Acta Pzdiatr Scand 68: 547-552. 1979
SMOKING DURING PREGNANCY-EFFECTS ON THE FETUS AND ON THIOCYANATE LEVELS IN MOTHER AND BABY A. MEBERG, H. SANDE, 0. P. FOSS and J . T. STENWIG From the Department ojPaediatrics, the Depurtmenr of Obstetrics rind Gynecology, the Department of Clinical Chemistry and the Department of Pathology, Ullevrjl Hospital, Oslo, Norway
ABSTRACT. Meberg, A., Sande, H., Foss, 0. P. and Stenwig, J. T. (Departments of Paediatrics, Obstetrics and Gynecology, Clinical Chemistry and Pathology, UllevBI Hospital, Oslo, Norway). Smoking during pregnancy-effects on the fetus and on thiocyanate levels in mother and baby. Acta Paediatr Scand, 68: 547, 1979.-Twenty-eight mothers smoking 10-20 cigarettes daily during pregnancy had significantly higher serum thiocyanate concentrations at delivery compared to 25 non-smoking controls. The thiocyanate levels were positively correlated to cigarette consumption and inversely correlated to the birth weights of the infants. A highly significant correlation existed between serum thiocyanate levels of the mother and umbilical cord serum thiocyanate levels, reflecting a nearly complete equilibration. The thiocyanate concentrations in human milk on the 4th day after delivery were considerably lower than the serum concentrations, and no correlation existed between serum and milk concentrations. The infants of smoking mothers had significantly decreased weight and length at birth compared to infants of non-smokers. Birth weights were 33441 434 g and 3620k504 g respectively @0.05
4.4k4.5
20
-2-1 1
3.9k3.4
>0.05
52-173
109.6i29.9
25
23-82
48.2k16
0.05
49-83 &2 1
-2.5-16
4-53 3942 2 4 8 M 160 47-53.5
3 344k434 49.8k1.7
13/12 25 25
27 28
32.5-37 100-290
34.821.2 173.6k50.9
24 25
32.5-39 50-310
28
3-7
3.5k1.0
25
3-5
3.3k0.5
>0.05
28
40G700
560 4 86.4
25
450-750
S90f 89.9
>o.os
25 25
370-560 16.6-21
25 22
400-690 I5 .5-22.5
517k76 19.3k I .8
>0.05
18.8k1.5
21
1.6 1-3.17
2.32k0.51
17
1.47-3.44
2.42f0.59
>0.05
16/12 28 28
-
. 490k61
were the first non-smoking women admitted for delivery after a mother in the smoking group and that fulfilled all the other selection criteria. An additional 21 healthy non-pregnant non-smoking women 21-30 years old (23.4k 2.5 years; mean k S.D.) were investigated for serum thiocyanate concentrations. The mothers' age, marital status, height, weight before pregnancy and weight gain during pregnancy were registered from the hospital records, as were weight, length and head circumference of the infants at birth. Infant body weight was registered daily, and the loss of weight after birth calculated. Tliiocyunute investigations Venous blood samples were taken from the mothers within 24 hours before delivery and again on the 4th
0.05
day after delivery. Cord blood samples were taken at delivery from the placental part of the cord. A milk sample was collected from the mothers on the 4th day after delivery. Blood samples were rapidly centrifuged, and all serum samples were stored at -3O"C, together with the milk samples. The serum and milk samples were analyzed for thiocyanate by an automated moditication of the method of Pettigrew & Fell (15).
Hi.,tologiccil in rvstigtrtions Placentas were weighed after separating the cord at the placental insertion, and also weighed after stripping of the membranes fixed in 4 % formalin. The diameter of each placenta was registered as the mean of two angularly measured diameters. The placentas were studied grossly and cut in transverse sections 1.5 cm wide.
Smoking during pregnancy
--
200-
I 0
E
a
: l o oi .
0 -
.. / .
-0
/
I I-
2
Y
=
49.52 + 4.041x
r
=
0 800
t=9333
3
o! u, v1
P < 0.001
I 0
10
15
C IG A R E TT E
20
s/
DA Y
Fig. I . Relation between serum thiocyanate concentrations at delivery in 51 women and their smoking level during pregnancy.
