Objective
The objective of the study was to evaluate the effects of maternal exposure to severe life events during different stage of gestation on preterm birth and infant birthweight.
Study Design
A sample of 1800 women who delivered after 32 weeks’ gestation were assessed with questionnaires that measured stressful life events during different stages of pregnancy. Demographic characteristics and birth outcomes were collected through the interviews and medical charts.
Results
There was an increased risk of preterm birth among women with higher levels of life events stress during the first trimester (adjusted risk ratio, 2.40; 95% confidence interval, 1.13–5.09) and second trimester (adjusted risk ratio, 2.86; 95% confidence interval, 1.26–6.47). Each unit increase of perceived life events stress during first trimester was associated with a 99.09 g decrease in infant birthweight.
Conclusion
Prenatal severe life events, especially in the first trimester, may play an important role in increasing the risk of preterm birth and low birthweight.
In China, preterm delivery, which occurs in approximately 5-15% of all births, is the leading cause of neonatal morbidity and mortality. Although numerous exposures including social, psychological, biological, and genetic factors are known to be associated with preterm birth and low birthweight, in more than 50% of all preterm deliveries, the cause remains unknown or unclear.
Several previous studies suggest that maternal psychological stress, such as pregnancy-related anxiety, depression, or distress, may be associated with increased risk of preterm birth or low birthweight. Women may manage the psychological stress through coping. Coping refers to the cognitive and behavioral efforts used when faced with specific demands appraised as taxing or exceeding one’s resources.
Research found different coping efforts resulted in different degrees of distress in pregnant women. Some investigators believe that the response to environmental stresses and the adequacy of social resources, which were not fully accounted for in the important role of context in constructing or shaping maternal adaptive responses to stressors in most studies, are the main mediating routes by which stress effects affect adverse birth outcomes.
Although the majority of researchers have reported a significant association between preterm delivery and maternal stress, other studies have questioned the association. Most previous studies pay attention to life events on birth outcomes, but they neglected the gestational time window when stress exposure produces the greatest impact on preterm birth and birthweight, although it is crucial for understanding mechanisms underlying specific effects of prenatal stress on birth outcome. Only a few of them focus on the timing effects of life events on birth outcomes, and regretfully they evaluated only 2 or 3 severe life events such as disaster and death or serious illness in close relatives, which might cause the limitation in assessing the effect of life events on birth outcomes.
Current human epidemiologic studies regarding gestational time window of prenatal psychological stress is inadequate. One study showed that women with first-trimester exposure gave birth earlier than those with third trimester exposure. Conversely, another study considered that second- and third-trimesters exposures were associated with low birthweight and preterm birth, whereas exposure before 16 weeks of gestation was unrelated.
In the present study, we examined the association between maternal stressful life events and the risk of preterm birth and low birthweight and explored the gestational time window when stress exposure produces the greatest impact on preterm birth and birthweight. To evaluate the unique contribution of maternal life events stress to preterm birth and birthweight, it is important to exclude other potential factors. Therefore, the individual-level factors known to be associated with maternal stress and birth outcome including income, education, age, complication with pregnancy, history of pregnant outcome, infant sex, and psychosocial factors were controlled in this study.
Materials and Methods
Study subjects
This study is part of a prospective longitudinal project, which investigates the influence of prenatal psychosocial stress on the pregnancy outcome and postnatal development of infants.
Subjects were recruited from 3316 married pregnant women who received the third-trimester prenatal visit in the Department of Gynecology and Obstetrics of Hefei Maternal and Child Health Hospital from March to November 2008. A total of 2552 pregnant women participated in the project willingly.
In this study, women with age greater than 35 years (n = 147), delivery before 32 weeks of gestation (n = 14), or medically indicated preterm birth (n = 22), stillbirth (n = 11), birth defect (n = 12), pregnancy with assisted reproductive technology (n = 6), mental disorder (n = 2), complications with pregnancy including diabetes mellitus, hypertension, abnormal heart function, glandula thyreoidea disease, intrahepatic cholestasis of pregnancy, moderate and severe anemia (n = 429), or a history of abnormal pregnancy outcome (including premature birth, spontaneous abortion, fetal death, stillbirth, birth defect, neonatal death) (n = 240), or superfetation (n = 48) were excluded from the study.
