MRC Environmental Epidemiology Unit (University of Southampton), Southampton General Hospital, Southampton
MRC Environmental Epidemiology Unit (University of Southampton), Southampton General Hospital, Southampton
Correspondence: Dr C.Gale, MRC Environmental Epidemiology Unit, Southampton General Hospital, Southampton SO16 6YD, UK.Tel: 44 (0) 23 80764080; fax: 44 (0) 23 80704021; e-mail: crg{at}mrc.soton.ac.uk
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ABSTRACT |
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Aims To examine the relation between birth weight and riskof psychological distress and depression.
Method At age 16 years 5187 participants in the 1970 British Cohort Study completed the 12-item General Health Questionnaire to assess psychological distress. At age 26 years 8292 participants completed the Malaise Inventory to assess depression and provided information about a history of depression.
Results Women whose birth weight was 3 kg had an increased risk
of depression at age 26 years (OR=1.3; 95% CI1.01.5) compared with
those who weighed >3.5 kg. Birth weight was not associated with a reported
history of depression or with risk of psychological distress at age 16
years.In men there were no associations between any measurement and the full
range of birth weight but, compared with men of normal birth weight, those
born weighing
2.5 kg were more likely to be psychologically distressed at
age 16 years (OR=1.6,95% CI1.12.5) and to report a history of
depression at age 26 years (OR=1.6,95% CI1.12.3).
Conclusions Impaired neurodevelopment during foetal life may increase susceptibility to depression.
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INTRODUCTION |
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METHOD |
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Of 16 500 surviving cohort members who were invited to take part in the 16-year follow-up, 11 622 (70%) responded. However, strikes by teachers and public examinations among cohort members reduced the number of respondents for some elements of the survey so that data on psychological distress were available for only 5631 cohort members (34% of those invited to participate). Of these, 5187 (31% of those invited to participate) had taken part in the initial study and had data on birth weight so could be included in our analyses.
A total of 13 475 surviving cohort members were traced and were eligible to take part in the 26-year follow-up. Of these, 9003 returned their postal questionnaire. Data on depression were available for 8976 cohort members (67% of those invited to participate). Of these, 8292 (62% of those invited to participate) had taken part in the initial study and had data on birth weight so could be included in our analyses.
Measures of psychological distress and depression
Psychological distress at the age of 16 years was assessed by the 12-item
General Health Questionnaire (GHQ12;
Goldberg, 1978). The GHQ is a
screening questionnaire for non-psychotic psychological distress, largely
depression, suitable for use in general population surveys. A score 3 on
the GHQ12 was used to identify cases of psychological distress
(Banks, 1983).
Rutters 24-item Malaise Inventory was used to assess the presence of
depression at the age of 26 years (Rutter
et al, 1970). This inventory is a self-completion scale
developed from the Cornell Medical Index
(Brodman et al, 1949)
to measure levels of psychiatric morbidity. A score 7 on the Malaise
Inventory has been used to identify cases of depression
(Rodgers et al,
1999). The Malaise Inventory was also used to assess the presence
of depression in the mothers of cohort members during the 5-year follow-up. As
part of a series of questions on health in the 26-year follow-up, participants
were asked Have you suffered from depression for more than a few days
since you were 16?
Missing data
In our analyses we used information from the birth survey (gestational age,
fathers social class, mothers age, parity and smoking status
during pregnancy), from the 5-year follow-up (maternal depression, separation
from mother for >1 month, tenure of accommodation, parental
divorce/separation and experience of local authority care) and from the
10-year and 16-year follow-ups (parental divorce/separation and experience of
local authority care). A preliminary analysis comparing cohort members with
and without complete data on these potential confounding variables showed that
the strength of the relation between birth weight and score on the Malaise
Inventory differed between the two groups. In order to avoid bias due to
sample selection, we therefore decided to retain all cohort members in the
analyses. This was done by using a distinct category for missing data within
each of the potential confounding variables.
Statistical analysis
We used analysis of variance and the 2 test to examine the
relation between birth weight, the presence of depression (defined as a score
of
7 on the Malaise Inventory) and characteristics of the participants. We
used logistic regression to examine the relation between the presence of
depression at age 26 years, a reported history of depression between the ages
of 16 and 26 years, psychological distress at age 16 years and birth weight,
adjusting for gestational age and potential confounding factors. Gestational
age was split into five categories (<37 weeks, 3739 weeks,
4042 weeks, >42 weeks, not known/unreliable). Birth weight was split
into four categories (
2.50 kg, 2.513.00 kg, 3.013.50 kg and
>3.50 kg); P values are given for the trend in the odds ratios
across the birth weight categories.
