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.     

Determinants of intrauterine growth retardation: evidence against maternal depletion

This analysis examines the relationship between length of preceding birth interval and risk of intrauterine growth retardation using data on Swedish infants from the 1973 World Health Organization study of perinatal mortality. Results of a multivariate logit analysis demonstrate that the lower than average mean birth weight of infants born after short birth intervals cannot be completely attributed to their shorter mean gestation length. Infants born after birth intervals of 12 months or less are 30% more likely to be small for gestational age (SGA) than infants born 18-59 months after the previous birth, even when the effects of maternal age and parity are controlled. The results obtained here do not support maternal depletion as an explanation for the association between short birth intervals and elevated risk of SGA, since there is no evidence of an attenuation of the risk of SGA with increasing length of interval in the under 18 month birth interval range.     

Maternal asthma,asthma medication use,and the risk of congenital heart defects

BACKGROUND: Asthma is a common problem that complicates pregnancy. Several drugs are considered acceptable for use during pregnancy, although none have been classified as safe. Few studies have assessed the health impact of maternal asthma/medication use on the fetus. METHODS: A population‐based case‐control study was conducted in New York State to determine if cardiac congenital malformations in offspring were associated with maternal use of asthma medication and/or maternal asthma. Cases were cardiac anomalies in the New York State Congenital Malformations Registry. Controls were live births without any major birth defects randomly selected from birth certificates and frequency matched by year of birth. Data were collected through a 30 min telephone interview. Exposure was maternal asthma/medication use, maternal asthma/no medication use, no asthma/medication use, and no asthma/no medication use (reference). RESULTS: A total of 502 (59.4%) cases and 1,066 (53.8%) controls participated. A positive association was seen between any heart defect and women with asthma who used medication (OR 2.38; 95% CI: 1.18, 4.82). No significant associations were observed between heart defects and either women with asthma who did not use medication or women without asthma who used asthma medications. When considering types of medication used, offspring of women with asthma who used bronchodilators had an increased risk of any heart defect (OR 2.20; 95%CI: 1.05, 4.61). CONCLUSIONS: These results suggest that both maternal asthma status (controlled vs. uncontrolled; severe vs. mild) and asthma medication use, particularly bronchodilators, may play a role in cardiac malformations in offspring. Birth Defects Research (Part A), 2009. © 2008 Wiley‐Liss, Inc.     

Maternal birthplace and major congenital malformations among New York Hispanics

BACKGROUND: Little is known about the association between maternal nativity and congenital malformations among Hispanics living in the United States. METHODS: We conducted a cross-sectional study to investigate the association between maternal nativity and various congenital malformations among singleton live-births born to Hispanic women in New York from 1993 to 2001. Birth certificates, used to identify maternal birthplace, were linked with congenital malformation registry files to obtain birth defects outcome. We examined how the risk of birth defects varied by maternal birthplace by estimating the adjusted odds ratios (aORs) using logistic regression. RESULTS: A foreign maternal birth showed statistically negative associations with overall congenital malformations (aOR, 0.70; 95% CI, 0.68-0.73), cardiovascular defects (aOR, 0.85; 95% CI, 0.77-0.93), central nervous system defects (aOR, 0.76; 95% CI, 0.63-0.91), and multiple defects (aOR, 0.80; 95% CI, 0.74-0.86). Specifically, foreign-born Hispanic women were statistically at reduced risk to deliver live babies with cleft palate (aOR, 0.56; 95% CI, 0.40-0.80), atresia and stenosis of rectum or anus (aOR, 0.58; 95% CI, 0.35-0.97), and craniosynostosis (aOR, 0.71; 95% CI, 0.51-0.99). Hispanic mothers born in Puerto Rico had a similar risk of delivering children with birth defects compared to U.S.-born Hispanic mothers. In contrast, Hispanic mothers born in Mexico, or Cuba and Central and South America were at reduced risk of delivering infants with overall congenital malformations (aOR, 0.64; 95% CI, 0.60-0.67) and (aOR, 0.65; 95% CI, 0.63-0.68), respectively. CONCLUSIONS: Foreign-born Hispanic mothers had a slightly lower risk to deliver live-born singleton infants with major congenital malformations than did U.S. born Hispanic mothers.     