Blocks were taken from the cord, membranes, central and peripheral placental areas, and processed in a routine fashion. In addition 2-3 cm long pieces of cord were taken 10 cm from the placental insertion, and fixed in buffered 4% formalin (pH 7.4). Transverse sections were made and stained by the Verhoff-van Gieson method to visualize the elastic lamina and the medial smooth muscle. The arteries were photographed through a microscope. In those cut at a right angle and with complete obliteration of the lumen, the area between the internal lamina elastica and the outer margins of the media was calculated by an electronic morphometric calculator (Kontron Messgerate GMBH), as a measure for the arterial medial muscle mass.
Dietary inquiry A written inquiry was sent to the mother after discharge from the hospital, concerning her weight 10 days after delivery, iron and vitamin supplementation, and food intake during pregnancy.
equal with regard t o parity of the mothers, mothers’ weight and height before pregnancy, weight gain during pregnancy and weight gain of the mother herself, as calculated from her weight 10 days after birth. The sex distribution of the infants was equal in both groups, as was gestational age. Significantly higher serum thiocyanate levels were present in smokers compared to nonsmokers. The thiocyanate concentration in serum fell slightly from just before delivery until the 4th day after delivery, however, not significantly. In the 21 non-pregnant, nonsmoking controls, serum thiocyanate concentration was 55k15.5 pmol/l, and similar to that in the pregnant non-smokers ( p >0.05). The thiocyanate concentration in human milk was considerably lower than in serum, and no difference existed between smokers and nonsmokers. No correlation was present between the serum and milk concentrations of thiocyanate ( p >0.05). Significantly increasing thiocyanate concentrations were found with increasing cigarette consumption (Fig. 1). A highly significant correlation existed between the thiocyanate concentration of the mother within 24 hours before delivery and the umbilical cord serum thiocyanate con-
I
-
CORD
h 0
E a I
Statisticul methods p-Values were obtained by means of the Chi-square test, two-sided t-test and by simple linear regression analysis.
549
1 5 0 ~
I
Lu
+-
4
$ t
ONON-SMOKERS *SMOKERS
loo{
// . ~ ~ 1 2 t30 .78 8 2 x
RESULTS Table 1 presents the clinical and laboratory data concerning the mothers, the infants, the placentas and the umbilical cords in the two groups. Smoking mothers were of lower age than non-smokers and the group contained more single women than the controls, who were nearly all married. The groups were 36-792874
r = o 984 t = 38.659 p0.05). The infants of smoking mothers had significantly lower weight and length at birth. These differences were also present when calculated for only the married women in the two groups. Weight loss after birth was equal in both groups of infants, as was the timing for the lowest weight after birth. N o difference was found on placental size (weight, diameter) between smokers and nonsmokers. Histological investigation of the placentas (25 placentas from each group) showed syncytial knots, small infarctions, small calcifications and fibrinoid necrosis of villi in most
DISCUSSION Serum thiocyanate concentrations of smoking mothers were found to be positively correlated to their smoking levels (Fig. 1). This is in accordance with other investigations (1, 20). Pregnancy did not seem to influence the thiocyanate concentration as judged from our results in non-smokers. The thiocyanate concentration of serum in smokers therefore may be used as an objective measure for the smoke exposure. However, non-smokers also have a considerable and variable amount of thiocyanate in serum, mostly caused by the thiocyanate content in food (20). This limits the accuracy of the thiocyanate concentrations reflecting the smoking level. The thiocyanate concentrations in cord blood serum were found to be nearly identical with maternal serum thiocyanate concentrations at delivery, as well as on the 4th day after delivery. Thus cord serum thiocyanate seems to reflect the mother's smoking habits in the same way as her own serum thiocyanate concentration. Whether the fetal thiocyanate level reflects only passive diffusion of thiocyanate from the mother, or also cyanide detoxication in the fetus itself, remains unknown. However, a dynamic equilibration exists between thiocyanate formed by detoxication of cyanide and reverse oxidation of thiocyanate to cyanide by enzymes present in red blood cells and other cells ( 5 ) . The
