AMERICAN JOUHNALOTEPIDEMIOLOGY
Copyright © 1979 by The Johns Hopkins University School of Hygiene and Public Health All rights reserved
Vol 110, No 2 Printed in UJ5-A
GROSS DIFFERENCES OBSERVED IN THE PLACENTAS OF SMOKERS AND NONSMOKERS ROBERTA E CHRISTIANSON1 Christlanson, R. E. (Child Health and Development Studies, 3867 Howe St., Oakland, CA 94611). Gross differences observed In the placentas of smokers and nonsmokers. Am J Epidemiol 110:178-187, 1979. Gross placental characteristics of 7651 smokers and nonsmokers are compared In light of the previous finding that placentas of smokers are heavier for the weight of their fetuses than are those of nonsmokers. Subchorionlc fibrin deposits and placental calcification are more prevalent In the placentas of smokers than in those of nonsmokers. While mean placental weights and placental weight distributions for light and heavy smokers combined do not differ from those of nonsmokers, other placental measurements do differ. Smokers have thinner, rounder placentas than nonsmokers and the distance from the edge of rupture of the membranes to the placental margin Is reduced among smokers. These findings are discussed In relation to placental changes observed at high altitudes and complications of pregnancy that differ for smokers and nonsmokers. altitude; birth weight; ethnic groups; hypoxia; placenta; pregnancy complications; smoking
Although many effects of smoking on the human body are well documented, its effect on the placenta is still not clearly defined. In detailed studies on small samples, Welch et al. (1) observed differences in placental enzymes of smokers and nonsmokers while Asmussen and Kjeldsen (2) observed pronounced intimal changes in the umbilical arteries from infants delivered to women who smoked. In previous large studies the ratio of placental weight to birth weight (placental ratio) has been shown to be higher for
Received for publication August 14, 1978, and in final form January 8, 1979. 1 Child Health and Development Studies, School of Public Health, University of California, Berkeley. (Reprint requests to Child Health and Development Studies, 3867 Howe St, Oakland, CA 94611) This study was supported by grant HD07256 of the National Institute of Child Health and Human Development of NIH The author thanks Dr Kurt Benirschke, Dr. Ernest Page and Mr. Harald Kipp for their suggestions and assistance.
smokers than nonsmokers and to increase with the amount of smoking (3-5). Wilson (5) suggested that this increase might signify a response of the placenta to chronic fetal hypoxia. Similar increases in the placental ratio have been observed in conjunction with births at high altitudes, births to women suffering severe anemia, and births to women with cyanotic cardiac malformations (6-10). These similar findings in recognized states of hypoxia and the knowledge that carboxyhemoglobin levels are increased among smokers (11) support Wilson's hypothesis. To expand on these findings the present investigation examines gross differences observed in the placentas of smokers and nonsmokers who were members of a large prospective study. MATERIALS AND METHODS
The data are based on the obstetric population studied during the years 1959 to 1967 by the Child Health and De-
178
PLACENTAL DIFFERENCES BY MATERNAL SMOKING STATUS
velopment Studies (CHDS). The patients were members of the Kaiser Foundation Health Plan, a prepaid medical care program in the San Francisco East Bay Area of California. The patients represent a broad range of social, economic and educational backgrounds deficient only in the very affluent and the very indigent segments of the population. At an interview early in pregnancy, information was obtained about numerous factors including smoking habits. Women who indicated they smoked one or more cigarettes daily have been classified as smokers. Those who smoked less than 20 cigarettes per day are referred to as light smokers and those who smoked 20 or more per day are designated heavy smokers. At birth, the placentas were examined according to the Benirschke protocol for gross examination (12). Detailed macroscopic placental examinations were completed for more than 11,000 births in our cohort of some 20,000 births. Placental weight is available on another large segment of the population, but this group is not included in the present study. The availability of trained personnel was the only factor determining whether or not a detailed placental examination was done and all such examinations were done without knowledge of the information derived from interviews. The nature of many of the items included in the macroscopic placental examination does not lend itself to a high degree of precision in measurement. Such imprecision increases the variability of the measurements and makes a comparison of absolute values with other studies very difficult. However, it does not bias comparisons between smokers and nonsmokers. This analysis is based on 5699 single, white live births and 1952 single, black live births. Birth weight and length of gestation had to be known for a birth to be included in the analysis as did maternal
