Are our Babies Becoming Bigger?

Analysis of Sex-Specific Gene-by-Cohort and Genetic Correlation-by-Cohort Interaction in Educational and Reproductive Outcomes Using the UK Biobank Data

Synthesizing prior gene-by-cohort (G×C) interaction studies, we theorize that changes in genetic effects by social conditions depend on the level of resource constraints, the distribution and use of resources, structural constraints, and constraints on individual choice. Motivated by the theory, we explored several sex-specific G×C trends across a set of outcomes using 30 birth cohorts of UK Biobank data (N = 400,000). We find that genetic coefficients on years of schooling and secondary educational attainment substantially decrease, but genetic coefficients on college attainments only moderately increase. On the other hand, genetic coefficients for education ranks are stable. Genetic coefficients on reproductive behavior increase for younger cohorts. Additional genetic-correlation-by-cohort analysis shows shifting genetic correlations between education and reproductive behavior. Our results suggest that the G×C patterns are highly heterogenous and that social and genetic factors jointly shape the diversity of human phenotypes.

Evolution of the human birth canal

It seems puzzling why humans have evolved such a small and rigid birth canal that entails a relatively complex process of labor compared with the birth canal of our closest relatives, the great apes. This study reviewed insights into the evolution of the human birth canal from recent theoretical and empirical studies and discussed connections to obstetrics, gynecology, and orthopedics. Originating from the evolution of bipedality and the large human brain million years ago, the evolution of the human birth canal has been characterized by complex trade-off dynamics among multiple biological, environmental, and sociocultural factors. The long-held notion that a wider pelvis has not evolved because it would be disadvantageous for bipedal locomotion has not yet been empirically verified. However, recent clinical and biomechanical studies suggest that a larger birth canal would compromise pelvic floor stability and increase the risk of incontinence and pelvic organ prolapse. Several mammals have neonates that are equally large or even larger than human neonates compared to the size of the maternal birth canal. In these species, the pubic symphysis opens widely to allow successful delivery. Biomechanical and developmental constraints imposed by bipedality have hindered this evolutionary solution in humans and led to the comparatively rigid pelvic girdle in pregnant women. Mathematical models have shown why the evolutionary compromise to these antagonistic selective factors inevitably involves a certain rate of fetopelvic disproportion. In addition, these models predict that cesarean deliveries have disrupted the evolutionary equilibrium and led to new and ongoing evolutionary changes. Different forms of assisted birth have existed since the stone age and have become an integral part of human reproduction. Paradoxically, by buffering selection, they may also have hindered the evolution of a larger birth canal. Many of the biological, environmental, and sociocultural factors that have influenced the evolution of the human birth canal vary globally and are subject to ongoing transitions. These differences may have contributed to the global variation in the form of the birth canal and the difficulty of labor, and they likely continue to change human reproductive anatomy.

There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form

Compared to other primates, modern humans face high rates of maternal and neonatal morbidity and mortality during childbirth. Since the early 20th century, this "difficulty" of human parturition has prompted numerous evolutionary explanations, typically assuming antagonistic selective forces acting on maternal and fetal traits, which has been termed the "obstetrical dilemma." Recently, there has been a growing tendency among some anthropologists to question the difficulty of human childbirth and its evolutionary origin in an antagonistic selective regime. Partly, this stems from the motivation to combat increasing pathologization and overmedicalization of childbirth in industrialized countries. Some authors have argued that there is no obstetrical dilemma at all, and that the difficulty of childbirth mainly results from modern lifestyles and inappropriate and patriarchal obstetric practices. The failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions is sometimes interpreted as empirical support for discarding an obstetrical dilemma. Here we explain why these points are important but do not invalidate evolutionary explanations of human childbirth. We present robust empirical evidence and solid evolutionary theory supporting an obstetrical dilemma, yet one that is much more complex than originally conceived in the 20th century. We argue that evolutionary research does not hinder appropriate midwifery and obstetric care, nor does it promote negative views of female bodies. Understanding the evolutionary entanglement of biological and sociocultural factors underlying human childbirth can help us to understand individual variation in the risk factors of obstructed labor, and thus can contribute to more individualized maternal care.

The obstetrical dilemma hypothesis: there's life in the old dog yet

The term 'obstetrical dilemma' was coined by Washburn in 1960 to describe the trade-off between selection for a larger birth canal, permitting successful passage of a big-brained human neonate, and the smaller pelvic dimensions required for bipedal locomotion. His suggested solution to these antagonistic pressures was to give birth prematurely, explaining the unusual degree of neurological and physical immaturity, or secondary altriciality, observed in human infants. This proposed trade-off has traditionally been offered as the predominant evolutionary explanation for why human childbirth is so challenging, and inherently risky, compared to that of other primates. This perceived difficulty is likely due to the tight fit of fetal to maternal pelvic dimensions along with the convoluted shape of the birth canal and a comparatively low degree of ligamentous flexibility. Although the ideas combined under the obstetrical dilemma hypothesis originated almost a century ago, they have received renewed attention and empirical scrutiny in the last decade, with some researchers advocating complete rejection of the hypothesis and its assumptions. However, the hypothesis is complex because it presently captures several, mutually non-exclusive ideas: (i) there is an evolutionary trade-off resulting from opposing selection pressures on the pelvis; (ii) selection favouring a narrow pelvis specifically derives from bipedalism; (iii) human neonates are secondarily altricial because they are born relatively immature to ensure that they fit through the maternal bony pelvis; (iv) as a corollary to the asymmetric selection pressure for a spacious birth canal in females, humans evolved pronounced sexual dimorphism of pelvic shape. Recently, the hypothesis has been challenged on both empirical and theoretical grounds. Here, we appraise the original ideas captured under the 'obstetrical dilemma' and their subsequent evolution. We also evaluate complementary and alternative explanations for a tight fetopelvic fit and obstructed labour, including ecological factors related to nutrition and thermoregulation, constraints imposed by the stability of the pelvic floor or by maternal and fetal metabolism, the energetics of bipedalism, and variability in pelvic shape. This reveals that human childbirth is affected by a complex combination of evolutionary, ecological, and biocultural factors, which variably constrain maternal pelvic form and fetal growth. Our review demonstrates that it is unwarranted to reject the obstetrical dilemma hypothesis entirely because several of its fundamental assumptions have not been successfully discounted despite claims to the contrary. As such, the obstetrical dilemma remains a tenable hypothesis that can be used productively to guide evolutionary research.

Pelvic and neonatal size correlations in light of evolutionary hypotheses

OBJECTIVE

This study aimed to analyze the correlations between maternal size, neonatal size, and gestational variables.

METHODS

Our sample comprises 131 mother-infant dyads. We investigated correlations between five neonatal traits (gestational age, birthweight, head, suboccipito-brematic, and abdominal girths), three maternal traits (height, BMI, and uterus height), and three pelvic variables (conjugate, inter-spinous diameters, and sub-pubic angle) using computed tomography pelvimetry.

RESULTS

We found that the five neonatal traits were significantly intercorrelated. BMI was not correlated with neonatal traits while maternal height was correlated with birthweight, suboccipito-brematic, and abdominal girth. In the multiple regression models, gestational age was correlated with birthweight, head, and abdominal girth. Among the neonatal and pelvimetry correlations, conjugate diameter was slightly correlated with suboccipito-bregmatic girth, but inter-spinous and sub-pubic angle were not correlated with neonatal traits. Uterus height predicted all neonatal variables, but it was not correlated with gestational age.

DISCUSSION

Our results suggest that fetal growth is shaped by maternal phenotype rather than external ecological factors. The association of the inlet size with suboccipito-bregmatic girth reflects the tight fit between the neonatal brain and the maternal pelvis dimensions, an adaptation that would reduce the risk of cephalo-pelvic disproportion, while the absence of tight fit at the midplane and outlet could be due to the effect of the pelvic relaxation. Uterus distention is not the only mechanism involved in the initiation of parturition. Birth and pregnancy are complex processes and we suggest that maternal-neonatal associations are the result of a combination of multiple obstetric tradeoffs.

