New assessment of the effects of birth order and socioeconomic status on birth weight.

A survey of the 20 698 singleton births occurring in one year to women resident in the Greater Dublin area provided information on birth weight, birth order, and social class. Low (less than or equal to 2500 g), suboptimal (less than or equal to 3000 g), and optimal (3001-4499 g) birth weights all showed a linear relation with social class. The incidence of low and suboptimal birth weight was highest in first, fifth, and subsequent births, and conversely optimal weight was commonest in second, third, and fourth births. Analysis indicated that a major part of the birth-order effect was attributable to social class. Birthweight categories give information which may be distorted when using mean weight alone. The ue of suboptimal and optimal weight offers the possibility of more accurate assessment of trends in performance, particularly in small samples, than does the conventional sole use of low birth weight. Low and suboptimal birth weights are uncommon in Dublin.     

The effect of race on the incidence of low birth weight: persistence of effect after controlling for socioeconomic, educational, marital, and risk status

The purpose of this study was to determine whether the elevated risk for low birth weight (LBW) infants among black mothers would persist when biologic, behavioral, and socioeconomic factors (as measured by socioeconomic status, level of education, and marital status) were controlled. It was found that the odds ratios for the risk of LBW for blacks/whites persisted above 1.5, regardless of what subgroups were used and what factors were controlled. The black/white odds ratios were, however, less than 2.0 when cigarette smoking was not a risk factor and higher than 2.0 when it was. In fact, the highest odds ratios, up to 2.65, occurred among the smoking group. These data suggest that smoking may have a more strongly negative effect among black than white pregnant mothers. In general, the effect of race on the LBW risk was much less strong than that of risk factors that can be influenced, such as adverse maternal practices.     

Genome-wide association study of birth weight in sheep

Birth weight is the earliest available growth trait with considerable impacts on lamb survivability and growth performance traits. This study was conducted to perform a genome-wide association study of birth weight in a meat-type sheep. A total of 132 Lori-Bakhtiari sheep were selected based on estimated of breeding values (EBVs) for BW analyses. The selected animals were genotyped using Illumina Ovine SNP50 Bead Chip. After quality control, a total of 41 323 single-nucleotide polymorphisms (SNPs) and 130 sheep were used for subsequent analyses. Plink 1.90 beta software was used for the analyses. Seven SNPs on chromosomes 1, 16, 19 and 22 were detected based on genome-wide unadjusted P-values (P <10⁻⁶), which jointly accounted for 1.2% of total genetic variation. However, based on Bonferroni-adjusted P-values, only three SNPs on chromosome 1 had significant associations with EBVs for birth weight (P <0.05), which jointly explained 0.8% of total genetic variation. A total of seven genes were found in 50 kb intervals from the three significant SNPs on chromosome 1, but only three genes, including RAB6B (a member of RAS oncogene family), Tf serotransferrin and GIGYF2 (a GRB10 interacting GYF protein 2), could be considered as candidate genes for birth weight in future studies. The results of this study may facilitate potential use of the genes involving in growth and production traits for genetic improvement of productivity in sheep.     

Patterns of low birth weight in the Bengali newborns

This paper examines the distribution of low birth weight (2500 g or less) by gestation time, sex, maternal age, parity (birth order), socioeconomic conditions, and season of birth among 5117 single live births born to Bengali mothers at the Ramakrishna Mission Seva Pratisthan Hospital in Calcutta, India. Preterm infants have low birth weight significantly more often than their full term counterparts. Female infants have low birth weights significantly more often than male infants. The infants of poor mothers have lower birth weights in higher order births more often than infants of higher orders born to well-off mothers. Teenaged mothers produce low birth weight babies significantly more often than older mothers. Although the relationship is not significant, low birth weight infants occur more often among 1st and late born infants and less often among 2nd born infants. The season of birth is not significantly associated with birth weight. Less than 10% of low birth weight infants are pre-term, while the rest are full term. The great majority of low birth weight infants are small-for-gestational-age; the minority are small due to curtailed gestational age. The proportion of infants weighing less than 2001 g is only 9%; this figure tallies closely with earlier studies of India.     

