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

Birthweights at term have increased globally: insights from a systematic review of 183 million births

OBJECTIVE

This study aimed to assess global trends in mean birthweights at term, as reported in peer-reviewed literature.

DATA SOURCES

We electronically searched PubMed, Embase, and Web of Science up to September 2023, using combinations of the search terms: "birth weight"; "birth-weight"; "birthweight"; "trend". There were no restrictions based on language or geographic area.

STUDY ELIGIBILITY CRITERIA

We included all ecological and observational studies reporting mean birthweight at term as a continuous numerical variable over time.

METHODS

We assessed the quality of included studies using the Dufault and Klar checklist modified by Betran et al. Univariate and multivariate linear models were used to examine the effects of time (years) and geographical origins. Subgroup analyses focused on national data sources and on data collected from 1950 onward.

RESULTS

Among 6447 reviewed articles, 29 met our criteria, reporting mean birthweight data from over 183 million infants worldwide. Most studies were hospital-based (48.3%), 44.8% used national data, and a minority used municipality, community, or regional data (6.9%). Geographically, North America (31.0%) had the highest representation, followed by Asia and Europe (27.6% each), and South America and Oceania (6.9% each). Our univariate linear regression model (Model 1) revealed a significant increase in mean birthweight at term over time (4.74 g/y; 95% confidence interval, 3.95-5.53; P<.001). Model 2, incorporating continental dummy variables into the first model, confirmed this trend (3.85 g/y; 95% confidence interval, 2.96-4.74; P<.001). Model 3, focusing on available national data, did not find a significant relationship. Model 4 narrowed its focus on records from 1950 onward, reporting a robust annual increase of 7.26 g/y (95% confidence interval, 6.19-8.33; P<.001). Model 5, adjusting for the number of participants included in each study, reported a conclusive mean term birthweight increase of 1.46 g/y (95% confidence interval, 0.74-2.18; P<.001).

CONCLUSION

This systematic review of 29 studies shows an increase in term birthweights over time, particularly when considering data since 1950. Limitations include study quality variations, data source diversity, and data sparsity, underscoring the need for future research to use precise gestational age distinctions and predetermined time frames to gain a deeper understanding of this trend and its implications for maternal and child health.

A Scoping Review of Socioeconomic Inequalities in Distributions of Birth Outcomes: Through a Conceptual and Methodological Lens

INTRODUCTION

The extant literature has examined social inequalities in high-risk categories of birth weight and gestational age (i.e., low birth weight and preterm birth) with little attention given to their distributional nature. As such, a scoping review was conducted to understand how researchers have conceptualized and analyzed socioeconomic inequalities in entire distributions of these birth outcomes.

METHODS

Bibliographic databases were searched from their inception until August 2016 for articles from five similar, English-speaking, advanced capitalist democracies: Canada, United States, United Kingdom, Australia and New Zealand.

RESULTS

Twenty-one studies were included in the review, all of which provided rationales for examining socioeconomic inequalities in the entire distribution of birth weight. Yet, only three studies examined non-uniform associations of socioeconomic factors across the distribution of birth weight using conditional quantile regression, while the majority focused on mean birth weight using descriptive analysis or linear regression to analyze inequalities. Nevertheless, study results indicated that socioeconomic inequalities exist throughout the distribution of birth weight, extending beyond the high-risk category of low birth weight.

DISCUSSION

Although social inequalities in distributions of birth weight have been conceptualized, few studies have analytically engaged with this concept. As such, this review supports further investigation of distributional inequalities in birth outcomes using methodology which allows one to empirically quantify and explain differences in population risk distributions, rather than solely between infants born low birth weight or preterm birth, versus not.

Evaluation of Health in Pregnancy grants in Scotland: a natural experiment using routine data

Background

Pregnancy and the period around birth are critical for the development and improvement of population health as well as the health of mothers and babies, with outcomes such as birthweight influencing adult health.

Objectives

We evaluated the clinical effectiveness and cost-effectiveness of the Health in Pregnancy (HiP) grants in Scotland, looking for differential outcomes when the scheme was in place, as well as before its implementation and after its withdrawal.

Design

The HiP grants were evaluated as a natural experiment using interrupted time series analysis. We had comparison groups of women who delivered before the grants were introduced and after the grants were withdrawn.

