lnr J Gpm~l
Obsr~~r. 1991. 36: 23-27
International
Federation
Determinants Antilles H.I.J. Wildschut”
(Received
March
23rd.
23
of Gynecology
and Obstetrics
of preterm birth in CuraCao, Netherlands and T.J. Petersb
1990)
(Revised and accepted August 30th.
1990)
Abstract In order to identtfy risk factors for preterm birth in singletons, data from a populutionbased case control survey on the island of Curacao were re-analysed. Both medical and sociodemogruphic variables were examined. Overall, a history of previous preterm birth and severe hypertension during the index pregnuncy were indicators of adverse pregnancy outcome, in terms of preterm birth. The contribution of sociodemographic factors to the risk of preterm birth is relatively low.
Preterm birth; Poor obstetric history; Hypertension; Marital status; Socioeconomic status; West Indies. Keywords:
Introduction It is widely recognized that preterm birth (PTB) is a major determinant of fetal and neonatal mortality, short-term morbidity and long-term morbidity, in particular retinopathy and cerebral palsy [ 1,12,15,18]. During 1984 and 1985 a nationwide case control survey was carried out in Curacao, Netherlands Antilles. The principle aims were to analyse the causes of fetal and neonatal deaths that occurred on this Caribbean island and to use 0020-7292/91/$03.50 0 1991 International
this information as a basis for future maternity health care planning [21-231. From the results of this study it was apparent that the majority (66%) of the deaths occurred in infants of less than 37 weeks gestation. Overall, immaturity emerged as a significant risk factor for fetal and neonatal mortality. These tindings are in agreement with results from similar population-based investigations in the Caribbean region. For example, a large study in Guadeloupe, which was conducted from 1984 to 1985, demonstrated that among singleton pregnancies a high proportion (73%) of the fetal and neonatal deaths was associated with curtailed gestation [6]. There is evidence suggesting that both PTB and low birthweight are more prevalent among West Indian communities in Europe as compared with European communities [8] and among blacks living in the United States as compared with nonblacks [ 191. However, the extent to which low socioeconomic status explains the adverse influence of race on the incidence of PTB remains controversial [4,14,20]. The primary objective of the present research was to investigate whether sociodemographic factors yielded any additional information to medical factors in terms of the risk of PTB on the island of Curacao. To this end we analysed the data that were collected for the Curacao Perinatal Mortality Survey. Clinical and Clinical
Federation
Published and Printed in Ireland
of Gynecology
and Obstetrics
Reseurch
24
Wildschut and Peters
Subjects and methods
Details of the fetal and neonatal mortality survey in Curacao have been published previously [21-231. Briefly, this populationbased survey was conducted on the island of Curacao (population 160 000; estimated birth rate 20 per 1000). From January lst, 1984 to December 3 lst, 1985 detailed information was obtained on each fetal and neonatal death as it occurred (fetal death included stillborn infants weighing 500 g and over; neonatal death related to live born infants of 500 g and over who died within 28 days of life). In addition, information was gathered on women allocated to the control group. This group comprised a sample of women who gave birth to a liveborn infant in one of six periods, irrespective of the place of delivery. These periods, totalling 14 weeks, were selected prior to the initiation of the survey. Accordingly, women among the control group represented approximately 15% of the parturients who did not experience fetal or neonatal death during the survey period. In both groups women not resident in Curacao and multiple pregnancies were excluded. Because of the prospective design of the study and the full collaboration of all parties involved we were able to obtain a virtually complete data set (i.e. no values missing or out of range). Definition of PTB (i.e. birth occurring prior to 37 completed weeks gestation) is based on recommendations set by the World Health Organization [7]. Length of gestation at delivery was based on the best obstetric estimate [23]. Parity is defined as the number of completed pregnancies of more than 16 weeks, excluding the index pregnancy. The term prior first trimester termination refers to a history of an induced first trimester pregnancy termination. Poor obstetric history (POH) represents a history of spontaneous late abortion and/or preterm delivery (16-36 weeks). Income relates to all monthly earnings of the mother and/or her partner. In concordance with the 1981 national census the following three categories were considered: monthly Int J Gynecol Obstet 36