The impact of IVF on birthweight from 1991 to 2015: a cross-sectional study

STUDY QUESTION

Has birthweight (BW) changed over time among IVF-conceived singletons?

SUMMARY ANSWER

Singleton BW has increased markedly over the past 25 years.

WHAT IS KNOWN ALREADY

IVF conceived singletons have had a higher incidence of low BW compared to spontaneously conceived singletons, and this has raised concerns over long-term increased risks of cardio-metabolic disease. However, few causal links between IVF procedures and BW have been robustly established, and few studies have examined whether BW has changed over time as IVF techniques have developed.

STUDY DESIGN, SIZE, DURATION

A total of 2780 live born singletons conceived via IVF or ICSI treated in the reproductive medicine department of a single publicly funded tertiary care centre between 1991 and 2015 were included in this retrospective study. The primary outcome measure was singleton BW adjusted for gestational age, maternal parity and child gender. Multivariable linear regression models were used to estimate the associations between patient prognostic factors and IVF treatment procedures with adjusted BW.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All singletons conceived at the centre following IVF/ICSI using the mother's own oocytes, and non-donated fresh or frozen/thawed embryos with complete electronic data records, were investigated. Available electronic records were retrieved from the Human Fertilization and Embryology Authority for dataset collation. Multiple linear regression analysis was used to evaluate associations between IVF treatment parameters and BW, after adjusting for the year of treatment and patient characteristics and pregnancy factors.

MAIN RESULTS AND THE ROLE OF CHANCE

In the primary multivariable model, singleton BW increased by 7.4 g per year (95% CI: 3.2-11.6 g, P = 0.001), an increase of close to 180 g throughout the 25-year period after accounting for gestational age, maternal parity, child gender, IVF treatment parameters, patient prognostic characteristics and pregnancy factors. Fresh and frozen embryo transfer-conceived singletons showed a similar increase in BW. Frozen/thawed embryo transfer conceived singletons were on average 53 g heavier than their fresh embryo conceived counterparts (95% CI: 3.7-103.3 g, P = 0.035).

LIMITATIONS, REASONS FOR CAUTION

The independent variables included in the study were limited to those that have been consistently recorded and stored electronically over the past two decades.

WIDER IMPLICATIONS OF THE FINDINGS

There has been a progressive BW increase in IVF singletons over time in one large centre with consistent treatment eligibility criteria. Such a change is not seen in the general population of live born singletons in the UK or other developed countries, and seems to be specific to this IVF population. This may be a reflection of changes in practice such as undisturbed extended embryo culture to the blastocyst stage, optimized commercial culture media composition, single embryo transfer and ICSI. Moreover, singletons conceived from frozen/thawed embryos had higher birth weights when compared to their fresh embryo transfer counterparts. The causal pathway is unknown; however, it could be due to the impact on embryos of the freeze/thaw process, self-selection of embryos from couples who produce a surplus of embryos, and/or embryo replacement into a more receptive maternal environment.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the EU FP7 project grant, EpiHealthNet (FP7-PEOPLE-2012-ITN-317146). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Mean birth weight among term newborns: direction, magnitude and associated factors

A trend towards increasing birth weight has been shown, but factors that explain these trends have not been elucidated. The objectives of this study were to evaluate changes in mean birth weight of term newborns and to identify factors associated with them. All cohorts are population-based studies in which random samples of births (Ribeirão Preto, São Paulo State in 1978/1979, 1994 and 2010; Pelotas, Rio Grande do Sul State in 1982, 1993 and 2004; and São Luís, Maranhão State in 1997/1998 and 2010, Brazil). A total of 32,147 full-term, singleton live births were included. Mean birth weight reduced in the first study period (-89.1g in Ribeirão Preto from 1978/1979 to 1994, and -27.7g in Pelotas from 1982 to 1993) and increased +30.2g in Ribeirão Preto from 1994 to 2010 and +24.7g in São Luís from 1997 to 2010. In the first period, in Ribeirão Preto, mean birth weight reduction was steeper among mothers with high school education and among those born 39-41 weeks. In the second period, the increase in mean birth weight was steeper among mothers with low schooling in Ribeirão Preto and São Luís, females and those born 37-38 weeks in Ribeirão Preto and cesarean section in São Luís. Birth weight decreased in the first study period then increased thereafter. The variables that seem to have been able to explain these changes varied over time.

Secular changes in body height predict global rates of caesarean section

The massive global variation in caesarean-section (C-section) rate is usually attributed to socio-economic, medical and cultural heterogeneity. Here, we show that a third of the global variance in current national C-section rate can be explained by the trends of adult body height from the 1970s to the 1990s. In many countries, living conditions have continually improved during the last century, which has led to an increase in both fetal and adult average body size. As the fetus is one generation ahead of the mother, the fetus is likely to experience better environmental conditions during development than the mother did, causing a disproportionately large fetus and an increased risk of obstructed labour. A structural equation model revealed that socio-economic development and access to healthcare affect C-section rate via multiple causal pathways, but the strongest direct effect on C-section rate was body height change. These results indicate that the historical trajectory of socio-economic development affects-via its influence on pre- and postnatal growth-the intergenerational relationship between maternal and fetal dimensions and thus the difficulty of labour. This sheds new light on historic and prehistoric transitions of childbirth and questions the World Health Organization (WHO) suggestion for a global 'ideal' C-section rate.

Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma

Without cesarean delivery, obstructed labor can result in maternal and fetal injuries or even death given a disproportion in size between the fetus and the maternal birth canal. The precise frequency of obstructed labor is difficult to estimate because of the widespread use of cesarean delivery for indications other than proven cephalopelvic disproportion, but it has been estimated that at least 1 million mothers per year are affected by this disorder worldwide. Why is the fit between the fetus and the maternal pelvis so tight? Why did evolution not lead to a greater safety margin, as in other primates? Here we review current research and suggest new hypotheses on the evolution of human childbirth and pelvic morphology. In 1960, Washburn suggested that this obstetrical dilemma arose because the human pelvis is an evolutionary compromise between two functions, bipedal gait and childbirth. However, recent biomechanical and kinematic studies indicate that pelvic width does not considerably affect the efficiency of bipedal gait and thus is unlikely to have constrained the evolution of a wider birth canal. Instead, bipedalism may have primarily constrained the flexibility of the pubic symphysis during pregnancy, which opens much wider in most mammals with large fetuses than in humans. We argue that the birth canal is mainly constrained by the trade-off between 2 pregnancy-related functions: while a narrow pelvis is disadvantageous for childbirth, it offers better support for the weight exerted by the viscera and the large human fetus during the long gestation period. We discuss the implications of this hypothesis for understanding pelvic floor dysfunction. Furthermore, we propose that selection for a narrow pelvis has also acted in males because of the role of pelvic floor musculature in erectile function. Finally, we review the cliff-edge model of obstetric selection to explain why evolution cannot completely eliminate cephalopelvic disproportion. This model also predicts that the regular application of life-saving cesarean delivery has evolutionarily increased rates of cephalopelvic disproportion already. We address how evolutionary models contribute to understanding and decision making in obstetrics and gynecology as well as in devising health care policies.

Magnitude of fetal macrosomia and its associated factors at public health institutions of Hawassa city, southern Ethiopia

Objectives

This study aimed to determine the magnitude of fetal macrosomia and associated factors at public health institutions of Hawassa city, southern Ethiopia.