Setting

Scotland, UK.

Participants

A total of 525,400 singleton births delivered between 24 and 44 weeks in hospitals across Scotland between 1 January 2004 and 31 December 2014.

Intervention

The HiP grant was a universal, unconditional cash transfer of £190 for women in Great Britain and Northern Ireland reaching 25 weeks of pregnancy if they had sought health advice from a doctor or midwife. The grant was introduced for women with a due date on or after 6 April 2009 and subsequently withdrawn for women reaching the 25th week of pregnancy on or after 1 January 2011. The programme was paid for by Her Majesty’s Treasury.

Main outcome measures

Our primary outcome measure was birthweight. Secondary outcome measures included maternal behaviour, measures of size, measures of stage and birth outcomes.

Data sources

The data came from the Scottish maternity and neonatal database held by the Information and Services Division at the NHS National Services Scotland.

Results

There was no statistically significant effect on birthweight, with births during the intervention period being, on average, 2.3 g [95% confidence interval (CI) –1.9  to 6.6 g] lighter than would have been expected had the pre-intervention trend continued. Mean gestational age at booking (i.e. the first antenatal appointment with a health-care professional) decreased by 0.35 weeks (95% CI 0.29 to 0.41 weeks) and the odds of booking before 25 weeks increased by 10% [odds ratio (OR) 1.10, 95% CI 1.02 to 1.18] during the intervention but decreased again post intervention (OR 0.91, 95% CI 0.83 to 1.00). The odds of neonatal death increased by 84% (OR 1.84, 95% CI 1.22 to 2.78) and the odds of having an emergency caesarean section increased by 7% (OR 1.07, 95% CI 1.03 to 1.10) during the intervention period.

Conclusions

The decrease in the odds of booking before 25 weeks following withdrawal of the intervention makes it likely that the HiP grants influenced maternal health-care-seeking behaviour. It is unclear why neonatal mortality and emergency caesarean section rates increased, but plausible explanations include the effects of the swine flu outbreak in 2009 and the global financial crisis. The study is limited by its non-randomised design. Future research could assess an eligibility threshold for payment earlier than the 25th week of pregnancy.

Funding

The National Institute for Health Research Public Health Research programme. The Social and Public Health Sciences Unit is core funded by the Medical Research Council (MC_UU_12017/13) and the Scottish Government Chief Scientist Office (SPHSU13).

Pathways between Socioeconomic Disadvantage and Childhood Growth in the Scottish Longitudinal Study, 1991-2001

Socioeconomically disadvantaged children are more likely to be of shorter stature and overweight, leading to greater risk of obesity in adulthood. Disentangling the mediatory pathways between socioeconomic disadvantage and childhood size may help in the development of appropriate policies aimed at reducing these health inequalities. We aimed to elucidate the putative mediatory role of birth weight using a representative sample of the Scottish population born 1991-2001 (n = 16,628). Estimated height and overweight/obesity at age 4.5 years were related to three measures of socioeconomic disadvantage (mother's education, Scottish Index of Multiple Deprivation, synthetic weekly income). Mediation was examined using two approaches: a 'traditional' mediation analysis and a counterfactual-based mediation analysis. Both analyses identified a negative effect of each measure of socioeconomic disadvantage on height, mediated to some extent by birth weight, and a positive 'direct effect' of mother's education and Scottish Index of Multiple Deprivation on overweight/obesity, which was partly counterbalanced by a negative 'indirect effect'. The extent of mediation estimated when adopting the traditional approach was greater than when adopting the counterfactual-based approach because of inappropriate handling of intermediate confounding in the former. Our findings suggest that higher birth weight in more disadvantaged groups is associated with reduced social inequalities in height but also with increased inequalities in overweight/obesity.