earnings less than US$588 (low income); US$588-1679 (middle income); US$l680 or more (high income). Analysis
Data analyses were conducted in two distinct stages. First, statistics were computed on the potential risk factors taking each one separately, using PTB as a dichotomous outcome variable. In order to adjust for disproportionate sample size these analyses were carried out on weighted samples. As the total number of singleton births to Curacao women in 1984-1985 was known (n = 6318) an estimate of the weighting coefficient for the controls could be calculated. In short, one group (n = 205) represents all women who were delivered in 1984-1985 and whose pregnancy outcome was unfavorable in terms of fetal or neonatal death whereas the other (n = 913) comprises a subsample of women who were not faced with fetal or neonatal death during the study period (n = 63 18 - 205 = 6113). To adjust for the disproportionate samples a weighting coefficient of 1 was used for the deaths and 6.7 (6113/913) for the survivors (controls). The basic measure of association is the odds ratio (OR), given in the formula: OR
=
p,/(l - p,) p241- P2)
where P, denotes the proportion of PTB among the exposed group, whereas P, denotes the proportion of PTB among the unexposed group [2]. OR values of greater/less than one indicate an increased/decreased risk among the exposed group (i.e. positive for the risk factor) compared with the unexposed group (i.e. risk factor negative). A confidence interval (CI) which does not include unity can be considered statistically significant. Crude ORs of PTB for each potential risk factor were calculated first within the deaths and controls separately. A combined OR together with 95% CI were obtained basically using the standard method of Woolf but with an addi-
Determinants
tional element, as described above, to account for disproportionate sampling [2]. In this way an unselected sample was effectively produced. Since the separation into deaths and survivors is essentially arbitrary in the context of PTB, any differences between the two groups in terms of risk factors for PTB are irrelevant. In the second stage logistic regression analysis, fitted by maximum likelihood (BMDP logistic regression program) was undertaken to determine factors independently associated with PTB. Once again these analyses were carried out initially for deaths and survivors separately and a weighted combination of them was subsequently obtained. In line with the objectives of this study, sociodemographic factors were included in these analyses together with the potential medical risk factors for PTB as suggested in the first stage of the analysis. Interactions between the variables were not considered because of limitations of sample size. Pregnant women with uncertain income status were excluded (n = 46).
of preterm birth at Curaqao
25
Table I. Relative frequencies of the risk factors and crude odds ratios and 95% confidence intervals of preterm birth by various risk factors,
weighted
for the disproportionate
sampling
of
deaths and survivors. Maternal
Relative
Crude
95%
characteristic
frequency
odds
confidence
(‘%I)
ratio
interval
Age (years) II
1.00
2&34
Under
20
79
0.92
0.43-1.94
35 and over
IO
0.93
0.34-2.57
Parity Nulliparous
41
1.00
Multiparous
59
I.00
Marital
0.62-1.61
status
Married
48
1.00
Unmarried
52
1.22
Non-Black
I8
1.00
Black
82
1.87
High
IO
I.00
Medium
29
1.54
0.61-3.64
Low
57
I.12
0.462.74
0.76---I
.95
Ethnicity 0.88-3.96
income
Uncertain
4
Results Maximum
PTB occurred in 133 (64.8%) of the 205 pregnant women who faced fetal or neonatal death and in 61 (6.7%) of their 913 controls. Table 1 shows the results of the analyses in the first stage. POH and severe hypertension (110 mmHg and greater) were the only factors significantly associated with PTB. These factors, however, have a relatively low prevalence in the community and, consequently, their contribution to the problem of PTB is negligible. Surprisingly, neither a linear nor a quadratic relationship of maternal age with PTB could be established. As determined by logistic regression analyses both POH and severe hypertension emerged as independent predictors of PTB (Table 2). Marital status, ethnicity and gross family income were not associated with an increased risk of PTB (Table 2).
