Effects of perinatal factors on body mass index and physical fitness of school-age children

Data on pregnancy complications, labour, delivery, and perinatal outcomes are being extensively collected in all developed countries. However, due to logistic difficulties of a long-term follow-up, only the short-term outcomes, such as Apgar scores, neonatal respiratory morbidity, admission to neonatal intensive care units (NICU), etc., are mostly analysed (1). Of all perinatal factors, prematurity has been the most studied in terms of its long-term consequences. Preterm birth has been shown in observational studies to be associated with decreased physical fitness and impaired cognitive functions in later life (2,3,4,5,6,7,8,9). Studies on impacts of other perinatal factors, such as hypertensive disorders of pregnancy, gestational diabetes, intrauterine growth restriction, plurality, parity, mode of delivery, etc., on long-term health are, however, lacking.

Studies on children born preterm suggest that childhood obesity and poor physical fitness could be among potential adverse long-term effects of complications in the perinatal period (2,3,4,5,6,7,8,9,10,11,12,13,14). Childhood obesity and poor physical fitness at school-age are associated with many preventable diseases and present a serious current and future public health problem, especially because they track well into adulthood and are associated with numerous adverse health outcomes (15,16,17,18). With global prevalence of childhood obesity continually growing, it is important to identify potential perinatal risk factors that could be effective targets of future public health initiatives tackling obesity (19, 20). Moreover, poor physical fitness in childhood has been associated with unfavourable psychological, social and cognitive development (21,22,23,24,25,26,27,28,29,30,31,32). It is, therefore, important to establish the impact of perinatal factors, such as preterm birth and others, on long-term physical development of children.

All births in Slovenia are being registered in the Slovenian National Perinatal Information System (NPIS) since 1987. The country also has a monitoring system of children’s motor and physical development, the SLOfit system, implemented in all schools in 1987, which includes almost the entire school-going population from ages 6 to 18. The aim of the present study was to link the data from both registers in order to examine the potential relationship between several biological and environmental perinatal factors and child’s body mass index (BMI) and physical fitness at school-age.

A total of 6,894 neonates were born at our institution in 2008. Ninety stillbirths and early neonatal deaths were excluded leaving 6,804 children for analysis. We were able to match 2,929 (43%) of these children from SLOfit database to NPIS data due to unavailability of complete identifiers in the NPIS register. In other words, NPIS includes mothers’ data for identification of children and the initial names of children are later often changed. The SLOfit database only includes children’s data from official school records.

Table 1 presents the comparison between maternal and neonatal characteristics in the study group (the group for which SLOfit and NPIS data could be matched) and in the group in which we were unable to match the SLOfit and NPIS data.

Table 1

The comparison between maternal and neonatal characteristics in the study group and in the group in which SLOfit and NPIS data could not be matched.

Table 2

The relationship between perinatal factors and child’s body mass index (BMI) at the age of eight.

Table 3

The relationship between perinatal factors and child’s physical fitness index (PFI) at the age of eight.

Tables 2 and 3 present the results of the regression analysis. Children born to mothers with lower prepregnancy BMI and higher education had lower BMI and higher PFI (p<0.001). Physical fitness was lso inversely associated with nulliparity (p<0.001) and NICU admission (p=0.020), but not with other factors, including very preterm birth (p=0.719).

Our findings emphasize the importance of maternal education and lifestyle on children’s motor and physical development. Higher maternal education and lower pre-pregnancy maternal BMI were associated with lower BMI and higher physical fitness of children at age 8. Children’s physical fitness was also linked to parity (first-borns having lower physical fitness than their siblings) and NICU admission irrespective of gestational age.

These results are in accordance with several previously published studies. Finger et al. showed lower parental education level to be associated with higher BMI and lower fitness capacity among adolescents (34). Parental education and occupation were more strongly related to adolescents’ physical activity and fitness outcomes than to family income (31). Two other studies reported similar results, but they were both based on surveys and not on objective fitness capacity measurements (35, 36). Children from families with lower socioeconomic status have also been shown to have higher rates of metabolic syndrome, impaired fasting glucose and type 2 diabetes in adulthood (37). Special preventive measures for these families with programs focused on healthy nutrition and fitness stimulation could effectively decrease the burden of metabolic syndrome in adulthood.

Very preterm birth (at <32 weeks’ gestation) was not an independent risk factor for increased child’s BMI at the age of eight years. This is not in accordance with the results from Vasylyeva et al., who showed preterm birth to be associated with the highest risk for excessive weight gain during childhood (10). However, late preterm birth, and not very preterm birth, was the main factor contributing to excessive weight gain in their study (10). A possible explanation for this could be that altered appetite regulation or altered insulin secretion are responsible for childhood obesity only in preterm infants with higher birth mass, i.e., those born in the late preterm period (11, 12). Physical fitness was also not associated with very preterm delivery. However, admission to the NICU was an independent risk factor for decreased physical fitness at school-age. This may be explained by increased pain sensitivity, increased avoidance behaviour, and social hypervigilance, which are all possible consequences of untreated NICU associated pain in early infancy and are unrelated to gestational age at NICU admission (13). Decreasing stress in the NICU and active encouraging of parents to stimulate their NICU children to participate in regular childhood physical activities and sports could, therefore, be very important to decrease the negative influence of NICU on physical fitness in childhood.

The association between birth order and physical fitness has not been well studied to date. We found first-born children to have lower exercise capacities, in contrast to Barclay and Myrskyla, who reported the opposite, i.e., better physical fitness in first-borns (38). It is important to notice that they analysed only males, who were born in a different time period (1965–1977). They interpreted their findings as being the consequence of social upbringing within the family rather than prenatal experience. Our results seem to suggest that older siblings positively influence the physical activity of their younger brother or sister. The important influence of peer stimulation is supported by the fact that children who attended higher school grades at the same age had better PFI in our study.

The main limitation of the study is its retrospective observational nature, which does not allow accounting for all potential confounders. It also does not allow deriving definitive conclusions on causal relations between factors studied and children’s BMI and physical fitness. Moreover, we were not able to match the data of all children from the SLOfit database and NPIS. The group in which we were unable to link children’s data from SLOfit to NPIS differed in many maternal and neonatal characteristics from the group for which data from these databases could be matched. Many of these differences were statistically important due to large numbers, but clinically irrelevant, e.g., the 94 g difference in birth mass between the two groups. Other differences, such as higher proportion of nulliparous women in the non-matched group, however, could indicate a systemic bias. Our results should, therefore, be interpreted with caution. To allow this, we decided to present also maternal and neonatal characteristics of pregnancies of the non-matched data. We have not stratified BMIs in subgroups, but only determined a correlation between maternal and child’s BMI and other factors. Further studies will, therefore, be needed in order to more exactly determine which BMIs (in which subgroups) are correlated with which outcomes. We believe, however, that our results highlight the importance of maternal pre-pregnancy BMI and will lead to additional studies in this field.

In conclusion, our results seem to suggest that factors such as high maternal pre-pregnancy BMI and low maternal education level seem to be among the most important determinants of worse child’s physical health at schoolage. These public health domain factors seem to be of greater importance for child’s long-term development than many perinatal outcomes, such as very preterm birth, SGA, LGA or low Apgar scores, on which perinatal medicine is currently mostly focused. Finally, our study shows that social factors seem to significantly determine the developmental outcome of children, which gives lots of opportunities for effective interventions in the preschool and school age.