Girls born prematurely tend to be shorter as adults: study

Baby girls born prematurely are almost three times more to be shorter as adults than those born at term, a new study has found.

The study by researchers from the University of Auckland in New Zealand and Uppsala University in Sweden, found women born very premature (before 32 weeks) were 2.3 centimetres shorter on average as adults than their sisters born at term (37-41 weeks).

"We were a little surprised by the results. There is some evidence that babies who were born premature tend to be shorter in childhood, but they usually catch up with those born at term in late adolescence," said Jose Derraik, from University of Auckland.
 

"However, our study shows that women who were born very preterm fail to reach the stature you would expect based on their parent's and sibling's heights," said Derraik.

The researchers have been analysing data from more than 200,000 Swedish women to explore questions about the long-term effects of early life events occurring before, during and after pregnancy.

The data was collected between 1991 and 2009 from women aged over 18 years.

"This is one of the very few studies that has specifically investigated the association between premature birth and adult height," said Derraik.

Comparing siblings allowed researchers to control for possible genetic effects on height.

"The 2.3 cm height difference between women born very premature and their adult sisters born at term may not sound much, but to put it into perspective, women born during the Great Chinese Famine in 1959-1961, who experienced severe malnutrition early in life, were about 1.7 cm shorter as adults," he said.

Researchers are yet to establish why premature birth should lead to shorter adult stature.

"It may be related to the fact that premature babies are often quite thin at birth," said Derraik.

"One of the study's collaborators from the University of Auckland's Liggins Institute has previously shown that small size at birth is associated with changes in the way growth hormone works in the body, which could eventually reduce adult height," he said.

Worldwide, it is estimated that 9.6 to 11.1 per cent of all babies are born premature, with rates significantly higher in poor countries.

The study was published in the American Journal of Epidemiology.