diastolic blood pressure (mmHg)
Under 90
19
1.00
90-99
I5
1.63
0.X7-3.05
loo-lo9
4
1.54
0.52-4.62
I IO and above
2
IO.11
4.25S24.0
Poor obstetric history No Yes
96
1.00
4
4.30
I .98-9.38
Prior first trimester termination No
79
1.00
Yes
21
I .04
0.59-1.82
Discussion
The approximate PTB-rate in Curacao is 86 per 1000 total births (CI 71-103 per 1000). This figure is comparable with the crude PTB rate given for the United States (89 per 1000 live births) [ 191. The PTB rate in Curacao Clinical and Clinical Research
26
Wildschut and Peters
Table 2. Adjusted odds ratios of preterm birth for factors in the logistic regression model, each with 95% confidence intervals (Cl ). weighted for disproportionate Maternal
characteristic
sampling of death and survivors. Adjusted
95%
odds ratio
confidence internal
Maximum diastolic blood pressure (mmHg) Under 90
1.00
90-99
1.70
0.x9-
3.23
loo-lo9
1.60
0.52-
4.90
100 and above
10.6
I
4.34-26.
Poor obstetric history POH
vs. no POH
4.53
2.00-10.3
1.64
0.92-2.93
I.55
0.69-3.49
0.68
0.26
1.22
0.45-3.26
Marital status Unmarried
vs. married
Ethnicity Black vs. non-Black
Income Low income vs. high income Medium
I .92
income vs. high
income
compares favorably with other islands in the Caribbean, e.g. for Jamaica approximates 140 per 1000 births (Samms-Vaughan, personal communication). In the United Kingdom the recorded PTB rate varies between 6% and 8%
[161. It is widely recognized that multiple pregnancy is associated with an increased risk of preterm delivery. From an epidemiologic point of view, however, it is relevant to consider multiple pregnancies separately from singleton pregnancies. Our study, which is confined to singleton pregnancies, showed that a poor obstetric history emerged as a major risk factor for PTB, even after allowing for potential confounders. This is in concordance with other studies [3,14]. As indicated, the finding of POH is relatively uncommon. Therefore, with regard to the prevention of PTB, the importance of this risk factor is very limInr J Gpwcot
Ohstet 36
ited. High blood pressure (L 1 IO mmHg) is also significantly associated with PTB in Curacao. Although the acceptable standard of management of women with hypertensive disorders during pregnancy is still a matter of contention, it is well established that deferring labor in this group of women is counterproductive. In general, efforts to identify and treat these particular subgroups of high-risk women have not resulted in a substantial reduction of the incidence of PTB [5]. Although induced abortion is illegal in Curacao, a relatively high proportion (20.9%) of women admitted having had an early pregnancy termination previously. However, from our observations there appeared to be no association between a history of induced abortion and PTB (in Curacao, virtually all first trimester terminations are performed by physicians). A recent prospective study in England came to a similar conclusion [9]. Several sociodemographic risk factors for PTB were examined. Our findings indicate that the contribution of ethnicity to the risk of PTB is relatively low. The same is true for socioeconomic and marital status. It is noteworthy that socioeconomic and marital status themselves are unlikely to have a direct influence on the outcome of pregnancy. They should merely be regarded as a proxy for various nutritional, and environmental behavioral conditions during pregnancy [ 131. These include for example maternal dietary habits, lifestyle (including smoking and drinking patterns), negative attitude towards pregnancy, failure to seek and/or receive optimal medical care, stress, physical exercise and susceptibility to infection. Detailed information on these sociocultural aspects was not available. In conclusion, it would seem more logical to prevent preterm birth rather than deal with its consequences [ 151. Unfortunately, the traditional medical risk factors known to be associated with PTB are extremely difficult to alter. However, apart from better provision of obstetrical care [23], an integrated pragmatic approach to conditions underlying the sociodemographic deter-
Determinants
minants of poor reproductive outcome could prove to be beneficial to both mother and child [ 10,11,17]. The latter issue, however, requires further investigation.
preterm delivery through perinatal study in Martinique. Int J Gynecol II I2
Acknowledgments I3
This work was supported by The Wellcome Trust. We would like to thank Victor Wiedijk who helped to conduct this study. We also want to make grateful acknowledgment to Pete Thomas for his advice and David Carmichael for the assistance with computer programming.