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RESULTS |
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We calculated odds ratios for depression according to birth weight in women
and men separately (Table 2).
In univariate analysis there was a statistically significant linear
association between birth weight and risk of depression in women
(P<0.001 for trend). Compared with women who had weighed >3.50
kg at birth, women who had weighed 2.50 kg at birth had an odds ratio for
depression of 1.5 (95% CI 1.12.0). Women who had weighed between 2.51
and 3.00 kg at birth had an odds ratio of 1.3 (95% CI 1.11.6). After
adjustment for all the potential confounding factors shown in
Table 1, together with
gestational age at birth, the relation between birth weight and risk of
depression was weakened slightly but remained statistically significant
(P=0.016 for trend). When we repeated this analysis but excluding
women born at <37 weeks gestation, the relation between birth weight
and risk of depression became slightly stronger (P=0.009). We
investigated whether this relation was moderated by any risk factors listed in
Table 1 but there were no
statistically significant interactions.
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In men there was a trend towards increasing risk of depression with decreasing birth weight, but this was not statistically significant and it disappeared after adjustment for gestational age and other risk factors (Table 2).
In total, 1335 (16.1%) participants at the 26-year follow-up reported that
they had suffered from depression for more than a few days since the 16-year
follow-up. These men and women were much more likely to gain scores indicative
of current depression on the Malaise Inventory (for men: odds ratio=9.1, 95%
CI 7.111.5; for women: odds ratio=6.8, 95% CI 5.78.1). We found
no statistically significant linear trends between birth weight and a reported
history of depression in either men or women
(Table 3). There was evidence,
however, that men who had weighed 2.50 kg at birth were more likely than
those of normal birth weight to report that they had been depressed in the
past. This relation persisted after adjusting for gestational age and
potential confounding factors (odds ratio=1.6, 95% CI 1.12.3). It was
weakened when men born at <37 weeks gestation were excluded,
although the risk estimate changed little (odds ratio=1.5, 95% CI
0.92.4). No such association was seen in women.
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At the 16-year follow-up, 1458 (28.1%) of the 5187 participants scored
above the threshold of 3 on the GHQ12, indicating psychological
distress: 32.6% of girls scored 3 on the GHQ12 compared with 22.1%
of boys (P<0.001). Among those participants who took part in both
the 16-year and 26-year follow-ups, psychological distress at 16 years was a
significant predictor of depression at 26 years (for girls: odds ratio=2.4,
95% CI 1.92.9; for boys: odds ratio=2.0, 95% CI 1.42.8). We
found no evidence of a linear association between birth weight and risk of
psychological distress in either girls or boys
(Table 4). However, boys who
had weighed
2.5 kg at birth were more likely to be distressed than boys
whose birth weight was normal (odds ratio=1.6, 95% CI 1.12.5, after
multivariate adjustment). This relation remained statistically significant
when boys born at <37 weeks gestation were excluded (odds ratio=1.7,
95% CI 1.02.9).
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DISCUSSION |
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Strengths and limitations
This study used data from a national birth cohort that has been followed up
into adulthood. Detailed information is available about the family and social
environment of cohort members from the perinatal period onwards. When
examining the relations between birth weight and risk of psychological
distress or depression we were able to take account of a number of factors
known to increase a childs risk of subsequent psychiatric morbidity,
including socio-economic status, maternal depression, early separation from
the mother, parental marital disruption and experience of local authority
care. The associations shown here between birth weight and risk of depression
in women and between low birth weight (2.5 kg) and a reported history of
depression or risk of psychological distress in men persisted after adjustment
for these and other potential confounding factors, such as maternal age,
parity and smoking status during pregnancy.
In common with other national birth cohorts that have been followed up into
adult life, cohort members born to single mothers, teenage mothers or whose
fathers were in manual occupations had lower response rates at follow-up. In
the 26-year follow-up, for example, 62% of cohort members were born into a
manual social class compared with 64.1% in the initial birth survey. Males
were underrepresented in both the 16-year and 26-year follow-ups, making up
42.8% and 45.2% of the participants respectively compared with 51.1% of the
original sample. Cohort members who weighed 2.5 kg at birth were also
underrepresented at these follow-ups, accounting for 5.6% compared with 6.6%
of the original sample that survived the neonatal period. Nevertheless, the
size of the differences between the original sample and the achieved samples
at ages 16 and 26 years was small. In general, the cohort has remained
representative of those who took part in the initial birth survey.
