Women who have babies later in life are more likely to have superior cognitive skills in their old age, a new study has claimed.

Researchers found postmenopausal women were likely to be mentally sharper if they had used hormonal contraceptives for more than 10 years, began their menstrual cycle before the age of 13 or had their last baby after turning 35.

Postmenopausal women who had their last pregnancy after 35 also had better verbal memory and those who had their first pregnancy after the age of 24 had better executive function, which includes attention control, working memory, reasoning and problem solving.

The study, published in the Journal of the American Geriatrics Society, is the first of its kind to investigate the correlation between age at last pregnancy and cognitive function post-menopause.

"Based on the findings, we would certainly not recommend that women wait until they're 35 to close their family, but the study provides strong evidence that there is a positive association between later age at last pregnancy and late-life cognition,” said lead author Roksana Karim, assistant professor of clinical preventive medicine at the Keck School of Medicine at the University of Southern California.

830 women with an average age of 60 were given a series of tests including assessments of verbal memory, psychomotor speed, attention and concentration, planning and visual perception as part of the research.

The study lends weight to the idea that a longer exposure to oestrogen and progesterone in life could counter postmenopausal memory decline.

"Starting your period early means you have higher levels of the female sex hormone being produced by the ovaries," Ms Karim said.

"Girls are receiving the optimal levels early, so it's possible that their brain structures are better developed compared to those who are exposed to estrogen levels associated with menstrual cycles at a later age."

Researchers also found use of the contraceptive pill produced better cognitive function in later life.

"Oral contraceptives maintain and sustain a stable level of sex hormones in our bloodstream, stable is good,” Ms Karim said.

The findings also found women who didn’t carry their pregnancy to full-term had better overall cognitive ability.

"The finding that even incomplete pregnancies are beneficial was novel and surprising," said Wendy Mack, the study's senior author and professor of preventive medicine at the Keck School of Medicine.

"In general, our findings are intriguing and are supported by other clinical studies and animal studies."

Ms Mack also criticised previous studies that found evidence of “pregnancy brain”, where pregnant women have poorer verbal memory.

"The issue is the human studies haven't followed women for the long term," she said.