low birth weight

Last reviewed 01/2018

Low birth weight is defined as all babies weighing 2500g or less at birth. It may be used as a blanket term including very and extremely low birth weight.

Perinatal mortality has fallen from 70% of very low birth weight infants (VLBW) - those with a birth weight below 1500g -in the 1950s to 20% today - this remainder represent a core of lethal mutations, unexplained intrauterine deaths and stillbirths.

The increased survival is due to multiple causes, not least the introduction of ventilation for neonates in the 1970s.

Low birth weight may be due to premature birth, before 37 weeks - preterm infant - or poor fetal growth - small for dates infant. Some babies may be born both preterm and small for dates.