I4 I5
I6
References I7 I
2
3
4 5
Alberman ED: Epidemiology of retinopathy of prematurity. In: Retinopathy in Prematurity: Contemporary Issues in Fetal and Neonatal Medicine (eds WA Silverman. JT Flynn). p 249. Blackwell Scientific, Boston, 1985. Armitage P, Berry G: Statistical Methods in Medical Research, 2nd edn, p 455. Blackwell Scientific. Oxford. 1987. Bakketeig LS, Hoffman J, Harley EE: The tendency to repeat gestational age and birth weight in successive births. Am J Obstet Gynecol 135: 1086, 1979. Behrman RE: Premature births among black women. N Engl J Med 317: 763, 1987. Bouyer J. Papiernik E. Gueguen S: Changes in the frequency of risk factors for preterm delivery and their predictive value over time. In: Effective Prevention of Preterm Birth: The French Experience Measured at Haguenau teds E Papiernik. LG Keith, J Bouyer. J Dreyfus. Ph Lazar), p 115. INSERM. New York, 1987.
6
I
8
9
IO
Caunes F de: Mortalite Perinatale en Guadeloupe. Premiers Resultats de I’Enquete de la Mortalite Perinatale 198685. New York, INSERM. 1987. Chiswick ML: Commentary on current World Health Organization definitions used in perinatal statistics. Br J Obstet Gynaecol Y3: 1236. 1986. Doornbos JPR. Nordbeck HJ: Perinatal mortality. Obstetric risk factors in a community of mixed ethnic origin in Amsterdam. Amsterdam, Thesis, 1985. Frank PI, Kay CR, Scott LM. Hannaford PC, Harran D: Pregnancy following induced abortion: maternal morbidity, congenital abnormalities and neonatal death. Br J Obstet Gynaecol 94: 836. 1987. Goujon H. Papiernik E, Maine
D: The prevention
of
of preterm birth at Curacao
I8 I9
20
21
22
23
27
care: an intervention Obstet 22: 339. 1984.
Greenberg RS: The impact of prenatal care in different social groups. Am J Obstet Gynecol 145: 797. 1983. Hagberg B. Hagberg G. Zetterstrom R: Decreasing perinatal mortality - increase in cerebral palsy morbidity? Acta Paediatr Stand 178: 664. 1989. Hendriks CH: Delivery pattern and reproductive efficiency among groups of differing socioeconomic status and ethnic groups. Am J Obstet Gynecol 97: 609. 1967. Hibbard B: The etiology of preterm labour. Br Med J 294: 594. 1987. Lumley J: The prevention of preterm birth: unsolved problems and work in progress. Aust Paediatr J 24: 101, 1988. MacFarlane A. Mugford M: Variations in births and deaths. In: Birth Count Statistics of Pregnancy and Childbirth (eds A MacFarlane. M Mugford). London. HMSO. 1984. Moore TR, Origel W. Key TC. Resnik R: The perinatal and economic impact of prenatal care in lowsocioeconomic population. Am J Obstet Gynecol 154: 29. 1986. Nelson KB, Ellenberg JH: Antecedents of cerebral palsy. Multivariate analysis of risk. N Engl J Med 315: 8 I, 1986. Shiono PH. Klebanoff MA: Ethnic differences in preterm and very preterm delivery. Am J Public Health 76: 1317. 1986. Stein A, Campbell EA. Day A. McPherson K. Cooper PJ: Social adversity, low birth weight and preterm delivery. Br Med J 295: 291. 1987. Wildschut HlJ. Tutein Nolthenius-Puylaert MCBJE, Wiedijk V. Treffers PE, Huber J: Fetal and neonatal mortality: a matter of care? Report from a survey in Curacao, Netherlands Antilles. Br Med J 294: 894, 1987. Wildschut HIJ, Wiedijk V, Oosting J. Voorn W. Huber J. Treffers PE: Predictors of foetal and neonatal mortality in Curacao, Netherlands Antilles. A multivariate analysis. Sot Sci Med 28: 837, 1989. Wildschut HIJ. Wiedijk V, Tutein Nolthenius-Puylaert MCBJE: Birth asphyxia versus the quality of care in Curacao, Netherlands Antilles. Int J Gynecol Obstet 32. 117. 1990.
