Within-family standards for birth-weight

Secular Dynamics of Body Height and Weight in Russian Children Aged 0–17

This study deals with long-term temporal changes of body height and weight during various stages of ontogeny: newborns, infancy, early age, fi rst childhood, second childhood, adolescence, and youth. Each age/sex group numbers ca 100 persons, the total sample size is ca 2 000. The meta-analysis is based primarily on growth standards for Russian children, regularly renewed by the Research Institute for the Hygiene and Health Protection of Children and Adolescents and mostly relating to separate decades of the 20th century. The intensity of the secular trends was assessed through the analysis of scatter plots. The largest share in the secular increase of bodily dimensions belongs to intense growth during the second year of life and during the adolescent growth spurt. The smallest share is that of intrauterine growth, limited by the mother’s body size, and that of growth during adolescence, when the mature body size has been virtually reached and growth rate is minimal. Boys, who are more eco-sensitive, demonstrate greater secular changes than girls, who are eco-resistant. Smaller secular changes in weight than in height in both boys and girls result in the increase of leptosomy. This heterochrony concerns mostly newborns, whose body mass is a standard example of stabilizing selection.

High birth weight and perinatal mortality among siblings: A register based study in Norway, 1967-2011

BACKGROUND

Perinatal mortality according to birth weight has an inverse J-pattern. Our aim was to estimate the influence of familial factors on this pattern, applying a cohort sibling design. We focused on excess mortality among macrosomic infants (>2 SD above the mean) and hypothesized that the birth weight-mortality association could be explained by confounding shared family factors. We also estimated how the participant's deviation from mean sibling birth weight influenced the association.

METHODS AND FINDINGS

We included 1 925 929 singletons, born term or post-term to mothers with more than one delivery 1967-2011 registered in the Medical Birth Registry of Norway. We examined z-score birth weight and perinatal mortality in random-effects and sibling fixed-effects logistic regression models including measured confounders (e.g. maternal diabetes) as well as unmeasured shared family confounders (through fixed effects models). Birth weight-specific mortality showed an inverse J-pattern, being lowest (2.0 per 1000) at reference weight (z-score +1 to +2) and increasing for higher weights. Mortality in the highest weight category was 15-fold higher than reference. This pattern changed little in multivariable models. Deviance from mean sibling birth weight modified the mortality pattern across the birth weight spectrum: small and medium-sized infants had increased mortality when being smaller than their siblings, and large-sized infants had an increased risk when outweighing their siblings. Maternal diabetes and birth weight acted in a synergistic fashion with mortality among macrosomic infants in diabetic pregnancies in excess of what would be expected for additive effects.

CONCLUSIONS

The inverse J-pattern between birth weight and mortality is not explained by measured confounders or unmeasured shared family factors. Infants are at particularly high mortality risk when their birth weight deviates substantially from their siblings. Sensitivity analysis suggests that characteristics related to maternal diabetes could be important in explaining the increased mortality among macrosomic infants.

Genetic influences on the association between fetal growth and susceptibility to type 2 diabetes

The fetal insulin hypothesis proposes that low birth weight and susceptibility to type 2 diabetes (T2D) could both be two phenotypes of the same genotype. Insulin is a key growth factor in utero, and T2D is characterized by insulin resistance and/or beta-cell dysfunction. Therefore, genetic variants impacting on insulin secretion and action are likely to alter both fetal growth and susceptibility to T2D. There are three lines of evidence in support of this hypothesis. (1) Studies of rare monogenic diabetes have shown mutations in a single gene, such as GCK or KCNJ11, can cause diabetes by reducing insulin secretion, and these mutations are also associated with reduced birth weight. (2) Epidemiological studies have indicated that children born to fathers with diabetes are born smaller. As the father cannot influence the intrauterine environment, this association is likely to reflect genes inherited by the fetus from the father. (3) The most compelling evidence comes from recent genome-wide association studies. Variants in the CDKAL1 and HHEX-IDE genes that predispose to diabetes, if present in the fetus, are associated with reduced birth weight. These data provide evidence for a genetic contribution to the association between low birth weight and susceptibility to T2D. This genetic background is important to take into consideration when investigating the impact of environmental determinants and developing strategies for intervention and prevention.