Results

In this study, the magnitude of fetal macrosomia found to be 11.86%. Being a male (AOR = 2.2, 95% CI 1.1–4.2), ≥ 37 weeks gestational age (AOR = 6.0, 95% CI 3.1–11.1) and having previous history of fetal macrosomia (AOR = 14.5, 95% CI 7.2–29.2) had a higher odds of fetal macrosomia. Moreover, the magnitude of fetal macrosomia is found be in the global range. Sex of the child, previous history of fetal macrosomia and gestational age were significantly associated with fetal macrosomia. The obstetric care providers should assess all pregnant women for history of fetal macrosomia which would help them to be prepared for the managements of maternal and perinatal complications.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-4005-2) contains supplementary material, which is available to authorized users.

Birth weight trends in England and Wales (1986-2012): babies are getting heavier

INTRODUCTION

Birth weight is a strong predictor of infant mortality, morbidity and later disease risk. Previous work from the 1980s indicated a shift in the UK towards heavier births; this descriptive analysis looks at more recent trends.

METHODS

Office for National Statistics (ONS) registration data on 17.2 million live, single births from 1986 to 2012 were investigated for temporal trends in mean birth weight, potential years of birth weight change and changes in the proportions of very low (<1500 g), low (<2500 g) and high (≥4000 g) birth weight. Analysis used multiple linear and logistic regression adjusted for maternal age, marital status, area-level deprivation and ethnicity. Additional analyses used the ONS NHS Numbers for Babies data set for 2006-2012, which has information on individual ethnicity and gestational age.

RESULTS

Over 27 years there was an increase in birth weight of 43 g (95% CI 42 to 44) in females and 44 g (95% CI 43 to 45) in males, driven by birth weight increases between 1986-1990 and 2007-2012. There was a concurrent decreased risk of having low birth weight but an 8% increased risk in males and 10% increased risk in females of having high birth weight. For 2006-2012 the birth weight increase was greater in preterm as compared with term births.

CONCLUSIONS

Since 1986 the birth weight distribution of live, single births in England and Wales has shifted towards heavier births, partly explained by increases in maternal age and non-white ethnicity, as well as changes in deprivation levels. Other potential influences include increases in maternal obesity and reductions in smoking prevalence particularly following the introduction of legislation restricting smoking in public places in 2007.

Cliff-edge model predicts intergenerational predisposition to dystocia and Caesarean delivery

The cliff-edge model explains the evolutionary persistence of relatively high incidences of fetopelvic disproportion (FPD), the mismatch of fetal and maternal dimensions during human childbirth. It also predicts that FPD rates have increased evolutionarily since the regular use of Caesarean sections. Here we show that the model also explains why women born by Caesarean because of FPD are about twice as likely to develop FPD in their own childbirth compared with women born vaginally. This theoretical prediction of a complex epidemiological pattern lends support to the cliff-edge model and its underlying assumptions.

Recently, we presented the cliff-edge model to explain the evolutionary persistence of relatively high incidences of fetopelvic disproportion (FPD) in human childbirth. According to this model, the regular application of Caesarean sections since the mid-20th century has triggered an evolutionary increase of fetal size relative to the dimensions of the maternal birth canal, which, in turn, has inflated incidences of FPD. While this prediction is difficult to test in epidemiological data on Caesarean sections, the model also implies that women born by Caesarean because of FPD are more likely to develop FPD in their own childbirth compared with women born vaginally. Multigenerational epidemiological studies indeed evidence such an intergenerational predisposition to surgical delivery. When confined to anatomical indications, these studies report risks for Caesarean up to twice as high for women born by Caesarean compared with women born vaginally. These findings provide independent support for our model, which we show here predicts that the risk of FPD for mothers born by Caesarean because of FPD is 2.8 times the risk for mothers born vaginally. The congruence between these data and our prediction lends support to the cliff-edge model of obstetric selection and its underlying assumptions, despite the genetic and anatomical idealizations involved.

Cliff-edge model of obstetric selection in humans

The strikingly high incidence of obstructed labor due to the disproportion of fetal size and the mother's pelvic dimensions has puzzled evolutionary scientists for decades. Here we propose that these high rates are a direct consequence of the distinct characteristics of human obstetric selection. Neonatal size relative to the birth-relevant maternal dimensions is highly variable and positively associated with reproductive success until it reaches a critical value, beyond which natural delivery becomes impossible. As a consequence, the symmetric phenotype distribution cannot match the highly asymmetric, cliff-edged fitness distribution well: The optimal phenotype distribution that maximizes population mean fitness entails a fraction of individuals falling beyond the "fitness edge" (i.e., those with fetopelvic disproportion). Using a simple mathematical model, we show that weak directional selection for a large neonate, a narrow pelvic canal, or both is sufficient to account for the considerable incidence of fetopelvic disproportion. Based on this model, we predict that the regular use of Caesarean sections throughout the last decades has led to an evolutionary increase of fetopelvic disproportion rates by 10 to 20%.

The Growth Pattern of Tibetan Infants at High Altitudes: a Cohort Study in Rural Tibet region

Studies on growth pattern of Tibetan infants and the difference from other child groups were limited due to its special living environment and unique customs. In this study, 253 Tibetan infants were followed-up from their birth to 12^th month in rural Tibet. Five visits were conducted and weight and length were measured at each visit. Mixed model was employed to analyze the growth pattern of Tibetan infants and its comparison to the Han infants. Propensity Scores (PS) technique was adopted to control for the potential confounding factors. The mixed model found that the birth weight/length had a negative impact on the increment of Tibetan infants after birth (weight: β = -0.6819, P < 0.0001, length: β = -0.9571, P < 0.0001). The weight increment of Tibetan infants was greater than Han infant with age (β_age*ethnic = 0.0345, P < 0.001), after using PS as a covariant. And another mixed model in which PS was used as a matching factor found similar trend. Compared with Chinese Han infants, Tibetan infants were lower weight and shorter length within one year after birth but they had greater increment of weight, suggesting that Tibetan infants might have a significant catch-up growth within the first year of life.

Education, infant mortality, and low birth weight in Sweden 1973—1990: Emergence of the low birth weight paradox

Aims: Educational differences in infant mortality, birth weight, and birth weight-specific infant mortality in Sweden were analysed. The ``low birth weight paradox'', where low birth weight infants have a lower mortality risk if born to women of lower rather than higher social strata, was addressed. Methods: The study includes about a million single births 1973—90 to women born 1946—60. There were 6,544 infant deaths and 35,334 low birth weight infants. Analysis conducted on six-year time periods was restricted to 652,859 births to women aged 25—32 at the time of delivery. Odds ratios and 95% CI were estimated by logistic regression. Birth weight-specific infant mortality rates were calculated by education. Results: Infants of women with low/low intermediate education had significantly higher odds ratios than those of highly educated women of being of low birth weight or of dying. If one compares only the infants of women with low and high education, these differences were accentuated over time. The low birth weight paradox appears over time. Conclusion: The widening differences in infant mortality and low birth weight over time may be caused by the decrease in women with low education, signifying increased selection and growing social disadvantage in this group. The emergence of the low birth weight paradox suggests that the distribution of causes of low birth weight differs between educational groups, and further that these causes are differently related to infant mortality. To disentangle these two groups of causes and their effects on infant mortality seems highly relevant.

Routinely collected English birth data sets: comparisons and recommendations for reproductive epidemiology

BACKGROUND

In England there are four national routinely collected data sets on births: Office for National Statistics (ONS) births based on birth registrations; Hospital Episode Statistics (HES) deliveries (mothers' information); HES births (babies' information); and NHS Numbers for Babies (NN4B) based on ONS births plus gestational age and ethnicity information. This study describes and compares these data, with the aim of recommending the most appropriate data set(s) for use in epidemiological research and surveillance.

METHODS

We assessed the completeness and quality of the data sets in relation to use in epidemiological research and surveillance and produced detailed descriptive statistics on common reproductive outcomes for each data set including temporal and spatial trends.