Sex-Differences in the Metabolic Health of Offspring of Parents with Diabetes: A Record-Linkage Study

Maternal diabetes in pregnancy affects offspring health. The impact of parental diabetes on offspring health is unclear. We investigated the impact of parental diabetes on the metabolic-health of adult-offspring who did not themselves have diabetes. Data from the Generation Scotland: Scottish Family Health Study, a population-based family cohort, were record-linked to subjects’ own diabetes medical records. From F₀-parents, we identified F₁-offspring of: mothers with diabetes (OMD, n = 409), fathers with diabetes (OFD, n = 468), no parent with diabetes (ONoPD, n = 2489). Metabolic syndrome, body, biochemical measurements and blood-pressures were compared between F₁-offspring groups by sex. A higher proportion of female OMD had metabolic syndrome than female OFD or ONoPD (P<0.0001). In female offspring, predictors of metabolic syndrome were: having a mother with diabetes (OR = 1.78, CI 1.03–3.07, [reference ONoPD]), body mass index (BMI, OR = 1.21, CI 1.13–1.30) and age (OR = 1.03, CI 1.01–1.06). In male offspring, predictors of metabolic syndrome were: BMI (OR = 1.18, CI 1.09–1.29) and percent body-fat (OR = 1.12, CI 1.05–1.19). In both sexes, OMD had higher blood-pressures than OFD (P<0.0001). In females, OMD had higher glucose (P<0.0001) and percent body-fat (P<0.0001) compared with OFD or ONoPD. OMD and OFD both had increased waist-measurements (P<0.0001), BMI (P<0.0001) and percent body-fat (P<0.0001) compared with ONoPD. Female OMD and OFD had lower HDL-cholesterol levels (P<0.0001) than female ONoPD. Parental diabetes is associated with higher offspring-BMI and body-fat. In female offspring, maternal diabetes increased the odds of metabolic syndrome, even after adjusting for BMI. Further investigations are required to determine the mechanisms involved.

[Study of low birth weight associated with maternal age and parity in a population of mother and children in Lubumbashi]

Introduction

Evaluer l'influence de l’âge maternel et de la parité sur la naissance d'un faible poids de naissance (FPN) à Lubumbashi.

Méthodes

Il s'agit d'une étude basée sur une analyse documentaire des dossiers médicaux des accouchées enregistrées dans les maternités des 10 hôpitaux généraux de référence (HGR) de la ville de Lubumbashi en République Démocratique du Congo entre le 1er décembre 2013 et le 31 mars 2014. Ces accouchées ont été réparties en deux groupes, en fonction du poids de naissance de leurs enfants: groupe I (femmes ayant accouché de nouveau-nés vivants dont le poids était inférieur à 2500 grammes) et groupe II (femmes ayant accouché de nouveau-nés vivants dont le poids était supérieur ou égal à 2500 grammes). Il s'agissait dans tous les cas de grossesses monofoetales âgées de 28 semaines ou plus. L’âge maternel et la parité ont été étudiés et comparés dans les deux groupes. Les données ont été analysées à l'aide des logiciels Épi info version 7.0 et SPSS version 19. Les différences étaient jugées significatives pour un seuil p < 0,05.

Résultats

La prévalence du FPN chez les nouveau-nés issus de ces accouchées était ainsi de 6,4% (71/1112). En analyse univariée, les femmes d’âge < 20 ans présentent un risque multiplié par 2,47 fois d'avoir un nouveau-né de FPN comparativement à celles de ≥20 ans (OR = 2,47; IC95%: 1,26-4,78) et celui pour les primipares d'avoir un enfant de FPN est 2,3 fois supérieur à celui de multipares (OR = 2,32; IC95%: 1,34-3,99). En faisant la régression logistique, nous avons observé que seule la parité est significativement corrélée au poids de naissance (OR ajusté = 2,61; IC95%: 1,43-4,74).

Conclusion

L’étude que nous avons menée montre que le taux de FPN diminue considérablement avec l’âge de la mère à partir de 20 ans et la multiparité.

The social determinants of infant mortality and birth outcomes in Western developed nations: a cross-country systematic review

