Women who have high-risk pregnancies could benefit from Doppler ultrasound scans, a new study has revealed.
Using the technique to monitor the baby's health could reduce caesarean sections and the number of babies who die, according to experts.
Doppler ultrasound can monitor how fast blood is moving in the umbilical blood flow.
Medical staff can then see whether the blood flow is normal - which could show whether the foetus is healthy or under stress.
This could help decide which high-risk pregnancies need assistance in delivering the baby, and which do not.
The Cochrane systematic review looked at 18 studies which included 10,000 women in "high risk" groups.
These included women who had previously lost babies during pregnancy, those carrying growth restricted babies and women with hypertension or diabetes.
Women who were examined with Doppler ultrasound were compared with those who were not, or those where only the baby's heartbeat was monitored.
The study found that Doppler reduced infant deaths, possibly because caesarean sections were better timed.
However, the researchers said the studies they looked at were of questionable quality, and some experts have argued that using Doppler can lead to some unnecessary early interventions.
Lead researcher Zarko Alfirevic, from the University of Liverpool, said more trials of Doppler ultrasound were needed.
"A case could certainly be made for a higher quality, multi-centre trial of Doppler ultrasound than we have so far seen," said Professor Alfirevic.
"It is quite possible that for some so-called high risk groups fetal Doppler offers little or no benefit. Women with diabetes
are one such group where fetal Doppler may, in fact, give false reassurance.
"It is important to point out, of course, that it is the clinical decision that follows a Doppler ultrasound examination that changes the outcome for the baby, and currently there is little agreement on what intervention should follow an abnormal Doppler finding."