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Adolescent coitus and infant birthweight
JOURNALOF ADOLESCENTHEALTHCARE1986;7:96-100
Adolescent Coitus and Infant Birthweight E L I Z A B E T H R. M c A N A R N E Y I M . D . ~ C Y N T H I A A. BAYER~ R . N . i B.S. C H R I S T I N E F. K O G U T / R . N . I B . S . r M A R Y G. S I L V E R M A N r R . N . ~ B.S. A N D H O W A R D P. IKERI P H . D .
Seventy-nine percent of a group of adolescent mothers reported coitus during pregnancy. There was a significant difference between the mean birthweight and gestational age of infants born to mothers who reported coitus within 90 days of delivery compared to the mean birthweight and gestational age of infants of mothers who reported no coitus within 90 days of delivery. Thirty-nine percent of the variance in birthweight was explained by maternal factors alone, but only 1.0% of the variance in birthweight was accounted for by the interval between last coitus and delivery. Prepregnancy weight (r = 0.380)and weight gain during pregnancy (r = 0.327) contributed 19.1% and 7.4% of the variance in birthweight, respectively.
KEYWORDS: Pregnancy Coitus Infants of adolescents Adolescents bear proportionately more low-birthweight infants than adults. Fourteen percent of infants born to mothers < 15 years old weigh -< 2,500 g compared to 9.9% of infants born to w o m e n aged 1519 years and 6.5% of infants born to w o m e n aged 2029 years (1). These infants born to adolescents are primarily premature babies, i.e., having gestations < 38 weeks (2). There is evidence that prenatal care of adolescent mothers (3) and particularly the very young adolescent mother (4) improves neonatal outcome, a s reflected by the birth of fewer small infants.
From the Division of General Pediatrics and Adolescent Medicine, University of Rochester Medical Center, Strong Memorial Hospital, Rochester, New York. Address correspondence to: Elizabeth R. McAnarriey, M.D., Box 690, 601 Elmwood Avenue, Rochester, N Y 14642. Manuscript accepted April 19, 1985.
96 0197-0070/86/$3.50
There are still questions, however, about the relative contribution of adolescent maternal factors to birthweight (5), including low birthweight associated with coitus late in pregnancy (6). In an effort to understand more about the possible relationship of coitus late in pregnancy and the etiology of low birthweight of the infants of adolescents, we posed the following questions. 1. What percentage of adolescents enrolled in an adolescent maternity project will report that they have had coitus during pregnancy? 2. Is there a relationship between the interval in day s between their last coitus, delivery date, and the birthweight of infants of adolescents? 3. What is the relative contribution of coitus during pregnancY (when considered with other maternal factors) to the birthweight of infants of adolescents?
Methods
Subjects
The subjects for this study were 99 consecutive adolescents w h o received prenatal care in the Rochester Adolescent Maternity Project (RAMP) between August 1980 and December 1981 and their infants. The mean age of the mothers was 16.9 years (range 14:0M9.4 years). Sixty-three (64%) were nonwhite (of w h o m 95% were black) and 36 (36%) were white. Sixth-three (64%) were of lower socioeconomic status and 36 (36%) were of lower middle socioeconomic status, making a total of 100% Who were lower or lower middle socioeconomic status. Eighty-four (85%) were primiparous; and the remaining 15 (15%) were carrying their second preg-
©Societyfor AdolescentMedicine,1986 Publishedby ElsevierSciencePublishingCo., Inc., 52VanderbiltAve.,NewYork,NY10017
MARCH 1986
nancy. Eighty-two (82%) of the infants weighed - 2500 g and 17 (18%) weighed < 2500 g. The mean birthweight of the infants was 3088.2 g (range 8504960 g) and mean gestational age was 38.6 weeks (range 27-42 weeks). The methods for this study included semistructured interviews and chart reviews. Semistructured Interviews
As part of the routine postpartum in-hospital health assessment and instruction conducted by the adolescents' primary nurses, data were sought from semistructured interviews about the adolescents' coital activity during pregnancy and the interval between last coitus and delivery. Data were sougt~t about frequency of coitus and orgasm during pregnancy, but the findings w e r e so inconsistent that we dropped these variables from the analysis. It was not clear whether the adolescents understood what orgasm was, even though the nurses used several descriptors. Chart Reviews
The chart of each subject was reviewed by her primary nurse after delivery. Demographic data included maternal age, socioeconomic status, race, and changes in living situation. Obstetric and medical data included parity, prepregnancy weight, weight gain during pregnancy, Substance use icigarettes smoked, alcohol ingested, marijuana smoked, cocaine and heroin used) per day, and cervical infections (primarily gonococcal disease). We were unable to document nongonococcal cervical infections as our laboratory did not have the capability of pr o cessing such cultures at the time of the study. Neonatal data included birthweight and gestational age, which was defined by the average of menstrual dating and Dubowitz scoring. Data Analysis
The initial step in the data analysis was to determine the percentage of adolescents who reported coitus during pregnancy. Subjects were then divided into those who had and those who had not had coitus within the last trimester of pregnancy (within 90 days of delivery). Differences in birthweight and gestational age between the two groups were examined by t-test. Chi-square analyses were also used. There were 92 subjects for these analyses as seven adolescents could not recall the date of last coitus before delivery.
