Cohort study of birthweight, mortality, and disability

Effect of low-cost kitchen with improved cookstove on birthweight of neonates in Shahjadpur, Bangladesh: a cluster-randomised controlled trial

Background

Smoke from biomass fuels used for cooking in traditional cookstoves contains a variety of health-damaging pollutants. Inhalation of these pollutants by pregnant women has been linked to abnormal foetal development and adverse pregnancy outcomes, including low birthweight (LBW). There is a dearth of data on environmental interventions that have the potential to reduce exposure to biomass fuel during pregnancy and improve birth outcomes. International Centre for Diarrheal Disease Research, Bangladesh (icddr,b) therefore, designed a low-cost kitchen with an improved cookstove and examined the impact of this intervention on the birthweight of neonates.

Methods

icddr,b conducted a cluster-randomised controlled trial of a 'low-cost kitchen with improved cookstove' intervention among 1,267 pregnant women who used traditional cookstoves in a rural sub-district of Bangladesh. All participants were enrolled during the first trimester of pregnancy among 104 randomly selected clusters after obtaining informed consent. The model kitchens were installed in 628 participants' households of the intervention group, and 639 participants continued to use traditional cookstoves as the control group. The primary outcome was the proportion of LBW neonates between the intervention and control groups. The study also examined if the intervention would reduce CO exposure, measured by the differences in maternal blood carbon monoxide saturation (SpCO) levels and prevalence of LBW in neonates. We performed a generalized structural equation model for jointly assessing the simultaneous relationships of biomass fuel exposure to LBW of neonates and the relationships of LBW of neonates to maternal blood SpCO level. This trial was registered with ClinicalTrials.gov (NCT02923882).

Findings

We found that in the intervention group using 'low-cost kitchen with improved cookstove', the risk of LBW reduced by 37% (adjusted risk ratio: 0.63, 95% CI [0.45, 0.89]). Between the second and third trimester, the mean maternal blood SpCO level was significantly reduced from 10.4% to 8.9% (p-value <0.01) in the intervention group but remained unchanged in the control group (11.6% and 11.5%). Of the total effects of the intervention on the risk of LBW, 48.3% was mediated through maternal blood SpCO level.

Interpretation

The risk of LBW among rural neonates was reduced in the intervention group using 'low-cost kitchen with improved cookstove', which may be attributed to the reduction in maternal blood SpCO level. Additional research is needed to identify other mechanisms through which biomass fuel exposure might lead to adverse pregnancy outcomes.

Funding

Grand Challenges Canada: Rising Stars in Global Health Programme.

Birth weight and long-term risk of mortality among US men and women: Results from three prospective cohort studies

Background

Weight at birth has been associated with the development of various adult diseases, but its association with mortality remains unclear.

Methods

We included 22,389 men from the Health Professionals Follow-up Study (1994-2018) and 162,231 women from the Nurses' Health Study (1992-2018) and the Nurses' Health Study II (1991-2019). The hazard ratios (HRs) of mortality according to birth weight were estimated by Cox proportional hazards regression models with adjustment for potential confounders.

Findings

Compared to women reporting a birth weight of 3.16-3.82 kg, the pooled HRs for all-cause mortality were 1.13 (95% CI, 1.08 to 1.17), 0.99 (95% CI, 0.96 to 1.02), 1.04 (95% CI, 1.00 to 1.08), and 1.03 (95% CI, 0.96 to 1.10), respectively, for women with a birth weight of <2.5, 2.5-3.15, 3.83-4.5, and >4.5 kg. In cause-specific mortality analyses, women reporting birth weight >4.5 kg had a higher risk of cancer mortality (HR=1.15, 95% CI: 1.00 to 1.31), whereas women with a birth weight <2.5 kg had an elevated risk of mortality from cardiovascular diseases (HR=1.15; 95% CI, 1.05 to 1.25) and respiratory diseases (HR=1.35; 95% CI, 1.18 to 1.54). Birth weight was unrelated to all-cause mortality among men, but cause-specific mortality analyses showed an inverse association with cardiovascular disease mortality and a positive association with cancer mortality (p for linear trend = 0.012 and 0.0039, respectively).