Infant mortality (IM) and birth outcomes, key population health indicators, have lifelong implications for individuals, and are unequally distributed globally. Even among western industrialized nations, striking cross-country and within-country patterns are evident. We sought to better understand these variations across and within the United States of America (USA) and Western Europe (WE), by conceptualizing a social determinants of IM/birth outcomes framework, and systematically reviewing the empirical literature on hypothesized social determinants (e.g., social policies, neighbourhood deprivation, individual socioeconomic status (SES)) and intermediary determinants (e.g., health behaviours). To date, the evidence suggests that income inequality and social policies (e.g., maternal leave policies) may help to explain cross-country variations in IM/birth outcomes. Within countries, the evidence also supports neighbourhood SES (USA, WE) and income inequality (USA) as social determinants. By contrast, within-country social cohesion/social capital has been underexplored. At the individual level, mixed associations have been found between individual SES, race/ethnicity, and selected intermediary factors (e.g., psychosocial factors) with IM/birth outcomes. Meanwhile, this review identifies several methodological gaps, including the underuse of prospective designs and the presence of residual confounding in a number of studies. Ultimately, addressing such gaps including through novel approaches to strengthen causal inference and implementing both health and non-health policies may reduce inequities in IM/birth outcomes across the western developed world.

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.

No improvement in socioeconomic inequalities in birthweight and preterm birth over four decades: a population-based cohort study

BACKGROUND

Birthweight and gestational age are associated with socioeconomic deprivation, but the evidence in relation to temporal changes in these associations is sparse. We investigated changes in the associations between socioeconomic status (SES) and birthweight and gestational age in Newcastle upon Tyne, North of England, during 1961-2000.

METHODS

We used population-based data from hospital neonatal records on all singleton births to mothers resident in Newcastle (births with complete covariate information n = 113,182). We used linear regression to analyse the associations between neighbourhood SES and birthweight over the entire 40-year period and by decade, and logistic regression for associations with low birthweight (LBW) and preterm birth, adjusting for potential confounders.

RESULTS

There was a significant interaction between SES and decade of birth for birthweight (p = 0.028) and preterm birth (p < 0.001). Socioeconomic gradients were similar in each decade for birthweight outcomes, but for preterm birth, socioeconomic disparities were more evident in the later decades [for 1961-70, odds ratio (OR) was 1.1, 95% CI 0.9, 1.3, for the most deprived versus the least deprived quartile, while for 1991-2000, the corresponding OR was 1.5, 95% CI 1.3, 1.7]. In each decade, there was a significant decrease in birthweight adjusted for gestational age for the most deprived compared to the least deprived SES group [1961-1970: -113.4 g (95% CI-133.0, -93.8); 1991-2000: -97.5 g (95% CI-113.0, -82.0)], while there was a significant increase in birthweight in each SES group over time.

CONCLUSIONS

Socioeconomic inequalities did not narrow over the four decades for birthweight and widened for preterm birth. Mean birthweight adjusted for gestational age increased in all socioeconomic groups, suggesting an overall increase in fetal growth.

Use of multiple linear regression and logistic regression models to investigate changes in birthweight for term singleton infants in Scotland

AIM

To illustrate the use of regression and logistic regression models to investigate changes over time in size of babies particularly in relation to social deprivation, age of the mother and smoking.

BACKGROUND

Mean birthweight has been found to be increasing in many countries in recent years, but there are still a group of babies who are born with low birthweights.

DESIGN

Population-based retrospective cohort study.

METHOD

Multiple linear regression and logistic regression models are used to analyse data on term 'singleton births' from Scottish hospitals between 1994-2003.

RESULTS

Mothers who smoke are shown to give birth to lighter babies on average, a difference of approximately 0.57 Standard deviations lower (95% confidence interval. 0.55-0.58) when adjusted for sex and parity. These mothers are also more likely to have babies that are low birthweight (odds ratio 3.46, 95% confidence interval 3.30-3.63) compared with non-smokers. Low birthweight is 30% more likely where the mother lives in the most deprived areas compared with the least deprived, (odds ratio 1.30, 95% confidence interval 1.21-1.40).

CONCLUSIONS

Smoking during pregnancy is shown to have a detrimental effect on the size of infants at birth. This effect explains some, though not all, of the observed socioeconomic birthweight. It also explains much of the observed birthweight differences by the age of the mother.

RELEVANCE TO CLINICAL PRACTICE

  Identifying mothers at greater risk of having a low birthweight baby as important implications for the care and advice this group receives.

The influence of both individual and area based socioeconomic status on temporal trends in Caesarean sections in Scotland 1980-2000

BACKGROUND

Caesarean section rates have risen over the last 20 years. Elective Caesarean section rates have been shown to be linked to area deprivation in England, women in the most deprived areas were less likely to have an elective section than those in the most affluent areas. We examine whether individual social class, area deprivation or both are related to Caesarean sections in Scotland and investigate changes over time.

