BRITISH MEDICAL JOURNAL 8 MARCH 1975 553 fetal breathing movements; but further control studies will have to be done to exclude the possibility ofthe degree of inhalation varying with the type of cigarette. Cigarette smoking in pregnancy is suspected of being detrimental to the fetus. Statistical surveys have shown that the babies are smaller at birth (Butler et al., 1972) and suggested an increase in prematurity and perinatal mortality. It is not easy to relate our observations on the acute effects of smoking two cigarettes to the long-term epidemiological reports. Nevertheless, physiological factors such as hypoxia and hypoglycaemia, which might be expected to have a detrimental effect on the fetus, also reduce the normal incidence of fetal breathing movements in animals and man (Boddy and Dawes, 1975; Boddyet al., 1975). Whether the similar effect of cigarette smoking is to be interpreted in the same way is as yet a matter for conjecture. The size of the transient change observed (see fig.) was less than the normal diurnal variation in the incidence of fetal breathing. We make this report because clinical physiologists and obstetricians in several countries are beginning touse fetal breathing movements asan index of health. These observations are best made some hours after the last cigarette has been smoked to exclude the acute effects of this variable.

This work was carried out with the aid of a grant from the Medical Research Council. We thank Professors GS Dawes and Alec Turnbull for their help, the consulting staff of the department of obstetrics for access to their patients, the nursing staff, and the subjects. who volunteered for the study.