Interpretation

low birth weight was associated with a greater risk of cardiovascular and respiratory disease mortality among women, while large birth weight was associated with a greater cancer mortality risk in both men and women.

Funding

The National Institutes of Health grants U01-HL145386, U01-CA176726, R01-HL034594, R01-HL088521, UM-CA186107, P01-CA87969, R01-CA49449, R01-CA67262, U01-HL145386, U01-CA167552, R01-HL35464, and R24-ES028521-01 support this study.

Immigrant ancestry and birthweight across two generations born in Sweden: an intergenerational cohort study

INTRODUCTION

Differences in birthweight are often seen between migrants and natives. However, whether migrant-native birthweight inequalities widen, narrow or remain persistent across generations when comparing the descendants of immigrants and natives remains understudied. We examined inequalities in birthweight of mothers (G2) and daughters (G3) of foreign-born grandmothers (G1) compared with those of Swedish-born grandmothers.

METHODS

We used population registers with multigenerational linkages to identify 314 415 daughters born in Sweden during the period 1989-2012 (G3), linked to 246 642 mothers (G2) born in Sweden during 1973-1996, and to their grandmothers (G1) who were Swedish or foreign-born. We classified migrants into non-western, Eastern European, the rest of Nordic and Western. We used multivariable methods to examine mean birthweight and low birthweight (<2500 g; LBW).

RESULTS

Birthweight between individuals with Swedish background (G1) and non-western groups increased from -80 g to -147 g between G2 (mothers) and G3 (daughters), respectively. Furthermore, the odds of LBW increased among the G3 non-western immigrants compared with those with Swedish grandmothers (OR: 1.38, 95% CI 1.12 to 1.69). Birthweight increased in both descendants of Swedes and non-western immigrants, but less so in the latter (83 g vs 16 g).

CONCLUSION

We observed an increase in birthweight inequalities across generations between descendants of non-western immigrants and descendants of Swedes. This finding is puzzling considering Sweden has been lauded for its humanitarian approach to migration, for being one of the most egalitarian countries in the world and providing universal access to healthcare and education.

Economic gradient of onset of disability in India

Background

Disability in India is associated with increasing non-communicable diseases, rising longevity, and increasing accidents and injuries. Though studies have examined prevalence, patterns, and socioeconomic correlates of disability, no attempt has been made in estimating age of onset of disability in India.

Objective

This paper investigates the economic gradient of age of onset of locomotor, visual, hearing, speech, mental retardation, mental illness, and other disabilities in India.

Method

We use nationally representative data of 106,894 disabled individuals from the 76th round of National Sample Survey (NSS), 2018. Descriptive statistics, kernel density, Kaplan-Meier survival curves, and linear regression models are used in the analysis.

Result

The disability rate in India was 2184 per 100,000 persons. The disability rate was highest for locomotor (1353) followed by hearing (296), visual (234), speech (228), mental retardation (158), and mental illness (131). Over 85% of mental retardation and 80% of speech disabilities occur at birth, while 82% of locomotor and 81% of visual disabilities occur after birth. Among those who had disability after birth, the median age for mental retardation was 2 years followed by mental illness (28 years), speech (29 years), locomotor (42 years), visual (55 years), and 56 years for hearing disability. Adjusting for socioeconomic covariates, the age of onset of locomotor and speech disabilities among the poorest individuals were 7 and 11 years earlier than the richest, respectively.

Conclusion

The economic gradient of onset of locomotive and speech disabilities are strong. The age of onset of disability was earliest for mental retardation followed by mental illness and speech disability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-10826-5.