Notes on the statistics of growth standards

The problems of constructing population standards for measurements such as height and age points such as menarche are discussed. Extreme centiles, such as the 3rd, estimated from a Gaussian distribution have a considerable imprecision, the amount of which is detailed. Non-parametric estimation, as usually used for weight, is compared with transformation to Gaussianity and thence parametric estimation. Regression standards are discussed, whereby the subject is compared with a relevant subsection of the population rather than all of it, and it is suggested that velocity of growth standards might be couched in these terms.

Sibling birthweight as a predictor of macrosomia in women with type 1 diabetes

AIMS/HYPOTHESIS

The aim of this study was to establish the value of maternal HbA1c levels and older sibling birthweight as predictors of birthweight and macrosomia in the offspring of women with type 1 diabetes.

SUBJECTS AND METHODS

A total of 214 pregnancies of 107 women with type 1 diabetes were studied. Regression analysis was performed to test the predictive value of the birthweight of the first-born infant, HbA(1)c levels, maternal BMI, maternal age and time between subsequent births on the birthweight of the second-born infant. Birthweights were corrected for sex and gestational age. The percentages of first- and second-born infants with macrosomia (weight >90th centile) were calculated and compared.

RESULTS

Only the birthweight of earlier born infants was significantly related to that of second-born infants (p<0.001) and 40-50% of the variation in the birthweight of second-born infants could be explained by the birthweight of the first-born infants. About 85% of the mothers who gave birth to a macrosomic infant had a macrosomic infant in a subsequent pregnancy.

CONCLUSIONS/INTERPRETATION

Although it is clear that glycaemic control contributes to birthweight in women with type 1 diabetes, the birthweight of an earlier born infant appears to be a much better predictor of the birthweight of a subsequent infant than HbA1c levels during pregnancy. It may, therefore, be used to identify patients at risk of giving birth to a macrosomic infant. Daily home monitoring of glucose levels, rather than HbA1c levels, should be used for assessment of maternal glycaemia during pregnancy.

Birthweight and perinatal mortality: paradoxes, social class, and sibling dependencies

BACKGROUND

Birthweight distributions among second-born infants depend on the birthweights of older siblings, with implications for weight-specific perinatal mortality. We wanted to study whether these relations were explained by socioeconomic levels, and to study time trends in a situation with decreasing perinatal mortality rates.

METHODS

Births in the Norwegian Medical Birth Registry from 1967 to 1998 were linked to their mothers through their national identification numbers. The study population was 546 688 mothers with at least two singletons weighing >/==" BORDER="0">500 g at birth. Weight-specific perinatal mortality for second-born siblings in families with first-born siblings in either the highest or the lowest birthweight quartile was analysed. Maternal education and cohabitation status were used as measures of socioeconomic level.

RESULTS

For all 500-g categories below 3500 g, mortality rates were significantly higher among second-born infants with an older sibling in the highest rather than the lowest weight quartile. This pattern was the same across three educational levels. The exclusion of preterm births did not change the effect pattern. A comparison of perinatal mortality among second siblings in terms of relative birthweight (z-scores) showed a reversal of the relative risks, although these were only significantly different from unity for the smallest infants. Conclusion The crossover in weight-specific perinatal mortality for second siblings by weight of first sibling is largely independent of socioeconomic level, and is not weakened by the decreasing perinatal mortality rates in the population over time. Family data should be taken into consideration when evaluating the risk of adverse pregnancy outcome relating to weight.

Integrated perinatal health framework. A multiple determinants model with a life span approach

BACKGROUND

Despite great strides in improving prenatal care utilization among American women, key perinatal indicators have remained stagnant or worsened in the past decade, and the United States continues to rank near the bottom compared to other developed countries. A new approach is needed if we are to achieve improvements in perinatal health.

METHODS

To propose a new framework that integrates a "life span" approach with a multiple determinants model.