Address for reprints: H.I.J. Wildschut Division of Epidemiology Institute of Child Health University of Bristol Bristol BS2 8BJ. UK
Clinical
und Clinicul
Research
Obsr~~r. 1991. 36: 23-27
International
Federation
Determinants Antilles H.I.J. Wildschut”
(Received
March
23rd.
23
of Gynecology
and Obstetrics
of preterm birth in CuraCao, Netherlands and T.J. Petersb
1990)
(Revised and accepted August 30th.
1990)
Abstract In order to identtfy risk factors for preterm birth in singletons, data from a populutionbased case control survey on the island of Curacao were re-analysed. Both medical and sociodemogruphic variables were examined. Overall, a history of previous preterm birth and severe hypertension during the index pregnuncy were indicators of adverse pregnancy outcome, in terms of preterm birth. The contribution of sociodemographic factors to the risk of preterm birth is relatively low.
Preterm birth; Poor obstetric history; Hypertension; Marital status; Socioeconomic status; West Indies. Keywords:
Introduction It is widely recognized that preterm birth (PTB) is a major determinant of fetal and neonatal mortality, short-term morbidity and long-term morbidity, in particular retinopathy and cerebral palsy [ 1,12,15,18]. During 1984 and 1985 a nationwide case control survey was carried out in Curacao, Netherlands Antilles. The principle aims were to analyse the causes of fetal and neonatal deaths that occurred on this Caribbean island and to use 0020-7292/91/$03.50 0 1991 International
this information as a basis for future maternity health care planning [21-231. From the results of this study it was apparent that the majority (66%) of the deaths occurred in infants of less than 37 weeks gestation. Overall, immaturity emerged as a significant risk factor for fetal and neonatal mortality. These tindings are in agreement with results from similar population-based investigations in the Caribbean region. For example, a large study in Guadeloupe, which was conducted from 1984 to 1985, demonstrated that among singleton pregnancies a high proportion (73%) of the fetal and neonatal deaths was associated with curtailed gestation [6]. There is evidence suggesting that both PTB and low birthweight are more prevalent among West Indian communities in Europe as compared with European communities [8] and among blacks living in the United States as compared with nonblacks [ 191. However, the extent to which low socioeconomic status explains the adverse influence of race on the incidence of PTB remains controversial [4,14,20]. The primary objective of the present research was to investigate whether sociodemographic factors yielded any additional information to medical factors in terms of the risk of PTB on the island of Curacao. To this end we analysed the data that were collected for the Curacao Perinatal Mortality Survey. Clinical and Clinical
Federation
Published and Printed in Ireland
of Gynecology
and Obstetrics
Reseurch
24
Wildschut and Peters
Subjects and methods
Details of the fetal and neonatal mortality survey in Curacao have been published previously [21-231. Briefly, this populationbased survey was conducted on the island of Curacao (population 160 000; estimated birth rate 20 per 1000). From January lst, 1984 to December 3 lst, 1985 detailed information was obtained on each fetal and neonatal death as it occurred (fetal death included stillborn infants weighing 500 g and over; neonatal death related to live born infants of 500 g and over who died within 28 days of life). In addition, information was gathered on women allocated to the control group. This group comprised a sample of women who gave birth to a liveborn infant in one of six periods, irrespective of the place of delivery. These periods, totalling 14 weeks, were selected prior to the initiation of the survey. Accordingly, women among the control group represented approximately 15% of the parturients who did not experience fetal or neonatal death during the survey period. In both groups women not resident in Curacao and multiple pregnancies were excluded. Because of the prospective design of the study and the full collaboration of all parties involved we were able to obtain a virtually complete data set (i.e. no values missing or out of range). Definition of PTB (i.e. birth occurring prior to 37 completed weeks gestation) is based on recommendations set by the World Health Organization [7]. Length of gestation at delivery was based on the best obstetric estimate [23]. Parity is defined as the number of completed pregnancies of more than 16 weeks, excluding the index pregnancy. The term prior first trimester termination refers to a history of an induced first trimester pregnancy termination. Poor obstetric history (POH) represents a history of spontaneous late abortion and/or preterm delivery (16-36 weeks). Income relates to all monthly earnings of the mother and/or her partner. In concordance with the 1981 national census the following three categories were considered: monthly Int J Gynecol Obstet 36
