Incidence and prognosis of asthma to age 33

EDITOR,-As an obstetrician with mild asthma, I was interested to read David P Strachan and colleagues' paper on their long term cohort study of the incidence and prognosis of asthma. 1 Several perinatal factors showed an independent association with asthma in the study population: the odds ratio was 2.98 (95% confidence interval 1.33 to 6.66) for antepartum haemorrhage in the third trimester and asthma at age 8-16; 1.63 (1.14 to 2.34) for albuminuria during pregnancy and asthma at age 17-33; and 1.72 (1.11 to 2.67) for maternal smoking (in pregnancy only) and asthma at age 0-7.