Mortality Rate and Major Causes of Death by Gestational Age in Korean Children under 5 Years of Age

BACKGROUND

Preterm birth is associated with increased infant mortality. However, it is not clear whether prematurity is associated with mortality after 1 year of age. There is a lack of research on mortality rate and causes of death after infancy in preterm babies in Korea. We aimed to analyze the mortality rates and causes of deaths up to 5 years of age in Korea.

METHODS

Using the Microdata Integrated Service of Statistics Korea database, this retrospective cohort study screened infants born between 2010 and 2012. After applying the exclusion criteria, 1,422,913 live births were classified into the following groups by gestational age: those born at < 32 weeks' gestation (n = 10,411), those born between 32 and 36 weeks' gestation (n = 75,657), and those born at ≥ 37 weeks' gestation (n = 1,336,845). The association of gestational age with mortality in infancy (< 1 year of age) and childhood (1-5 years of age) was analyzed, with and without covariates. The major causes of death in infancy and childhood were analyzed by gestational age.

RESULTS

Overall, 4,930 (0.3%) children died between birth and 5 years of age, with 19.1% of these deaths occurring after infancy. Adjusted hazard ratios (HRs) for infant death were 78.79 (95% confidence interval [CI], 71.33-87.04) and 4.62 (95% CI, 4.07-5.24) for the < 32 and 32-36 weeks groups, respectively, compared to the full-term group; the adjusted HRs for deaths occurring at ages 1-5 years were 9.25 (95% CI, 6.85-12.50) and 2.42 (95% CI, 1.95-3.01), respectively. In infancy, conditions originating in the perinatal period were the most common cause of deaths in the < 32 and 32-36 weeks groups (88.7% and 41.9%, respectively). Contrarily, in the ≥ 37 weeks group, conditions originating in the perinatal period explained 22.7% of infant deaths, with congenital malformations primarily accounting for 29.6% of these deaths. The most common cause of death in children (after infancy) in the < 32 weeks group was perinatal causes (25.0%); in the 32-36 weeks group, congenital malformation and nervous system disease were the common causes (21.7% and 19.1%, respectively). In the ≥ 37 weeks group, injury, poisoning, and other consequences of external causes explained 26.6% of childhood deaths, followed by neoplasms and nervous system disease (15.7% and 14.7%, respectively).

CONCLUSION

Low gestational age is associated with not only infant mortality but also child mortality. The major causes of death differed by gestational age in infancy and childhood. For the care of preterm infants, especially those born at < 32 weeks' gestation, particular attention and continuous monitoring are needed in consideration of the major causes of deaths until 5 years of age.

Birth characteristics and all-cause mortality: a sibling analysis using the Uppsala birth cohort multigenerational study

This paper investigates the association between perinatal health and all-cause mortality for specific age intervals, assessing the contribution of maternal socioeconomic characteristics and the presence of maternal-level confounding. Our study is based on a cohort of 12,564 singletons born between 1915 and 1929 at the Uppsala University Hospital. We fitted Cox regression models to estimate age-varying hazard ratios of all-cause mortality for absolute and relative birth weight and for gestational age. We found that associations with mortality vary by age and according to the measure under scrutiny, with effects being concentrated in infancy, childhood or early adult life. For example, the effect of low birth weight was greatest in the first year of life and then continued up to 44 years of age (HR between 2.82 and 1.51). These associations were confirmed in within-family analyses, which provided no evidence of residual confounding by maternal characteristics. Our findings support the interpretation that policies oriented towards improving population health should invest in birth outcomes and hence in maternal health.

All-Cause Mortality of Low Birthweight Infants in Infancy, Childhood, and Adolescence: Population Study of England and Wales

BACKGROUND

Low birthweight (LBW) is associated with increased mortality in infancy, but its association with mortality in later childhood and adolescence is less clear. We investigated the association between birthweight and all-cause mortality and identified major causes of mortality for different birthweight groups.