Parturition in gilts: duration of farrowing, birth intervals and placenta expulsion in relation to maternal, piglet and placental traits

Large White x Meishan F2 crossbred gilts (n = 57) were observed continuously during farrowing while the placentae of their offspring were labeled in order to examine the duration of farrowing and placenta expulsion in relation to maternal-, piglet- and placental traits and the duration of birth interval in relation to birth weight, birth order and placental traits. Independently from each other, litter size, gestation length and offspring directed aggression significantly (P 0.05) affected duration of farrowing. An increase in litter size was associated with an increase of duration of farrowing and an increase in gestation length was associated with a decrease of duration of farrowing. Aggressive gilts took longer to farrow, compared to non-aggressive ones. After taking into account litter size, gestation length and offspring directed aggression, placental thickness (i.e., placental weight corrected for placental surface area) was significantly (P < 0.05) related to duration of farrowing, i.e., litters with on average thicker placentae took longer to farrow. The latter effect is the result of the fact that individual placental thickness significantly (P < 0.01) affected individual birth interval, independent of birth weight. The piglet has to break its own membranes to be able to start its journey through the uterus towards the birth channel. Apparently, a thicker placenta offers more resistance and thus prolongs the process of birth. Independent of placental thickness, birth interval significantly (P < 0.01) decreased with an increase in birth order (first born to last born). The high variation of birth intervals for the last born piglets, caused a slight increase in average birth interval for the latter piglets. Litters with on average more areolae per placenta took significantly (P < 0.001) less time to be born than litters with on average less areolae per placenta (independent of total number of piglets born and other placental traits), while birth intervals within litters were not affected by this trait. Thus, these results are probably due to a gilt trait rather than a piglet trait. Since the number of areolae represent the number of uterine glands present, the gilt trait might be uterine development. Duration of placenta expulsion significantly (P < 0.01) increased with an increase of duration of farrowing. Furthermore, the first placenta was expelled significantly (P < 0.01) earlier relative to last piglet when duration of farrowing was protracted, while there was no relation of the time interval between first placenta and last piglet and the duration of placenta expulsion. In conclusion, the most important finding of this study is that placental thickness rather than birth weight appears to play an important role in the duration of birth intervals and as a result, of duration of parturition in gilts.     

Effect of parental anthropometric parameters on neonatal birth weight and birth length

Data on 550 healthy pregnant women, 550 healthy fathers and their healthy term neonates born from singleton pregnancies (37(+0) through 41(+6) week) during a one-year period were reviewed. Maternal mean age was 27.7 +/- 9.37 years, mean pregestational weight 64.0 +/- 9.50 kg, mean gestational weight gain 15.4 +/- 4.33 kg, mean height 169.7 +/- 5.81 cm, and mean gestational age 40.1 +/- 0.95 weeks. Paternal mean age was 31.4 +/- 6.22 years, mean weight 84.6 +/- 10.35 kg, and mean height 182.8 +/- 6.84 cm. Mean birth weight was 3,709.8 +/- 500.48 g and 3,562.5 +/- 443.02 g, and mean birth length 51.5 +/- 1.91 cm and 50.7 +/- 1.62 cm in male and female newborns, respectively, yielding a birth weight greater by 147.3 g and birth length by 0.8 cm in the former. Study variables showed statistically significant correlations: maternal age contributed to the significant correlation between maternal weight and parity, maternal pregestational weight, weight at delivery, gestational weight gain and body height correlated significantly with neonatal birth weight and birth length, gestational age correlated significantly with neonatal weight and length (p = 0.01 all), parity had no major impact (p > 0.05). Paternal height and weight correlated significantly with neonatal birth weight and birth length (p = 0.01). Study results pointed to a significant correlation of maternal pregestational weight, gestational weight gain and body height, and of paternal weight and height with the neonate birth weight and birth length.     

