PARAMETROS DE CONFIGURACIÓN DE UN CURSO VIRTUAL

All factors examined were significantly associated with height of G2 at age 7 (Table 5.3). Their influences on height were reduced but remained significant after adjusting first for mid-parental height, and then for fetal and infant factors. After allowing for all childhood factors, the influences of breastfeeding, father’s social class, parental divorce and maternal education on height were no longer significant, suggesting that their impact on childhood height was explained by other early life factors.

Mid-parental height

Parental height was the strongest predictor for height of children; for every unit increase in mid-parental height SDS, the mean height SDS for cohort members increased by 0.56 (2.9 cm) at age 7. The relationship remained strong after allowing for all other factors (Table 5.3).

Maternal smoking

Maternal smoking during pregnancy was significantly associated with childhood height in G2. Variable and heavy smokers were combined as the strength of their effects was similar. Table 5.3 shows that children of heavy/variable smokers were shorter than those of non­ smoking mothers by a height SDS of 0.24 (1.2 cm) at age 7. The difference reduced to 0.13 (0.7 cm), but was still significant after adjusting for birthweight, indicating that birthweight was a pathway factor in the relationship between smoking and childhood growth as shown in Chapter 4. The difference further reduced to 0.06 (0.3 cm), though it remained

significant after adjusting for other factors. Therefore, maternal smoking had only a weak effect on height in G2 once birthweight and all other factors were taken into account.

Birthweight

A significant linear relationship was found between birthweight and height in G2 in childhood (Table 5.3). For every 1kg increase in birthweight, the mean height SDS increased by 0.51 (2.6 cm) at age 7. The relationship was weakened but remained highly significant after adjusting for parental height. However, further adjusting for fetal, infant, and childhood factors did not affect the linear relationship.

Breastfeeding

Breastfeeding had a significant effect on childhood height in G2. Cohort members who were breastfed were taller on average than those who were never breastfed by a height SDS of 0.15 (0.8 cm) at age 7. The difference reduced by 40% to 0.09 once mid-parental height was accounted for. The relationship was no longer significant after adjusting for early life factors, suggesting that the influence of breastfeeding on height was explained by parental height and other early life factors.

Maternal age

A weak but significant linear relationship between maternal age at childbirth and height was seen at 7 years in G2. The relationship strengthened after allowing for early life factors, possibly due to the negative confounding effect of birth order; later-bom children were more likely to be bom to older mothers and were shorter on average than early bom children.

0.32 (1.7 cm). The effect of birth order on height changed little after adjusting for other early life factors, suggesting that its impact on height was independent of other early life factors. However, the difference reduced to 0.08 (0.4 cm) after adjusting for family size (data not presented). Cohort members with few younger siblings (none or one) were taller on average than those with three or more, by a height SDS of 0.37 (2.0 cm). The difference reduced to 0.07 (0.4 cm) and was no longer significant after adjusting for family size (data not presented). Therefore, effects of birth order and number of younger siblings were mainly explained by the effect of family size in G2; later-bom children and those with more siblings were shorter because they came from larger families.

Social class

Social class was significantly associated with height of G2 at age 7, with clear social class gradients (Table 5.3). The difference in height SDS between classes I&II and classes IV&V was pronounced (0.39) and was reduced but remained significant after adjusting for mid- parental height, suggesting that some of the social class effect on height was explained by parental height, a combined genetic and environmental factor. The relationship between social class and childhood height was no longer significant after further allowing for other childhood factors.

Housing tenure and household crowding

The association between housing tenure and height was significant in G2, with children from owner occupied properties being the tallest, followed by children from private rental accommodation (Table 5.3). Children from council/housing association rental

0.08 (0.4 cm) after allowing for all other early life factors, including social class and crowding (although still significant).

As shown in Table 5.3, the effect of crowding on height was also significant in G2, with a clear trend according to level of crowding. The difference in height SDS between children from households with less than one person per room and households with more than 1.5 persons per room was 0.65 (3.4 cm). It was reduced to 0.22 (1.1 m) but remained significant after allowing for other early life factors.

Parental divorce/separation

Cohort members who had experienced parental separation or divorce were on average shorter than those who had not, by a height SDS of 0.20 (1.0 cm). The relationship was not affected by fetal and infant factors, but became non-significant after allowing for other early life factors. As shown in Chapter 4, the age of the child when the separation or divorce took place was found to have an impact on growth. Cohort members whose parents divorced between ages 4 and 7 years were not only significantly shorter on average than children whose parents were not divorced by a height SDS of 0.35 (1.8 cm), but also shorter than children whose parents divorced before the age of 4 years by 0.27 (1.4 cm), though borderline significant (p=0.06). The association remained with a significant

difference of 0.22 (1.1 cm) after allowing for all other early life factors (data not presented).

Maternal education