The expression "childbearing hips" should be reserved for women between 25 and 40, a new study suggests.

Researchers have tracked the development of pelvis growth and found that a woman's pelvis adjusts for childbearing years.

After the onset of puberty, the female pelvis widens until it reaches its widest point when a woman is between 25 and 30 years old, according to experts from the University of Zurich in Switzerland.

At the age of 40 the pelvis begins to narrow again, according to the study published in the Proceedings of the National Academy of Sciences.

Using computed tomographic data, the researchers tracked pelvic development from birth to old age.

They found that until puberty, male and female pelves are similar in width.

But after the onset of puberty, the male pelvis remains on the same developmental trajectory, while the female pelvis develops in an entirely new direction, becoming wider and reaching its full width around the age of 25 to 30 years, and then narrowing after a woman turns 40.

The researchers suggest that the changes may be steered by hormonal levels.