Study of placenta of children born with congenital malformations

The malformations in this study were observed in a series of 279,642 consecutive births of known outcome registered in our Registry of congenital anomalies. For each case, more than 50 factors included in the registration forms were studied. One of the factors studied was the placenta. For each malformed child, a control was chosen. Cases with maternal known factors impairing placenta function, i.e. vasculopathy and diabetes, were excluded. In each category of malformations studied, the malformed children were divided into isolated and non-isolated (multiple malformed) cases. The weight of placenta of isolated cases was not lower than the weight of placenta of the controls. In contrast, the weight of placenta of the cases with non-isolated malformations was lower than the weight of placenta of the controls and of the isolated cases, for all categories of malformations but gastroschisis and omphalocele. The mean weights at birth of the cases with multiple malformations were also lower than those of the controls. The human placenta discounts a principal functional part, the maternal blood in the intervillous space. Congenital malformations may interact with this function.     

Gastroschisis, low maternal age, and fetal morbidity outcomes

OBJECTIVE: To determine if the risk for fetal growth inhibition among gastroschisis-afflicted fetuses is heightened among younger gravidas (teen mothers). METHOD: This was a retrospective cohort study on live-born infants with isolated gastroschisis delivered in New York State from 1983 through 1999. We compared infants of mature (>20 years) mothers with those of younger (<20 years) mothers with respect to the following indices of fetal morbidity outcomes: low birth weight and very low birth weight, preterm and very pre-term, and small for gestational age. We used adjusted odds ratios to approximate relative risks. RESULTS: A total of 368 infants with isolated gastroschisis were analyzed. The two groups differed in terms of mean gestational age at delivery [Mean + standard deviation(SD) for infants with gastroschisis born to mature mothers = 37.2 weeks +/- 2.8 versus 36.3 weeks + 3.6 for those of teenage mothers(p = 0.01)], as well as mean birth weight [mean birth weight +/- SD for infants with gastroschisis born to mature mothers = 2562.4 grams +548.8 versus 2367.9 grams +/- 645.2 for those of younger mothers (p = 0.004)]. Infants of teen mothers were about twice as likely to be of low birth weight (OR = 1.70; 95% CI = 1.05-2.77) and about three times as likely to be born very preterm when compared to those of mature mothers (OR = 2.80; 95% Cl = 1.02-8.00). No significant differences were observed with respect to very low birth weight, pre-term and small for gestational age. CONCLUSION: Low maternal age appears to be a risk factor for low birth weight and very preterm birth among gastroschisis-affected fetuses. This information is potentially useful for planning by care providers and in counseling affected parents.     

Maternal fatness and viability of preterm infants

To investigate the effect of maternal fatness on the mortality of infants born preterm up to the corrected age of 18 months 795 mother-infant pairs were studied. Maternal fatness was defined by Quetelet''s index (weight/(height²)) and all infants weighed less than 1850 g at birth. In 771 mother-infant pairs maternal age, complications of pregnancy, mode of delivery, parity, social class, and the baby''s sex and gestation were analysed by a logistic regression model for associations with infant mortality (but deaths from severe congenital abnormalities and those occurring during the first 48 hours after birth were excluded). In a subgroup of 284 mother-infant pairs all infant deaths except those from severe congenital abnormalities were analysed in association with the infant''s birth weight and gestation and the mother''s height and weight; this second analysis included another 24 infants who had died within 48 hours after birth. In the first analysis mortality overall was 7% (55/771), rising from 4% (71/173) in thin mothers (Quetelet''s index <20) to 15% (6/40) in mothers with grades II and III obesity (Quetelet''s index >30). After adjusting for major demographic and antenatal factors, including serious complications of pregnancy, maternal fatness was second in importance only to length of gestation in predicting death of infants born preterm. In the second analysis mortality overall was 15% (44/284), rising from 9% (5/53) in thin mothers to 47% (8/17) in mothers with grades II and III obesity. In both analyses the relative risk of death by 18 months post-term was nearly four times greater in infants born to obese mothers than in those born to thin mothers. In addition, maternal fatness was associated with reduced birth weight, whereas it is associated with macrosomia in term infants.These data differ fundamentally from those reported in full term babies of obese mothers. It is speculated that the altered metabolic milieu in obesity may reduce the ability of the fetus to adapt to extrauterine life if it is born preterm.     