ADOLESCENTCOITUSAND INFANTBIRTHWEIGHT
97
The next step in data analysis was a multivariate analysis using a simultaneous multiple regression procedure. First, using the continuous variables of gestational age, interval between last coitus and delivery, and Seven maternal factors as independent variables, we initially determined the independent contribution of each to the dependent measure of birthweight: The seven factors were: prepregnancy weight (7), weight gain during pregnancy (7), smoking frequency (8), drug frequency (9), race (10), cervical infections, and living changes. Socioeconomic status (11), maternal age (1), and parity (12) were also recorded, but these variables were removed because they had minimal variability. Second, we dropped the gestational age variable and repeated the multiple regression analysis with only the eight maternal factors. Complete data on all of these factors were available for a total of 84 subjects, and these patients comprised the pool on which the multiple regressions were computed. The loss of the eight subjects, for w h o m data were incomplete, did not significantly change the mean maternal age or mean birthweight. The Pearson correlation of the original 92 subjects was 0.190 for the interval between last coitus and delivery and birthweight compared to 0.161 for the 84 subjects who had complete data available. The percent of variance of birthweight accounted for each of the eight maternal factors was calculated using squared semipartial correlation. The Statistical Package for the Social Sciences (SPSS) was used.
Results Seventy-nine percent of the study population reported coitus during pregnancy. The mean interval between last coitus and delivery was 106.4 days with a standard deviation of 99.7. Seventy-one percent of those reporting coitus stated that it occurred within 90 days of delivery. Table 1 shows the mean birthweight of w o m e n grouped by interval between last coitus and delivery. Table 1. Birthweight as a Function of Interval Between Last Coitus to Delivery (n = 92)
Days between last coitus to delivery
Birthweight (g)
Standard error
1-7 8-30 31-90 90+
2920.3 2914.4 3051.5 3245.8
147.1 156.3 175.7 84.1
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McANARNEY ET AL.