RESULTS

ONS births is a high quality complete data set but lacks interpretive and clinical information. HES deliveries showed good agreement with ONS births but HES births showed larger amounts of missing or unavailable data. Both HES data sets had improved quality from 2003 onwards, but showed some local spatial variability. NN4B showed excellent agreement with ONS and HES deliveries for the years available (2006-2010). Annual number of births increased by 17.6% comparing 2002 with 2010 (ONS births). Approximately 6% of births were of low birth weight (2.6% term low birth weight) and 0.5% were stillbirths.

CONCLUSIONS

Routinely collected data on births provide a valuable resource for researchers. ONS and NN4B offer the most complete and accurate record of births. Where more detailed clinical information is required, HES deliveries offers a high quality data set that captures the majority of English births.

Large for Gestational Age Births Among South Indian Women: Temporal Trend and Risk Factors from 1996 to 2010

BACKGROUND/PURPOSE

Mean birth weight is a good health indicator for any population. In the recent past, there have been many reports in the West indicating that there has been an increase in the proportion of large for gestational age (LGA) babies. The objective is to describe the change in the incidence of LGA babies from 1996 to 2010 in South India and the maternal risk factors.

METHODS

A rotational sampling scheme was used, i.e., the 12 months of the year were divided into 4 quarters and a month was from each quarter was selected rotationally. All deliveries for that month were considered. Only deliveries that occurred between 28 and 42 weeks of pregnancy were considered. The association between risk variables was studied using multivariable logistic regression.

RESULTS

There were 35,718 deliveries that occurred during these 15-year-study period in the gestational age 28-42 weeks were registered through the outpatient clinics. The incidence of LGA was 9.4 % that has mostly remained at the same level. The incidence of LGA in mothers with gestational diabetes was 6.7, 3 and 17.6 % in overweight, obese and gestational l diabetes mothers. Overweight, obesity in pregnant women and cesarean section were significant risk factors.

CONCLUSION

Unlike in Western countries, where the incidence of LGA babies has spiraled upward, has remained nearly at the same level over one and a half decades, in South India. The risk factors for giving birth to LGA babies in South India were similar to other studies.

Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma

Compared with other primates, childbirth is remarkably difficult in humans because the head of a human neonate is large relative to the birth-relevant dimensions of the maternal pelvis. It seems puzzling that females have not evolved wider pelvises despite the high maternal mortality and morbidity risk connected to childbirth. Despite this seeming lack of change in average pelvic morphology, we show that humans have evolved a complex link between pelvis shape, stature, and head circumference that was not recognized before. The identified covariance patterns contribute to ameliorate the "obstetric dilemma." Females with a large head, who are likely to give birth to neonates with a large head, possess birth canals that are shaped to better accommodate large-headed neonates. Short females with an increased risk of cephalopelvic mismatch possess a rounder inlet, which is beneficial for obstetrics. We suggest that these covariances have evolved by the strong correlational selection resulting from childbirth. Although males are not subject to obstetric selection, they also show part of these association patterns, indicating a genetic-developmental origin of integration.

Infant birthweight and risk of childhood cancer: international population-based case control studies of 40 000 cases

BACKGROUND

High birthweight is an established risk factor for childhood leukaemia. Its association with other childhood cancers is less clear, with studies hampered by low case numbers.

METHODS

We used two large independent datasets to explore risk associations between birthweight and all subtypes of childhood cancer. Data for 16 554 cases and 53 716 controls were obtained by linkage of birth to cancer registration records across five US states, and 23 772 cases and 33 206 controls were obtained from the UK National Registry of Childhood Tumours. US, but not UK, data were adjusted for gestational age, birth order, plurality, and maternal age and race/ethnicity.

RESULTS

Risk associations were found between birthweight and several childhood cancers, with strikingly similar results between datasets. Total cancer risk increased linearly with each 0.5 kg increase in birthweight in both the US [odds ratio 1.06 (95% confidence interval 1.04, 1.08)] and UK [1.06 (1.05, 1.08)] datasets. Risk was strongest for leukaemia [USA: 1.10 (1.06, 1.13), UK: 1.07 (1.04, 1.10)], tumours of the central nervous system [USA: 1.05 (1.01, 1.08), UK: 1.07 (1.04, 1.10)], renal tumours [USA: 1.17 (1.10, 1.24), UK: 1.12 (1.06, 1.19)] and soft tissue sarcomas [USA: 1.12 (1.05, 1.20), UK: 1.07 (1.00, 1.13)]. In contrast, increasing birthweight decreased the risk of hepatic tumours [USA: 0.77 (0.69, 0.85), UK: 0.79 (0.71, 0.89) per 0.5 kg increase]. Associations were also observed between high birthweight and risk of neuroblastoma, lymphomas, germ cell tumours and malignant melanomas. For some cancer subtypes, risk associations with birthweight were non-linear. We observed no association between birthweight and risk of retinoblastoma or bone tumours.

CONCLUSIONS

Approximately half of all childhood cancers exhibit associations with birthweight. The apparent independence from other factors indicates the importance of intrauterine growth regulation in the aetiology of these diseases.

Adverse effects of parental smoking during pregnancy in urban and rural areas

Background

Parental smoking during pregnancy is associated with lower birthweight and gestational age, as well as with the risks of low birthweight (LBW) and preterm birth. The present study aims to assess the association of parental smoking during pregnancy with birth outcomes in urban and rural areas.

Methods

This was a secondary analysis of data collected in the Indonesia Family Life Survey, between 1993 and 2007, the first national prospective longitudinal cohort study in Indonesia. Retrospective data of parental smoking habits, socioeconomic status, pregnancy history and birth outcomes were collected from parents with children aged 0 to 5 years (n = 3789). We assessed the relationships between the amount of parental smoking during pregnancy with birthweight (LBW) and with gestational age (preterm birth).

Results

We found a significant reduction in birthweight to be associated with maternal smoking. Smoking (except for paternal smoking) was associated with a decrease in the gestational age and an increased risk of preterm birth. Different associations were found in urban area, infants born to smoking fathers and both smoking parents (>20 cigarettes/day for both cases) had a significant reduction in birthweight and gestational age as well as an increased risk of LBW and preterm birth.

Conclusions

Residence was found to be an effect modifier of the relation between parental smoking during pregnancy, amount of parental smoking, and birth outcomes on their children. Smoking cessation/reduction and smoking intervention program should be advised and prioritized to the area that is more prone to the adverse birth outcomes.

Predictors and pregnancy outcomes associated with a newborn birth weight of 4000 g or more in Lusaka, Zambia

OBJECTIVE

To identify predictors and outcomes associated with a birth weight of 4000g or more in Lusaka, Zambia.

METHODS

Data from women who delivered between February 2006 and August 2011 were obtained from electronic perinatal records at 25 public sector facilities in Lusaka. Macrosomia was defined as a birth weight of 4000g or more and normal birth weight as 2500-3999g. Maternal and newborn characteristics were analyzed for association with macrosomia.

RESULTS

There were 4717 macrosomic and 187 117 normal birth weight newborns. The strongest predictors of macrosomia were high BMI (adjusted odds ratio [AOR], 2.88; 95% confidence interval [CI], 1.95-4.24), prior macrosomic newborn (AOR, 7.60; 95% CI, 6.81-8.49), and history of diabetes (AOR, 3.09; 95% CI, 1.36-6.98). Macrosomic newborns were at increased risk for cesarean delivery (AOR, 1.63; 95% CI, 1.35-1.96), fresh stillbirth (AOR, 2.24; 95% CI, 1.56-3.21), Apgar score of under 7 at 5minutes (AOR, 2.03; 95% CI, 1.33-3.11), and neonatal intensive care admission (AOR, 2.07; 95% CI, 1.32-3.23).

CONCLUSION

Screening for macrosomia should be considered for high-risk patients in Sub-Saharan Africa. Institutional delivery at facilities with operating rooms and neonatal intensive care services should be encouraged.

Adverse maternal outcomes associated with fetal macrosomia: what are the risk factors beyond birthweight?