METHODS

Routine maternity discharge data from live singleton births in Scottish hospitals from three time periods were used; 1980-81 (n = 133,555), 1990-91 (n = 128,933) and 1999-2000 (n = 102,285). Multilevel logistic regression, with 3 levels (births, postcode sector and Health Board) was used to analyse emergency and elective Caesareans separately; analysis was further stratified by previous Caesarean section. The relative index of inequality (RII) was used to assess socioeconomic inequalities.

RESULTS

Between 1980-81 and 1999-2000 the emergency section rate increased from 6.3% to 11.9% and the elective rate from 3.6% to 5.5%. In 1980-81 and 1990-91 emergency Caesareans were more likely among women at the bottom of the social class hierarchy compared to those at the top (RII = 1.14, 95%CI 1.00-1.25 and RII = 1.13, 1.03-1.23 respectively) and also among women in the most deprived areas compared to those in the most affluent (RII = 1.18, 1.05-1.32 and RII = 1.13, 1.02-1.26 respectively). In 1999-2000 the odds of an elective section were lower for women at the bottom of the social class hierarchy than those at the top (RII = 0.87, 0.76-1.00) and also lower in women in the most deprived areas compared to those in the most affluent (RII = 0.85, 0.73-0.99).

CONCLUSIONS

Both individual social class and area deprivation are independently associated with Caesarean sections in Scotland. The tendency for disadvantaged women to be more likely to receive emergency sections disappeared at the same time as the likelihood of advantaged groups receiving elective sections increased.

The association of daily physical activity and birth outcome: a population-based cohort study

The potential relationship between daily physical activity and pregnancy outcome remains unclear because of the wide variation in study designs and physical activity assessment measures. We sought to prospectively quantify the potential effects of the various domains of physical activity on selected birth outcomes in a large unselected population. The sample consisted of 11,759 singleton pregnancies from the Avon longitudinal study of parents and children, United Kingdom. Information on daily physical activity was collected by postal questionnaire for self-report measures. Main outcome measures were birth weight, gestational age at delivery, preterm birth and survival. After controlling for confounders, a sedentary lifestyle and paid work during the second trimester of pregnancy were found to be associated with a lower birth weight, while ‘bending and stooping’ and ‘working night shifts’ were associated with a higher birth weight. There was no association between physical exertion and duration of gestation or survival. Repetitive boring tasks during the first trimester was weakly associated with an increased risk of preterm birth (<37 weeks) (adjusted odds ratio [OR] = 1.25, 95% CI 1.04–1.50). ‘Bending and stooping’ during the third trimester was associated with a reduced risk of preterm birth (adjusted OR = 0.73, 95% CI 0.63–0.84). Demanding physical activities do not have a harmful effect on the selected birth outcomes while a sedentary lifestyle is associated with a lower birth weight. In the absence of either medical or obstetric complications, pregnant women may safely continue their normal daily physical activities should they wish to do so.

Socio-economic and medical determinants of low birth weight in Iran: 20 years after establishment of a primary healthcare network

OBJECTIVE

Establishment of a primary healthcare network in Iran has provided free and universal access to primary health care. Although the health status of Iranians has improved since this network was established, the low-birthweight rate has not decreased. The objective of the present study was to describe socio-economic and medical factors related to low birth weight in the context of free and universal access to primary health care.

DESIGN

Descriptive, hospital-based prospective study.

METHODS

Data about socio-economic, reproductive and prenatal condition of 4510 live singleton births from June to October 2004 were gathered using a standard questionnaire by interview and record review. The effect of these conditions on birth weight was investigated using a logistic regression model.

RESULTS

Of 4510 newborns, 305 (6.8%) were low birth weight. Among these low-birthweight newborns, there were 159 preterm and 146 term newborns. Mothers with a primary and secondary education [odds ratio (OR) 6.83, 95% confidence interval (CI) 2.35-7.34 and OR 4.81, 95%CI 1.95-6.37, respectively], who lived with farmer and unskilled worker husbands (OR 2.52, 95%CI 1.12-4.66 and OR 2.91, 95%CI 1.35-2.52, respectively), with a birth interval of 1 year or less (OR 3.54, 95%CI 1.80-5.95) and height less than 155cm (OR 1.82, 95%CI 1.12-3.31) were more likely to have low-birthweight infants.