Smoking during pregnancy
fetus of smoking mothers therefore may be exposed to toxic cyanide levels in utero. The lower concentrations of thiocyanate in human milk, and the lack of correlation between serum and milk concentrations, may be due to the handling of the thiocyanate ion in the mammary gland. Thiocyanate shows a physical and chemical similarity to halogen ions, and behaves much like chloride ions in the body (20), which also are found in low concentration in human milk compared to serum concentration. There has been discussion on whether cigarette smoking acts as an exogenous factor which interferes with intra-uterine development of the fetus (1, 12, 13) or whether smoking women are a self-selected group more likely both to smoke and to have infants with lower birth weights (10). In our study the maternal serum thiocyanate levels were inversely correlated to infant birth weight, indicating that smoking itself interferes with fetal growth in a dose related manner. Similar inversity has been found in far greater series between birth weight and maternal smoking levels (12, 13). The growth retardation did not seem to be caused by differences in the two groups of nutritional factors during pregnancy (maternal weight gain), genetical potential for growth (maternal size) or marital status of the mothers. Ultrastructural changes are found in umbilical cord vessels after maternal smoking during pregnancy (3, 4) as well as in placental vessels (2). In our study we did not investigate small changes, and probably therefore were not able to show differences between smokers and non-smokers. Hypertrophy of medial smooth muscle is found in conditions associated with increased vascular resistance (1 1). If the decreased blood flow through the placenta found in smokers (19) is caused by an increased vascular resistance, it might have been reflected in hypertrophy of smooth muscle in the umbilical cord arteries. We were, however, not able to demonstrate this with the method used.
551
ACKNOWLEDGEMENTS This work is supported from The Norwegian Research Council for Science and the Humanities, and from The Norwegian Council on Cardiovascular Diseases.
REFERENCES 1. Andrews, J.: Thiocyanate and smoking in pregnancy.
Br J Obstet Gynuecol, 80: 810, 1973. 2. Asmussen, I.: Ultrastructure of the human placenta at term. Observations on placentas from newborn children of smoking and non-smoking mothers. Actu Obstet Gynecol Scand, 56: 119, 1977. 3. Asmussen, 1.: Ultrastructure of human umbilical vessels. Observations on veins from newborn children of smoking and nonsmoking mothers. Actu Obstet Gynecol Scund, 57: 253, 1978. 4. Asmussen, I . & Kjeldsen, K.: Intimal ultrastructure of human umbilical arteries. Observations on arteries from newborn children of smoking and nonsmoking mothers. Circ Res, 36: 579, 1975. 5. Chung, J. & Wood, J. L.: Oxidation of thiocyanate to cyanide catalyzed by hemoglobin. J B i d Chem, 246:555, 1971. 6. Cole, P. V . , Hawkins, L. H. & Roberts, D.: Smoking during pregnancy and its effects on the fetus. Br J Obstet Gynuecol, 79: 782, 1972. 7. Comstock, G. W., Shah, F. K., Meyer, M. B. & Abbey, H.: Low birth weight and neonatal mortality related to maternal smoking and socioeconomic status. A m J Obstet Gynecol, 111: 5 3 , 1971. 8. Dunn, H. G . , McBurney, A. K., Ingram, S. & Hunter, C . M.: Maternal ~ g a r e t t esmoking during pregnancy and the child’s subsequent development. I . Physical growth to the age of 66 years. Cun J Public Health, 67: 499, 1976. 9. Dunn, H. G . , McBurney, A. K., Ingram, S. & Hunter, C. M.: Maternal cigarette smoking during pregnancy and the child’s subsequent development. 11. Neurological and intellectual maturation to the age of 66 years. Can J Pithlic Heulth, 68: 43, 1977. 10. Hickey, R. J., Clelland, R. C. & Bowers, E. J.: Maternal smoking, birth weight, infant death, and the self-selection problem. A m J Ohstet Gynecol, 131: 805, 1978. 1 1 . Levin, D. L., Fixler, D. E., Morriss, F. C. B Tyson, J.: Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors. J Pediatr, Y2: 478, 1978. 12. MacMahon, B., Alpert, M. & Salber, E. J.: Infant weight and parental smoking habits. A m J Epidemiol, 82: 247, 1966. 13. Meyer, M. B., Jonas, B. S. & Tonascia, J . A.: Perinatal events associated with maternal smoking during pregnancy. A m J Epidemiol, 103: 464, 1976. 14. Murphy, J. F., Mulchay, R. & Drumm, J. E.: Smoking and the fetus. Lancet, If: 36, 1977. 15. Pettigrew, A. R. & Fell, G. S.: Simplified colorimetric determination of thiocyanate in biological fluids, and its application to investigation of the toxic amblyopias. CIin Chern, 18: 996, 1972.