Background

To identify risk factors, beyond fetal weight, associated with adverse maternal outcomes in delivering infants with a birthweight of 4000 g or greater, and to quantify their role in maternal complications.

Methods

All women (n = 1564) with singleton pregnancies who attempted vaginal delivery and delivered infants weighing at least 4000 g, in two French tertiary care centers from 2005 to 2008, were included in our study. The studied outcome was maternal complications defined as composite item including the occurrence of a third- or fourth-degree perineal laceration, or the occurrence of severe postpartum hemorrhage requiring the use of prostaglandins, uterine artery embolization, internal iliac artery ligation or haemostatic hysterectomy, or the occurrence of blood transfusion. Univariate analysis, multivariable logistic regression and estimation of attributable risk were used.

Results

Maternal complications were increased in Asian women (adjusted odds ratio [aOR], 3.1; 95% confidence interval [CI], 1.1–9.3, Attributable risk (AR): 3%), in prolonged labor (aOR = 1.9 [95% CI; 1.1–3.4], AR = 12%) and in cesarean delivery during labor (aOR = 2.2 [95% CI; 1.3–3.9], AR = 17%). Delivering infants with a birthweight > 4500 g also increased the occurrence of maternal complications (aOR = 2.7 [95% CI; 1.4–5.1]) but with an attributable risk of only 10%. Multiparous women with a previous delivery of a macrosomic infant were at lower risk of maternal complications (aOR = 0.5 [95% CI; 0.2–0.9]).

Conclusion

In women delivering infants with a birthweight of 4000 g or greater, some maternal characteristics as well as labor parameters may worsen maternal outcome beyond the influence of increased fetal weight.

New reference curves for head circumference at birth, by gestational age

BACKGROUND

The measurement of head circumference (HC) at birth reflects intrauterine brain development. HC charts currently used in Canada are either dated, mixed-gender, nonrepresentative of lower gestational ages (GAs), or reflective of other populations.

METHODS

To create both birth weight and HC curves, we combined weight and HC data from the Canadian Neonatal Network (CNN) database (admissions in NICUs across Canada) with McGill's Obstetrical Neonatal Database (MOND; all births at a tertiary hospital in Montreal, Canada). We included CNN data for GAs of 23 to 34 weeks (2003-2007) and MOND data for GAs of 35 to 41 weeks (1995-2006). Nonsingletons, congenital anomalies, and measurements greater than ±4 SD from the mean were excluded. Distributions of birth weight and HC at each GA were statistically (penalized spline regression) smoothed. Birth weight curves were compared with recent Canadian reference curves and HC curves with historical and/or frequently used curves.

RESULTS

We included 39,896 births (3121 births at <30 weeks' GA) to generate the curves. Current weight curves were similar to Canadian reference charts for both genders. Weight and HC measurements in boys were higher than in girls. When classified according to recent international references, the proportion of CNN-MOND infants at ≥32 weeks' GA with HCs <10th percentile was significantly underestimated. When classified according to historical reference curves, a significant number of CNN-MOND infants of all GAs with HCs <10th and >90th percentiles were misclassified.

CONCLUSIONS

We developed recent gender-specific reference curves for HC at birth for singletons at 23 to 41 completed weeks' GA, which included a large number of very premature infants, reflecting the current geotemporal Canadian population.

Growth in small-for-gestational-age preterm-born children from 0 to 4 years: the role of both prematurity and SGA status

BACKGROUND

Fullterm small-for-gestational-age children (SGAs) are known for their ability to catch up on growth. Nevertheless, increased risk of growth restriction remains. Evidence on preterm SGA children's growth is lacking.

OBJECTIVE

To determine absolute gains in height and weight, relative growth, and growth restriction in preterm SGAs from 0 to 4 years and how prematurity and SGA status affect these measures.

DESIGN/METHODS

Community-based cohort study, n = 1,648 preterm-born (gestational age <36 weeks, 57 SGA) and 605 term-born (12 SGA). We defined SGA as a birth weight less than -2 SD (P 2.3) compared to counterparts matched for gestational age. Height, weight, and head circumference were obtained from medical records and translated to z-scores. We defined growth restriction as height or weight less than -2 SD compared to fullterm appropriate-for-gestational-age children (AGAs).

RESULTS

Absolute height and weight gains were similar, but the relative growth of preterms and fullterms differed. Preterm AGAs and fullterm SGAs, although not reaching it, caught up towards the fullterm AGA median (z-scores at 4 years: -0.3 to -1.0). By contrast, preterm SGA children's z-scores were still -1.4 to -1.7. Head circumference growth was less affected by prematurity and SGA birth (z-scores at 1 year: 0.1 to -0.7). Catch-up growth mainly took place during infancy. 30-39% of all preterm SGAs showed growth restriction at 4 years.

CONCLUSIONS

Growth in preterm SGAs is affected considerably by the joint effects of preterm birth and SGA status, resulting in a high proportion of growth restriction.

Maternal Characteristics and Temporal Trends in Birth Outcomes: Comparison between Spanish and Migrant Mothers

Low birth weight and preterm babies have been increasing in Spain since 1980, coinciding with important changes in the social and demographic structure of childbearing populations—including the contribution of a 25% of foreign mothers—and with increasing medical intervention in births. This study, based on 5,990,613 births, compares the temporary trends in reproductive patterns and birth outcomes in Spanish and foreign mothers during the period 1996–2009 and evaluates for the years 2007 to 2009 the relative contribution of mother's origin and Caesarean section to birth weight variability. Foreign mothers maintain their own reproductive pattern, whereas negative birth outcomes increase in all groups. Results from logistic regression analysis show that besides late maternity and primiparity also Caesarean section increases the risk for low birth weight. The reduction in Caesarean section rates between 2007 and 2009 might explain the reduction of low birth weight detected. A change of tendency simultaneously appears in most maternal and newborn characteristics, and in the mode of delivery in all ethnic groups since 2008. Coincidence in the timing of the change of trends points to a common factor. We suggest that the current world financial crisis could be this common cause, a hypothesis to be contrasted in future research.

Eighty-year trends in infant weight and length growth: the Fels Longitudinal Study

OBJECTIVES

To investigate secular trends in weight and length growth from birth to 3 years of age in infants born from 1930 to 2008, and to assess whether these trends were associated with concurrent trends in pace of infant skeletal maturation and maternal body mass index.

STUDY DESIGN

Longitudinal weight and length data from 620 infants (302 girls) were analyzed with mixed effects modeling to produce growth curves and predicted anthropometry for infants born from 1930 to 1949, 1950 to 1969, 1970 to 1989, and 1990 to 2008.

RESULTS

The most pronounced differences in growth occurred in the first year of life. Infants born after 1970 were approximately 450 g heavier and 1.4 cm longer at birth, but demonstrated slower growth to 1 year of age than infants born before 1970. Growth trajectories converged after 1 year of age. There was no evidence that relative skeletal age, maternal body mass index, or maternal age together mediated associations between cohort and growth.

CONCLUSIONS

Recent birth cohorts may be characterized not only by greater birth size, but also by subsequent catch-down growth. Trends over time in human growth do not increase monotonically, and growth velocity in the first year may have declined compared with preceding generations.