CONCLUSION

In the context of free and universal access to health care, it is recommended that policy makers should place more emphasis on education as it imparts knowledge and thus influences dietary habits and birth-spacing behaviour. This will lead to a better nutritional status, particularly in dealing with pregnancy, resulting in lower rates of low birth weight.

Diet and deprivation in pregnancy

Deprivation is associated with poor pregnancy outcome but the role of nutrition as a mediating factor is not well understood. We carried out a prospective cohort study of 1461 singleton pregnancies in Aberdeen, UK during 2000-6. We measured nutrient intake and supplement use, B vitamin and homocysteine status, birth weight, gestational age, neonatal treatment and socio-economic deprivation status. Women in the most deprived deciles were approximately 6 years younger and half as likely to take folic acid supplements periconceptually as the least deprived mothers. Deprivation was associated with low blood folate, high homocysteine and diets low in protein, fibre and many of the vitamins and minerals. The diets of the more deprived women were also characterised by low intakes of fruit, vegetables and oily fish and higher intakes of processed meat, fried potatoes, crisps and snacks. Deprivation was related to preterm birth (OR 1.14 (95 % CI 1.03, 1.25); P = 0.009) and whether the baby required neonatal treatment (OR 1.07 (95 % CI 1.01, 1.14); P = 0.028). Low birth weight was more common in women consuming diets low in vitamin C (OR 0.79 (95 % CI 0.64, 0.97); P = 0.028), riboflavin (OR 0.77 (95 % CI 0.63, 0.93); P = 0.008), pantothenic acid (OR 0.79 (95 % CI 0.65, 0.97); P = 0.023) and sugars (OR 0.78 (95 % CI 0.64, 0.96); P = 0.017) even after adjustment for deprivation index, smoking, marital status and parity. Deprivation in pregnancy is associated with diets poor in specific nutrients and poor diet appears to contribute to inequalities in pregnancy outcome. Improving the nutrient intake of disadvantaged women of childbearing age may potentially improve pregnancy outcome.

Investigating socio-economic disparities in preterm birth: evidence for selective study participation and selection bias

Selective study participation can theoretically lead to selection bias. We explored this issue in the context of a multicentre cohort study of socio-economic disparities in preterm birth. Women with singleton pregnancies were recruited from four large Montreal maternity hospitals and invited to return for an interview, vaginal examination and venepuncture at 24-26 weeks of gestation. We compared the observed preterm birth rate (ultrasound confirmed) among the 5146 cohort women to that expected based on all 108 724 Montreal Census Metropolitan Area (CMA) singleton births for 1998-2000. The observed preterm birth rate in the study cohort was 5.1%, compared with 6.3% in the CMA (P < 0.001) (unadjusted morbidity ratio [95% CI] = 0.80 [0.71, 0.90]). Within each stratum of maternal education and neighbourhood income (the latter based on postal code matched links to the 2001 Canadian census), cohort women had substantially lower rates of preterm birth than women from the CMA. No significant association between socio-economic status (SES) and preterm birth was observed in the study cohort, except among 'indicated' (non-spontaneous) cases. The association between neighbourhood income and preterm birth was biased to the null in the study cohort, with adjusted odds ratios in the poorest vs. richest quintiles of 1.01 [0.63, 1.64] in the cohort vs. 1.28 [1.18, 1.39] in the CMA, although no such bias was observed for the association with maternal education assessed at the individual level. We speculate that the lower-than-expected preterm birth rate and attenuated association between neighbourhood income and preterm birth may be related to selective participation by women more psychologically invested in their pregnancies. Investigators should consider the potential for biased associations in pregnancy/birth cohort studies, especially associations based on SES or race/ethnicity, and carry out sensitivity analyses to gauge their effects.

Temporal changes in key maternal and fetal factors affecting birth outcomes: a 32-year population-based study in an industrial city

Background

The link between maternal factors and birth outcomes is well established. Substantial changes in society and medical care over time have influenced women's reproductive choices and health, subsequently affecting birth outcomes. The objective of this study was to describe temporal changes in key maternal and fetal factors affecting birth outcomes in Newcastle upon Tyne over three decades, 1961–1992.