552
A . Mebevg et al.
16. Pettigrew, A. R., Logan, R. W. & Willcocks, J.:
Smoking in pregnancy-effects on birth weight and on cyanide and thiocyanate levels in mother and baby. Br J Obstet Gynuecol, 84: 31, 1977. 17. Prigge, E. & Hochrainer, D.: Effects of carbon monoxide inhalation on erythropoiesis and cardiac hypertrophy in fetal rats. Toxicol Appl Pharmacol, 42: 225, 1977. 18. Rush, D. & Kass, E. H.: Maternal smoking: A reassessment of the association with perinatal mortality. A m J Epidemiol, 96: 183, 1972. 19. Spira, A., Fournier, R., Grob, J. C . , Dreyfus, J . & Schwartz, D.: Smoking during pregnancy and pla-
cental blood flow. Proc 6 t h Congress of Perinutul Medicine, Vienna 1978. 20. Stoa, K . F.: Studies on thiocyunute in serum. 2nd Medical Yearbook, University of Bergen, 1957. Submitted Nov. 21, 1978 Accepted Febr. 7, 1979
(A. M.) Department of Paediatrics Ullevhl Hospital Oslo Norway
SMOKING DURING PREGNANCY-EFFECTS ON THE FETUS AND ON THIOCYANATE LEVELS IN MOTHER AND BABY A. MEBERG, H. SANDE, 0. P. FOSS and J . T. STENWIG From the Department ojPaediatrics, the Depurtmenr of Obstetrics rind Gynecology, the Department of Clinical Chemistry and the Department of Pathology, Ullevrjl Hospital, Oslo, Norway
ABSTRACT. Meberg, A., Sande, H., Foss, 0. P. and Stenwig, J. T. (Departments of Paediatrics, Obstetrics and Gynecology, Clinical Chemistry and Pathology, UllevBI Hospital, Oslo, Norway). Smoking during pregnancy-effects on the fetus and on thiocyanate levels in mother and baby. Acta Paediatr Scand, 68: 547, 1979.-Twenty-eight mothers smoking 10-20 cigarettes daily during pregnancy had significantly higher serum thiocyanate concentrations at delivery compared to 25 non-smoking controls. The thiocyanate levels were positively correlated to cigarette consumption and inversely correlated to the birth weights of the infants. A highly significant correlation existed between serum thiocyanate levels of the mother and umbilical cord serum thiocyanate levels, reflecting a nearly complete equilibration. The thiocyanate concentrations in human milk on the 4th day after delivery were considerably lower than the serum concentrations, and no correlation existed between serum and milk concentrations. The infants of smoking mothers had significantly decreased weight and length at birth compared to infants of non-smokers. Birth weights were 33441 434 g and 3620k504 g respectively @0.05
4.4k4.5
20
-2-1 1
3.9k3.4
>0.05
52-173
109.6i29.9
25
23-82
48.2k16
0.05
49-83 &2 1
-2.5-16
4-53 3942 2 4 8 M 160 47-53.5
3 344k434 49.8k1.7
13/12 25 25
27 28
32.5-37 100-290
34.821.2 173.6k50.9
24 25
32.5-39 50-310
28
3-7
3.5k1.0
25
3-5
3.3k0.5
>0.05
28
40G700
560 4 86.4
25
450-750
S90f 89.9
>o.os
25 25
370-560 16.6-21
25 22
400-690 I5 .5-22.5
517k76 19.3k I .8
>0.05
18.8k1.5
21
1.6 1-3.17
2.32k0.51
17
1.47-3.44
2.42f0.59
>0.05
16/12 28 28
-
. 490k61
were the first non-smoking women admitted for delivery after a mother in the smoking group and that fulfilled all the other selection criteria. An additional 21 healthy non-pregnant non-smoking women 21-30 years old (23.4k 2.5 years; mean k S.D.) were investigated for serum thiocyanate concentrations. The mothers' age, marital status, height, weight before pregnancy and weight gain during pregnancy were registered from the hospital records, as were weight, length and head circumference of the infants at birth. Infant body weight was registered daily, and the loss of weight after birth calculated. Tliiocyunute investigations Venous blood samples were taken from the mothers within 24 hours before delivery and again on the 4th