JOURNAL OF ADOLESCENT HEALTH CARE Vol. 7, No. 2
Table 2. Birthweight and Gestational Age as a Function of Last-Trimester Coitus (n = 92) Within 90 days of delivery (n = 55)
Not within 90 days of delivery (n = 37)
2,962.1 92.3 38.2 0.4
Birthweight (g) Mean standard error Gestational age Mean Standard error
t
p
3,245.8 84.1
2.272
< 0.03
39.3 0.2
2.460
< 0.03
These differences were not significantly different. As noted in Table 2, h6wever, there was a significant difference between the mean birthweight and the mean gestational age of infants of mothers who reported coitus within 90 days of delivery compared to the infants of mothers who reported no coitus within 90 days of delivery. Twelve percent of adolescents who reported coitus within 90 days of delivery, compared to 8% who reported no coitus within 90 days of delivery, had infants weighing < 2500 g and having a gestational age of < 38 weeks. This difference was not significantly different. On multivariate analysis, interval between last coitus and delivery was neither significantly Correlated with birthweight (r = 0.161) nor gestational age (r = 0.181). Prepregnancy weight (r = 0.380) and weight gain during pregnancy (r = 0.327) were both significantly correlated with birthweight (Table 3). Gestational age accounted for 52.0% of the variance in birthweight, and the eight maternal factors accounted for 13.0% of the variance. Less than 1% of the variance in birthweight was accounted for by the interval between last coitus and delivery. Because gestational age and birthweight were so highly correlated (r = 0.731, p < 0.0005), we elimi-
nated gestational age to examine the relationship between the eight maternal factors and birthweight. The multiple correlation was 0.6248 (p < 0.001) with 39.0% of the variance in birthweight accounted for by the combination of these eight maternal factors alone (Table 3). Interval between last coitus and delivery accounted for only 1.0% of the variance and was not significant. Prepregnancy weight accounted for 19,1%, weight gain 7.4%, smoking frequency 5.0%, and race 3.9% of the variance. These last four variables made contributions significant at or beyond p < 0.030. The combination of the four significant variables accounted for 35.4% of the variance or 91.0% of the total 39.0% of variance accounted for by maternal factors. The results of the multiple regression of the dichotomous variable were essentially identical to that of the initial multiple regression analysis. The birthweights did not differ On average by more than 0.006 R2 thus showing a change of 0.4%. Consequently, coitus did not contribute significantly to the variance in birthweight in any of the multiple regression analyses.
Discussion We investigated adolescent coitus and its potential relationship to infant birthweight in an effort to find potentially preventable causes of prematurity in the infants of adolescents. Our interest in this potential relationship was based on a series of studies from the adult literature in which there was a diversity of opinion as to whether coitus late in pregnancy was related to prematurity. Goodlin and Colleagues (13) reported that 50% of the study w o m e n who delivered prematurely had experienced orgasm after 32 weeks of pregnancy compared to 24% of the w o m e n who delivered at
Table 3. Relationships Between Maternal Factors and Birthweight (n = 84) Bivariate correlation
Multiple correlation
Variable
Simple r
p
Birthweight
Variance (%)
Prepregnancy weight Weight gain Smoking Race Cervical infections Living changes Coitus to delivery Drugs ,
0.380 0.327 -0.162 0.148 -0.103 0.041 0.161 -0.150
<0.02 0.02 0.11 0.15 0.20 0.89 0.11 0.13
0.448 0.282 -0.289 0.241 -0.141 0.121 0.119 -0.042
19.1 7.4 5.0 3.9 1.8 1.1 1.0 0.0
Multiple R = 0.6248 (dr = 8,75); p < 0.001; R2 = 0.3904.
<0.001 0.008 0.025 0.030 0.130 0.220 0.220 0.999
MARCH 1986
full-term. A potentially confounding variable in this study was that those mothers who delivered prematurely experienced less weight gain during pregnancy than those who did not. In another study, Pugh and Fernandez (14) stated: "An application of the "t" test to the average time of coitus of the cases exhibiting premature labor, compared with all other cases, revealed a statistically significant difference" (p. 640). The authors thought that a cause and effect relationship between coitus and premature birth was unlikely as the mean time of last coitus was 48 days prior to delivery. In a retrospective study, Rayburn and Wilson (6) reported that there were no differences between two groups (those who delivered prematurely and those who delivered at term) regarding the percentage who were coitally active within the previous week before either delivery or interview, the average frequency of coitus within the previous week, or the incidence of orgasm during pregnancy. Perkins, in a retrospective study (15), reported no significant association between coitus and orgasm and the proximity to delivery for the study population. The majority of pregnant adolescents in our study reported coitus during pregnancy and of these 71% were active