earnings less than US$588 (low income); US$588-1679 (middle income); US$l680 or more (high income). Analysis
Data analyses were conducted in two distinct stages. First, statistics were computed on the potential risk factors taking each one separately, using PTB as a dichotomous outcome variable. In order to adjust for disproportionate sample size these analyses were carried out on weighted samples. As the total number of singleton births to Curacao women in 1984-1985 was known (n = 6318) an estimate of the weighting coefficient for the controls could be calculated. In short, one group (n = 205) represents all women who were delivered in 1984-1985 and whose pregnancy outcome was unfavorable in terms of fetal or neonatal death whereas the other (n = 913) comprises a subsample of women who were not faced with fetal or neonatal death during the study period (n = 63 18 - 205 = 6113). To adjust for the disproportionate samples a weighting coefficient of 1 was used for the deaths and 6.7 (6113/913) for the survivors (controls). The basic measure of association is the odds ratio (OR), given in the formula: OR
=
p,/(l - p,) p241- P2)
where P, denotes the proportion of PTB among the exposed group, whereas P, denotes the proportion of PTB among the unexposed group [2]. OR values of greater/less than one indicate an increased/decreased risk among the exposed group (i.e. positive for the risk factor) compared with the unexposed group (i.e. risk factor negative). A confidence interval (CI) which does not include unity can be considered statistically significant. Crude ORs of PTB for each potential risk factor were calculated first within the deaths and controls separately. A combined OR together with 95% CI were obtained basically using the standard method of Woolf but with an addi-
Determinants
tional element, as described above, to account for disproportionate sampling [2]. In this way an unselected sample was effectively produced. Since the separation into deaths and survivors is essentially arbitrary in the context of PTB, any differences between the two groups in terms of risk factors for PTB are irrelevant. In the second stage logistic regression analysis, fitted by maximum likelihood (BMDP logistic regression program) was undertaken to determine factors independently associated with PTB. Once again these analyses were carried out initially for deaths and survivors separately and a weighted combination of them was subsequently obtained. In line with the objectives of this study, sociodemographic factors were included in these analyses together with the potential medical risk factors for PTB as suggested in the first stage of the analysis. Interactions between the variables were not considered because of limitations of sample size. Pregnant women with uncertain income status were excluded (n = 46).
of preterm birth at Curaqao
25
Table I. Relative frequencies of the risk factors and crude odds ratios and 95% confidence intervals of preterm birth by various risk factors,
weighted
for the disproportionate
sampling
of
deaths and survivors. Maternal
Relative
Crude
95%
characteristic
frequency
odds
confidence
(‘%I)
ratio
interval
Age (years) II
1.00
2&34
Under
20
79
0.92
0.43-1.94
35 and over
IO
0.93
0.34-2.57
Parity Nulliparous
41
1.00
Multiparous
59
I.00
Marital
0.62-1.61
status
Married
48
1.00
Unmarried
52
1.22
Non-Black
I8
1.00
Black
82
1.87
High
IO
I.00
Medium
29
1.54
0.61-3.64
Low
57
I.12
0.462.74
0.76---I
.95
Ethnicity 0.88-3.96
income
Uncertain
4
Results Maximum
PTB occurred in 133 (64.8%) of the 205 pregnant women who faced fetal or neonatal death and in 61 (6.7%) of their 913 controls. Table 1 shows the results of the analyses in the first stage. POH and severe hypertension (110 mmHg and greater) were the only factors significantly associated with PTB. These factors, however, have a relatively low prevalence in the community and, consequently, their contribution to the problem of PTB is negligible. Surprisingly, neither a linear nor a quadratic relationship of maternal age with PTB could be established. As determined by logistic regression analyses both POH and severe hypertension emerged as independent predictors of PTB (Table 2). Marital status, ethnicity and gross family income were not associated with an increased risk of PTB (Table 2).