Samples of 1800 pregnant women were admitted. The study was approved by the ethical committee of the Anhui Medical University, and informed consent was obtained from the participants.
Investigational methods
All the participants were recruited from obstetric clinics who received prenatal check-ups after 32 completed weeks. With informed consent, they were required to complete a questionnaire including Life Events Checklist, Social Support Scale, and Coping Style Questionnaire. Demographic characteristics and pregnancy history were assessed through the interview, and delivery outcomes including gestational age at birth and birthweight were obtained from medical charts after delivery.
Dependent variables
The main birth outcomes for the study were gestational age at birth and birthweight. Preterm births (births with gestational age <37 completed weeks) were calculated from the gestational age (in completed weeks) based on the difference between the date of the last menstrual period and the date of delivery which were obtained from hospital records. Low birthweight was defined as an infant with weight less than 2500 g.
Independent variables
Participants were invited to answer a 19-item inventory of stressful life events to assess the occurrence of specific events during the first trimester (0-12 weeks), second trimester (13-24 weeks), and third trimester (25-36 weeks), respectively. According to the 19-item checklist of life events, which was designed on the basis of previous investigations, participants were asked to indicate whether the event had occurred during pregnancy, using a dichotomous (yes-no) response scale. If the event occurred, they were asked to weight their perception of its impact on their lives, from no impact (0) to extreme impact (4). The sum of the value of each event ratings were used to assess perception of stress.
This assumes that the effects of the stressful life events are cumulative and additive across the various events. Total value of self-perceived impact rating of 0, 1, and 2 or greater is defined as no stress, modest stress, and severe stress, respectively.
The checklist was adapted from the Life Event Scale with a little modification, which included merging some items that usually occur during pregnancy and deleting some unsuitable items. All the 19 items could be classified into 4 domains as financial (4 items including, husband lost job, subject herself lost job, fortune loss, and stolen from or cheated), emotion (6 items including, moved to new address, live apart, housing stress, fright, family member gambling, and spouse went to jail), traumatic events (5 items including, husband ill, husband died, subject herself ill, family member ill, and family member died), and spousal related (4 items including, divorce, argument with partner, in-fight, and poor marital relation). Two blank items were added into the checklist in case of any missing life events that might be excluded from the 19 items mentioned above.
Covariates
Covariates were considered on findings in other studies of risks for preterm birth. The individual-level variables reported are maternal age (20-24, 25-29, 30-34 years), measures of maternal socioeconomic characteristics (income, education), and psychosocial factor (social support and coping style). Income level was categorized as perceived status (lower, medium, or higher). Educational attainment was similarly categorized as middle school and less (≥9 years), or high school and beyond (>9 years of completed schooling).
The Chinese Revised Edition of the Social Support Scale including 10 items with the total score range from 12 to 64 was used to assess social support as a buffer of stress and categorized as lower support, medium-low support, medium-high support, and high support by using quartiles. The more scores, the more psychological resources.
In addition, the Chinese Revised Edition of the Coping Style Questionnaire including 10 items with the total score range from 10 to 50 assessed negative coping style to stress and was categorized as lower negative coping (NC), medium-low NC, medium-high NC, and high NC by using quartiles. The more scores, the more tendency to using negative coping style to stress.
Statistical analysis
Interquartile ranges of coping style and social support subscale were used in statistical analyses. Crude risk ratios (RRs) and 95 percent confidence intervals (CIs) were generated for associations of maternal socioeconomic characteristics and psychosocial factors with preterm birth and low birthweight using the χ 2 test. Confounding by covariates for association between life events stress and preterm was assessed by univariate analysis.
Adjusted risk ratios were generated with regression modeling using the SPSS binary logistic regression (SPSS Inc, Chicago, IL). The unadjusted regression coefficients of linear regression model were generated for the association between prenatal life events stress and birthweight, and adjusted regression coefficients were given after controlling for gestation age at birth and other maternal-level covariates. SPSS software (Statistical Package for the Social Sciences, version 10.0) was used for all statistical analyses.