0.05
day after delivery. Cord blood samples were taken at delivery from the placental part of the cord. A milk sample was collected from the mothers on the 4th day after delivery. Blood samples were rapidly centrifuged, and all serum samples were stored at -3O"C, together with the milk samples. The serum and milk samples were analyzed for thiocyanate by an automated moditication of the method of Pettigrew & Fell (15).
Hi.,tologiccil in rvstigtrtions Placentas were weighed after separating the cord at the placental insertion, and also weighed after stripping of the membranes fixed in 4 % formalin. The diameter of each placenta was registered as the mean of two angularly measured diameters. The placentas were studied grossly and cut in transverse sections 1.5 cm wide.
Smoking during pregnancy
--
200-
I 0
E
a
: l o oi .
0 -
.. / .
-0
/
I I-
2
Y
=
49.52 + 4.041x
r
=
0 800
t=9333
3
o! u, v1
P < 0.001
I 0
10
15
C IG A R E TT E
20
s/
DA Y
Fig. I . Relation between serum thiocyanate concentrations at delivery in 51 women and their smoking level during pregnancy.
Blocks were taken from the cord, membranes, central and peripheral placental areas, and processed in a routine fashion. In addition 2-3 cm long pieces of cord were taken 10 cm from the placental insertion, and fixed in buffered 4% formalin (pH 7.4). Transverse sections were made and stained by the Verhoff-van Gieson method to visualize the elastic lamina and the medial smooth muscle. The arteries were photographed through a microscope. In those cut at a right angle and with complete obliteration of the lumen, the area between the internal lamina elastica and the outer margins of the media was calculated by an electronic morphometric calculator (Kontron Messgerate GMBH), as a measure for the arterial medial muscle mass.
Dietary inquiry A written inquiry was sent to the mother after discharge from the hospital, concerning her weight 10 days after delivery, iron and vitamin supplementation, and food intake during pregnancy.
equal with regard t o parity of the mothers, mothers’ weight and height before pregnancy, weight gain during pregnancy and weight gain of the mother herself, as calculated from her weight 10 days after birth. The sex distribution of the infants was equal in both groups, as was gestational age. Significantly higher serum thiocyanate levels were present in smokers compared to nonsmokers. The thiocyanate concentration in serum fell slightly from just before delivery until the 4th day after delivery, however, not significantly. In the 21 non-pregnant, nonsmoking controls, serum thiocyanate concentration was 55k15.5 pmol/l, and similar to that in the pregnant non-smokers ( p >0.05). The thiocyanate concentration in human milk was considerably lower than in serum, and no difference existed between smokers and nonsmokers. No correlation was present between the serum and milk concentrations of thiocyanate ( p >0.05). Significantly increasing thiocyanate concentrations were found with increasing cigarette consumption (Fig. 1). A highly significant correlation existed between the thiocyanate concentration of the mother within 24 hours before delivery and the umbilical cord serum thiocyanate con-
I
-
CORD
h 0
E a I
Statisticul methods p-Values were obtained by means of the Chi-square test, two-sided t-test and by simple linear regression analysis.