diastolic blood pressure (mmHg)
Under 90
19
1.00
90-99
I5
1.63
0.X7-3.05
loo-lo9
4
1.54
0.52-4.62
I IO and above
2
IO.11
4.25S24.0
Poor obstetric history No Yes
96
1.00
4
4.30
I .98-9.38
Prior first trimester termination No
79
1.00
Yes
21
I .04
0.59-1.82
Discussion
The approximate PTB-rate in Curacao is 86 per 1000 total births (CI 71-103 per 1000). This figure is comparable with the crude PTB rate given for the United States (89 per 1000 live births) [ 191. The PTB rate in Curacao Clinical and Clinical Research
26
Wildschut and Peters
Table 2. Adjusted odds ratios of preterm birth for factors in the logistic regression model, each with 95% confidence intervals (Cl ). weighted for disproportionate Maternal
characteristic
sampling of death and survivors. Adjusted
95%
odds ratio
confidence internal
Maximum diastolic blood pressure (mmHg) Under 90
1.00
90-99
1.70
0.x9-
3.23
loo-lo9
1.60
0.52-
4.90
100 and above
10.6
I
4.34-26.
Poor obstetric history POH
vs. no POH
4.53
2.00-10.3
1.64
0.92-2.93
I.55
0.69-3.49
0.68
0.26
1.22
0.45-3.26
Marital status Unmarried
vs. married
Ethnicity Black vs. non-Black
Income Low income vs. high income Medium
I .92
income vs. high
income
compares favorably with other islands in the Caribbean, e.g. for Jamaica approximates 140 per 1000 births (Samms-Vaughan, personal communication). In the United Kingdom the recorded PTB rate varies between 6% and 8%
[161. It is widely recognized that multiple pregnancy is associated with an increased risk of preterm delivery. From an epidemiologic point of view, however, it is relevant to consider multiple pregnancies separately from singleton pregnancies. Our study, which is confined to singleton pregnancies, showed that a poor obstetric history emerged as a major risk factor for PTB, even after allowing for potential confounders. This is in concordance with other studies [3,14]. As indicated, the finding of POH is relatively uncommon. Therefore, with regard to the prevention of PTB, the importance of this risk factor is very limInr J Gpwcot
Ohstet 36
ited. High blood pressure (L 1 IO mmHg) is also significantly associated with PTB in Curacao. Although the acceptable standard of management of women with hypertensive disorders during pregnancy is still a matter of contention, it is well established that deferring labor in this group of women is counterproductive. In general, efforts to identify and treat these particular subgroups of high-risk women have not resulted in a substantial reduction of the incidence of PTB [5]. Although induced abortion is illegal in Curacao, a relatively high proportion (20.9%) of women admitted having had an early pregnancy termination previously. However, from our observations there appeared to be no association between a history of induced abortion and PTB (in Curacao, virtually all first trimester terminations are performed by physicians). A recent prospective study in England came to a similar conclusion [9]. Several sociodemographic risk factors for PTB were examined. Our findings indicate that the contribution of ethnicity to the risk of PTB is relatively low. The same is true for socioeconomic and marital status. It is noteworthy that socioeconomic and marital status themselves are unlikely to have a direct influence on the outcome of pregnancy. They should merely be regarded as a proxy for various nutritional, and environmental behavioral conditions during pregnancy [ 131. These include for example maternal dietary habits, lifestyle (including smoking and drinking patterns), negative attitude towards pregnancy, failure to seek and/or receive optimal medical care, stress, physical exercise and susceptibility to infection. Detailed information on these sociocultural aspects was not available. In conclusion, it would seem more logical to prevent preterm birth rather than deal with its consequences [ 151. Unfortunately, the traditional medical risk factors known to be associated with PTB are extremely difficult to alter. However, apart from better provision of obstetrical care [23], an integrated pragmatic approach to conditions underlying the sociodemographic deter-
Determinants
minants of poor reproductive outcome could prove to be beneficial to both mother and child [ 10,11,17]. The latter issue, however, requires further investigation.
preterm delivery through perinatal study in Martinique. Int J Gynecol II I2
Acknowledgments I3
This work was supported by The Wellcome Trust. We would like to thank Victor Wiedijk who helped to conduct this study. We also want to make grateful acknowledgment to Pete Thomas for his advice and David Carmichael for the assistance with computer programming.