Increasing prevalence of macrosomia in Flanders, Belgium: an indicator of population health and a burden for the future

Macrosomia, defined as birth weight > 4 kg, increased in Flanders from 7.3% (4899/67143) in 1991 to 8.63% (6034/69924) in 2010 (p < 0.0001) in singleton pregnancies at term. There are at least 3 important factors contributing to this evolution. (1) Increase of maternal stature and length: during the last century, mean length of Belgian women increased with approximately 10cm to the current value of 1.66 m. (2) Increase of maternal age: the proportion of pregnant women aged 35 years or more increased significantly from 6.1% in 1991 to 14.3% in 2010. (3) Increase of maternal overweight or obesity: between 1994 and 2000, there was an increase of 4% for both overweight and obesity in women and today, 44% of Belgians are overweight (BMI > 25 kg/m²), and 12% are obese (BMI > 30 kg/m²). From these data, rate and increase of macrosomia can be -considered indirect indicators of general public health. Next to the risks for obstetrical complications, neonates > 4 kg are at risk for development of adult obesity and type 2 diabetes with related diseases, such as hypertension and metabolic syndrome. As adults, they also tend to deliver macrosomic baby's themselves. As such, macrosomia at birth is a burden for a community's future health status, health care and related costs. Prenatal health care workers should be aware of the relevance to prevent macrosomia in the first generation by -implementing guidelines on nutrition, physical activity and appropriate weight gain into routine preconceptional and prenatal care, screening for gestational diabetes with strict monitoring of blood sugar levels in affected -individuals, and promotion of breastfeeding.

Secular trends of macrosomia in southeast China, 1994-2005

Background

The rate of macrosomia (birth weight≥4, 000 g) increased over the past four decades in many parts of the world. Macrosomia is associated not only with higher risks of maternal and neonatal complications but also with health risks in adulthood. We examined trends in neonatal macrosomia and large-for-gestational-age (LGA) births among singleton, live, term and postterm births (≥37 complete weeks' gestation) in southeast China from 1994 to 2005 and explored possible causes of the temporal trends.

Methods

Data from Perinatal Health Care Surveillance System in 12 cities and counties in southeast China were analyzed for trends in birth weight, neonatal macrosomia and LGA from 1994 to 2005. A total of 594, 472 singleton live births were included. We conducted multiple logistic regression analyses to relate these trends to changes in maternal and pregnancy characteristics.

Results

The rate of macrosomia rose from 6.00% in 1994 to 8.49% in 2000 and then levelled off to 7.83% in 2005. Similar trends were observed in mean birth weight. The incidence of LGA births increased continuously from 13.72% in 1994 to 18.08% in 2000, but the LGA rate remained relatively stable from 2002 to 2005. There was a decrease in gestational age and a significant increase in frequency of prelabor caesarean delivery from 1994 to 2005. In an adjusted multivariable model, the increase in LGA rate from 1994 to 2000 was associated with increasing net gestational weight gain, maternal age, maternal height and maternal education. But they didn't fully explain the increase. The trends of 2002-2005 LGA declined after adjusted for maternal and neonatal characteristics.

Conclusions

In southeast China, the incidence of macrosomia increased from 1994 to 2000 was mainly related to increasing net gestational weight gain. The incidence of macrosomia has levelled off in recent years partly due to increasing use of prelabor caesarean delivery and earlier delivery and partly due to moderation of gestational weight gain.

Poluição ambiental, residência materna e baixo peso ao nascer

Estudo caso-controle, que objetivou analisar os fatores de risco associados ao baixo peso ao nascer de recém-nascidos de mães de Rio Grande-RS residentes nas proximidades da área industrial. Foram entrevistadas mães que deram à luz nas maternidades do município, durante os meses de abril a novembro de 2003. A amostra compreendeu 138 casos e 409 controles. Foi realizada análise estatística bivariada e multivariada. O Baixo Peso ao Nascer (BPN) manteve-se associado positivamente com natimortos prévios, BPN prévios, presença de hipertensão arterial durante a gestação e ameaça de aborto durante a gravidez atual. Foi possível identificar os principais fatores de risco a que estão expostas as gestantes e que interferem no peso ao nascer de seus filhos, os quais vêm somar-se àqueles decorrentes de uma maior exposição a poluentes, por residirem próximo às indústrias.

Decreased term and postterm birthweight in the United States: impact of labor induction

OBJECTIVE

We sought to assess recent trends in falling mean birthweight (BW) and gestational age (GA) among US non-Hispanic white singleton live births >or=37 weeks of gestation and the contribution of increased rates of induction to these trends.

STUDY DESIGN

This was an ecological study based on US vital statistics from 1992 through 2003.

RESULTS

From 1992 through 2003, mean BW fell by 37 g, mean GA by 3 days, and macrosomia rates by 25%. Rates of induction nearly doubled from 14% to 27%. Our ecological state-level analysis showed that the increased rate of induction was significantly associated with reduced mean BW (r = -0.54; 95% confidence interval [CI], -0.71 to -0.29), mean GA (r = -0.44; 95% CI, -0.65 to -0.17), and rate of macrosomia (r = -0.55; 95% CI, -0.74 to -0.32).

CONCLUSION

Increasing use of induction is a likely cause of the observed recent declines in BW and GA. The impact of these trends on infant and long-term health warrants attention and investigation.

Trends in birth weight and gestational length among singleton term births in the United States: 1990-2005

OBJECTIVE

To estimate changes over time in birth weight for gestational age and in gestational length among term singleton neonates born from 1990 to 2005.

METHODS

We used data from the U.S. National Center for Health Statistics for 36,827,828 singleton neonates born at 37-41 weeks of gestation, 1990-2005. We examined trends in birth weight, birth weight for gestational age, large and small for gestational age, and gestational length in the overall population and in a low-risk subgroup defined by maternal age, race or ethnicity, education, marital status, smoking, gestational weight gain, delivery route, and obstetric care characteristics.

RESULTS

In 2005, compared with 1990, we observed decreases in birth weight (-52 g in the overall population, -79 g in a homogenous low-risk subgroup) and large for gestational age birth (-1.4% overall, -2.2% in the homogenous subgroup) that were steeper after 1999 and persisted in regression analyses adjusted for maternal and neonate characteristics, gestational length, cesarean delivery, and induction of labor. Decreases in mean gestational length (-0.34 weeks overall) were similar regardless of route of delivery or induction of labor.

CONCLUSION

Recent decreases in fetal growth among U.S., term, singleton neonates were not explained by trends in maternal and neonatal characteristics, changes in obstetric practices, or concurrent decreases in gestational length.

LEVEL OF EVIDENCE

III.

Trends in birth size and macrosomia in Queensland, Australia, from 1988 to 2005

The objectives of this study were to explore temporal changes in birth measures in Queensland, Australia, and examine whether secular trends are similar to those in other countries. This study used data from the Queensland Perinatal Data Collection, including singleton livebirths (n = 831 375) from 1988 to 2005. Recorded birthweight (BW, g), birth length (BL, cm), gestational age (weeks), maternal age, ethnic origin and calculated ponderal index (PI, kg/m(3)) were used. Temporal trends were assessed over the intervals 1988-2005 for BW and 2001-2005 for BW, BL and PI. Mean BW increased during the 17-year interval by approximately 1.9 g/year at a relatively low rate compared with reports from other countries. The proportion of high BW infants (> or = 4000 g) rose by 0.8% per year. Stratification by Indigenous status indicated that the increase in mean BW and prevalence of high BW was confined to non-Indigenous newborns only. The secular increase in BW was further modified by gestational age, and maternal age. The increase in BW was larger in term infants (4.2 g/year) than in preterm infants (1.8 g/year), and larger in infants of younger mothers than in those of older mothers (5.0 g/year vs. 3.1 g/year). There were no trends in mean BL and mean PI at birth from 2001 to 2005. In Queensland, mean BW increased moderately in the last 17 years, as did the proportion of high BW infants. The trend in rising BW remained after controlling for other perinatal characteristics. Birth measures per se and related trends differed by Indigenous status and warrant further investigation.

Fetal macrosomia and adolescence obesity: results from a longitudinal cohort study

OBJECTIVE

To assess the association between fetal macrosomia and adolescent obesity.

DESIGN

Longitudinal cohort study of the association between macrosomia and adolescent obesity.

