British Journal of Obstetrics and Gynaecology April 1976. Vol83. pp 262-270
CIGARETTE SMOKING AND FETAL BREATHING MOVEMENTS BY
F. A. MANNING AND
C. FEYERABEND" The Nufield Institute for Medical Research University of Oxford
Summary Cigarette smoking caused a reduction in the incidence of fetal breathing movements in normal and abnormal pregnancies. The size of the reduction varied, being greatest in small-for-dates pregnancies and pregnancies complicated by fetal distress in labour and least in pre-eclamptic pregnancies. The fall in the amount of fetal breathing movements was significantly related to the rise in maternal plasma nicotine after smoking but was unrelated to the rise in carboxyhaemoglobin. Smoking non-nicotine (herbal) cigarettes produced increases in carboxyhaemoglobin concentrations similar to those observed after smoking tobacco cigarettes, and was not associated with a fall in the incidence of fetal breathing movements. Chewing gum containing nicotine produced rises in plasma nicotine concentration similar to those observed after smoking tobacco cigarettes and was associated with a significant reduction in the incidence of fetal breathing movements. Hence nicotine appeared to be the factor in cigarette smoke responsible for the reduction in the incidence of fetal breathing movements. Nicotine was present in the cord blood of infants whose mothers smoked. The possible mechanism by which nicotine caused a reduction in the incidence of fetal breathing movements and its possible relevance to the detrimental effects of smoking on the fetus are considered.
EPIDEMIOLOGICAL studies have shown that cigarette smoking during pregnancy is associated with an increased incidence of smalI-for-dates infants, prematurity, an increase in perinatal mortality (Butler et al, 1972) and possibly a reduction in intellectual development (Butler and Goldstein, 1973). The factor or factors in cigarette smoke responsible for these effects are unknown. The presence of normal fetal breathing movements is a good index of fetal health, being reduced by fetal hypoxia, acidemia and hypoglycaemia (Boddy and Dawes, 1975). Cigarette smoking also causes a statistically significant
reduction in the incidence of fetal breathing movement in normal pregnancies (Manning et al, 1975). The present observations were undertaken to study the effect in high risk pregnancies and to determine the factor in cigarette smoke responsible for the depression of fetal breathing.
METHODS Continuous records of fetal chest wall movements in utero were made using the A-scan ultrasound method (Boddy and Robinson, 1971).Sixty-four women, all in the third trimester of pregnancy and all chronic smokers, were studied. Observations were made in the morning after the patient had eaten a normal breakfast and had abstained from smoking overnight.
address: Poisons Unit, New Cross Hospital,
SMOKING AND FETAL BREATHING
Fetal breathing movements were recorded for at least 30 minutes before the smoking and for at least 60 minutes afterwards. The time of onset of smoking was not marked on the record but was recorded in a separate book. All but 12 of the records obtained were cut into fiveminute intervals, coded, randomized and analyzed ; the remaining records were analyzed intact. The proportion of time during which fetal breathing movements were present for each interval was determined and expressed as a percentage. Fetal breathing movements were measured before and after smoking two consecutive tobacco cigarettes in 19 women with normal pregnancies, 10 with pre-eclampsia, 12 with diabetic pregnancies (two were insulin-dependent) and 6 women who were ultimately delivered of an infant weighing less than the 5th centile for gestational age and sex (Milner and Richards, 1974). Thirty-eight of these women had uneventful labours ; the remaining nine developed fetal distress in labour as evidenced by late decelerations of the fetal heart and/or acidemia (pH< 7.25) on scalp sampling, and/or a five-minute Apgar score of less than 7. Maternal venous blood, for nicotine and blood glucose concentrations, was sampled before smoking and 90 seconds, 15 minutes, 30 minutes and 60 minutes after the second cigarette was extinguished. Samples were obtained from 16 women with normal pregnancies, 8 with pre-eclampsia, 10 /with diabetes, and 5 delivered of small-for-dates infants. In 13 women with normal pregnancies, a sample of venous blood for carboxyhaemoglobin determination was taken anaerobically before and 30 minutes after smoking. Mixed arterial-venous cord blood was collected at delivery from another 49 infants whose mothers smoked and from 12 infants whose mothers were non-smokers. Herbal cigarettes. Fetal breathing movements were recorded in 10 women with normal pregnancies before and after smoking two consecutive herbal cigarettes (Honey Rose Specials). Five had been studied with tobacco cigarettes on a previous occasion. Venous blood samples for carboxyhaemoglobin determination were collected anaerobically before and 30 minutes after smoking the second cigarette.
Nicotine gum. Fetal breathing movements were measured in 12 women before and after chewing gum (NicoretteR). Seven were given a single piece of gum containing 4 mg nicotine, and five were given two pieces simultaneously. The patients were asked to chew the gum vigorously for at least 20 minutes. Venous blood for nicotine determination was obtained during the control period and 30 and 60 minutes after the onset of chewing. Nicotine, carboxyhaemoglobin and blood sugar. Samples for nicotine analysis were heparinized, centrifuged at 3000 rpm at 4 "C for 15 minutes and the plasma removed and frozen. Plasma nicotine concentration was determined by gas chromatography to within 5 0 . 1 ng/ml (Feyerabend et al, 1975). Venous blood samples for carboxyhaemoglobin analysis were heparinized. Carboxyhaemoglobin concentration was measured by a spectro-photometric technique to within 0.1 per cent at a concentration of less than 20 per cent (Commins and Lawther, 1965). Plasma glucose concentration was determined by the glucokinase method.
RESULTS Observations with tobacco cigarettes Normal pregnancies. Fetal breathing movements were present for 69.752.66 per cent of the time before smoking. There was a significant reduction in the proportion of time during which fetal breathing movements were present within five minutes after the start of smoking (p