Fetal Doppler Facts

Bouncing soundwaves through the pregnant uterus and measuring the feedback produces an image of the fetus. Ultrasound pictures are extremely detailed, and are safer than X-rays. Hand-held dopplers use the same technology to "hear" the unborn baby's heartbeat. Like other electronics, dopplers have become more affordable and are widely available for public use.

History

The term "doppler" originated with Austrian physicist Christian Doppler, who discovered in 1845 that a shift in the frequency of sound waves between a moving object and an observer produces varying pitch. The "Doppler effect" can be heard, for example, when an ambulance siren races past an open window. The first fetal listening device using sound waves was invented by physician Edward Hon in 1958. Dopplers work by emitting low ultrasonic waves which, when bounced off the moving chambers of the fetal heart, transmit sounds corresponding to the fetal heart rate.

Effects

The fetal heartbeat can be heard through the mother's abdomen with a special stethoscope, or fetoscope. It sounds like a watch ticking under a pillow, and such devices are useless until about 20 weeks' gestation, according to Helen Varney, certified nurse midwife and author of "Varney's Midwifery." In contrast, Varney says the fetal heart rate can be heard with a doppler as early as 10 to 12 weeks' gestation. For professionals, auscultation of fetal heart tones confirms intrauterine pregnancy. For mothers, hearing the fetal heart rate is reassuring and increases emotional attachment to the fetus as a person.

Benefits

A doppler makes it possible to differentiate blood flow through the umbilical cord, the uterine artery, the placenta and the baby's heart. These landmarks help determine fetal position. During labor, fetal heart rate changes in relation to maternal contractions. When the placenta is functioning well and the umbilical cord is not compressed, these changes are characteristic of healthy adaptations. If the baby is distressed by poor circulation and a lack of oxygen, proper use of a doppler will reveal abnormal patterns.

Considerations

Researchers at the University of Washington studied 189 children born prematurely whose heart rates were monitored either by continuous electronic fetal monitoring or by hand-held dopplers at regular intervals. The findings, published in the March 1990 issue of the "New England Journal of Medicine," revealed that there was a greater incidence of cerebral palsy in babies monitored by EFM. The difference seems attributable to the length of time abnormal heart rate patterns continued. In this study, the average time from when fetal distress was noted until delivery of the baby was 104 minutes with EFM and 60 minutes with periodic doppler auscultation.

Safety

Fetal dopplers are regulated by the Food and Drug Administration as a class II device. Medical grade fetal dopplers are permitted for home use with the approval of a physician. These devices use a low ultrasound power. The American Institute of Ultrasound in Medicine's position regarding fetal harm from ultrasound use in imaging is that there is no evidence that diagnostic procedures cause low birth weight, delayed speech, dyslexia or other adverse effects.