1 Department of Health Education and Promotion, East Carolina University, Greenville, NC.
2 University of Michigan School of Public Health and Center for Research on Ethnicity, Culture and Health, Ann Arbor, MI.
3 Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA.
Received for publication December 21, 2001; accepted for publication June 19, 2002.
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ABSTRACT |
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depression; depressive disorder; gestational age; pregnancy outcome
Abbreviations: Abbreviations: BMI, body mass index; CES-D, Center for Epidemiologic Studies Depression.
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INTRODUCTION |
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During the past decade, interest has been expressed in the potential etiologic association of psychosocial factors, including maternal depression, with preterm birth (8, 9). Hoffman and Hatch noted in 1996 that "accumulating evidence" suggested that maternal depression during pregnancy might be associated with preterm birth, but they added that the evidence was not conclusive (9). The relation between maternal depression and preterm birth is, in reality, poorly understood, and prior research has produced conflicting results. Several previous studies have measured variables such as "distress" as a proxy for depression, without actually measuring depression or depressive symptoms during pregnancy (1012). Other research on this topic has focused on outcomes of pregnancy other than preterm birth, such as spontaneous preterm labor (13), which is distinct from preterm birth (14). A retrospective study, using data from the 1988 Maternal and Infant Health Survey, reported an association between scores on the Center for Epidemiologic Studies Depression (CES-D) Scale with low birth weight (15). However, the data on depressive symptoms during pregnancy were collected after the birth of the infant (sometimes as much as 1 year later), and this information could be biased because of problems with recall and also by events that may have occurred during or after the pregnancy, including the birth (or death) of a low-birth-weight infant.
One in five women will experience an episode of depression during her lifetime (16), and Weissman and Olfson noted that depression is primarily a disorder of women of childbearing age (17). Thus, depression is a prevalent condition among women of childbearing ages, and there is a need for an improved understanding of the relation between maternal prenatal depression and preterm birth.
In the prospective study reported on in this paper, we measured depressive symptoms in a sample of low-income, clinic-attending, African-American women. At the end of their pregnancies, we assessed the outcome of their pregnancies, which enabled us to ascertain the association between maternal prenatal depressive symptoms and preterm birth outcomes.
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MATERIALS AND METHODS |
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The CES-D Scale was included in the questionnaire to assess depressive symptoms. It was developed by the National Institute of Mental Health to assess depressive symptoms in samples drawn from communities (18). The CES-D Scale contains 20 items and is self-administered; the women were able to complete it in about 15 minutes while waiting to be seen during their first prenatal visit. Reliability and validity of the CES-D Scale are well established (1820), and the instrument has been widely used in epidemiologic studies to assess depressive symptoms as an exposure variable. By using the CES-D Scale, respondents indicate the presence of salient symptoms of depression, such as sadness, crying, hopelessness, and sleep and appetite changes. Clinicians generally use the presence of these symptoms as a basis for diagnosing clinical depression. CES-D scores range from 0 to 60, with a score of 16 or higher used as the customary cutpoint to define the high-risk or "exposed" group. While it does not provide a diagnosis of clinical depression, the CES-D Scale gives a valid and reliable indication of the presence of elevated levels of symptoms of depression.
Using the CES-D Scale among pregnant women involves special assessment problems. Certain common symptoms of pregnancy, such as fatigue and sleep or appetite changes, are also common symptoms of depression. As a result, the CES-D scores of pregnant women could be elevated for reasons other than depression per se. To address this problem, we took a more conservative approach to defining "high-risk"; namely, only those women whose scores were in the upper 10 percent were considered "high risk." We reasoned that few, if any, women would rank in the upper 10 percent of CES-D scores solely on the basis of pregnancy-related symptoms. Others have similarly raised the usual cutpoint of the CES-D Scale, with the rationale that those in the highest group of scores would be likely to meet the criteria for a diagnosable depressive disorder (21).
The CES-D Scale repeatedly has been demonstrated to be a valid and reliable measurement tool in diverse populations (18, 22, 23). Prior research has shown that, among adults, about 4050 percent of those with elevated CES-D scores (using the traditional cutpoint of 16 or higher) would be classified as clinically depressed (19). Scores on the CES-D Scale correlate well with clinical assessments (18, 23), and CES-D scores decrease when depression is treated (18). Whereas elevated depressive symptoms (sometimes called depressive syndrome) are not the same as clinical depression, the upper 10 percent of scores identifies women with a large number and frequency of symptoms. Likely, more than half of these women would meet the criteria for clinical depression. Furthermore, prospective research has demonstrated that elevated levels of depressive symptoms is a significant classification by itself and is a prodrome to clinical depression (24).