One potential weakness of the study is that psychiatric morbidity was
assessed solely by means of self-completion scales: the GHQ12 during
the 16-year follow-up and the Malaise Inventory at age 26 years. However,
these scales have been widely used in general population samples and their
effectiveness at identifying psychiatric morbidity has been demonstrated. In a
study of 17-year-olds, for example, the GHQ12 with a cut-point of 3
correctly identified 83% of those who had a diagnosis of anxiety or depression
by clinical interview with 71% sensitivity and 80% specificity
(Banks, 1983). A score 7 on
the Malaise Inventory was able to detect cases of clinically diagnosed
depression in women with 73% sensitivity and 81% specificity
(Rodgers et al,
1999).
Comparison with other studies
In an investigation of a Dutch birth cohort, risk of major depression
requiring hospitalisation was increased in groups of men and women who were
exposed to famine during mid to late gestation in the Hunger Winter of
19441945 (Brown et al,
2000). An Italian casecontrol study of 41
casecontrol pairs found that patients admitted to hospital with
depression were more likely than controls to have been small for gestational
age and they had a lower mean birth weight, although this latter difference
was of borderline statistical significance
(Preti et al, 2000). Neither study made adjustments for potential confounding factors, although the
casecontrol pairs were matched by gender, time and parity of birth,
maternal age and marital status. Both of these studies provide some support
for the notion that environmental factors during foetal life may increase
susceptibility to depression, but they have the disadvantage that they rely
solely on cases severe enough to require hospitalisation.
In a recent study examining the relation between birth weight and depression in 882 elderly men and women in Hertfordshire, UK, cases were identified by means of the Geriatric Depression Scale and the Geriatric Mental State Examination (Thompson et al, 2001). There was a strong association between lower birth weight and risk of depression in men but no such relation was present in women. The authors suggest that one explanation for this discrepancy might be that female foetuses are less vulnerable to the effects of retarded growth in utero. But in the present study of over 8000 men and women aged 26 years, lower birth weight was a significant risk factor for depression in women. There was a non-significant trend in men towards increasing risk of depression with decreasing birth weight, but this disappeared after adjustment for potential confounding factors. In the Hertfordshire study, little information was available about potential confounding factors in the participants early environment apart from social class at birth (Thompson et al, 2001).
Middle to late adolescence is a peak risk period for the onset of
depression (Lewinsohn et al,
1986). In a longitudinal study of 386 children in the USA who were
followed from the age of 5 years, girls who had weighed 2.5 kg at birth
had a higher risk of depressive symptoms at the age of 18 years, although
there was no relation between low birth weight and depressive symptoms in boys
(Frost et al, 1999).
No information was available on maternal and family factors in early life and
the study relied on maternal reports of low birth weight. These findings
contrast with those of the present, much larger, study in which boys whose
birth weight was
2.5 kg were nearly twice as likely as those of normal
birth weight to be psychologically distressed at age 16 years, but this
association was not present in girls. A recent study of over 90 000
18-year-old Swedish boys found that performance on a test of psychological
functioning and stress susceptibility was poorest in those with low birth
weight and improved with increasing birth weight, but data on potential
confounding factors in early life were limited to maternal age and parity
(Nilsson et al,
2001).
Explanations
One explanation for the associations found between lower birth weight and
risk of depression or psychological distress may be that adverse environmental
exposures in utero influence both size at birth and the set point of
the hypothalamicpituitaryadrenal axis. Animal models have shown
that exposure to various stressors during pregnancy results in offspring with
lower birth weights, with raised basal or stress-induced glucocorticoid
secretion and with increased corticotrophin-releasing hormone activity
(Weinstock, 2001). These
physiological features are very similar to those seen in people with
depression (Steckler et al,
1999) and suggest that gestational stress at a critical time
during foetal development may increase susceptibility to this condition.
Women who are depressed during pregnancy are at higher risk of having children whose birth weight is low (Orr & Miller, 1995; Paarlberg et al, 1999). Their children are also more likely to develop emotional problems (Luoma et al, 2001). One reason for this might be that the gestational stress of maternal depression causes permanent changes in hypothalamicpituitaryadrenal axis settings, but it could also be due to the postnatal effects of exposure to negative maternal affect, cognitions and behaviour and to the stress of living with a depressed mother (Goodman & Gotlib, 1999). We had no data on maternal depression during pregnancy so we were unable to examine whether this explained any of the associations found here, although adjustment for maternal depression at the age of 5 years had little effect on estimates of risk.
The results of this study suggest that women whose birth weight was low or
at the lower end of the normal range are more likely to become depressed as
young adults. Having a birth weight at the lower end of the normal range did
not appear to increase the risk for men, but those whose birth weight was
2.5 kg were more likely to be psychologically distressed at age 16 years
and to report a history of depression at age 26 years. Impaired
neurodevelopment during foetal life may increase susceptibility to affective
illness.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication April 29, 2003. Revision received August 11, 2003. Accepted for publication August 12, 2003.
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