baby is only a little larger than the tip of a ballpoint pen.

Seeing and Hearing

Because the heart is so tiny, it may be difficult to see on an ultrasound right away. Still, if you do have an ultrasound around the fifth or sixth week of pregnancy, you may be able to see a small flicker, according to Dr. Spock’s website. Hearing the heartbeat comes later. While it can be heard as early as the 10th week, the baby’s heartbeat is not usually heard consistently until the end of the first trimester.

Doppler

The instrument used to listen to and measure your baby’s heartbeat is called a Doppler. This machine works by bouncing sound waves off the baby’s body. As the baby’s heart beats, the motion of the heart changes the sound waves, resulting in a sound that you can hear — and count. A normal heart rate for a baby is between 120 and 160 beats per minute, according to Dr. Spock’s website.

Considerations

Seeing and hearing your baby’s heartbeat is a miraculous feeling for many moms-to-be, but the first trimester is a fragile time in the development of a baby. A firm heartbeat does not always mean that the baby is developing normally. If the baby is not healthy, a miscarriage may occur at this time. The majority of miscarriages and elective abortions occur between the 8th and 12th week of pregnancy, according to the American Pregnancy Association and the Guttmacher Institute, shortly after the heart starts beating. Miscarriages are not the norm, however. About one in four women will have a spontaneous miscarriage, according to the American Pregnancy Association.