RESULTS

We recognize that (1) powerful influences on outcome occur long before pregnancy begins; (2) pregnancy outcome is shaped by social, psychological, behavioral, environmental, and biological forces; and (3) the demography of pregnancy has changed dramatically in the last few decades with more women delaying their first birth. Approaches that simultaneously consider the entire life span as well as multiple determinants may need to be adopted. We propose a framework that integrates these approaches and is supported by the research literature. The life span perspective focuses attention toward the preconceptional and interconceptional periods as targets for intervention in improving perinatal health. The multiple determinants model distinguishes among concepts of disease, health and functioning, and well-being for both women and their offspring.

CONCLUSIONS

Our intent is to influence how policymakers, public health professionals, clinicians, and researchers approach perinatal health.

New standards for birth weight by gestational age using family data

OBJECTIVE

This study was undertaken to provide new standards for birth weight according to gestational age through the addition of family data on maternal birth weight and birth weights of previous siblings.

STUDY DESIGN

The analyses were based on 1.7 million births in Norway from 1967 through 1998. These population data were arranged into sibships and mother-offspring units through unique personal numbers. We categorized first births by sex and maternal birth weight and second births by sex and birth weight of the older sibling.

RESULTS

Standards for birth weight per gestational age percentiles differed by >1100 g when the birth weight of an older sibling was considered and by almost 700 g when maternal birth weight was considered. The value of these new standards for birth weight according to gestational age was demonstrated through variation in perinatal mortality.

CONCLUSION

Maternal birth weight and birth weights of previous siblings allow improved predictions of birth weight according to gestational age and should be used for classification of small-for-gestational-age births.

Familial aggregation of low birth weight among whites and blacks in the United States

BACKGROUND

Studies have shown that the birth weight of infants is correlated with the birth weights of their siblings and their mothers. We investigated whether the birth weights of mothers and index children were jointly associated with the risk of low birth weight in the siblings of the index children.

METHODS

We used data on the live-birth cohort of the 1988 National Maternal and Infant Health Survey. The analysis included 1691 white and 1461 black mothers, each of whom had two or more live-born, singleton children. Multiple logistic regression with generalized-estimation equations was used to assess the risk of low birth weight among an index child's siblings. Four groups were studied: that in which neither the mother nor the index child had low birth weight (group 1), that in which only the mother had low birth weight (group 2), that in which only the index child had low birth weight (group 3), and that in which both the mother and the index child had low birth weight (group 4). There was adjustment for other maternal and infant covariates.

RESULTS

Among white siblings in groups 1, 2, 3, and 4, 3.6, 8.3, 21.2, and 38.9 percent, respectively, had low birth weight, as compared with 8.0, 19.0, 31.1, and 57.1 percent of black siblings. When group 1 was used as the reference group, the adjusted odds ratios (and 95 percent confidence intervals) for low birth weight in groups 2, 3, and 4 were 2.5 (1.4 to 4.3), 6.8 (4.7 to 9.8), and 15.4 (9.2 to 25.5), respectively, among white siblings and 2.6 (1.8 to 3.8), 4.7 (3.5 to 6.4), and 13.9 (9.2 to 20.9) among black siblings. These associations were consistently found for birth weights below 1500 g and those ranging from 1500 to 2499 g in both races and after stratification for the mother's age, parity, education, cigarette-smoking status, and weight and height before pregnancy and the infant's sex.

CONCLUSIONS

Although selection and recall biases cannot be excluded with certainty, our data suggest a strong familial aggregation of low birth weight among both whites and blacks in the United States.