Methods

For these descriptive analyses we used data from a population-based birth record database constructed for the historical cohort Particulate Matter and Perinatal Events Research (PAMPER) study. The PAMPER database was created using details from paper-based hospital delivery and neonatal records for all births during 1961–1992 to mothers resident in Newcastle (out of a total of 109,086 singleton births, 97,809 hospital births with relevant information). In addition to hospital records, we used other sources for data collection on births not included in the delivery and neonatal records, for death and stillbirth registrations and for validation.

Results

The average family size decreased mainly due to a decline in the proportion of families with 3 or more children. The distribution of mean maternal ages in all and in primiparous women was lowest in the mid 1970s, corresponding to a peak in the proportion of teenage mothers. The proportion of older mothers declined until the late 1970s (from 16.5% to 3.4%) followed by a steady increase. Mean birthweight in all and term babies gradually increased from the mid 1970s. The increase in the percentage of preterm birth paralleled a two-fold increase in the percentage of caesarean section among preterm births during the last two decades. The gap between the most affluent and the most deprived groups of the population widened over the three decades.

Conclusion

Key maternal and fetal factors affecting birth outcomes, such as maternal age, parity, socioeconomic status, birthweight and gestational age, changed substantially during the 32-year period, from 1961 to 1992. The availability of accurate gestational age is extremely important for correct interpretation of trends in birthweight.

Influence of maternal and social factors as predictors of low birth weight in Italy

Background

The purpose of this study is to provide insight into the determinants of low birth weight (LBW) in Italy.

Methods

The study was carried out in a non-teaching hospital in Catanzaro (Italy). All LBW and very LBW newborns (200) were included in the study and a random sample of 400 newborns weighing ≥ 2500 g was selected. Data were collected from the delivery certificates during one year. Smoking activity of mother and familiar and/or social support during pregnancy was gathered through telephone interviews.

Results

Overall annual LBW rate was 11.8%. Among LBW newborn there were 125 preterm and 75 term. Younger mothers, those who smoked during pregnancy, and had fewer prenatal care visits were more likely to deliver a LBW child; moreover, preterm newborns, delivered by caesarean section, and twin or multiple birth were significantly more likely to have a LBW. The comparison of very LBW (<1500 g) to LBW newborns showed that a very LBW was significantly more likely in newborns delivered by less educated mothers, those who work outside the home, live in smaller towns, and had less echographies; moreover, as expected, very LBW newborns were more likely to be preterm.

Conclusion

Several modifiable factors affect the risk of LBW, even when universal access to health care is freely available, but socio-economic status appears to correlate only to very LBW.

Social class inequalities in perinatal outcomes: Scotland 1980-2000

OBJECTIVE

To examine social class inequalities in adverse perinatal events in Scotland between 1980 and 2000 and how these were influenced by other maternal risk factors.

DESIGN

Population based study using routine maternity discharge data.

SETTING

Scotland.

PARTICIPANTS

All women who gave birth to a live singleton baby in Scottish hospitals between 1980 and 2000 (n=1,282,172).

MAIN OUTCOME MEASURES

Low birth weight (LBW), preterm birth, and small for gestational age (SGA).

RESULTS

The distribution of social class changed over time, with the proportion of mothers with undetermined social class increasing from 3.9% in 1980-84 to 14.8% in 1995-2000. The relative index of inequality (RII) decreased during the 1980s for all outcomes. The RII then increased between the early and late 1990s (LBW from 2.09 (95%CI 1.97, 2.22) to 2.43 (2.29, 2.58), preterm from 1.52 (1.44, 1.61) to 1.75 (1.65, 1.86), and SGA from 2.28 (2.14, 2.42) to 2.49 (2.34, 2.66) respectively). Inequalities were greatest in married mothers, mothers aged over 35, mothers taller than 164 cm, and mothers with a parity of one or more. Inequalities were also greater by the end of the 1990s than at the start of the 1980s for women of parity one or more and for mothers who were not married.

CONCLUSION

Despite decreasing during the 1980s, inequalities in adverse perinatal outcomes increased during the 1990s in all strata defined by maternal characteristics.