Results
As shown in Table 1 , the majority of respondents had completed high school and beyond (82.8.0%). Maternal income levels of the respondents showed considerable variations. More than three-quarters of the respondents reported a medium income (73.6%), and the lower income category had 14.4%.
| Mother’s characteristics | n (n = 1800) | % | Preterm, % | RR | 95% CI | P value | LBW, % | RR | 95% CI | P value |
|---|---|---|---|---|---|---|---|---|---|---|
| Mother’s age, y | ||||||||||
| 20-24 | 323 | 17.9 | 10.8 | 2.46 | 1.63–3.73 | .01 | 6.5 | 2.74 | 1.57–4.78 | .01 |
| 25-29 | 1137 | 63.2 | 4.4 | 1.00 | 2.4 | 1.00 | ||||
| 30-34 | 340 | 18.9 | 3.2 | 0.74 | 0.39–1.40 | .34 | 2.1 | 0.88 | 0.38–1.99 | .73 |
| Mother’s education, y | ||||||||||
| ≤9 | 310 | 17.2 | 11.3 | 2.76 | 1.85–4.10 | .01 | 7.7 | 3.61 | 2.15–6.06 | .01 |
| >9 | 1490 | 82.8 | 4.1 | 1.00 | 2.1 | 1.00 | ||||
| Income a | ||||||||||
| Lower | 259 | 14.4 | 9.3 | 2.01 | 1.28–3.16 | .01 | 5.0 | 1.90 | 1.02–3.54 | .04 |
| Medium | 1325 | 73.6 | 4.6 | 1.00 | 2.6 | 1.00 | ||||
| Higher | 216 | 12.0 | 5.1 | 1.11 | 0.59–2.07 | .76 | 3.2 | 1.23 | 0.55–2.72 | .62 |
| Social support b | ||||||||||
| Low | 504 | 28.0 | 5.8 | 1.04 | 0.61–1.77 | .90 | 3.3 | 1.09 | 0.53–2.27 | .81 |
| Medium-low | 466 | 25.9 | 5.8 | 1.05 | 0.62–1.77 | .86 | 2.8 | 0.94 | 0.44–1.98 | .87 |
| Medium-high | 430 | 23.9 | 4.3 | 0.77 | 0.44–1.35 | .36 | 3.2 | 1.08 | 0.54–2.19 | .83 |
| High | 400 | 22.2 | 5.6 | 1.00 | 3.0 | 1.00 | ||||
| Negative coping style c | ||||||||||
| Low | 393 | 21.8 | 5.1 | 1.00 | 2.3 | 1.00 | ||||
| Medium-low | 485 | 27.0 | 5.8 | 1.13 | 0.65–1.98 | .66 | 3.7 | 1.62 | 0.74–3.57 | .22 |
| Medium-high | 403 | 22.4 | 4.0 | 0.78 | 0.41–1.48 | .45 | 2.0 | 0.87 | 0.34–2.22 | .77 |
| High | 519 | 28.8 | 6.2 | 1.21 | 0.70–2.09 | .49 | 3.9 | 1.68 | 0.78–3.66 | .18 |
a Income was categorized as lower, medium, or higher according to perceived status;
b Social support was categorized as lower support, medium-low support, medium-high support, and high support by using quartiles;
c Negative coping (NC) style was categorized as lower NC, medium-low NC, medium-high NC, and high support by using quartiles.
In this study, the mean gestational age at delivery was (38.96 ± 1.53) weeks, ranging from 32 to 42 weeks, with 96 preterm births (5.3%). The mean birthweight was 3363.61 ± 458.45 g, ranging from 1500 to 5500 g, with 55 low birthweight infants (3.1%). In all infants, there were 957 boy infants (53.2%) and 843 girl infants (46.8%).
