Mothers should wait at least a year between giving birth and getting pregnant again to reduce health risks to mother and baby, a new study says.
But researchers say they need not wait as long as the 18 months recommended in the current World Health Organization guidelines.
Small gaps between pregnancies risk premature births, smaller babies and infant and mother mortality.
The researchers hope the findings will be "reassuring" for older women.
Senior study author Dr Wendy Norman said it was "encouraging news" for women over 35 who were planning their families.
"Older mothers for the first time have excellent evidence to guide the spacing of their children," she said.
"Achieving that optimal one-year interval should be doable for many women and is clearly worthwhile to reduce complication risks."
The study, of nearly 150,000 births in Canada, by University of British Columbia (UBC) and the Harvard TH Chan School of Public Health is published in
The study found 12-to-18 months was the ideal length of time between giving birth and becoming pregnant again.