New York, Aug 19 (IANS): Shorter mothers are at an increased risk of delivering smaller, premature babies, says a new study.

"Our finding shows that a mother's height has a direct impact on how long her pregnancy lasts," said Louis Muglia from Cincinnati Children's Hospital Medical Centre in Ohio, US.

"The explanation for why this happens is unclear but could depend not only on unknown genes but also on woman's lifetime of nutrition and her environment," Muglia noted.

Worldwide, 15 million babies are born preterm, and more than one million die due to complications of an early birth, the study highlighted.

Babies who survive an early birth face serious and lifelong health problems, including breathing problems, jaundice, vision loss, cerebral palsy and intellectual delays.

The researchers looked at 3,485 Nordic women and their babies, and found that maternal height, which is determined by genetic factors, helped shape the fetal environment, influencing the length of pregnancy and frequency of prematurity.

In contrast, birth length and birth weight are mainly influenced by transmitted genes.

"That a woman's height influences gestational length, independent of the genes she passes on that determine fetal size, is a major finding by our research networks, and the first of what we expect to be many genetic contributions," Joe Leigh Simpson, senior vice president for research at the March of Dimes Prematurity Research Centre in the US, noted.

The study was published in the journal PLOS Medicine.