within 90 days of delivery. The mean interval between last coitus and delivery was 106.4 days, more than twice the mean of 48 days reported for 15-19-year-old primiparous w o m e n studied by Pugh and Fernandez (14). In Pugh and Fernandez' sample, the mean was 71 days for all unmarried females and 72 days for all black, primiparous females. Thus, even though the majority of adolescents in our study were unmarried, black, and primiparous, our patients on the average had almost twice the interval in days between last coitus and delivery as Pugh and Fernandez' sample. This difference may be due to a difference in the mean age of the two groups as, on the average, younger adolescents have a lower frequency of coitus than older adolescents (16). In our study, the infants of adolescent mothers who reported coitus within 90 days of delivery were significantly smaller and had lower gestational ages than the infants of mothers not reporting coitus within the same period before delivery. On further analysis, these findings become less striking. That is, there was no difference in the percentage of premature births (< 2500 g and < 38 weeks gestation) among those adolescents who reported coitus within 90 days and those who did not. When the interval between last coitus and delivery was considered with seven other maternal factors known to be associated
ADOLESCENTCOITUSAND INFANTBIRTHWEIGHT
99
with low birthweight (7-12), the coital variable accounted for a negligible percent of the variance in birthweight. As found by others, prepregnancy weight (7), weight gain during pregnancy (7), smoking frequency (8), and race (10) were the major maternal factors accounting for the variance in birthweight. The methodologic challenges of a study of the potential relationship of coitus late in pregnancy in adolescents to the birthweight of their infants are major. As is true of the majority of completely (6,14,15,17) or partially retrospective (13), studies regarding the birthweight question in adults, standardization of the time of interview may be an important consideration of the method regardless of whether the study is retrospective or prospective. Inquiry about sensitive, personal data such as coitus and orgasm can be problematic, particularly with adolescents. Their primary nurses, with w h o m they had established rapport in the ambulatory setting, conducted the interviews. Compliance was 100% and in fact several adolescents requested their interview with their nurse before they were actually scheduled for an interview. A major limitation in the completeness of our data was our inability to obtain consistent data about the frequency of coitus and orgasm, the latter of which some adolescents did not seem to understand, despite the nurses' attempts to use words they might comprehend. We concluded that coitus alone during pregnancy in adolescents does not account for a significant amount of the variance in infant birthweight. Promising leads in determining the etiology of low birthweight of the infants of adolescents are weight gain during pregnancy (7) and smoking (8).
Summary The majority of pregnant adolescents in one adolescent maternity project reported they were coitally active during their pregnancy. Even though there was a significant difference between the mean birthweight and gestational age of infants born to mothers who reported coitus within 90 days of delivery compared to mothers who reported no coitus within 90 days of delivery, the interval between the last coitus and delivery accounted for only 1.0% of the variance in infant birthweight w h e n the relationship of several other maternal factors to infant birthweight was also considered. Prepregnancy weight and weight gain during pregnancy accounted for more of the variance than any other maternal factors examined.
100
McANARNEYET AL.
Support of this research was made possible by Gerber Medical Grant-in-Aidand Robert Wood Johnson Foundation Grant #7265 and #7886. The consultations of Dr. Marilyn J. Aten and Dr. Henry N. Ricciuti are gratefully acknowledged.
References 1. Stickle G. Overview of incidence, risks, and consequences of adolescent pregnancy and childbearing. In McAnarney ER, Stickle G, eds. Pregnancy and childbearing during adolescence: Research priorities for the 1980's. New York: Alan R. Liss, Inc., 1981;9. 2. Hoffman HJ, Lundin FE, Bakketeig LS, et al. Classification of births by weight and gestational age for future studies of prematurity. In Reed DM, Stanley FJ, eds. The epidemiology of prematurity. Baltimore, MD: Urban and Schwarzenberg, 1977;310. 3. McAnarney ER, Roghmann KJ, Charney E, et al. A comparison of obstetric, neonatal and psychosocial outcome of pregnant adolescents. Pediatrics 1978;61:199-205. 4. Felice M, Granados JJ, Ances IG, et al. The young pregnant teenager: Impact of comprehensive prenatal care. J Adol Health Care 1981;1:193-7. 5. Zuckerman B, Alpert JJ, Dooling E, et al. Neonatal outcome: Is adolescent pregnancy a risk factor? Pediatrics 1983;71:489-93. 6. Rayburn WF, Wilson EA. Coital activity and premature delivery. Am J Obstet Gynecol 1980;137:972-4.
