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T Forsén a National Public Health Institute, Department of
Epidemiology and Health Promotion, Diabetes and Genetic Epidemiology
Unit, Mannerheimintie 166, Helsinki, Finland, b Medical
Research Council Environmental Epidemiology Unit, University of
Southampton, Southampton General Hospital, Southampton SO16 6YD
Correspondence to: D J P Barker
david.barker{at}mrc.soton.ac.uk
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Abstract |
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Objective:
To examine whether women who develop
coronary heart disease have different patterns of fetal and childhood
growth from men in the same cohort who develop the disease.
Design:
Follow up study of women whose body size at birth was recorded and who had an average of 10 measurements of height
and weight during childhood.
Setting:
Helsinki, Finland.
Subjects:
3447 women who were born in Helsinki
University Central Hospital during 1924-33 and who went to school in Helsinki.
Main outcome measures:
Hazard ratios for hospital
admission for or death from coronary heart disease.
Results Coronary heart disease among women was associated with
low birth weight (P=0.08 after adjustment for gestation, P=0.007 after
adjustment for placental weight) and was more strongly associated with
short body length at birth (P=0.001 and P<0.0001, respectively). The
hazard ratio for women developing coronary heart disease increased by
10.2% (95% confidence interval 4.3 to 15.7) for each cm decrease in
length at birth. The effect of short length at birth was greatest in
women whose height "caught up" after birth so that as girls they
were tall. Such girls tended to have tall mothers. In contrast, men in
the same cohort who developed the disease were thin at birth rather
than short, showed "catch up" growth in weight rather than height,
and their mothers tended to be overweight rather than tall.
Conclusion:
Coronary heart disease among both women
and men reflects poor prenatal nutrition and consequent small body size
at birth combined with improved postnatal nutrition and "catch up"
growth in childhood. The disease is associated with reductions in those
aspects of body proportions at birth that distinguish the two
sexes
short body length in women and thinness in men.
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Key messages
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Introduction |
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In both men and women the development of coronary heart disease
has been shown to be associated with low birth weight in relation to
the length of gestation.1-3 An interpretation of this is
that coronary heart disease originates through adaptations that the fetus makes when it is undernourished.4 These adaptations
include alterations in metabolism, hormonal output, and the
distribution of cardiac output, and they may be combined with slowing
of growth.5 Birth weight is a crude marker of fetal
growth, as the same birth weight may be the outcome of many different
paths of growth.6 Insights into the fetal adaptations that
lead to coronary heart disease have come from studying body proportions
at birth. Thinness at birth and shortness at birth
outcomes of
different paths of reduced fetal growth
have been found to be
associated with different biological risk factors for coronary heart
disease.4 Placental weight has also been found to be an
independent predictor of coronary heart disease in some
studies.
7 8
We have previously described death rates from coronary heart disease among a group of men who were born in Helsinki during 1924-33. 8 9 Their body size at birth was recorded in detail. As expected coronary heart disease was associated with low birth weight, after adjustment for gestation, but was more strongly associated with thinness at birth, measured by a low ponderal index (birth weight/length3). The growth of these men through childhood and their living conditions were also recorded. This allowed us to examine for the first time the association between childhood growth and death from coronary heart disease, taking into account size at birth. We found that the highest death rates from coronary heart disease occurred in boys who were thin at birth but whose weight caught up so that they had an above average body mass from the age of 7 years.
We report here findings among the corresponding cohort of women born in
the same hospital over the same period of time. The tempo of fetal and
childhood growth differs in boys and girls.
10 11
Hence
the paths of early growth that lead to coronary heart disease may
differ in the two sexes.
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Methods |
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We studied a sample of women who were born at the University
Central Hospital during 1924-33 and who went to school in the city of
Helsinki; 60% of all births in the city occurred in this hospital.