METHODS AND FINDINGS

We conducted a population study of all live births occurring in England and Wales between 1 January 1993 and 31 December 2011. Following exclusions, the 12,355,251 live births were classified by birthweight: 500-1,499 g (very LBW [VLBW], n = 139,608), 1,500-2,499 g (LBW, n = 759,283), 2,500-3,499 g (n = 6,511,411), and ≥3,500 g (n = 4,944,949). The association of birthweight group with mortality in infancy (<1 y of age) and childhood/adolescence (1-18 y of age) was quantified, with and without covariates, through hazard ratios using Cox regression. International Classification of Diseases codes identified causes of death. In all, 74,890 (0.61%) individuals died between birth and 18 y of age, with 23% of deaths occurring after infancy. Adjusted hazard ratios for infant deaths were 145 (95% CI 141, 149) and 9.8 (95% CI 9.5, 10.1) for the VLBW and LBW groups, respectively, compared to the ≥3,500 g group. The respective hazard ratios for death occurring at age 1-18 y were 6.6 (95% CI 6.1, 7.1) and 2.9 (95% CI 2.8, 3.1). Male gender, the youngest and oldest maternal age bands, multiple births, and deprivation (Index of Multiple Deprivation score) also contributed to increased deaths in the VLBW and LBW groups in both age ranges. In infancy, perinatal factors, particularly respiratory issues and infections, explained 84% and 31% of deaths in the VLBW and LBW groups, respectively; congenital malformations explained 36% and 23% in the LBW group and ≥2,500 g groups (2,500-3,499 g and ≥3,500 g groups combined), respectively. Central nervous system conditions explained 20% of deaths in childhood/adolescence in the VLBW group, with deaths from neoplasms and external conditions increasingly prevalent in the 1,500-2,499 g and ≥2,500 g birthweight groups. The study would have benefited had we had access to information on gestational age and maternal smoking, but since the former is highly correlated with birthweight and the latter with deprivation, we believe that our findings remain robust despite these shortcomings.

CONCLUSIONS

LBW is associated with infant and later child and adolescent mortality, with perinatal factors and congenital malformations explaining many of the deaths. By understanding and ameliorating the influences of upstream exposures such as maternal smoking and deprivation, later mortality can be decreased by reducing the delivery of vulnerable infants with LBW.

Maternal characteristics influencing birth weight and infant weight gain in the first 6 weeks post-partum: A cross-sectional study of a post-natal clinic population

Background:

To investigate the relationship between certain maternal characteristic and infant birth weight and weight gain in puerperal women seen at a tertiary health centre.

Materials and Methods:

We measured the weight of 318, randomly selected infants after a complete physical examination at birth and at 6 weeks postnatal using standard procedures and related them to certain maternal characteristics.

Results:

There were 318 women and baby pairs. Maternal ages ranged from 16 to 42 years, with a mean of 25.6±1.3 years. Mean birth weight of babies was 3.10±1.89 kg; mean gestational age was 36±4.6 weeks, with 9.4% and 3.0% of babies born having low birth weight or Macrosomia respectively. Mothers from the North of the country, multiparity and systolic and/or diastolic hypertensions were factors associated with low birth weight. At 6 weeks, 27.1% of infants failed to gain weight as expected for their age. Similarly, 37.0% of infants born to mothers with some tertiary education showed slowed weight gain compared with those who had secondary (19.2%) or primary (14.7%) education, P=0.03. Maternal weight at delivery positively correlated with birth weight of the infant (r=0.357, P<0.001). However, maternal weight and blood pressure negatively correlated with infant weight gain at 6 weeks post-delivery.

Conclusion:

Our study demonstrates that certain maternal characteristics could play a role in the birth weight and early infant weight gain, and are preventable through simple public health approaches.

Birthweight and mortality in adulthood: a systematic review and meta-analysis

BACKGROUND

Small birth size may be associated with increased risk of cardiovascular diseases (CVD), whereas large birth size may predict increased risk of obesity and some cancers. The net effect of birth size on long-term mortality has only been assessed in individual studies, with conflicting results.

