Respiratory function among preterm infants whose mothers smoked during pregnancy

We examined whether the adverse effects of prenatal exposure to tobacco on lung development are limited to the last weeks of gestation by comparing respiratory function in preterm infants whose mothers had and had not smoked during pregnancy. Maximal forced expiratory flow ((V) over dot max(FRC)) and time to peak tidal expiratory flow as a proportion of total expiratory time (T-PTEF:T-E) were measured prior to discharge from hospital in 108 preterm infants (mean [SD] gestational age, 33.5 [1.8] wk), 40 of whose mothers had smoked during pregnancy. Infant urinary cotinine was less than 4 ng/ml in those born to nonsmokers, but it was as high as 458 ng/ml in exposed infants (p < 0.0001). T-PTEF:T-E was significantly lower in infants exposed to tobacco in utero (mean [SD], 0.369 [0.109]) when compared with those who were not (0.426 [0.135]) (p less than or equal to 0.02). (V) over dot max(FRC) was also reduced in exposed infants (mean [SD], 85.2 [41.7] ml/s versus 103.8 [49.7] ml/s) (p = 0.07). After allowing for sex, ethnic group, body size, postnatal age, and socioeconomic status, TPTEF:JE remained significantly diminished in infants exposed prenatally to tobacco (p < 0.05). Thus, impaired respiratory function is evident in infants born on average 7 wk prior to the expected delivery date, suggesting that the adverse effects of prenatal exposure to tobacco are not limited to the last week. of pregnancy.