179
smoking habits and detailed gross placental information. RESULTS
Morphologic characteristics observed to have a consistent relationship to smoking status by our primary placental examiners and observed to be significantly different in either or both ethnic groups are shown in table 1. Since several placental indices differ for white and black women, the data are presented separately for the two ethnic groups. Repetition of similar patterns in both ethnic groups also has the advantage of giving added strength to the relationships observed. Calcification, primarily of the maternal surface, has a much higher prevalence in the placentas of smokers than nonsmokers (see table 1). Patchy subchorionic fibrin deposits also occur with greater relative frequency in the placentas of smokers. The observed increase in the prevalence of these two conditions among smokers also holds true when maternal age, gestation and birth weight are held constant. The increased prevalence of calcification and patchy subchorionic fibrin in the placentas of smokers was highly significant in both ethnic groups. Abnormal cord coloration was also observed to be significantly higher for white smokers than white nonsmokers, but the observations among black births did not support this finding. Maternal floor infarcts (a heavy deposition of fibrin producing a smooth yellowwhite maternal surface) were observed to have a higher prevalence in the placentas of nonsmokers in both ethnic groups. The differences were significant, however, only in the larger white population. Adjustments for gestational age did not alter the findings. True infarcts were also observed to occur more frequently in the placentas of white mothers who were nonsmokers, but among black births the prevalence of true infarcts did not differ with regard to maternal smoking status.
180
ROBERTA E CHRISTIAN8ON TABLE 1
Per cent of placentas observed to have certain characteristics, by mother's ethnic group and smoking status
p-value*
Nonsmoker (N = 1300)
Black Smoker (N - 652)
60.8
Copyright © 1979 by The Johns Hopkins University School of Hygiene and Public Health All rights reserved
Vol 110, No 2 Printed in UJ5-A
GROSS DIFFERENCES OBSERVED IN THE PLACENTAS OF SMOKERS AND NONSMOKERS ROBERTA E CHRISTIANSON1 Christlanson, R. E. (Child Health and Development Studies, 3867 Howe St., Oakland, CA 94611). Gross differences observed In the placentas of smokers and nonsmokers. Am J Epidemiol 110:178-187, 1979. Gross placental characteristics of 7651 smokers and nonsmokers are compared In light of the previous finding that placentas of smokers are heavier for the weight of their fetuses than are those of nonsmokers. Subchorionlc fibrin deposits and placental calcification are more prevalent In the placentas of smokers than in those of nonsmokers. While mean placental weights and placental weight distributions for light and heavy smokers combined do not differ from those of nonsmokers, other placental measurements do differ. Smokers have thinner, rounder placentas than nonsmokers and the distance from the edge of rupture of the membranes to the placental margin Is reduced among smokers. These findings are discussed In relation to placental changes observed at high altitudes and complications of pregnancy that differ for smokers and nonsmokers. altitude; birth weight; ethnic groups; hypoxia; placenta; pregnancy complications; smoking
Although many effects of smoking on the human body are well documented, its effect on the placenta is still not clearly defined. In detailed studies on small samples, Welch et al. (1) observed differences in placental enzymes of smokers and nonsmokers while Asmussen and Kjeldsen (2) observed pronounced intimal changes in the umbilical arteries from infants delivered to women who smoked. In previous large studies the ratio of placental weight to birth weight (placental ratio) has been shown to be higher for
Received for publication August 14, 1978, and in final form January 8, 1979. 1 Child Health and Development Studies, School of Public Health, University of California, Berkeley. (Reprint requests to Child Health and Development Studies, 3867 Howe St, Oakland, CA 94611) This study was supported by grant HD07256 of the National Institute of Child Health and Human Development of NIH The author thanks Dr Kurt Benirschke, Dr. Ernest Page and Mr. Harald Kipp for their suggestions and assistance.
