Study shows slow-growing babies reach normal weights by early teens

New parents are pleased when their baby gains weight as expected, but if the rate of weight gain is slow parents can become worried and concerned about their child's future size.

New research from the Children of the 90s study at the University of Bristol shows that most babies who are slow to put on weight in the first nine months of life have caught up to within the normal range by the age of 13, but remain lighter and shorter than many of their peers. There are significant differences in the pattern of 'catchup', depending on the infant's age when the slow weight gain occurs.

The new findings, published today [Monday 25 February] in the journal Pediatrics, are based on data from 11,499 participants in Children of the 90s, and provide the most conclusive and reassuring evidence for parents to date that, with the right care, many infants who fail to put on weight quickly in the first nine months of life will catch up over time.

The study found that, of the 11,499 infants born at term, 507 were slow to put on weight before the age of eight weeks ('early group') and 480 were slow to gain weight between eight weeks and nine months ('late group'). Thirty children were common to both groups.

The infants in the early group recovered quickly and had almost caught up in weight by the age of two, whereas those in the later group gained weight slowly until the age of 7, then had a 'spurt' between 7 and 10 years, but remained considerably shorter and lighter than their peers and those in the early group at the age of 13. At that age, children in the later group were on average 5.5k lighter and almost 4cm shorter than their peers; those in the early group were on average 2.5k lighter and 3.25cm shorter than their peers.

Slow weight gain is often seen by parents and some healthcare professionals as a sign of underlying ill health and clinicians face a dilemma between taking steps to increase a child's energy intake and putting them at risk of obesity later in life by encouraging too rapid weight gain.

The study shows that there were very different patterns of recovery between the early and late groups, even when other factors like the mother's education, background, and her weight and height were taken into account, but that there was little difference between boys and girls.

Professor Alan Emond, the paper's main author explains:

'The reason the early group caught up more quickly may be because those infants had obvious feeding difficulties and were more readily identified at the eight-week check, resulting in early treatment leading to a more rapid recovery. However, as Children of the 90s is an observational study, there is limited information available about which infants received nutritional supplements or medical treatments.

'Those children who showed slow weight gain later in infancy took longer to recover, because of the longer period of slow growth and because their parents were smaller and lighter too.

'Overall parents can be re-assured that well babies showing slow weight gain in the first year do eventually recover to within the normal range, but at 13 years tend to be lighter and smaller than many of their peers.'

The findings highlight the importance of monitoring a baby's weight and height gain during the first few weeks and months, but not creating anxiety with parents of slow-growing babies who are well, as most of these babies will catch up to within the national average over time.

The message to health professionals is that, unless children require intervention due to ill health, their calorie intake should not be increased as this may predispose them to obesity later in life. Feeding habits in the second six months of life determine a child's future weight gain, so consuming too many calories in infancy can lead to weight problems later in life.