JOURNAL OF ADOLESCENT HEALTH CARE Vol. 7, No. 2
7. Garn SM, Petzold AS. Characteristics of the mother and child in teenage pregnancy. Am J Dis Child 1983;137:365-8. 8. Meyer MD, Tonascia JA. Maternal smoking, pregnancy complications, and perinatal mortality. Am J Obstet Gynecol 1977;128:494-502. 9. Ouelette EM, Rosett HL, Rosman HP, et al. Adverse effects of maternal alcohol abuse during pregnancy. N Engl J Med 1977;297:528-30. 10. Advance Report of Final Natality Statistics, 1981. Monthly Vital Statistics Report, National Center for Health Statistics, December 29, 1983;32(9):5. 11. Shapiro S. New reductions in infant mortality: The challenge of low birthweight. Am J Public Health 1981;71:365-6. 12. Jekel J, Harrison JT, Bancroft DRE, et al. A comparison of the health of index and subsequent babies born to school-age mothers. Am J Public Health 1975;65:370-4. 13. Goodlin RC, Keller DW, Raffin M. Orgasm during late pregnancy: Possible deleterious effects. Obstet Gynecol 1971; 38:916-20. 14. Pugh WE, Fernandez FL. Coitus in late pregnancy: A followup study of the effects of coitus on late pregnancy, delivery, and the puerperium. Obstet Gynecol 1953;2:636-42. 15. Perkins RP. Sexual behavior and response in relation to complications of pregnancy. Am J Obstet Gynecol 1979;134:498505. 16. Kantner JF, Zelnik M. Sexual experience of young unmarried women in the United States. Fam Plann Perspect 1972;4:9-18. 17. Wagner NN, Butler JC, SandersJP. Prematurity and orgasmic coitus during pregnancy: Data on a small sample. Fertil Steril 1976;27:911-15.
Adolescent Coitus and Infant Birthweight E L I Z A B E T H R. M c A N A R N E Y I M . D . ~ C Y N T H I A A. BAYER~ R . N . i B.S. C H R I S T I N E F. K O G U T / R . N . I B . S . r M A R Y G. S I L V E R M A N r R . N . ~ B.S. A N D H O W A R D P. IKERI P H . D .
Seventy-nine percent of a group of adolescent mothers reported coitus during pregnancy. There was a significant difference between the mean birthweight and gestational age of infants born to mothers who reported coitus within 90 days of delivery compared to the mean birthweight and gestational age of infants of mothers who reported no coitus within 90 days of delivery. Thirty-nine percent of the variance in birthweight was explained by maternal factors alone, but only 1.0% of the variance in birthweight was accounted for by the interval between last coitus and delivery. Prepregnancy weight (r = 0.380)and weight gain during pregnancy (r = 0.327) contributed 19.1% and 7.4% of the variance in birthweight, respectively.
KEYWORDS: Pregnancy Coitus Infants of adolescents Adolescents bear proportionately more low-birthweight infants than adults. Fourteen percent of infants born to mothers < 15 years old weigh -< 2,500 g compared to 9.9% of infants born to w o m e n aged 1519 years and 6.5% of infants born to w o m e n aged 2029 years (1). These infants born to adolescents are primarily premature babies, i.e., having gestations < 38 weeks (2). There is evidence that prenatal care of adolescent mothers (3) and particularly the very young adolescent mother (4) improves neonatal outcome, a s reflected by the birth of fewer small infants.
From the Division of General Pediatrics and Adolescent Medicine, University of Rochester Medical Center, Strong Memorial Hospital, Rochester, New York. Address correspondence to: Elizabeth R. McAnarriey, M.D., Box 690, 601 Elmwood Avenue, Rochester, N Y 14642. Manuscript accepted April 19, 1985.
96 0197-0070/86/$3.50
There are still questions, however, about the relative contribution of adolescent maternal factors to birthweight (5), including low birthweight associated with coitus late in pregnancy (6). In an effort to understand more about the possible relationship of coitus late in pregnancy and the etiology of low birthweight of the infants of adolescents, we posed the following questions. 1. What percentage of adolescents enrolled in an adolescent maternity project will report that they have had coitus during pregnancy? 2. Is there a relationship between the interval in day s between their last coitus, delivery date, and the birthweight of infants of adolescents? 3. What is the relative contribution of coitus during pregnancY (when considered with other maternal factors) to the birthweight of infants of adolescents?
