Background: It has been clear for some years now: overweight and obesity are a major problem for public health in developed and developing countries [WHO World Health Report 2002]. Changes in both physical activity levels and nutrition have contributed to this problem. These changes are partly due to changes in economic standards, culture and social norms, as well as to changes in our environment. Cars, computers, escalators, and remote controls have all made their entry in our lives in the past century. The discussion about whether and to what extent we can compensate and manage these changes, and what impact this would have on overweight and obesity prevalence, is ongoing. Changes in our environment have not been limited to the places where we live and work.

Because expectant mothers today are different from those who lived a century ago (for example they are generally fatter and less physically active during pregnancy [Kramer 2002]), the intrauterine environment has also changed over time. These changes in the intrauterine environment are reflected in the fact that birth weight increased between 1978-1996, with a corresponding drop in small-for-gestational age (SGA) babies and increase in large-for-gestational-age (LGA) babies [Kramer 2002].

The importance of birth weight for the development of chronic disease later in life was first recognised by Barker [1995]. His hypothesis was that SGA babies were at increased risk for cardiovascular disease later in life. Hence, the attention was at first predominantly on SGA babies. However, more recently, LGA babies have been found to be at risk as well. In addition to the fact that giving birth to an LGA baby is a risk for complications during childbirth [e.g. Oral 2001], these babies have disproportionately more fat in childhood. Hammami et al. [2001] have shown that body weight and length are the dominant predictors of body composition in LGA and appropriate-for-gestational age (AGA) neonates. They also found that LGA neonates have significantly higher proportions of total body fat and bone mineral content, but lower lean body mass as a percent of body weight. In contrast, Hediger et al. did not find a surfeit of fatness in infants born LGA within the first years after birth [Hediger 1998], but found an increase in fatness at the triceps and subscapular sites at 3 years of age [Hediger 1999]. Rogers et al. [2006] found that an increased relative weight-for-height at birth was associated with increased fat mass. Based on these findings, it seems that prevention of LGA births could be important in the prevention of overweight and obesity and related health problems later in life.

Several researchers have shown that increased maternal body mass index (BMI) is partly responsible for the rise in proportion of LGA births over time [Kramer 2002; Surkan 2004], and it is consistently related to the risk of LGA births [Orskou 2003; Schaefer- Graf 2002 & 2003]. Other lifestyle factors reducing the risk of LGA births are smoking and caffeine intake during pregnancy [Orskou 2003]. Since levels of smoking are falling in most Western countries, this may also contribute to a higher number of LGA babies [Kramer 2002].

Maternal glucose tolerance is another strong determinant of LGA birth. Women with gestational diabetes (GDM) have a strongly increased risk of giving birth to a LGA baby [Schaefer-Graf 2002 & 2003]. Not only is their risk of an LGA birth higher, the consequences of LGA are more pronounced in babies whose mothers had GDM. Evidence suggests that the increase in fat mass in LGA babies [Hediger 1998; Hammami 2001] is larger in LGA babies following GDM pregnancies, than in LGA babies whose mothers had normal glucose tolerance [Hammami 2001; Vohr 1997 & 1999]. Moreover, Vohr et al. have shown that fat mass in LGA children whose mothers had GDM was higher than in LGA babies from 'control' women, even at 7 years of age [Vohr 1999]. In addition to this increased adiposity, they also found that LGA babies of GDM mothers also had higher blood pressure and higher levels of serum glucose at 4-7 years of age. Adverse effects of LGA births also include a higher risk for the development of insulin intolerance and obesity during childhood [Strauss 1997].

In relation to maternal physical activity, Alderman et al. [1998] have shown that moderate or vigorous physical activity for two hours per week or more in any month of pregnancy is associated with decreased risk of LGA birth, but has no significant effect on risk of SGA birth or length of gestation. They postulate that this effect may be due to beneficial effects on glucose tolerance. If so, physical activity may not only reduce the risk of LGA birth, but may also reduce the associated increase in adiposity. This effect may be more pronounced in babies born to GDM mothers. However, the role of physical activity during pregnancy on fat distribution in infancy has not been studied to date. Given the strong influence of physical activity on glucose metabolism, this relationship is very plausible.