Details of the birth records kept there have been previously described.8 Data on the mothers include age, parity,
height, and date of last menstrual period, together with body weight
measured on admission in labour. Data on their newborn babies include
birth weight, length, head circumference, and placental weight. We
studied women who were born at the hospital and who went to school in the city of Helsinki and were still resident in Finland in 1971. School
health records for all children attending school in Helsinki are stored
in the city archive. Details of these records have been described
previously.9 They include an average of 10 (SD 4)
measurements of length and weight between the ages of 6 and 16 years,
recorded at periodic medical examinations. They also include the number
of other people living in the child's home
recorded at the time of
first examination
and the number of rooms. Since 1971 all residents of
Finland have been assigned a unique personal identification number.
From the birth and school health records and identification numbers we identified 3688 women who fulfilled the criteria. Of these women, 241 subsequently emigrated, and the date of emigration was not always recorded. We therefore excluded them from the study to leave 3447.
By using the personal identification number we identified all hospital admissions and deaths among the women during 1971-95. Because death rates from coronary heart disease are much lower among women than men we ascertained fatal and non-fatal coronary disease rather than fatal disease alone, as in our study of men. All hospital admissions in Finland are recorded in the national hospital discharge register. All deaths are recorded in the national mortality register. Causes of hospital admissions or deaths were recorded according to ICD-8 (international classification of diseases, 8th revision) until 1986; thereafter ICD-9 was used until 1995. The first three digits from the cause of admission or death were used to identify the occurrence of coronary heart disease (ICD-8 and ICD-9 codes 410-414). Using the father's occupation, which was on the birth records, we grouped the men according to a social classification used by the Central Statistical Office. Overall, 85% of the fathers were labourers, and 11% were classified as lower middle class. Together these constitute the lower social class as opposed to the upper social class.
Statistical analysis
We examined the trends in hazard
ratios with maternal, neonatal, and childhood measurements. Tests for trend were based on Cox's proportional hazards model. We converted each measurement of height, weight, and body mass index for each girl
to a Z score.12 We interpolated between successive Z
scores with a piecewise linear function and so obtained a Z score at each birthday from age 7 to 15 years. We back transformed these Z
scores to obtain the corresponding height, weight, and body mass index
at these ages.
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Results |
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Maternal, neonatal, and childhood characteristics of the 3447 women are shown in table 1. Of these women, 247 had been admitted to hospital for coronary heart disease, of whom 35 died from the disease. A further 32 had died without admission to hospital. We therefore analysed data on 279 women with coronary heart disease. The annual death rate at ages 45 to 64 years was 0.8 per 1000 compared with 3.9 per 1000 in men.
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Size at birth
Table 2 shows hazard ratios for coronary heart disease according
to size at birth. The ratios fell with increasing birth weight,
although this was not significant. Hazard ratios were not related to
the length of gestation, but adjustment for gestation strengthened the
association with birth weight. Hazard ratios fell more steeply with
increasing length. The hazard ratio for developing coronary heart
disease increased by 10.2% (95% confidence interval 4.3 to 15.7) for
each cm decrease in length at birth, adjusted for gestation. There were
no trends with head circumference or ponderal index.
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Growth in childhood
At each age from 7 to 15 years the mean heights and weights of
women who developed coronary heart disease were below those of all
other women. At 7 years, for example, their height was 0.42 cm less and
their weight 0.20 kg less. At no age, however, were the differences
significant. At birth their length was 0.17 SD below average; while at
7 and 15 years their heights were only 0.08 SD and 0.02 SD below
average, respectively. Therefore their heights and weights had largely
"caught up" between birth and 15 years. Table 4 shows the combined
effects of length at birth and height in childhood on hazard ratios for
coronary heart disease. Height at 7 years is used but the findings with
all other ages are similar. The hazard ratio for women who were longest at birth and tallest as children is set at 1.0. The fall in risk of
coronary heart disease with increasing length at birth was steeper
among women who were tallest as girls. This interaction between birth
length and childhood height was significant (P=0.02). At no age in
childhood was body mass index related to later coronary heart
disease.