Race and the inheritance of low birth weight

This paper uses intergenerational data from the Panel Study of Income Dynamics (PSID) to address the black-white difference in propensities toward low birth weight (LBW). We determine that socioeconomic conditions account for some variation in low birth weight across race. Further, while race differences in the risk of low birth weight cannot be explained entirely, we find that the inheritance of parental birth weight status dramatically reduces the black-white gap in low birth weight. Intergenerational legacies of poor infant health explain the largest share of racial disparities in filial birth weight. We then try to assess whether this intergenerational transmission of low birth weight is indeed genetic by using grandparent-fixed effects models to factor out, to a great extent, family socioeconomic circumstances. We find that even within this framework, both father's and mother's birth weight status have an important impact on filial outcomes. However, the degree of inheritance is weaker for African Americans than for other races. Finally, we theorize that the importance of paternal birth weight status implies a genetic association that does not work through the uterine environment but rather through the fetus itself.     

Change in social status and risk of low birth weight in Denmark: population based cohort study.

OBJECTIVE: To estimate the risk of having a low birthweight infant associated with changes in social, environmental, and genetic factors. DESIGN: Population based, historical cohort study using the Danish medical birth registry and Statistic Denmark''s fertility database. SUBJECTS: All women who had a low birthweight infant (< 2500 g) (index birth) and a subsequent liveborn infant (outcome birth) in Denmark between 1980 and 1992 (exposed cohort, n = 11,069) and a random sample of the population who gave birth to an infant weighing > or = 2500 g and to a subsequent liveborn infant (unexposed cohort, n = 10,211). MAIN OUTCOME MEASURES: Risk of having a low birthweight infant in the outcome birth as a function of changes in male partner, area of residence, type of job, and social status between the two births. RESULTS: Women in the exposed cohort showed a high risk (18.5%) of having a subsequent low birthweight infant while women in the unexposed cohort had a risk of 2.8%. After adjustment for initial social status, a decline in social status increased the absolute risk of having a low birthweight infant by about 5% in both cohorts, though this was significant only in the unexposed cohort. Change of male partner did not modify the risk of low birth weight in either cohort. CONCLUSION: Having had a low birthweight infant and a decline in social status are strong risk factors for having a low birthweight infant subsequently.     

Effect of birthplace on infants with low birth weight.

From December 1983 to June 1985, 162 infants of less than 32 weeks'' gestation or weighing less than 1,500 g, or both, were cared for at the regional neonatal intensive care unit in Leeds. Of the 162, 64 (40%) were born in the unit because their mothers had received antenatal care there, 58 (36%) were born in another hospital and subsequently transferred, and 40 (25%) were transferred in utero because of potential complications. The overall mortalities for each group were 14%, 38%, and 18% respectively. These differences were significant, but when they were corrected for gestation, birth weight, and mode of delivery there was no difference in either the mortality or the incidence of intraventricular haemorrhage in the three study populations. Although there seem to be no distinct advantages of in utero transfer in terms of mortality and morbidity, there are other psychological and emotional advantages.     

Chromosome breakage in low birth weight newborns.

The frequency of chromosome aberrations in cells cultured from umbilical cord blood was determined for 50 low birth weight (LBW) and 50 normal birth weight (NBW) euploid newborns matched for sex, race, and maternal age. The metaphase spreads had been prepared in the course of an earlier study of frequency of aneuploidy and results are from 72-h cultures, i.e., presumably, at the second division in vitro. There were no significant differences between the two groups in the frequency of cells with chromosome breakage, chromosome gaps, or hyperdiploid cells. There was, however, a significantly higher frequency of hypodiploid cells in the LBW group. The present findings differ from those of others who have reported an increase in chromosome breakage in premature newborns.     