Methods
Subjects
The subjects for this study were 99 consecutive adolescents w h o received prenatal care in the Rochester Adolescent Maternity Project (RAMP) between August 1980 and December 1981 and their infants. The mean age of the mothers was 16.9 years (range 14:0M9.4 years). Sixty-three (64%) were nonwhite (of w h o m 95% were black) and 36 (36%) were white. Sixth-three (64%) were of lower socioeconomic status and 36 (36%) were of lower middle socioeconomic status, making a total of 100% Who were lower or lower middle socioeconomic status. Eighty-four (85%) were primiparous; and the remaining 15 (15%) were carrying their second preg-
©Societyfor AdolescentMedicine,1986 Publishedby ElsevierSciencePublishingCo., Inc., 52VanderbiltAve.,NewYork,NY10017
MARCH 1986
nancy. Eighty-two (82%) of the infants weighed - 2500 g and 17 (18%) weighed < 2500 g. The mean birthweight of the infants was 3088.2 g (range 8504960 g) and mean gestational age was 38.6 weeks (range 27-42 weeks). The methods for this study included semistructured interviews and chart reviews. Semistructured Interviews
As part of the routine postpartum in-hospital health assessment and instruction conducted by the adolescents' primary nurses, data were sought from semistructured interviews about the adolescents' coital activity during pregnancy and the interval between last coitus and delivery. Data were sougt~t about frequency of coitus and orgasm during pregnancy, but the findings w e r e so inconsistent that we dropped these variables from the analysis. It was not clear whether the adolescents understood what orgasm was, even though the nurses used several descriptors. Chart Reviews
The chart of each subject was reviewed by her primary nurse after delivery. Demographic data included maternal age, socioeconomic status, race, and changes in living situation. Obstetric and medical data included parity, prepregnancy weight, weight gain during pregnancy, Substance use icigarettes smoked, alcohol ingested, marijuana smoked, cocaine and heroin used) per day, and cervical infections (primarily gonococcal disease). We were unable to document nongonococcal cervical infections as our laboratory did not have the capability of pr o cessing such cultures at the time of the study. Neonatal data included birthweight and gestational age, which was defined by the average of menstrual dating and Dubowitz scoring. Data Analysis
The initial step in the data analysis was to determine the percentage of adolescents who reported coitus during pregnancy. Subjects were then divided into those who had and those who had not had coitus within the last trimester of pregnancy (within 90 days of delivery). Differences in birthweight and gestational age between the two groups were examined by t-test. Chi-square analyses were also used. There were 92 subjects for these analyses as seven adolescents could not recall the date of last coitus before delivery.
ADOLESCENTCOITUSAND INFANTBIRTHWEIGHT
97
The next step in data analysis was a multivariate analysis using a simultaneous multiple regression procedure. First, using the continuous variables of gestational age, interval between last coitus and delivery, and Seven maternal factors as independent variables, we initially determined the independent contribution of each to the dependent measure of birthweight: The seven factors were: prepregnancy weight (7), weight gain during pregnancy (7), smoking frequency (8), drug frequency (9), race (10), cervical infections, and living changes. Socioeconomic status (11), maternal age (1), and parity (12) were also recorded, but these variables were removed because they had minimal variability. Second, we dropped the gestational age variable and repeated the multiple regression analysis with only the eight maternal factors. Complete data on all of these factors were available for a total of 84 subjects, and these patients comprised the pool on which the multiple regressions were computed. The loss of the eight subjects, for w h o m data were incomplete, did not significantly change the mean maternal age or mean birthweight. The Pearson correlation of the original 92 subjects was 0.190 for the interval between last coitus and delivery and birthweight compared to 0.161 for the 84 subjects who had complete data available. The percent of variance of birthweight accounted for each of the eight maternal factors was calculated using squared semipartial correlation. The Statistical Package for the Social Sciences (SPSS) was used.