Birth weight outcomes for repeat teenage pregnancy

To investigate the outcomes for repeat teenage pregnancy and the effect of interpregnancy interval on birth weight, birth certificate data were reviewed from all mothers under 26 years delivering their second baby during 1981-1983 at an urban teaching hospital. Initially, 409 mothers who had delivered their first baby at the same hospital were identified. Mothers were divided into three groups: mothers under 20 years for both births; mothers under 20 years for the first birth, with the second birth delayed until 20 to 25 years; and mothers 20-25 years for both births. Group 1 mothers had high but identical rates of low birth weight (17.5%) for both parities, high rates of very low birth weight infants (less than 1501 g), and no change in mean birth weight between the two pregnancies. Group 2 mothers were older at first birth and had better outcomes for first and second births than group 1 mothers. For group 1 mothers, the initiation of prenatal care was delayed at second pregnancy compared to first pregnancy (46% receiving first trimester care versus 59% at first delivery). In contrast, groups 2 and 3 showed improvement in accessing prenatal care for the second pregnancy. Interpregnancy interval had no influence on the birth weight of the second infant in any group.

Relative effect of parental birth weight on infant birth weight at term

The relations between some hereditary and environmental factors and the variation in infant birth weight were estimated by multiple linear regression analyses on a sample of 276 Scandinavian single term pregnancies. Gestational age explained 10.9%, fetal factors (maternal and paternal birth weights and fetal sex) 7.9%, maternal factors (parity, pre-pregnancy weight and height) 5.5% and external factors (adjusted weight gain and smoking) 5.8% of the variation in infant birth weight. It is concluded that maternal and paternal birth weights are rather poor predictors of infant birth weight. Together they explain only 5.6% of the variation in infant birth weight at term.

Accuracy of mothers' recall of birthweight and gestational age

Information on the birthweight and gestational age of previous siblings is usually dependent upon maternal recall. This information is of importance in assessing the current risk of perinatal morbidity and mortality. The validity of maternal recall of birthweight and gestational age of 880 children born to 97 multiparas was examined by comparison with hospital records. About 75% of all reported birthweights were accurate to within 100 g and a similar proportion of reported gestational ages was correct to within 1 week. Recall was most accurate for most recent births as well as for earliest births and was not related to maternal age or education. There was a tendency for the smallness of low birthweight infants to be exaggerated by mothers. We conclude that within defined limitations, maternal recall of birthweight and gestational age of previous children is sufficiently accurate for clinical and even for epidemiological use.

Growth and development of bodyweight, height and head circumference during the first two years of life: quantitative genetic aspects

Mother-offspring and sib-sib relationships enable estimation of the heritability coefficients (or more accurately, transmissibility coefficients) and the so-called 'genetic correlation' for stature (S), weight (W) and head circumference (HC) in Israeli infants from birth to about two years of age. Heritability coefficients for S and HC show a more or less defined trend towards increase during ontogenetic development. The family resemblance in weight remains relatively constant or independent of age. The genetic correlations between each pair of the characters studied were higher than the corresponding phenotypic ones and showed an obvious tendency to decrease with age. The environmental correlations (rE) between W and S and between W and HC increase significantly with age, while for S and HC they are independent of age.

Determinants of size at birth in a Canadian population

Anthropometric, medical, and sociodemographic characteristics and smoking habit of a random sample of postpartum women in a Canadian population were determined. These characteristics were analyzed in relation to the birth size of their babies. With controls for gestational age and fetal sex, the following maternal variables were positively correlated with birth weight: prepregnant weight, weight gain in pregnancy, stature, bicristal and biacromial diameter, calf and upper arm circumference, and triceps and subscapular skinfold thickness. Smoking during pregnancy reduced birth weight by 13 gm per cigarette smoked daily. Similar associations of maternal size and smoking habit were observed with respect to infant length, head circumference, and chest circumference. The predictors of birth weight are proposed for use in adjusting upward or downward the population distribution of birth weight to reflect the individual characteristics of the mother.

Conditional standards for growth in height of British children from 5.0 to 15.99 years of age

Conditional standards giving centiles for height at time (t + 1) given height at time (t) are illustrated and their use discussed with the aid of examples. Charts have been prepared for both sexes covering the age range of t of 5.0 to 15.99 years. In contrast to velocity standards, these standards utilize all the information inherent in height (t) and height (t + 1). The conditions of their use, however, must be carefully considered. It is stressed that they actually test the normality of height (t + 1) for a given height (t). They make no statement about the normality of height (t).