Iron stores at birth in a full-term normal birth weight birth cohort with a low level of inflammation

Iron stores at birth are essential to meet iron needs during the first 4–6 months of life. The present study aimed to investigate iron stores in normal birth weight, healthy, term neonates. Umbilical cord blood samples were collected from apparently normal singleton vaginal deliveries (n=854). Subjects were screened and excluded if C-reactive protein (CRP) > 5 mg/l or α1-acid glycoprotein (AGP) > 1 g/l, preterm (<37 complete weeks), term < 2500g or term > 4000g. In total, 762 samples were included in the study. Serum ferritin, soluble transferrin receptor (sTfR), hepcidin, and erythropoietin (EPO) were measured in umbilical cord blood samples; total body iron (TBI) (mg/kg) was calculated using sTfR and ferritin concentrations. A total of 19.8% newborns were iron deficient (ferritin 35 μg/l) and an additional 46.6% had insufficient iron stores (ferritin < 76 μg/l). There was a positive association between serum ferritin and sTfR, hepcidin, and EPO. Gestational age was positively associated with ferritin, sTfR, EPO, and hepcidin. In conclusion, we demonstrate a high prevalence of insufficient iron stores in a Chinese birth cohort. The value of cord sTfR and TBI in the assessment of iron status in the newborn is questionable, and reference ranges need to be established.     

Father's drinking and infant birth weight: report of an association

Parents' drinking in the month prior to conception was ascertained for 377 infants born to members of a health maintenance organization. If the father had an average of two or more drinks daily, or had at least five drinks on one occasion, a decrease of 137 gm in infant birth weight was predicted, by means of regression analysis. This result was independent of maternal drinking, although infants whose mothers were regular drinkers weighed less at birth. The lower mean birth weights of infants of regular-drinking fathers was not due to parents' smoking, maternal use of caffeine, marijuana, or other drugs, or 21 other measured variables. This is the first report of an association in humans between father's drinking prior to conception and decreased infant birth weight. However, interpretation of this finding is difficult because the biological mechanisms that might underlie it are obscure.     

Relative contributions of maternal social and biological characteristics to birth weight and gestation among mothers of different childhood socioeconomic status

There has been no reported systematic attempt to quantify the relative unique contribution of multiple social and biologic maternal characteristics to birthweight and gestational time among mothers of differing childhood socioeconomic backgrounds. This issue was examined in 3 nativity cohorts from a population of 766 black prenatal clinic patients in New York City using a series of stepwise hierarchical multiple regression analyses. Different variable sets contributed to birthweight variance in each group, although total variance explained was similar for the 3. Since the foreign-born cohort represented a different higher childhood socioeconomic background, but was similar to the other groups in current socioeconomic status, the differing observed associations of variable sets to birthweight may be related to childhood socioeconomic status. In all groups, social factors show more effect on gestation among those births more than 2500 grams than for smaller babies and thus account for more total explained birthweight variance for births over 2500 grams. Future research is necessary to replicate these results in the general population since this is the 1st study using multivariate techniques to look at social and biological factors associated with birthweight in groups with different childhood social backgrounds.     

Relative contributions of maternal social and biological characteristics to birth weight and gestation among mothers of different childhood socioeconomic status

Abstract

There has been no reported systematic attempt to quantify the relative unique contribution of multiple social and biologic maternal characteristics to birth weight and gestational time among mothers of differing childhood socioeconomic backgrounds. We examined this issue in three nativity cohorts from a population of 766 black prenatal clinic patients in New York City using a series of stepwise hierarchical multiple regression analyses. Different variable sets contributed to birth weight variance in each group, although total variance explained was similar for the three. Since the foreign‐born cohort represented a different higher childhood socioeconomic background, but was similar to the other groups in current SES, the differing observed associations of variable sets to birth weight may be related to childhood socioeconomic status. In all groups, social factors show more effect on gestation among births more than 2,500 grams than for smaller babies and thus account for more total explained birth weight variance for births over 2,500 grams.