549
1 5 0 ~
I
Lu
+-
4
$ t
ONON-SMOKERS *SMOKERS
loo{
// . ~ ~ 1 2 t30 .78 8 2 x
RESULTS Table 1 presents the clinical and laboratory data concerning the mothers, the infants, the placentas and the umbilical cords in the two groups. Smoking mothers were of lower age than non-smokers and the group contained more single women than the controls, who were nearly all married. The groups were 36-792874
r = o 984 t = 38.659 p0.05). The infants of smoking mothers had significantly lower weight and length at birth. These differences were also present when calculated for only the married women in the two groups. Weight loss after birth was equal in both groups of infants, as was the timing for the lowest weight after birth. N o difference was found on placental size (weight, diameter) between smokers and nonsmokers. Histological investigation of the placentas (25 placentas from each group) showed syncytial knots, small infarctions, small calcifications and fibrinoid necrosis of villi in most
DISCUSSION Serum thiocyanate concentrations of smoking mothers were found to be positively correlated to their smoking levels (Fig. 1). This is in accordance with other investigations (1, 20). Pregnancy did not seem to influence the thiocyanate concentration as judged from our results in non-smokers. The thiocyanate concentration of serum in smokers therefore may be used as an objective measure for the smoke exposure. However, non-smokers also have a considerable and variable amount of thiocyanate in serum, mostly caused by the thiocyanate content in food (20). This limits the accuracy of the thiocyanate concentrations reflecting the smoking level. The thiocyanate concentrations in cord blood serum were found to be nearly identical with maternal serum thiocyanate concentrations at delivery, as well as on the 4th day after delivery. Thus cord serum thiocyanate seems to reflect the mother's smoking habits in the same way as her own serum thiocyanate concentration. Whether the fetal thiocyanate level reflects only passive diffusion of thiocyanate from the mother, or also cyanide detoxication in the fetus itself, remains unknown. However, a dynamic equilibration exists between thiocyanate formed by detoxication of cyanide and reverse oxidation of thiocyanate to cyanide by enzymes present in red blood cells and other cells ( 5 ) . The
Smoking during pregnancy
fetus of smoking mothers therefore may be exposed to toxic cyanide levels in utero. The lower concentrations of thiocyanate in human milk, and the lack of correlation between serum and milk concentrations, may be due to the handling of the thiocyanate ion in the mammary gland. Thiocyanate shows a physical and chemical similarity to halogen ions, and behaves much like chloride ions in the body (20), which also are found in low concentration in human milk compared to serum concentration. There has been discussion on whether cigarette smoking acts as an exogenous factor which interferes with intra-uterine development of the fetus (1, 12, 13) or whether smoking women are a self-selected group more likely both to smoke and to have infants with lower birth weights (10). In our study the maternal serum thiocyanate levels were inversely correlated to infant birth weight, indicating that smoking itself interferes with fetal growth in a dose related manner. Similar inversity has been found in far greater series between birth weight and maternal smoking levels (12, 13). The growth retardation did not seem to be caused by differences in the two groups of nutritional factors during pregnancy (maternal weight gain), genetical potential for growth (maternal size) or marital status of the mothers. Ultrastructural changes are found in umbilical cord vessels after maternal smoking during pregnancy (3, 4) as well as in placental vessels (2). In our study we did not investigate small changes, and probably therefore were not able to show differences between smokers and non-smokers. Hypertrophy of medial smooth muscle is found in conditions associated with increased vascular resistance (1 1). If the decreased blood flow through the placenta found in smokers (19) is caused by an increased vascular resistance, it might have been reflected in hypertrophy of smooth muscle in the umbilical cord arteries. We were, however, not able to demonstrate this with the method used.
551
ACKNOWLEDGEMENTS This work is supported from The Norwegian Research Council for Science and the Humanities, and from The Norwegian Council on Cardiovascular Diseases.
REFERENCES 1. Andrews, J.: Thiocyanate and smoking in pregnancy.