METHODS

The Meta-analyses of Observational Studies in Epidemiology (MOOSE) guidelines for conducting and reporting meta-analysis of observational studies were followed. We retrieved 22 studies that assessed the association between birthweight and adult mortality from all causes, CVD or cancer. The studies were systematically reviewed and those reporting hazard ratios (HRs) and 95% confidence intervals (95% CIs) per kilogram (kg) increase in birthweight were included in generic inverse variance meta-analyses.

RESULTS

For all-cause mortality, 36,834 deaths were included and the results showed a 6% lower risk (adjusted HR = 0.94, 95% CI: 0.92-0.97) per kg higher birthweight for men and women combined. For cardiovascular mortality, the corresponding inverse association was stronger (HR = 0.88, 95% CI: 0.85-0.91). For cancer mortality, HR per kg higher birthweight was 1.13 (95% CI: 1.07-1.19) for men and 1.04 (95% CI: 0.98-1.10) for women (P(interaction) = 0.03). Residual confounding could not be eliminated, but is unlikely to account for the main findings.

CONCLUSION

These results show an inverse but moderate association of birthweight with adult mortality from all-causes and a stronger inverse association with cardiovascular mortality. For men, higher birthweight was strongly associated with increased risk of cancer deaths. The findings suggest that birthweight can be a useful indicator of processes that influence long-term health.

Weight at birth and all-cause mortality in adulthood

BACKGROUND

Small size at birth is associated with subsequent cardiovascular disease and diabetes, and large size is associated with obesity and cancer. The overall impact of these opposing effects on mortality throughout the lifespan is unclear because causes of death change with age.

METHODS

We investigated the association of birth weight with adult all-cause mortality using a Danish school-based cohort of 216,464 men and women born from 1936 through 1979. The cohort was linked to vital statistic registers. The main outcome was all-cause mortality from ages 25 through 68 years. Associations with death from cancer, circulatory disease, and all other causes were also examined.

RESULTS

During 5,205,477 person-years of follow-up, 11,149 deaths occurred among men and 6609 among women. The cumulative hazard ratios of the association between birth weight categories and all-cause mortality was constant for all ages investigated and did not differ between men and women. Compared with subjects having birth weights in the reference category (3251-3750 g), those with the lowest birth weights (2000-2750 g) had 17% higher mortality (95% confidence interval = 1.11-1.22), and those with the highest birth weights (4251-5500 g) had 7% higher mortality (1.01-1.15) from all causes. The association of birth weight with cancer increased linearly, whereas the association of birth weight with circulatory disease and all other causes was U-shaped.

CONCLUSIONS

To the degree that the association of birth weight with adult survival is causal, the U-shaped association between birth weight and adult mortality suggests that population increases in birth weight may not necessarily lead to improved health in adulthood.

Interactions between fetal HLA-DQ alleles and maternal smoking influence birthweight

Maternal smoking during pregnancy inhibits fetal growth, and is a major cause of childhood and adult morbidity, including increased risks of cardiovascular disease and diabetes. However, the use of birthweight as a proxy for future smoking-related morbidity is hindered by its wide variability, suggesting a role for other birthweight-modifying factors. We report here, for the first time, that interactions between specific fetal HLA-DQA1 and DQB1 alleles and maternal smoking can influence birthweight. We compared mean birthweights of a series of term, HLA-DQ typed white UK newborns (n = 552) whose mothers had either smoked (n = 211) or not smoked (n = 341) during pregnancy. Maternal smoking during pregnancy resulted in an average birthweight reduction of 244 g, but the combined effects of maternal smoking and fetal DQA1*0101 or DQB1*0501 alleles resulted in a 230 and 240 g further reduction in mean birthweight, respectively, resulting from interactions between smoking and these DQ types. Other fetal DQ allele-specific interactions with maternal smoking are suggested by a "protective" effect on smoking-associated birthweight reduction in newborns typing for DQA1*0201 and DQB1*0201. Our results suggest biological interactions between maternal cigarette smoking during pregnancy and specific fetal DQ alleles that affect fetal growth. The precise nature of these interactions merits further investigation, as knowledge of fetal HLA-DQ type may be useful in refining risk estimates of severe fetal growth restriction because of maternal smoking during pregnancy.

