Why teen mums are at risk of having low birthweight babies

The UK has the highest teenage pregnancy rate in Western Europe. In Scotland, one in ten babies are born to a teenage mother.

Teenage pregnancies are associated with increased risks of poor pregnancy outcome for both the mother and her newborn. Scientists in Aberdeen have been studying the problems of these teenage pregnancies using adolescent sheep as a model. They have shown that if adolescent sheep become pregnant while they are still growing, the nutrient supply from the mother to the fetus is reduced. This means that the lamb may not develop normally and will be very small at birth. These studies have implications for managing the pregnancies of the high numbers of teenagers worldwide who are becoming pregnant before they have stopped growing.

Dr Jacqueline Wallace at Aberdeen’s Rowett Research Institute who led the research said: “Our studies show that there is competition for nutrients between a mother and her developing offspring when the mother herself is still growing, and that it is the newborn who comes off worse in this situation. It follows that formulating correct dietary advice for teenage girls is likely to be complex, particularly if the mother is still growing. We suggest that assessments of growth and nutritional status at the time of conception and at mid-pregnancy, and the use of ultrasound to detect whether placental growth and function has been affected, may prove beneficial in the optimal management of teenage pregnancies,” said Dr Wallace.

Dr Wallace originally showed that overfeeding adolescent ewes during pregnancy to mimic rapid maternal growth in humans promoted the growth of the mother at the expense of the fetus. The reduction in fetal size occurred because the growth of the placenta was impaired and resulted in premature delivery of low birth weight lambs. Recent studies have focused on limiting the food intake of adolescent ewes during pregnancy to prevent maternal growth. This also reduced the nutrient supply to the fetus and slowed its growth. They also found that a change in the development of the blood vessels which supply nutrients to the womb and to the placenta may be a possible cause of the restricted growth of the fetus of these underfed adolescent sheep.

“Worryingly, we also found that these harmful effects on the growth of the fetus of undernourished adolescent ewes could only be partly reversed by returning the pregnant ewes to an optimal diet later on in their pregnancies. We believe that our research highlights the importance of ensuring that pregnant teenage girls gain adequate, but not excessive amounts of weight, especially during the early stages of their pregnancy when the placenta is formed” said Dr Wallace.

“The problems associated with being an adolescent or teenage mother are particularly serious when mothers are under sixteen years of age and hence still potentially growing. For these very young mothers, the risk of having a low birth weight baby is doubled. There is also an increased risk of a premature birth, infant mortality and maternal death due to obstetrical complications,” said Dr Wallace.

Professor Peter Morgan, Director of the Rowett Research Institute said 'The implications of this research are particularly relevant in the light of the current interest and priority given to health inequalities in the UK.”

The recent research was conducted in collaboration with colleagues at North Dakota State University and was funded by the National Institutes of Health, USA and the Scottish Government. The research was published in a recent edition of Biology of Reproduction and was been singled out by the Editors of the journal for a feature in the highlights section because of the calibre of the research findings.