Narrator: This is Science Today. A new approach to prenatal ultrasound could help doctors better identify fetuses that are small and at high-risk and tell them which ones are small but healthy. Rebecca Smith-Bindman, an assistant professor of radiology, epidemiology and biostatistics at the University of California, San Francisco, led the study.

Smith-Bindman: The purpose of this was to evaluate how ultrasound measurements of fetal size predict birth outcomes. So, an in-utero measurement, could that be used to give you some information about what happens at around the time of birth or after the time of birth?

Narrator: Smith-Bindman found that fetuses measuring in the 5th percentile during a prenatal ultrasound were between two and almost fifteen times as likely to have poor birth outcomes.

Smith-Bindman: And partly that's interesting because previous work has sort of suggested maybe the 10th percentile is a better cut-off and the problem with the 10th percentile is that identifies a lot of normal babies at being at risk when they're truly not at risk.

Narrator: For Science Today, I'm Larissa Branin.