SUBJECTS

Between 1 October 2005 and 1 February 2007, a follow-up study of live-born infants born in 1993-1995 in Wuxi, a suburban area of Shanghai, was conducted. Subjects with birth weight > 4000 g were selected as the exposed. For each exposed subject, one subject with a birth weight of 2500-4000 g, matched by year of birth, sex of infant, and type of institute at birth, was chosen as non-exposed. Clinical data were collected by structured interview and physical examination. Obesity was defined as body mass index (weight (kg)/height (m(2))) higher than the sex-age-specific criteria by the working group on obesity in China. Distribution of baseline characteristics and adolescent obesity rate between the exposed and non-exposed groups was compared.

RESULTS

A total of 1435 pairs of exposed and non-exposed subjects were included in the final analysis. No major difference in baseline characteristics (other than birth weight) was found between the exposed and non-exposed groups. Obesity rate was significantly higher in the exposed group (2.9%) than in the non-exposed group (1.6%). Adolescent obesity rates were 1.4, 1.9, 2.6, and 5.6%, respectively, in study subjects with a birth weight of 2500-3499, 3500-3999, 4000-4499, and > or =4500 g. The association between birth weight and adolescent obesity remained essentially the same when mother's demographic and anthropometric factors, breast feeding, and adolescent life-style factors were adjusted.

CONCLUSION

Compared with infants of normal birth weight, infants with birth weight >4000 g, especially those >4500 g, are at increased risk of adolescent obesity.

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.

How big is too big? The perinatal consequences of fetal macrosomia

OBJECTIVE

The objective of the study was to examine the birthweight at which risks of perinatal death, neonatal morbidity, and cesarean delivery begin to rise and the causes and timing (antenatal, early or late neonatal, or postneonatal) of these risks.

STUDY DESIGN

This was a cohort study based on 1999-2001 US-linked stillbirth, live birth, and infant death records. Singletons weighing 2500 g or larger born to white non-Hispanic mothers at 37-44 weeks of gestation were selected (n = 5,983,409).

RESULTS

Infants with birthweights from 4000 to 4499 g were not at increased risk of mortality or morbidity vs those at 3500-3999 g, whereas those 4500-4999 g had significantly increased risks of stillbirth, neonatal mortality (especially because of birth asphyxia), birth injury, neonatal asphyxia, meconium aspiration, and cesarean delivery. Births at 5000 g or larger had even higher risks, including risk of sudden infant death syndrome.

CONCLUSION

Birthweight greater than 4500 g, and especially greater than 5000 g, is associated with increased risks of perinatal and infant mortality and morbidity.

Milk consumption during pregnancy is associated with increased infant size at birth: prospective cohort study

BACKGROUND

Cow milk contains many potentially growth-promoting factors.

OBJECTIVE

The objective was to examine whether milk consumption during pregnancy is associated with greater infant size at birth.

DESIGN

During 1996-2002, the Danish National Birth Cohort collected data on midpregnancy diet through questionnaires and on covariates through telephone interviews and ascertained birth outcomes through registry linkages. Findings were adjusted for mother's parity, age, height, prepregnant BMI, gestational weight gain, smoking status, and total energy intake; father's height; and family's socioeconomic status The analyses included data from 50,117 mother-infant pairs.

RESULTS

Mean (+/-SD) consumption of milk was 3.1 +/- 2.0 glasses/d. Milk consumption was inversely associated with the risk of small-for gestational age (SGA) birth and directly with both large-for-gestational age (LGA) birth and mean birth weight (P for trend < 0.001). In a comparison of women drinking >or=6 glasses/d with those drinking 0 glasses/d, the odds ratio for SGA was 0.51 (95% CI: 0.39, 0.65) and for LGA was 1.59 (1.16, 2.16); the increment in mean birth weight was 108 g (74, 143 g). We also found graded relations (P < 0.001) for abdominal circumference (0.52 cm; 0.35, 0.69 cm), placental weight (26 g; 15, 38 g), birth length (increment: 0.31 cm; 0.15, 0.46 cm), and head circumference (0.13 cm; 0.04, 0.25 cm). Birth weight was related to intake of protein, but not of fat, derived from milk.

CONCLUSION

Milk intake in pregnancy was associated with higher birth weight for gestational age, lower risk of SGA, and higher risk of LGA.

Females born large for gestational age have a doubled risk of giving birth to large for gestational age infants

AIM

To analyse if females born large for gestational age (LGA) have an increased risk to give birth to LGA infants and to study anthropometric characteristics in macrosomic infants of females born LGA.

METHODS

The investigation was performed as an intergenerational retrospective study of women born between 1973 and 1983, who delivered their first infant between 1989 and 1999. Birth characteristics of 47,783 females, included in the Swedish Birth Register both as newborns and mothers were analysed. LGA was defined as >2 SD in either birth weight or length for gestational age. The infants were divided into three subgroups: born tall only, born heavy only and born both tall and heavy for gestational age. Multiple logistic and linear regression analyses were performed.

RESULTS

Females, born LGA with regard to length or weight, had a two-fold (adjusted OR 1.96, 95% Cl 1.54-2.48) increased risk to give birth to an LGA infant. Females, born LGA concerning weight only, had a 2.6 (adjusted OR 2.63, 95%, 1.85-3.75) fold increased risk of having an LGA offspring heavy only and no elevated risk of giving birth to an offspring that was tall only, compared to females born not LGA. In addition, maternal obesity was associated with a 2.5 (adjusted OR 2.56, 95%, 2.20-2.98) fold increased risk of having an LGA newborn, compared to mothers with normal weight.

CONCLUSION

Females, born LGA, have an increased risk to give birth to LGA infants, compared to mothers born not LGA. Maternal overweight increases this risk even further.

The thrifty phenotype as an adaptive maternal effect

Human diseases in adulthood are increasingly associated with growth patterns in early life, implicating early-life nutrition as the underlying mechanism. The thrifty phenotype hypothesis proposed that early-life metabolic adaptations promote survival, with the developing organism responding to cues of environmental quality by selecting an appropriate trajectory of growth. Recently, some authors have proposed that the thrifty phenotype is also adaptive in the longer-term, by preparing the organism for its likely adult environment. However, windows of plasticity close early during human development, and subsequent environmental changes may result in the selected trajectory becoming inappropriate, leading to adverse effects on health. This paradox generates uncertainty as to whether the thrifty phenotype is indeed adaptive for the offspring in humans. The thrifty phenotype should not be considered a dichotomous concept, rather it refers to the capacity of all offspring to respond to environmental information during early ontogenetic development. This article argues that the thrifty phenotype is the consequence of three different adaptive processes - niche construction, maternal effects, and developmental plasticity - all of which in humans are influenced by our large brains. While developmental plasticity represents an adaptation by the offspring, both niche construction and parental effects are subject to selection on parental rather than offspring fitness. The three processes also operate at different paces. Human offspring do not become net calories-producers until around 18 years of age, such that the high energy costs of the human brain are paid primarily by the mother, even after weaning. The evolutionary expansion of human brain volume occurred in environments characterised by high volatility, inducing strong selective pressure on maternal capacity to provision multiple offspring simultaneously. The thrifty phenotype is therefore best considered as a manipulation of offspring phenotype for the benefit of maternal fitness. The information that enters offspring phenotype during early development does not predict the likely future environment of the offspring, but rather reflects the mother's own developmental experience and the quality of the environment during her own maturation. Offspring growth trajectory thus becomes aligned with long-term maternal capacity to provision. In contemporary populations, the sensitivity of offspring development to maternal phenotype exposes the offspring to adverse effects, through four distinct pathways. The offspring may be exposed to (1) poor maternal metabolic control (e.g. gestational diabetes), (2) maternally derived toxins (e.g. maternal smoking), or (3) low maternal social status (e.g. small size). Adverse consequences of these effects may then be exacerbated by (4) exposure either to the "toxic" western environment in postnatal life, in which diet and physical activity levels are mismatched with metabolic experience in utero, or at the other extreme to famine. The rapid emergence of the epidemic of the metabolic syndrome in the 20th Century reflects the rapid acceleration in the pace of niche construction relative to the slower physiological combination of developmental plasticity and parental effects.

