Thursday, February 25, 1999 Published at 08:38 GMT
Two-year time gap for healthy babies
Babies born too close together or too far apart could have health problems
Mothers should wait about two years between having one baby and conceiving another if they want a healthy child, according to a US report.
Reseachers from the US Centres for Disease Control and Prevention in Atlanta studied the births of 173,205 children from Utah between 1989 and 1996.
They found that a baby conceived less than 18 months after his or her sibling's birth were 40% more likely to be premature or have a low birth weight than those born after an 18-month or 23-month delay.
Babies conceived over two years after their brother or sister were twice as likely to be underweight and 70% more likely to be born prematurely.
Part of the difference may be due to the fact that some of the women waited a long time between children and were therefore likely to be substantially older than mothers who only waited a short time between babies.
Children born to older women are known to have a greater risk of developing complications.
Writing in the New England Journal of Medicine, the researchers say they do not know why two years seems to be an optimal time gap.
Babies born prematurely or with a low birth weight have more health risks than other babies. Long-term dangers are thought to include a higher likelihood of developing heart disease in later life.