Ultrasound has been around for about 50 years now and so, is still a relatively new science without any long-term studies to show what the possible side effects may be. It appears to be much safer than X-rays due to the fact that ultrasound utilizes sound waves as opposed to mutagenic ionizing radiation which can pose hazards such as chromosome breakage and cancer.

Having said that, there are a few studies out there which are questioning the effects of continued fetal exposure to ultrasound waves. A Yale study in 2006 suggested exposure to ultrasound affected fetal brain development in mice. The study showed that rodent brain cells failed to migrate to their proper positions and remained scattered in incorrect parts of the brain. This misplacement of brain cells was linked to conditions such as mental retardation, childhood epilepsy, developmental dyslexia, autism and schizophrenia. This effect, however, was only detectable after 30 minutes of continuous scanning. The study said no link had been made between the mice and the possible effects on humans. A typical fetal scan, including evaluation for fetal malformations, typically takes 10 - 30 minutes.

Soundwaves, by their very nature pose 2 potential physiological effects:
1) they inhance inflammatory response and 2) they can heat soft tissue. The ultrasound energy produces a mechanical pressure wave through soft tissue. This pressure wave can cause microscopic bubbles in tissue. It also causes molecular friction which heats the tissue slightly.

So, should routine fetal ultrasounds be done - probably not. However, there are times when the benefits definately outweight the risks - especially when there is a suspected problem or when someone is planning for a homebirth and wants to be reassured that everything is in order.

As far as dopplers are concerned - many midwives use them because it is much easier to pick up early heartbeats, locate the placenta and it allows the mother to hear everything the midwife is hearing. A doppler uses 3-5 MHz, where as an imaging ultrasound will use 7-18 MHz, so there is a difference in the amount of energy being used.