Additionally, Table 1 shows the different birth outcomes of the newborns according to the demographic and psychosocial characteristics of those pregnant women. An increased risk for preterm birth occurred among women who were at a lower age at delivery (RR, 2.46; 95% CI, 1.63–3.73), had a lower education level (RR, 2.76; 95% CI, 1.85–4.10), and lower income level (RR, 2.01; 95% CI, 1.28–3.16). Women with lower age at delivery (RR, 2.74; 95% CI, 1.57–4.78), lower educational level (RR, 3.61; 95% CI, 2.15–6.06), and lower income level (RR, 1.90; 95% CI, 1.02–3.54) had higher risk of low birthweight. Lower social support and higher negative coping did not increase the risk of preterm birth and low birthweight.
Table 2 presents different levels of perceived life events stress during the first, second, and third trimesters according to the demographic and psychosocial characteristics of those pregnant women. There were significant differences of prenatal life events stress during the third trimester according to age and educational level but not the first and second trimester.
| Mother’s characteristic | n (n = 1800) | Exposure in first trimester | Exposure in second trimester | Exposure in third trimester | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | ≥2 | P value | 0 | 1 | ≥2 | P value | 0 | 1 | ≥2 | P value | ||
| Mother’s age, y | .92 | .07 | .01 | ||||||||||
| 20-24 | 323 | 88.2 | 7.4 | 4.4 | 93.5 | 3.7 | 2.7 | 90.4 | 5.6 | 4.1 | |||
| 25-29 | 1137 | 97.2 | 8.0 | 4.8 | 90.9 | 6.1 | 2.9 | 95.2 | 3.3 | 1.6 | |||
| 30-34 | 340 | 87.9 | 6.6 | 5.5 | 91.5 | 3.5 | 5.0 | 94.1 | 2.6 | 3.3 | |||
| Mother’s education, y | .68 | .84 | .04 | ||||||||||
| ≤9 | 310 | 87.7 | 6.8 | 5.4 | 92.3 | 4.5 | 3.3 | 91.6 | 4.2 | 4.2 | |||
| >10 | 1490 | 87.5 | 7.9 | 4.7 | 91.3 | 5.3 | 3.3 | 94.6 | 3.4 | 1.9 | |||
| Income a | .39 | .08 | .62 | ||||||||||
| Lower | 259 | 84.2 | 9.3 | 6.6 | 91.5 | 3.9 | 4.6 | 92.3 | 4.2 | 3.5 | |||
| Medium | 1325 | 87.8 | 7.6 | 4.6 | 91.0 | 5.4 | 3.6 | 94.3 | 3.6 | 2.2 | |||
| Higher | 216 | 89.8 | 6.5 | 3.7 | 94.4 | 5.1 | 0.5 | 95.4 | 2.8 | 1.8 | |||
| Social support b | .01 | .07 | .06 | ||||||||||
| Low | 504 | 80.8 | 9.8 | 9.6 | 88.0 | 7.5 | 4.5 | 91.0 | 6.0 | 3.0 | |||
| Medium-low | 466 | 90.0 | 7.4 | 2.5 | 93.7 | 4.2 | 2.1 | 94.7 | 2.6 | 2.8 | |||
| Medium-high | 430 | 89.7 | 7.1 | 3.2 | 93.1 | 3.9 | 3.0 | 94.8 | 3.4 | 1.7 | |||
| High | 400 | 88.9 | 6.7 | 4.4 | 90.9 | 5.4 | 3.8 | 95.4 | 2.6 | 2.0 | |||
| NC c | .01 | .03 | .03 | ||||||||||
| Low | 393 | 90.1 | 7.6 | 2.3 | 94.9 | 3.1 | 2.0 | 96.2 | 3.1 | 0.8 | |||
| Medium-low | 485 | 89.9 | 6.0 | 4.2 | 91.3 | 5.8 | 2.9 | 95.7 | 2.9 | 1.4 | |||
| Medium-high | 403 | 86.6 | 8.9 | 4.5 | 92.1 | 4.0 | 3.9 | 92.8 | 4.2 | 2.9 | |||
| High | 519 | 84.2 | 8.3 | 7.5 | 88.6 | 7.1 | 4.2 | 92.1 | 4.0 | 3.8 | |||
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