Women risk premature birth if they have second child too quickly. Mothers should wait at least 18 months after giving birth before having another child in case their next baby arrives dangerously early, experts say.

A short interval is defined as women who fall pregnant in less than 18 months and long intervals extent to a gap of 60 months.

From those surveyed, it was found that 30 per cent didn't wait long enough, falling pregnant again in less than 18 months after giving birth.

The study found short intervals may affect the risk of pregnancy complications to the baby such as pre-term birth, low birth weight, and small gestational age.