Evolution of viviparity in cold-climate lizards: testing the maternal manipulation hypothesis

We used a cold-climate viviparous lacertid lizard (Eremias prezwalskii) as a model system to test the maternal manipulation hypothesis. Twenty-four gravid females collected from a population in Inner Mongolia (northern China) were maintained in the laboratory for the whole gestation length, with 12 allowed to bask for 14-h daily and the other 12 for 10-h daily. Females selected lower body temperatures but did not thermoregulate more precisely when gravid. The mean gestation length was shorter in females provided with longer basking opportunity. Neonates in the two treatments differed in tail length and the number of ventral scales but not in other examined morphological traits, with offspring born in the 14-h treatment having longer tails but fewer ventral scales. Offspring were sexually dimorphic at birth, with females being smaller in tail length, head length and fore-limb length but having more ventral scales than males of the same size. Offspring born in the 14-h treatment were not only faster runners but also grew faster than did offspring born in the 10-h treatment. Our data validate the main predictions of the maternal manipulation hypothesis that females should shift selected body temperatures during gestation to provide optimal thermal conditions for developing embryos and that phenotypic traits determined by maternal thermoregulation should enhance offspring fitness. Our study is the first to demonstrate that the maternal manipulation hypothesis applies to cold-climate viviparous reptiles.     

Lack of effect of maternal body mass index on anthropometric characteristics of newborns in twin gestations

We examined the correlation between maternal prepregnancy body mass index (BMI) and newborn weight, length, BMI, and gestational order, in singleton and twin births. The sample comprised 381 mothers of multiple babies (562 twins), and 7979 singleton pregnancies, used as controls. The Mann-Whitney non-parametric test was used to compare the values between the two groups, and the Spearman's correlation test (rS) was applied to the quantitative variables. A significant positive correlation was found with singleton baby variables: the higher the maternal BMI, the higher the newborn's BMI, weight, length, and gestational order. However, no significant correlation was found between maternal BMI and any of these variables in twins. Maternal weight gain, in the twin group, showed a significant positive correlation with the newborn gestational order (rS = 0.154; P = 0.002), weight (rS = 0.493; P < 0.001), length (rS = 0.469; P < 0.001), and BMI (rS = 0.418; P < 0.001). In singletons, the correlation was positive with all the variables, except for the gestational order. The newborn BMI was significantly higher in twins born by C-section than those born by vaginal birth (Z = -4.974; P < 0.001). Mothers of singletons delivered by C-section had a significantly higher BMI than those of singletons born by vaginal birth (Z = -1.642; P < 0.001); however, no significant differences were observed in mothers of twins. Prepregnancy maternal BMI in twin births would not be predictive of newborns weight, length and BMI in this population. Maternal weight gain during pregnancy proved to be the most adequate for predicting the weight, length and BMI of twins delivered by C-section.     

Influence of level of nutrition during late pregnancy on reproductive productivity of red deer (2) Adult hinds gestating wapitixred deer crossbred calves