smokers than nonsmokers and to increase with the amount of smoking (3-5). Wilson (5) suggested that this increase might signify a response of the placenta to chronic fetal hypoxia. Similar increases in the placental ratio have been observed in conjunction with births at high altitudes, births to women suffering severe anemia, and births to women with cyanotic cardiac malformations (6-10). These similar findings in recognized states of hypoxia and the knowledge that carboxyhemoglobin levels are increased among smokers (11) support Wilson's hypothesis. To expand on these findings the present investigation examines gross differences observed in the placentas of smokers and nonsmokers who were members of a large prospective study. MATERIALS AND METHODS
The data are based on the obstetric population studied during the years 1959 to 1967 by the Child Health and De-
178
PLACENTAL DIFFERENCES BY MATERNAL SMOKING STATUS
velopment Studies (CHDS). The patients were members of the Kaiser Foundation Health Plan, a prepaid medical care program in the San Francisco East Bay Area of California. The patients represent a broad range of social, economic and educational backgrounds deficient only in the very affluent and the very indigent segments of the population. At an interview early in pregnancy, information was obtained about numerous factors including smoking habits. Women who indicated they smoked one or more cigarettes daily have been classified as smokers. Those who smoked less than 20 cigarettes per day are referred to as light smokers and those who smoked 20 or more per day are designated heavy smokers. At birth, the placentas were examined according to the Benirschke protocol for gross examination (12). Detailed macroscopic placental examinations were completed for more than 11,000 births in our cohort of some 20,000 births. Placental weight is available on another large segment of the population, but this group is not included in the present study. The availability of trained personnel was the only factor determining whether or not a detailed placental examination was done and all such examinations were done without knowledge of the information derived from interviews. The nature of many of the items included in the macroscopic placental examination does not lend itself to a high degree of precision in measurement. Such imprecision increases the variability of the measurements and makes a comparison of absolute values with other studies very difficult. However, it does not bias comparisons between smokers and nonsmokers. This analysis is based on 5699 single, white live births and 1952 single, black live births. Birth weight and length of gestation had to be known for a birth to be included in the analysis as did maternal
179
smoking habits and detailed gross placental information. RESULTS
Morphologic characteristics observed to have a consistent relationship to smoking status by our primary placental examiners and observed to be significantly different in either or both ethnic groups are shown in table 1. Since several placental indices differ for white and black women, the data are presented separately for the two ethnic groups. Repetition of similar patterns in both ethnic groups also has the advantage of giving added strength to the relationships observed. Calcification, primarily of the maternal surface, has a much higher prevalence in the placentas of smokers than nonsmokers (see table 1). Patchy subchorionic fibrin deposits also occur with greater relative frequency in the placentas of smokers. The observed increase in the prevalence of these two conditions among smokers also holds true when maternal age, gestation and birth weight are held constant. The increased prevalence of calcification and patchy subchorionic fibrin in the placentas of smokers was highly significant in both ethnic groups. Abnormal cord coloration was also observed to be significantly higher for white smokers than white nonsmokers, but the observations among black births did not support this finding. Maternal floor infarcts (a heavy deposition of fibrin producing a smooth yellowwhite maternal surface) were observed to have a higher prevalence in the placentas of nonsmokers in both ethnic groups. The differences were significant, however, only in the larger white population. Adjustments for gestational age did not alter the findings. True infarcts were also observed to occur more frequently in the placentas of white mothers who were nonsmokers, but among black births the prevalence of true infarcts did not differ with regard to maternal smoking status.
180
ROBERTA E CHRISTIAN8ON TABLE 1
Per cent of placentas observed to have certain characteristics, by mother's ethnic group and smoking status
p-value*
Nonsmoker (N = 1300)
Black Smoker (N - 652)
60.8