Br J Obstet Gynuecol, 80: 810, 1973. 2. Asmussen, I.: Ultrastructure of the human placenta at term. Observations on placentas from newborn children of smoking and non-smoking mothers. Actu Obstet Gynecol Scand, 56: 119, 1977. 3. Asmussen, 1.: Ultrastructure of human umbilical vessels. Observations on veins from newborn children of smoking and nonsmoking mothers. Actu Obstet Gynecol Scund, 57: 253, 1978. 4. Asmussen, I . & Kjeldsen, K.: Intimal ultrastructure of human umbilical arteries. Observations on arteries from newborn children of smoking and nonsmoking mothers. Circ Res, 36: 579, 1975. 5. Chung, J. & Wood, J. L.: Oxidation of thiocyanate to cyanide catalyzed by hemoglobin. J B i d Chem, 246:555, 1971. 6. Cole, P. V . , Hawkins, L. H. & Roberts, D.: Smoking during pregnancy and its effects on the fetus. Br J Obstet Gynuecol, 79: 782, 1972. 7. Comstock, G. W., Shah, F. K., Meyer, M. B. & Abbey, H.: Low birth weight and neonatal mortality related to maternal smoking and socioeconomic status. A m J Obstet Gynecol, 111: 5 3 , 1971. 8. Dunn, H. G . , McBurney, A. K., Ingram, S. & Hunter, C . M.: Maternal ~ g a r e t t esmoking during pregnancy and the child’s subsequent development. I . Physical growth to the age of 66 years. Cun J Public Health, 67: 499, 1976. 9. Dunn, H. G . , McBurney, A. K., Ingram, S. & Hunter, C. M.: Maternal cigarette smoking during pregnancy and the child’s subsequent development. 11. Neurological and intellectual maturation to the age of 66 years. Can J Pithlic Heulth, 68: 43, 1977. 10. Hickey, R. J., Clelland, R. C. & Bowers, E. J.: Maternal smoking, birth weight, infant death, and the self-selection problem. A m J Ohstet Gynecol, 131: 805, 1978. 1 1 . Levin, D. L., Fixler, D. E., Morriss, F. C. B Tyson, J.: Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors. J Pediatr, Y2: 478, 1978. 12. MacMahon, B., Alpert, M. & Salber, E. J.: Infant weight and parental smoking habits. A m J Epidemiol, 82: 247, 1966. 13. Meyer, M. B., Jonas, B. S. & Tonascia, J . A.: Perinatal events associated with maternal smoking during pregnancy. A m J Epidemiol, 103: 464, 1976. 14. Murphy, J. F., Mulchay, R. & Drumm, J. E.: Smoking and the fetus. Lancet, If: 36, 1977. 15. Pettigrew, A. R. & Fell, G. S.: Simplified colorimetric determination of thiocyanate in biological fluids, and its application to investigation of the toxic amblyopias. CIin Chern, 18: 996, 1972.
552
A . Mebevg et al.
16. Pettigrew, A. R., Logan, R. W. & Willcocks, J.:
Smoking in pregnancy-effects on birth weight and on cyanide and thiocyanate levels in mother and baby. Br J Obstet Gynuecol, 84: 31, 1977. 17. Prigge, E. & Hochrainer, D.: Effects of carbon monoxide inhalation on erythropoiesis and cardiac hypertrophy in fetal rats. Toxicol Appl Pharmacol, 42: 225, 1977. 18. Rush, D. & Kass, E. H.: Maternal smoking: A reassessment of the association with perinatal mortality. A m J Epidemiol, 96: 183, 1972. 19. Spira, A., Fournier, R., Grob, J. C . , Dreyfus, J . & Schwartz, D.: Smoking during pregnancy and pla-
cental blood flow. Proc 6 t h Congress of Perinutul Medicine, Vienna 1978. 20. Stoa, K . F.: Studies on thiocyunute in serum. 2nd Medical Yearbook, University of Bergen, 1957. Submitted Nov. 21, 1978 Accepted Febr. 7, 1979
(A. M.) Department of Paediatrics Ullevhl Hospital Oslo Norway