Association between fruit and vegetable consumption and birth weight: a prospective study among 43,585 Danish women

OBJECTIVE

To examine whether fruit and vegetable consumption in pregnancy is associated with birth weight in a Western population.

DESIGN

Prospective cohort study based on telephone interviews, a food frequency questionnaire (FFQ), and extractions of birth characteristics from national health registries.

SUBJECTS AND SETTING

The 43,585 Danish women from the Danish National Birth Cohort who had completed the FFQ in mid-pregnancy and on whom information about birth outcome was available. The exposures were frequency of green leafy vegetable (GLV) intake and quantified intake of fruit, fruit and vegetables, and fruit and vegetables and juice. The outcomes were birth weight and z-score for expected birth weight adjusted for sex and gestation week. Information on maternal height, weight, smoking, and other potential confounders was obtained through telephone interviews.

RESULTS

Significant associations were found for all exposures to fruit and vegetable intake with birth weight and most with z-score. The strongest association was found for fruit intake in which case birth weight increased by 10.7 g (95% CI 7.3-14.2) per quintile. All associations were stronger among lean women (BMI<20, n = 7,169), whose children's birth weight increased by 14.6 g (95% CI 6.4-22.9) per quintile increase in fruit intake. For GLV the results were more inconclusive. When adjusted for confounders, but not for energy, the association between GLV and birth weight was significant, but the same was not the case for z-score.

CONCLUSION

Fruit and vegetable consumption in pregnancy is positively associated with birth weight in well-nourished Danish women, especially among lean women.

Courbes de poids à la naissance: une revue de la littérature

There are many birthweight reference curves in the literature. This study reviews birthweight curves that are commonly used in France as well as references that provide birthweight by sex. The 19 curves selected for review were published between 1971 and 2001 using samples of between 300 to 3 million newborns in Europe, Australia and North America. Our objective was to summarize their main characteristics and to provide guidelines for analysis by explaining which factors are responsible for differences between curves, and discussing the methods used to construct them. The characteristics of the population must be taken into account and study samples must be recent and representative. The sample size must be sufficient to ensure stable estimates for premature infants. It is preferable to use different curves for boys and girls because sex is a key determinant of birth weight. The choice of appropriate birth weight reference remains difficult in some countries, in France particularly, and the use of individual customised birth weight curves provides an interesting alternative.

Duration of pregnancy in relation to seafood intake during early and mid pregnancy: prospective cohort

We examined the association between exposure to seafood intake during two periods of pregnancy on the one hand and risks of preterm delivery and postterm delivery on the other. In a prospective cohort of 8729 pregnant Danish women, we assessed frequency of fish meals during the first and second trimester of pregnancy by questionnaires completed around gestation weeks 16 and 30, respectively. When fish intake was based solely on intake reported for the early period of pregnancy, mean gestation length was shorter by 3.91 (95% CI: 2.24-5.58) days and odds of preterm delivery were increased 2.38 (1.23-4.61) times in those who never consumed fish (n = 308) vs. those who consumed both fish as main meal and fish in sandwiches at least once per week (n = 785). These measures were similar when fish intake was based solely on intake reported for mid-pregnancy. In the subgroup of women reporting same intake in the two trimesters, those who never consumed fish (n = 165) had 8.57 (5.46-11.7) days shorter mean gestation and 19.6 (2.32-165) times increased odds of preterm delivery, compared to high fish consumers (n = 127); odds of elective and postterm delivery were reduced by a factor 0.33 (0.11-1.02) and 0.34 (0.12-0.95), respectively, in zero fish consumers. All analyses were adjusted for potential confounding by factors such as maternal smoking, height, and prepregnant weight. We conclude that never consuming fish in the first two trimesters of pregnancy was an extremely strong risk factor for preterm delivery but was also associated with reduced risks of elective delivery and postterm delivery.

Endocrine and metabolic consequences of intrauterine growth retardation

Size at birth and early infancy growth rates have been linked to long-term risks for diseases, such as type 2 diabetes and cardiovascular disease. These associations could be explained by permanent programming of metabolic responses and selective survival of those genetically predisposed to such adaptations. These epidemiologic associations may also affect long-term disease risk in short small-for-gestational age children, who are often treated with growth hormone. Study of the mechanisms and genetic factors involved in the association between small size at birth, rapid postnatal weight gain, and adult disease may promote the early identification of subjects with the highest disease risk and new opportunities to develop targeted early interventions.

Social variations in fetal growth in a Russian setting: an analysis of medical records

PURPOSE

The study examines variations in fetal growth by maternal social circumstances in a Russian town.

METHODS

All pregnant women registered at the antenatal clinics in 1999 in Severodvinsk (north-west Russia) and their live born infants comprised the study base (n=1399). Multivariate linear regression analysis was applied to quantify the effect of socio-demographic factors on birthweight and the ponderal index (PI).

RESULTS

A clear gradient of birthweight in relation to mothers' education was revealed. Babies of the most educated mothers were 207 g (95% CI, 55, 358) heavier than babies of mothers with basic education. The average weight of those born to mothers with secondary and vocational levels of education was 172 g (95% CI, 91, 253) and 83 g (95% CI, 9, 163) lower compared with infants born to mothers with a university level of education after adjustment for age, parity, pre-pregnancy weight, marital status, maternal occupation, length of gestation, and sex of the baby. Maternal education also influenced the PI.

CONCLUSIONS

Further studies should focus on the mechanisms of the coherence of maternal education and fetal growth. To ensure that all parts of the society benefit equally from economic and social reforms, social variations in pregnancy outcomes should be monitored during the time of transition.

Secular trends of fetal growth in Canada, 1981 to 1997

Preterm birth and low birthweight in Canada have shown paradoxical temporal trends, with an increase in preterm birth and a decrease in low birthweight. Mean birthweight has increased in many industrialised countries, despite a recent rise in preterm birth, suggesting a temporal increase in fetal growth (birthweight for gestational age) in Canada. We thus described temporal trends in the distribution of fetal growth from 1981 to 1997, including means and proportions of infants at both the low and high ends of the fetal growth distribution. We used data for singleton live births from Statistics Canada's Canadian Birth Data Base for the years 1981-97 (excluding Ontario and Newfoundland) and analysed temporal trends in birthweight and birthweight-for-gestational-age z-score as continuous outcomes and the derived dichotomised outcomes [i.e. low birthweight (<2500 g), very low birthweight (<1500 g), small-for-gestational-age (<10th percentile), very small-for-gestational-age (<3rd percentile), high birthweight (>4000 g), very high birthweight (>4500 g), large-for-gestational-age (>90th percentile), and very large-for-gestational-age (>97th percentile)]. The birthweight-for-gestational-age was based on a newly developed population-based Canadian reference. The results showed that in the overall sample and in a subsample of term and post-term births, mean birthweight, mean z-score, rates of high birthweight, very high birthweight, large-for-gestational-age, and very large-for-gestational-age increased whereas rates of low birthweight, very low birthweight, small-for-gestational-age, and very small-for-gestational-age decreased between 1981-83 and 1995-97. The reverse was observed in preterm births. These temporal changes were larger for more extremely distributed measures of fetal growth. For example, compared with 1981-83, the decrease in 1995-97 for very small-for-gestational-age (<3rd percentile) was 38.9%, whereas the decrease for small-for-gestational-age (<10th percentile) was only 29.7%. Corresponding temporal increases were 21.4% for very large-for-gestational-age (>97th percentile) and 15.2% for large-for-gestational-age (>90th percentile). Among infants with gestational age 34-36 weeks, all measures of fetal growth, including the rates for all dichotomous outcomes, decreased in 1995-97 as compared with 1981-83. We conclude that Canadian infants are getting bigger, but only those born at term. The temporal trends for more extremely distributed fetal growth measures are particularly marked.