The present study aimed to relate feed intake of red deer hinds in the later stages of gestating wapitixred deer crossbred foetuses on dam body condition, gestation length, birth weight and calf growth. Multiparous hinds (N=18) conceiving at known dates to either wapiti (n=12) or red deer (n=6) sires were housed in individual pens from days 150-220 of pregnancy, during which time they were offered either ad libitum access to pelletised rations (n=6 crossbred-bearing hinds [HH] and n=6 red deer-bearing hinds [RH]) or a restricted offer (n=6 crossbred-bearing hinds [HL]) set at 70% of the average ad libitum intake of HH hind in the previous week. Hinds were returned to pasture at day 220 and calving was closely monitored. Liveweights, body condition score (BCS), and lactation score (LS) of hinds were recorded weekly from day 130 of pregnancy until calves were weaned at 12 weeks of age. Calves were tagged and weighed at birth, and subsequently weighed at 7 and 12 weeks of age. HH and RH hinds exhibited similar patterns and levels of MEI/kg0.75, which peaked at 7.8 MJME/kg0.75 at day 220. HL hinds peaked at approximately 5 MJME/kg0.75 and showed significantly lower rates of liveweight gain during pregnancy. Interestingly, both crossbred-bearing groups initiated mammary development in advance of the RH hinds. While there were significant effects of foetal genotype on mean gestation length (239 days versus 234 days for crossbred versus red deer) and mean birth weight (14.5 kg versus 10 kg), the nutritional contrast for gestation length of crossbred-bearing hinds (i.e. HH versus HL) was not significant but approached significance for birth weight (14.5 kg versus 11.9 kg; P=0.06). Regression analysis revealed weak relationships between changes in hind liveweight and gestation length (P>0.05) but a significant relationship with birth weight (P<0.05). However, change in hind BCS was significantly related to both gestation length and birth weight. Crossbred calves reared by HH hinds were 30% heavier at 7 and 12 weeks of age than the red deer calves. However, those reared by HL hinds were significantly lighter than their genotype contemporaries and only marginally heavier than the red deer calves. These results generally contrast with the previous studies on red deer hinds gestating red deer foetuses [Asher, G.W., Mulley, R.C., O'Neill, K.T., Scott, I.C., Jopson, N.B., Littlejohn, R. 2004. Influence of level of nutrition during late pregnancy on reproductive productivity of red deer, (1) Adult and primiparous hinds gestating red deer calves. Anim. Reprod. Sci., in press] and indicate that the genetically determined higher growth requirements of crossbred foetuses may override any mechanism of compensatory control of gestation length at the expense of calf birth weight. Furthermore, there were marked carryover effects of late gestational feeding on crossbred calf growth and their dam's BCS that highlight the high nutritional demands of lactation.     

Etiologic heterogeneity of neural tube defects. II. Clues from family studies.

We previously reported that among neural tube defects (NTDs) with no known causes the ones that occur alone (singles) have different epidemiologic characteristics from those that occur in combination with other defects (multiples), suggesting an underlying causal heterogeneity. In this study, we compared family histories of 223 single NTD cases and 66 multiple cases ascertained through the Metropolitan Atlanta Congenital Defects Program (MACDP) between 1970 and 1979. Compared with siblings of multiples, siblings of singles had a higher precurrence rate for NTDs (2.0% vs. 0.0%) and for birth defects in general (10.9% vs. 3.0%). Furthermore, siblings of singles that were born within 2 years before the birth of the index case had a higher precurrence rate for NTDs (8.0% vs. 1.1%) and for major birth defects (20.0% vs. 2.9%) than had those born earlier. These results further suggest that NTDs are etiologically heterogeneous, depending on the presence of associated defects, and point to important environmental influences in the increased risk for birth defects among siblings of singles. Larger studies are needed to confirm these data and show that single and multiple NTDs have different recurrence rates, not only for NTDs but also for other birth defects.     

Assessing the Causal Relationship of Maternal Height on Birth Size and Gestational Age at Birth: A Mendelian Randomization Analysis

Background

Observational epidemiological studies indicate that maternal height is associated with gestational age at birth and fetal growth measures (i.e., shorter mothers deliver infants at earlier gestational ages with lower birth weight and birth length). Different mechanisms have been postulated to explain these associations. This study aimed to investigate the casual relationships behind the strong association of maternal height with fetal growth measures (i.e., birth length and birth weight) and gestational age by a Mendelian randomization approach.

Methods and Findings

We conducted a Mendelian randomization analysis using phenotype and genome-wide single nucleotide polymorphism (SNP) data of 3,485 mother/infant pairs from birth cohorts collected from three Nordic countries (Finland, Denmark, and Norway). We constructed a genetic score based on 697 SNPs known to be associated with adult height to index maternal height. To avoid confounding due to genetic sharing between mother and infant, we inferred parental transmission of the height-associated SNPs and utilized the haplotype genetic score derived from nontransmitted alleles as a valid genetic instrument for maternal height. In observational analysis, maternal height was significantly associated with birth length (p = 6.31 × 10⁻⁹), birth weight (p = 2.19 × 10⁻¹⁵), and gestational age (p = 1.51 × 10⁻⁷). Our parental-specific haplotype score association analysis revealed that birth length and birth weight were significantly associated with the maternal transmitted haplotype score as well as the paternal transmitted haplotype score. Their association with the maternal nontransmitted haplotype score was far less significant, indicating a major fetal genetic influence on these fetal growth measures. In contrast, gestational age was significantly associated with the nontransmitted haplotype score (p = 0.0424) and demonstrated a significant (p = 0.0234) causal effect of every 1 cm increase in maternal height resulting in ~0.4 more gestational d. Limitations of this study include potential influences in causal inference by biological pleiotropy, assortative mating, and the nonrandom sampling of study subjects.