Changing patterns of inequality in birthweight and its determinants: a population-based study, Scotland 1980-2000

Birthweight is used as an indicator of individual and population health and is known to be strongly correlated with adult cardiovascular disease. This paper uses routinely collected maternity discharge data from Scotland between 1980 and 2000 to look at birthweight trends and the changes in the distribution of maternal risk factors for birthweight. We also examine the contributions of each of the risk factors to birthweight trends and investigate whether there has been a reduction in inequality in birthweight over time. Data from 1,282,172 singleton live births were used in the analysis. Both mean birthweight and low birthweight (LBW:<2500 g) were used as outcomes. The risk factors studied were maternal age, parity, maternal height, marital status and occupational social class of the father. The slope and relative indices of inequality were used to measure the change in inequalities over time. Mean birthweight increased from 3320 g in 1980 to 3410 g in 2000, while the percentage LBW decreased slightly from 5.7% in 1980 to 5.4% in 2000. The prevalence of many risk factors changed; there has been an increase in the proportion of older mothers, single mothers, taller mothers and mothers with undetermined social class. Although most risk factors had a significant change in effect over time, the inequalities in birthweight between groups did not appear to diminish over time. Both the slope and relative index of inequality had a quadratic relationship over time, with the inequalities in birthweight being greatest in the early 1980s and late 1990s.

Disabling conditions and registration for child abuse and neglect: a population-based study

OBJECTIVE

To study the relationship between disabling conditions and registration for child abuse and neglect in a 19-year whole-population birth cohort.

SETTING

West Sussex area of the United Kingdom.

STUDY DESIGN

Retrospective whole-population cohort.

MAIN OUTCOMES

Child-protection registration, physical abuse, sexual abuse, emotional abuse, and neglect. POPULATION AND PARTICIPANTS: Infants born in West Sussex (119729) between January 1983 and December 2001 with complete data including birth weight, gestational age, maternal age, and postal code.

RESULTS

Cerebral palsy, speech and language disorder, learning difficulties, conduct disorders, and nonconduct psychological disorders were all significantly associated with child-protection registration before adjustment, and all but cerebral palsy retained significance after adjustment for birth weight, gestational age, and socioeconomic status. Autism and sensory disabilities (vision and hearing) were not associated with an increased risk of child-protection registration. Conduct disorders and moderate/severe learning difficulty were associated with registration in each of the 4 categories after adjustment for socioeconomic status, birth weight, and gestational age. Children with speech and language disorders and mild learning difficulties were at increased risk of physical abuse, emotional abuse, and neglect. Nonconduct psychological disorders were associated with all categories except neglect, and cerebral palsy was associated with all categories except physical abuse and neglect.

CONCLUSIONS

Children with disabling conditions seem to be at increased risk of registration for child abuse and neglect, although the pattern of registration varies with the specific disabling condition. The strong association with registration noted for conditions such as conduct disorder and learning difficulties is likely to arise, in part, because these conditions share a common etiologic pathway with child abuse and neglect.

An intergenerational and lifecourse study of health and mortality risk in parents of the 1958 birth cohort: (I) methods and tracing

OBJECTIVES

This paper describes the methods used to obtain information on mortality and cancer registrations for the parents of the British 1958 birth cohort, in order to create a dataset that can be used to examine intergenerational relationships on health and growth.

STUDY DESIGN

Intergenerational cohort study.

METHODS

The 1958 cohort includes all births occurring during 1 week in March 1958 in England, Scotland and Wales. For more than four decades of follow-up, information has been collected on cohort members, their parents and children. Information on the National Health Service (NHS) numbers of the parents was not available, but other details were collated for the Office for National Statistics to trace and flag the biological parents of the cohort members.

