Short mums 'twice as likely' to have premature babies.

Short mothers have shorter pregnancies than taller mothers and are twice as likely to have premature babies, according to a new study.

Researchers from the Liggins Institute looked at antenatal data from 192,000 Swedish women to make their findings.

Decreasing height increased the odds of having an infant born preterm, according to collaborators from the University of Auckland and Uppsala University.

Among the women 155cm tall or shorter, 9.4 per cent of babies were born premature (less than 37 weeks pregnant) and 1.1 per cent were born very premature (less than 32 weeks).

This compared to 4.7 per cent mothers who were 179cm tall or above who had premature babies and 0.5 per cent had very premature babies.

“Around half of all premature births are spontaneous – apparently with complex and often unknown causes,” said study lead Dr José Derraik.

“But many studies worldwide have shown that maternal height may play a role. What complicates the picture is that there are probably a number of factors involved, such as the mother’s ethnicity and their level of affluence,” he said.

But the researchers concluded that “short stature” is a likely contributing factor to spontaneous preterm births worldwide.

“Researchers don’t know exactly what’s behind this association between the mothers’ height and spontaneous premature birth,” said Dr Derraik.

“But evidence from other studies suggests it could be anatomical constraints.

"Short mothers tend to have less space for the babies to grow before birth, and this seems to lead to premature delivery in some women,” he said

One reason may be because shorter women have smaller pelvises, the study concluded.

Dr Derraik suggests maternal height is one of the factors that needs to be considered when evaluating a woman’s risk of delivering a premature baby.