I4 I5
I6
References I7 I
2
3
4 5
Alberman ED: Epidemiology of retinopathy of prematurity. In: Retinopathy in Prematurity: Contemporary Issues in Fetal and Neonatal Medicine (eds WA Silverman. JT Flynn). p 249. Blackwell Scientific, Boston, 1985. Armitage P, Berry G: Statistical Methods in Medical Research, 2nd edn, p 455. Blackwell Scientific. Oxford. 1987. Bakketeig LS, Hoffman J, Harley EE: The tendency to repeat gestational age and birth weight in successive births. Am J Obstet Gynecol 135: 1086, 1979. Behrman RE: Premature births among black women. N Engl J Med 317: 763, 1987. Bouyer J. Papiernik E. Gueguen S: Changes in the frequency of risk factors for preterm delivery and their predictive value over time. In: Effective Prevention of Preterm Birth: The French Experience Measured at Haguenau teds E Papiernik. LG Keith, J Bouyer. J Dreyfus. Ph Lazar), p 115. INSERM. New York, 1987.
6
I
8
9
IO
Caunes F de: Mortalite Perinatale en Guadeloupe. Premiers Resultats de I’Enquete de la Mortalite Perinatale 198685. New York, INSERM. 1987. Chiswick ML: Commentary on current World Health Organization definitions used in perinatal statistics. Br J Obstet Gynaecol Y3: 1236. 1986. Doornbos JPR. Nordbeck HJ: Perinatal mortality. Obstetric risk factors in a community of mixed ethnic origin in Amsterdam. Amsterdam, Thesis, 1985. Frank PI, Kay CR, Scott LM. Hannaford PC, Harran D: Pregnancy following induced abortion: maternal morbidity, congenital abnormalities and neonatal death. Br J Obstet Gynaecol 94: 836. 1987. Goujon H. Papiernik E, Maine
D: The prevention
of
of preterm birth at Curacao
I8 I9
20
21
22
23
27
care: an intervention Obstet 22: 339. 1984.
Greenberg RS: The impact of prenatal care in different social groups. Am J Obstet Gynecol 145: 797. 1983. Hagberg B. Hagberg G. Zetterstrom R: Decreasing perinatal mortality - increase in cerebral palsy morbidity? Acta Paediatr Stand 178: 664. 1989. Hendriks CH: Delivery pattern and reproductive efficiency among groups of differing socioeconomic status and ethnic groups. Am J Obstet Gynecol 97: 609. 1967. Hibbard B: The etiology of preterm labour. Br Med J 294: 594. 1987. Lumley J: The prevention of preterm birth: unsolved problems and work in progress. Aust Paediatr J 24: 101, 1988. MacFarlane A. Mugford M: Variations in births and deaths. In: Birth Count Statistics of Pregnancy and Childbirth (eds A MacFarlane. M Mugford). London. HMSO. 1984. Moore TR, Origel W. Key TC. Resnik R: The perinatal and economic impact of prenatal care in lowsocioeconomic population. Am J Obstet Gynecol 154: 29. 1986. Nelson KB, Ellenberg JH: Antecedents of cerebral palsy. Multivariate analysis of risk. N Engl J Med 315: 8 I, 1986. Shiono PH. Klebanoff MA: Ethnic differences in preterm and very preterm delivery. Am J Public Health 76: 1317. 1986. Stein A, Campbell EA. Day A. McPherson K. Cooper PJ: Social adversity, low birth weight and preterm delivery. Br Med J 295: 291. 1987. Wildschut HlJ. Tutein Nolthenius-Puylaert MCBJE, Wiedijk V. Treffers PE, Huber J: Fetal and neonatal mortality: a matter of care? Report from a survey in Curacao, Netherlands Antilles. Br Med J 294: 894, 1987. Wildschut HIJ, Wiedijk V, Oosting J. Voorn W. Huber J. Treffers PE: Predictors of foetal and neonatal mortality in Curacao, Netherlands Antilles. A multivariate analysis. Sot Sci Med 28: 837, 1989. Wildschut HIJ. Wiedijk V, Tutein Nolthenius-Puylaert MCBJE: Birth asphyxia versus the quality of care in Curacao, Netherlands Antilles. Int J Gynecol Obstet 32. 117. 1990.
Address for reprints: H.I.J. Wildschut Division of Epidemiology Institute of Child Health University of Bristol Bristol BS2 8BJ. UK
Clinical
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