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Maternal characteristics
The mothers' heights and their weights and body mass indices
during pregnancy were unrelated to the occurrence of coronary heart
disease in their daughters. When, however, we divided the mothers
according to their height, using the median height of 1.58 metres as in
our previous analysis, we found that the interactive effects of short
length at birth and tallness in childhood on coronary heart disease was
stronger among the daughters of taller women (P=0.006 for interaction
between birth length and height at 7 years in daughters of tall women).
As expected, taller mothers tended to have taller daughters, the
correlation coefficient between mother's height and daughter's height
at 7 years being 0.36.
Crowding in the home and social class during childhood
An examination of the average number of inhabitants and
rooms in the homes where the girls grew up showed that 47% of them
lived in homes with only one room (see table 1). We used the ratio of
the number of inhabitants to the number of rooms as an index of
crowding. Table 5 shows that families living in less crowded homes were
of higher social class, and the daughters were taller at all ages.
Coronary heart disease, however, was unrelated to the number of
inhabitants, number of rooms, crowding, or social class in
childhood.
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Sex differences in fetal growth
In comparison with the men in the cohort the women had smaller
head circumferences at birth (34.3 cm v 34.9 cm), shorter
body lengths at birth (49.7 cm v 50.2 cm), and lower birth
weights (3315 g v 3443 g). Mean placental weights, however, were similar (628 g v 634 g). During childhood the heights
and weights of the men and women were similar until adolescence when, as expected, women became shorter and heavier. Table 6, which gives the
percentage of girls among term babies according to length at birth and
placental weight, shows that the small differences in average body size
at birth between the sexes conceal large differences in proportionate
size. Short body length in relation to high placental weight, the
pattern which predicts coronary heart disease in women (table 3), is
much more common among girls than boys (P<0.0001; table 6). In
contrast, table 7 shows that thinness at birth in relation to a large
head circumference is much more common among boys than girls
(P<0.0001); and it is thinness at birth that predicts coronary heart
disease in men.
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Discussion |
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In this study in Finland we have examined the paths of fetal and childhood growth that are associated with the later development of coronary heart disease in women. We found that these paths of growth differed from those of men in the same birth cohort who developed coronary heart disease. Because women have much lower rates of coronary heart disease we combined death and hospital discharge rates, whereas in our report on men we described only death rates.9 Among the women, however, the paths of growth associated with fatal and non-fatal disease were similar.
Our study was restricted to women who were born in Helsinki University Central Hospital. This would introduce a bias only if the associations between size at birth, childhood growth, and coronary heart disease differed between those born in the hospital and those born outside the hospital. The fathers of 85% of the women were classed as labourers. The women may therefore not be representative of all women living in Helsinki, although we know that in the early years of this century around 60% of men in the city were labourers. We ascertained coronary heart disease through the national mortality and national hospital discharge registers. The validity of these records has previously been reported. 13 14
Sex differences in fetal growth and coronary heart disease
In keeping with findings among women in the United
Kingdom,1 Sweden,2 the American nurses'
study,3 and India15 we found that coronary
heart disease among women in the Helsinki cohort was associated with
low birth weight (table 2). This trend was of only borderline
significance, after adjustment for length of gestation, but it became
strongly significant after adjustment for placental weight (table 3).