RESULTS

Tracing was successful in 90.2% of fathers (n = 14,334) and 94.9% of mothers (n = 15,076). The greatest success was achieved for parents in families where there was no indication for additional mother or father figures until the child was 16 years old (96.6% of the mothers traced, n = 14,274; 94.3% of the fathers traced, n = 13,256). Tracing rates were lower than average in unmarried mothers (59%) and for the small group who were separated, widowed or divorced in 1958 (81%); the rates were particularly poor for the corresponding fathers (24.4 and 54.7%, respectively). There were only small variations in tracing rates between different regions of Britain.

CONCLUSIONS

The tracing rates achieved were generally very high despite the lack of NHS number, especially where there was family stability throughout the childhood of cohort members. Parental status will need to be considered in future studies. With the high tracing rates achieved, the dataset provides an important resource with which to evaluate multigenerational associations with health and development in parents, their offspring and grandchildren.

Ethnic variations in birthweight percentiles in Kuwait

The objectives of this retrospective study were to assess the effect of ethnicity on birthweight percentiles and to compare ethnic-specific percentiles with other references. Analysis was made of 35 768 singleton live births from 22 to 44 completed weeks of gestation at two major obstetric hospitals in Kuwait, after exclusion of data with inaccurate gestational age, major congenital abnormalities, stillbirths, and outlying birthweights. The population included four major ethnic groups: Gulf Arabs, Mediterranean Arabs, Egyptians, and a group combining Indians and Southeast Asians. Total population and ethnic-specific smoothed birthweight percentiles according to gestational age were developed. Indians-Asians had the smallest birthweights, the highest prevalence of small-for-gestational-age (SGA) birthweights and the lowest prevalence of large-for-gestational-age (LGA) birthweights. On the contrary, Egyptians had the largest birthweights, the lowest prevalence of SGA birthweights and the highest prevalence of LGA birthweights. Plotting our birthweights on a reference from Canada resulted in a low prediction rate for SGA and a low sensitivity in identifying LGA of all ethnic groups. We conclude that interpretation of fetal growth and birthweight should involve locally derived and ethnically specific percentiles based on accurately calculated gestational age.

Birthweight and relationship with infant, child and adult mortality in the Jerusalem perinatal study

There is growing evidence that several chronic adult diseases, such as coronary heart disease and stroke, can result from events occurring in fetal life. The aim of this study was to examine the relation between birthweight and all-cause mortality in young adults. We studied total mortality in a population-based cohort of 80 936 offspring born in Jerusalem in 1964-76. During an average follow-up of 28.8 years 2 324 984 person-years were contributed and 2092 deaths occurred. Overall, in both genders, the univariable and the multivariable Cox-proportional hazard models indicated a strong negative relationship between birthweight and total mortality, mostly because of infant deaths. At ages 1-14 birthweight seemed unrelated to all-cause mortality. In males aged 15+, birthweight was again a significant predictor of death (Hazard ratio (HR) = 0.88, 95% confidence interval (CI) [0.78, 0.99], for 1 standard deviation (SD) increase in birthweight). The analysis by categories suggested a general decreasing of the risk of mortality with increasing birthweight (HRs = 1.0, 1.02, 0.85, 0.77, 0.57 for those belonging to birthweight groups of < 2500 g, 2500-2999 g, 3000-3499 g, 3500-3999 g and > or = 4000 g, respectively). In females aged 15+ there was a J-shaped relation between birthweight and mortality but these associations were not statistically significant. These findings add to a growing body of evidence that events during intrauterine life have remote consequences for adult health and underline the need to consider gender differences.

Social inequalities in low birth weight in England and Wales: trends and implications for future population health

STUDY OBJECTIVE

To examine social inequalities and trends in low birth weight in England and Wales.

DESIGN

Analysis of routine birth data, comparing (a) couple and sole registered births, and (b) manual and non-manual occupational groups.

SETTING

England and Wales, 1993-2000.