The dependent variable was spontaneous preterm birth. Prior research has suggested that preterm birth may actually be comprised of etiologically distinct categories (2527). Preterm births can be subdivided into those that are medically indicated (i.e., delivery is performed at less than 37 weeks of gestation in the absence of preterm labor or rupture of the chorioamniotic membranes, usually because of severe complications that threaten the fetus and/or mother) and those that are spontaneous. Spontaneous preterm births occur when a woman presents with either preterm labor or preterm premature rupture of the chorioamniotic membranes at less than 37 completed weeks of gestation. Prior research has suggested that focusing efforts on more homogeneous categories of preterm birth (e.g., spontaneous preterm births, the dependent variable in the study reported on in this paper) may lead to an enhanced understanding of this outcome (25, 26).
Length of gestation was obtained from obstetric, delivery, and nursery records. The obstetricians providing care to the women in the sample made a "best obstetric estimate" of gestational age at the time of labor and delivery based on sonograms, date of last menstrual period, when the first fetal heart rate was heard with a stethoscope, and fundal height. We used the traditional cutpoint of less than 37 weeks of completed gestation to define preterm birth. In addition, all preterm births were categorized as medically indicated or spontaneous (as described in the previous paragraph), depending on the presentation of the woman for delivery (i.e., with or without spontaneous labor or rupture of membranes). The physicians providing care to the women at the clinical sites addressed any questions about classification as spontaneous or medically indicated. Since our focus was on spontaneous preterm births, we excluded those women with medically indicated preterm births (1.4 percent of all births) from the analyses, since these are likely etiologically different from spontaneous preterm births (2527).
Two trained abstractors obtained data on potentially confounding factors from the clinical records of the women in the sample. Behavioral factors included in the data collection were alcohol consumption, illicit drug use, and cigarette smoking. Underreporting of these undesirable behaviors was of concern; however, in our sample, the percentages of women who reported smoking, drug use, and alcohol consumption were similar to those reported in other studies (28, 29). Data were also collected on clinical factors that were potential confounders, including current medical characteristics of the mother (such as low prepregnancy body mass index (BMI; weight (kg)/height (m)2), chronic diseases such as asthma, diabetes, and hypertension); previous reproductive history; and course of the current pregnancy (complications such as first- and second-trimester bleeding, hospitalization during pregnancy, poor total weight gain, preeclampsia, abruptio placentae, and placenta previa).
Multiple logistic regression analysis was used to estimate the independent contribution of maternal depressive symptoms to spontaneous preterm birth, controlling for clinical, behavioral, and demographic variables. The beta coefficients from the model were used to estimate the odds ratios and associated 95 percent confidence intervals.
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RESULTS |
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The demographic, behavioral, and clinical characteristics of the women in the sample are shown in table 1. As indicated in this table, approximately 81 percent of the women were 20 years of age or older, about 75 percent had at least a high school education, 22 percent were married or were living with a male partner, and 32 percent were employed outside of the home. Table 1 also shows that slightly over one quarter of the women smoked cigarettes, approximately 7 percent reported consuming alcohol during pregnancy, and about 9 percent used drugs. Regarding the clinical characteristics of the sample, approximately 27 percent had a chronic disease, 12 percent had a low BMI (20), 18 percent experienced poor weight gain (less than 21 pounds (9.53 kg)), and 29 percent had a history of a poor pregnancy outcome (i.e., prior preterm or low-birth-weight birth, stillbirth, or fetal death).
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Of the 1,399 women in the sample, 117 experienced spontaneous preterm deliveries (8.4 percent), representing 85 percent of all preterm births to women in the sample for which an etiologic category could be ascertained. Of the women with elevated levels of depressive symptoms, 12.7 percent experienced spontaneous preterm births; of the women with low levels of depressive symptoms, 8.0 percent had this outcome (relative risk = 1.59), as shown in table 1.