Low birth weight therefore predicts coronary heart disease in both
women and men. Our analysis of body proportions at birth, however, has
shown that the paths of intrauterine growth that led to low birth
weight and later coronary heart disease differed between the two sexes
in the same cohort. The women were born short in length while the men
were born thin; these associations being much stronger than those with birth weight. Stunting and thinness at birth may represent two different responses to fetal undernutrition, and published findings suggest that the long term consequences of these responses differ. While both have been found to be associated with raised blood pressure
in later life,
16 17
stunting is associated with
persistent changes in liver function, including raised serum
cholesterol concentration18 and plasma
fibrinogen,19 while thinness is associated with features
of the insulin resistance syndrome including impaired glucose tolerance
and dyslipidaemia.20
Sex differences in childhood growth and coronary heart disease
In both women and men the effects of reduced fetal growth on the
risk of coronary heart disease were increased by accelerated or
"catch up" growth. Among women the effect of being short at birth
was greatest in those who were tall in childhood (table 4). Men who
were thin at birth increased their risk by having an above average body
mass index in childhood. The risk among women was not influenced by
body mass in childhood, and risk among men was not influenced by
height. In our previous report we discussed several possible reasons
why catch up growth could be associated with adverse outcomes in later
life.9 One speculation is based on the observation that
restricted fetal growth leads to permanently reduced cell numbers in
tissues such as kidney, in which there is no further cell replication
after birth.24 Postnatal catch up growth could be
deleterious either because overgrowth of a limited cell mass disrupts
cell function or because large body size imposes an excessive metabolic
demand on a limited cell mass.
Sex differences in coronary heart disease
We have found that coronary heart disease among women and men is
associated with the body proportions at birth that distinguish the two
sexes. Women who develop coronary heart disease were short at birth,
particularly in relation to placental weight; the men were thin. It has
been suggested that the growth of every human fetus is constrained by
the mother through her limited capacity to deliver nutrients to
it.25 In the light of this, coronary disease could
represent the outcome of more severe constraint to which female and
male fetuses respond differently because female fetuses grow more
slowly. By the time of birth the girls have become short and the boys
thin. The long term changes in physiology and metabolism associated
with shortness and thinness at birth are different, and so too it seems
are the adverse effects of catch up growth in height and weight during
childhood. The lower rates of coronary heart disease among women may
originate in their slower rates of growth in utero.
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Acknowledgments |
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We thank Terttu Nopanen, Tiina Saarinen, Hillevi Öfverström-Anttila, Liisa Toivanen, Arja Purtonen, Tiina Valle, Hanna Pehkonen, and Ulla Tarvainen for abstracting the data from the records. Sigrid Rosten was responsible for data management.
Contributors: All the authors took part in the design and analysis of the study and jointly wrote the paper. The data abstraction and linkage were supervised by JGE and TF. JGE, CO, and DJPB will act as guarantors for the paper.
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Footnotes |
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Funding: British Heart Foundation, Jahnsson Foundation, Finska Läkaresällskapet, Orion Corporation Research Foundation, and Finnish Foundation for Cardiovascular Research.
Competing interests: None declared.
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References |
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| 1. | Osmond C, Barker DJP, Winter PD, Fall CHD, Simmonds SJ. Early growth and death from cardiovascular disease in women. BMJ 1993; 307: 1519-1524. |
| 2. |
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| 10. | Tanner JM. Foetus into man. 2nd ed. Castlemead: Ware, 1989. |
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| 19. | Martyn CN, Meade TW, Stirling Y, Barker DJP. Plasma concentrations of fibrinogen and factor VII in adult life and their relation to intra-uterine growth. Br J Haematol 1995; 89: 142-146[Medline]. |
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Lithell HO, McKeigue PM, Berglund L, Mohsen R, Lithell UB, Leon DA.
Relation of size at birth to non-insulin dependent diabetes and insulin concentrations in men aged 50-60 years.
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| 22. | Harding J, Liu L, Evans P, Oliver M, Gluckman P. Intrauterine feeding of the growth retarded fetus: can we help? Early Hum Dev 1992; 29: 193-197[Medline]. |
| 23. | Widdowson EM, McCance RA. The effect of finite periods of undernutrition at different ages on the composition and subsequent development of the rat. Proc Roy Soc Lond B 1963; 158: 329-342[Medline]. |
| 24. | Pitts GC. Cellular aspects of growth and catch-up growth in the rat: a reevaluation. Growth 1986; 50: 419-436[Medline]. |
| 25. | Ounsted M, Scott A, Ounsted C. Transmission through the female line of a mechanism constraining human fetal growth. Ann Hum Biol 1986; 13: 143-151[Medline]. |
(Accepted 24 August 1999)
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