The machine uses the interval between pulses to interpret the echo returns.
A later study in Lancet found a similar effect on fetal growth in women receiving repeated ultrasound exams, although measures of growth and development later in childhood (up to age eight) were similar in both groups.
A case control study of 72 children who had undergone a formal language evaluation found that children with delayed speech had a higher rate of ultrasound exposure in utero than normal controls.
There is no consensus on the significance of cavitation effects in human fetal tissue, but some evidence suggests that mammalian tissue may contain microbubbles that are susceptible to cavitation effects.
Acoustic streaming involves a jet of fluid created by the ultrasound wave, which causes a mechanical shearing force at the cell surface.
Their findings suggested that a child with delayed speech was twice as likely to have been exposed to prenatal ultrasound.