MAIN RESULTS

Social inequalities in low birth weight were evident throughout 1993-2000: relative to the non-manual group, there is an increased risk for the manual group (range in RR 1.22-1.35) and sole registrations (RR 1.51-1.67). An estimated 6.5% (2979 births) of low birth weight in 2000 could have been avoided if risks associated with the manual group were absent, and 2.8% (1290 births) avoided if risks associated with sole registration were absent. Between 1993 and 2000, the low birthweight rate increased significantly with an estimated overall increase of 11%. Increases were evident in all social groups (15% in manual, 11% in sole registrations and 9% in non-manual); however relative to non-manual the increase in RRs were not statistically significant for manual or sole registrations. When multiple births are excluded, the rate of low birth weight is reduced but there is still a significant increase over time and social differentials are undiminished.

CONCLUSIONS

There are social inequalities in low birth weight in England and Wales that have not narrowed over an eight year period, 1993-2000. These inequalities are likely to affect childhood and adult health inequalities in the future, hence strategies will need to address differences in low birth weight and further monitoring of trends is therefore desirable.

Impact of low birthweight on subsequent fertility: population-based register study

Adverse birth outcomes may influence a family's wish for additional children. We investigated the influence of low birthweight in live births on subsequent fertility, and estimated secular trends of such an effect in a population-based cohort study of births arranged in consecutive sibship records in the Medical Birth Registry of Norway. We included births of order one to seven to all 587 785 mothers in Norway who had a first singleton birth in 1967-91. Associations between birthweight in 1 158 072 surviving index births of order one to six, 1967-91, and subsequent fertility (probability of another birth), 1967-97, were estimated as fertility ratios in Cox regression analysis. Giving birth to a live infant weighing < 3000 g had a negative effect on subsequent fertility, increasingly strong for decreasing birthweight. Low birthweight (<2500 g) was associated with a fertility ratio of 0.88 [95% confidence interval 0.87, 0.89]. This negative impact was stronger if the mother had also given birth to surviving children of low birthweight previously, particularly if combined with caesarean section in the most recent birth. The negative fertility effect of low birthweight grew slightly stronger between 1967 and approximately 1980, according to year of first birth. This trend paralleled reduced population fertility in the same period. The moderate negative impact of giving birth to a live infant of low birthweight on subsequent fertility could result from the combination of reduced wish for additional children and biological subfertility.

Birth weight, childhood socioeconomic environment, and cognitive development in the 1958 British birth cohort study

OBJECTIVES

To examine the combined effect of social class and weight at birth on cognitive trajectories during school age and the associations between birth weight and educational outcomes through to 33 years.

DESIGN

Longitudinal, population based, birth cohort study.

PARTICIPANTS

10 845 males and females born during 3-9 March 1958 with information on birth weight, social class, and cognitive tests.

MAIN OUTCOME MEASURES

Reading, maths, draw a man, copying designs, verbal and non-verbal ability tests at ages 7, 11, and 16, highest qualifications achieved by 33, and trajectories of maths standardised scores at 7-16 years.

RESULTS

The outcome of all childhood cognitive tests and educational achievements improved significantly with increasing birth weight. Analysis of maths scores at 7 and of highest qualifications achieved by 33 showed that the relations were robust to adjustment for potential confounding factors. For each kilogram increase in birth weight, maths z score increased by 0.17 (adjusted estimate 0.15, 95% confidence interval 0.10 to 0.21) for males and 0.21 (0.20, 0.14 to 0.25) for females. Trajectories of maths z scores between 7 and 16 years diverged for different social class groups: participants from classes I and II increased their relative position on the score with increasing age, whereas classes IV and V showed a relative decline with increasing age. Birth weight explained much less of the variation in cognition than did social class (range 0.5-1.5% v 2.9-12.5%).

CONCLUSIONS

The postnatal environment has an overwhelming influence on cognitive function through to early adulthood, but these strong effects do not explain the weaker but independent association with birth weight.