Results Seventy-nine percent of the study population reported coitus during pregnancy. The mean interval between last coitus and delivery was 106.4 days with a standard deviation of 99.7. Seventy-one percent of those reporting coitus stated that it occurred within 90 days of delivery. Table 1 shows the mean birthweight of w o m e n grouped by interval between last coitus and delivery. Table 1. Birthweight as a Function of Interval Between Last Coitus to Delivery (n = 92)
Days between last coitus to delivery
Birthweight (g)
Standard error
1-7 8-30 31-90 90+
2920.3 2914.4 3051.5 3245.8
147.1 156.3 175.7 84.1
98
McANARNEY ET AL.
JOURNAL OF ADOLESCENT HEALTH CARE Vol. 7, No. 2
Table 2. Birthweight and Gestational Age as a Function of Last-Trimester Coitus (n = 92) Within 90 days of delivery (n = 55)
Not within 90 days of delivery (n = 37)
2,962.1 92.3 38.2 0.4
Birthweight (g) Mean standard error Gestational age Mean Standard error
t
p
3,245.8 84.1
2.272
< 0.03
39.3 0.2
2.460
< 0.03
These differences were not significantly different. As noted in Table 2, h6wever, there was a significant difference between the mean birthweight and the mean gestational age of infants of mothers who reported coitus within 90 days of delivery compared to the infants of mothers who reported no coitus within 90 days of delivery. Twelve percent of adolescents who reported coitus within 90 days of delivery, compared to 8% who reported no coitus within 90 days of delivery, had infants weighing < 2500 g and having a gestational age of < 38 weeks. This difference was not significantly different. On multivariate analysis, interval between last coitus and delivery was neither significantly Correlated with birthweight (r = 0.161) nor gestational age (r = 0.181). Prepregnancy weight (r = 0.380) and weight gain during pregnancy (r = 0.327) were both significantly correlated with birthweight (Table 3). Gestational age accounted for 52.0% of the variance in birthweight, and the eight maternal factors accounted for 13.0% of the variance. Less than 1% of the variance in birthweight was accounted for by the interval between last coitus and delivery. Because gestational age and birthweight were so highly correlated (r = 0.731, p < 0.0005), we elimi-
nated gestational age to examine the relationship between the eight maternal factors and birthweight. The multiple correlation was 0.6248 (p < 0.001) with 39.0% of the variance in birthweight accounted for by the combination of these eight maternal factors alone (Table 3). Interval between last coitus and delivery accounted for only 1.0% of the variance and was not significant. Prepregnancy weight accounted for 19,1%, weight gain 7.4%, smoking frequency 5.0%, and race 3.9% of the variance. These last four variables made contributions significant at or beyond p < 0.030. The combination of the four significant variables accounted for 35.4% of the variance or 91.0% of the total 39.0% of variance accounted for by maternal factors. The results of the multiple regression of the dichotomous variable were essentially identical to that of the initial multiple regression analysis. The birthweights did not differ On average by more than 0.006 R2 thus showing a change of 0.4%. Consequently, coitus did not contribute significantly to the variance in birthweight in any of the multiple regression analyses.
Discussion We investigated adolescent coitus and its potential relationship to infant birthweight in an effort to find potentially preventable causes of prematurity in the infants of adolescents. Our interest in this potential relationship was based on a series of studies from the adult literature in which there was a diversity of opinion as to whether coitus late in pregnancy was related to prematurity. Goodlin and Colleagues (13) reported that 50% of the study w o m e n who delivered prematurely had experienced orgasm after 32 weeks of pregnancy compared to 24% of the w o m e n who delivered at
Table 3. Relationships Between Maternal Factors and Birthweight (n = 84) Bivariate correlation
Multiple correlation
Variable
Simple r
p
Birthweight
Variance (%)
Prepregnancy weight Weight gain Smoking Race Cervical infections Living changes Coitus to delivery Drugs ,
0.380 0.327 -0.162 0.148 -0.103 0.041 0.161 -0.150
<0.02 0.02 0.11 0.15 0.20 0.89 0.11 0.13
0.448 0.282 -0.289 0.241 -0.141 0.121 0.119 -0.042
19.1 7.4 5.0 3.9 1.8 1.1 1.0 0.0
Multiple R = 0.6248 (dr = 8,75); p < 0.001; R2 = 0.3904.