Several variables were significantly (p < 0.05) associated with spontaneous preterm births in this sample, including abruptio placentae, bleeding, low prenatal BMI, drug use, poor weight gain (less than 21 pounds), previous poor pregnancy outcome, and smoking. We omitted abruptio placentae from the logistic regression analysis because the number of women experiencing this complication was small and the regression coefficient was unstable. Poor weight gain was also omitted from the logistic regression analyses because weight gain is so closely tied to length of gestation (i.e., a woman with a shortened pregnancy has less opportunity to gain weight).
The logistic regression model contained the following behavioral and clinical predictors associated with the outcome at p < 0.2 (30): bleeding, drug use, low prepregnancy BMI, previous poor pregnancy outcome, smoking, and depressive symptoms. Alcohol consumption was also included in the model because of its association with the exposure. As shown in table 2, the adjusted odds ratio for an elevated CES-D score was 1.96 (95 percent confidence interval: 1.04, 3.72). Low prepregnancy BMI was also associated with spontaneous preterm birth (odds ratio = 2.58, 95 percent confidence interval: 1.52, 4.35), as was previous poor pregnancy outcome (odds ratio = 1.59, 95 percent confidence interval: 1.01, 2.52).
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DISCUSSION |
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We used a valid and widely used tool, the CES-D Scale, to measure depressive symptoms. We also used a prospective design, thus reducing the risk of recall bias of symptoms of depression. In addition, we controlled for confounding by behavioral and clinical factors.
We conducted additional analyses to explore the possibility of a dose-response relation between depressive symptoms and spontaneous preterm birth. This possibility was evaluated in several ways, which involved developing quartiles, tertiles, and quintiles to represent CES-D scores in these exploratory analyses. There was no evidence of a dose-response association, probably because of an underlying threshold effect for "depression" (as indicated by very high scores on the CES-D Scale) and spontaneous preterm birth. It is likely that the biochemical or other processes that link CES-D scores to spontaneous preterm birth operate only when "depression" (i.e., the very highest CES-D scores) is present. This possibility warrants further study.
Approximately one in five women will experience an episode of clinical depression during her lifetime (16). The usual age of onset and time of greatest risk is 2040 years, thus coinciding with the childbearing years for most women. We assessed depressive symptoms, not clinical depression; however, elevated symptoms of depression (also known as depressive syndrome), the exposure of interest in our study, occur with even greater frequency than clinical depression and are viewed as a prodrome to clinical depression (24). Our exposure variable occurs with relatively high prevalence among women of childbearing age, although the validity of the CES-D Scale as a good measure of depression in pregnant women requires further study. If the findings reported here are causal, however, high levels of depressive symptoms may indeed be a major risk factor for poor pregnancy outcomes in African-American women.
Prior research has linked depression and elevated levels of depressive symptoms to a variety of deleterious health outcomes, such as cancer (3133), heart disease (34), and poor pregnancy outcome (8). One factor that may link depressive symptoms and depression to such diverse health outcomes is immune system functioning. Several studies have indicated that depression alters the functioning of the immune system (3539). Depression has been shown to be associated with measures of immunity such as reduction of natural killer (NK) cell activity and decreased lymphocyte proliferation (4042). Since reproductive tract infection is emerging as an important risk factor for preterm births (43, 44), it may be that altered host susceptibility to reproductive tract infection, associated with elevated levels of depressive symptoms, is a potential etiologic pathway through which elevated levels of depressive symptoms may be associated with risk of spontaneous preterm births. We did not have data on reproductive tract infection and thus could not directly examine this hypothetical etiologic pathway.
A recent report noted the lack of progress in reducing the rate of preterm birth in the United States in the past two decades (1). Until now, the main approach to preventing preterm births has been to focus largely on medically oriented interventions, with limited attention being given to psychosocial interventions, including interventions directed at improving the mental health of lower income, pregnant women. Treatment of elevated levels of depressive symptoms among pregnant women, especially economically disadvantaged African-American women, could result in a reduction of spontaneous preterm births in this population. If the findings reported in this study are shown to be reproducible in other settings, new and viable psychosocial approaches to preventing spontaneous preterm births may be possible.
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ACKNOWLEDGMENTS |
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The study protocol was reviewed and approved by the Johns Hopkins University Human Subject Protection Committee.
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NOTES |
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REFERENCES |
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