Lum, Sook-Yuen; (2002) Influence of low birthweight for gestational age on airway function during early infancy. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: There is increasing evidence from epidemiological studies suggesting an association between abnormalities of fetal growth and diseases in adult life. Low birth weight has been identified as an independent risk factor for wheezing in early childhood and it has been suggested that some of the clinico-pathological findings in sudden infant death syndrome (SIDS) may be related to intrauterine growth retardation. However, the physiological mechanisms underlying these associations have not been elucidated. Aim: The aim of this study was to test the hypothesis that, relative to infants of normal birthweight, those of low birthweight for gestational age have impaired airway function shortly after birth. Method: Healthy infants > 35 weeks gestation, of small (SGA) and appropriate (AGA) birthweight for gestational age, who were and were not exposed to maternal smoking in pregnancy were recruited shortly after birth during 1998 - 2000. Respiratory function was assessed in 79 SGA and 104 AGA infants prior to any lower respiratory illness, by measuring forced expiratory flow during tidal breathing and raised lung volume at a mean postnatal age of six weeks. Fetal and postnatal exposure to tobacco smoke was assessed from maternal report. This was compared with cotinine levels in infant urine and maternal saliva obtained at the time of respiratory function test. Findings: SGA infants were significantly shorter and lighter than AGA infants at time of test. In univariate analysis, lung volume as reflected by forced vital capacity (FVC), forced expired volume in 0.4 seconds (FEV0.4), and maximal expiratory flow at 25% vital capacity (MEF25), were significantly diminished in infants born SGA compared to AGA, but there was no difference in maximal flow at functional residual capacity (V'maxFRC). After adjusting for body size, maternal smoking status and postnatal age. FVC and FEV0.4 remained significantly reduced in SGA infants. When analysis was restricted to those not exposed to maternal smoking, this reduction appeared to be mediated primarily through the reduction in body size of SGA infants at time of test. Both parameters of peripheral airway function, MEF25 and V'maxFRC were significantly lower in boys than girls. V'maxFRC but not MEF25 was significantly lower among infants whose mothers smoked. Interpretation: The findings of this study suggests that airway function is diminished in SGA infants at birth and that this diminution precedes any lower respiratory tract illness. While this appears to be mediated primarily through the reductions in body size, it could contribute to the increased incidence of respiratory morbidity observed in such children during early life.

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