<0.001 0.008 0.025 0.030 0.130 0.220 0.220 0.999
MARCH 1986
full-term. A potentially confounding variable in this study was that those mothers who delivered prematurely experienced less weight gain during pregnancy than those who did not. In another study, Pugh and Fernandez (14) stated: "An application of the "t" test to the average time of coitus of the cases exhibiting premature labor, compared with all other cases, revealed a statistically significant difference" (p. 640). The authors thought that a cause and effect relationship between coitus and premature birth was unlikely as the mean time of last coitus was 48 days prior to delivery. In a retrospective study, Rayburn and Wilson (6) reported that there were no differences between two groups (those who delivered prematurely and those who delivered at term) regarding the percentage who were coitally active within the previous week before either delivery or interview, the average frequency of coitus within the previous week, or the incidence of orgasm during pregnancy. Perkins, in a retrospective study (15), reported no significant association between coitus and orgasm and the proximity to delivery for the study population. The majority of pregnant adolescents in our study reported coitus during pregnancy and of these 71% were active within 90 days of delivery. The mean interval between last coitus and delivery was 106.4 days, more than twice the mean of 48 days reported for 15-19-year-old primiparous w o m e n studied by Pugh and Fernandez (14). In Pugh and Fernandez' sample, the mean was 71 days for all unmarried females and 72 days for all black, primiparous females. Thus, even though the majority of adolescents in our study were unmarried, black, and primiparous, our patients on the average had almost twice the interval in days between last coitus and delivery as Pugh and Fernandez' sample. This difference may be due to a difference in the mean age of the two groups as, on the average, younger adolescents have a lower frequency of coitus than older adolescents (16). In our study, the infants of adolescent mothers who reported coitus within 90 days of delivery were significantly smaller and had lower gestational ages than the infants of mothers not reporting coitus within the same period before delivery. On further analysis, these findings become less striking. That is, there was no difference in the percentage of premature births (< 2500 g and < 38 weeks gestation) among those adolescents who reported coitus within 90 days and those who did not. When the interval between last coitus and delivery was considered with seven other maternal factors known to be associated
ADOLESCENTCOITUSAND INFANTBIRTHWEIGHT
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with low birthweight (7-12), the coital variable accounted for a negligible percent of the variance in birthweight. As found by others, prepregnancy weight (7), weight gain during pregnancy (7), smoking frequency (8), and race (10) were the major maternal factors accounting for the variance in birthweight. The methodologic challenges of a study of the potential relationship of coitus late in pregnancy in adolescents to the birthweight of their infants are major. As is true of the majority of completely (6,14,15,17) or partially retrospective (13), studies regarding the birthweight question in adults, standardization of the time of interview may be an important consideration of the method regardless of whether the study is retrospective or prospective. Inquiry about sensitive, personal data such as coitus and orgasm can be problematic, particularly with adolescents. Their primary nurses, with w h o m they had established rapport in the ambulatory setting, conducted the interviews. Compliance was 100% and in fact several adolescents requested their interview with their nurse before they were actually scheduled for an interview. A major limitation in the completeness of our data was our inability to obtain consistent data about the frequency of coitus and orgasm, the latter of which some adolescents did not seem to understand, despite the nurses' attempts to use words they might comprehend. We concluded that coitus alone during pregnancy in adolescents does not account for a significant amount of the variance in infant birthweight. Promising leads in determining the etiology of low birthweight of the infants of adolescents are weight gain during pregnancy (7) and smoking (8).
Summary The majority of pregnant adolescents in one adolescent maternity project reported they were coitally active during their pregnancy. Even though there was a significant difference between the mean birthweight and gestational age of infants born to mothers who reported coitus within 90 days of delivery compared to mothers who reported no coitus within 90 days of delivery, the interval between the last coitus and delivery accounted for only 1.0% of the variance in infant birthweight w h e n the relationship of several other maternal factors to infant birthweight was also considered. Prepregnancy weight and weight gain during pregnancy accounted for more of the variance than any other maternal factors examined.
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Support of this research was made possible by Gerber Medical Grant-in-Aidand Robert Wood Johnson Foundation Grant #7265 and #7886. The consultations of Dr. Marilyn J. Aten and Dr. Henry N. Ricciuti are gratefully acknowledged.
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