Conclusions

Our results demonstrate that the observed association between maternal height and fetal growth measures (i.e., birth length and birth weight) is mainly defined by fetal genetics. In contrast, the association between maternal height and gestational age is more likely to be causal. In addition, our approach that utilizes the genetic score derived from the nontransmitted maternal haplotype as a genetic instrument is a novel extension to the Mendelian randomization methodology in casual inference between parental phenotype (or exposure) and outcomes in offspring.     

Case fatality among infants with congenital malformations by lethality

OBJECTIVE: Infant mortality rates continue to show that congenital anomalies are the leading cause of infant death in the United States. However, studies of factors contributing to increased mortality across different types of congenital anomalies have been limited. The objective of this study was to assess whether the likelihood of infant mortality varied by maternal race and ethnic group while considering the severity of the birth defect. METHODS: A retrospective cohort analysis was conducted using data from Colorado's statewide, population-based birth defects surveillance system (CRCSN). The cohort included infants, born between 1995 and 2000 to Colorado resident mothers, who were diagnosed with major congenital malformations stratified by degree of lethality. Multiple logistic regression was performed for each level of lethality, and included the following potential explanatory variables: maternal race/ethnicity, clinical gestation, birth weight, maternal education level, maternal age, and sex of child. RESULTS: Within the low/very low lethality cohort, maternal race/ethnicity of Black/non-Hispanic was associated with increased risk of infant mortality, OR 2.81 (1.41-5.19), as were low and very low birth weight, OR 2.21 (1.12-4.04) and 19.31 (11.84-31.01), respectively. Maternal race/ethnicity was not a significant risk factor in either high or very high lethality groups; however, the interaction between birth weight and gestational age significantly increased the risk of mortality. CONCLUSIONS: Through the use of statewide, population-based birth defects surveillance data, a disparity in infant mortality has been identified in a specific subset of the population that could be investigated further and targeted for prevention activities.     

Maternal thyroid disease,thyroid medication use,and selected birth defects in the National Birth Defects Prevention Study

BACKGROUND: Although thyroid disorders are present in approximately 3% of pregnant women, little is known about the association between maternal thyroid disease and birth defects. METHODS: We assessed the association between maternal thyroid disease, thyroid medication use, and 38 types of birth defects among 14,067 cases and 5875 controls in the National Birth Defects Prevention Study, a multisite, population‐based, case‐control study. Infants in this study were born between October 1997 and December 2004. Information on exposures including maternal diseases and use of medications was collected by telephone interview. RESULTS: We found statistically significant associations between maternal thyroid disease and left ventricular outflow tract obstruction heart defects (1.5; 95% CI, 1.0–2.3), hydrocephaly (2.9; 95% CI, 1.6–5.2), hypospadias (1.6; 95% CI, 1.0–2.5), and isolated anorectal atresia (2.4; 95% CI, 1.2–4.6). Estimates for the association between periconceptional use of thyroxine and specific types of birth defects were similar to estimates for any thyroid disease. Given that antithyroid medication use was rare, we could not adequately assess risks for their use for most case groups. CONCLUSIONS: Our results are consistent with the positive associations between maternal thyroid disease or thyroid medication use and both hydrocephaly and hypospadias observed in some previous studies. New associations with left ventricular outflow tract obstruction heart defects and anorectal atresia may be chance findings. Birth Defects Research (Part A), 2009. © 2009 Wiley‐Liss, Inc.     

Influence of the dam and sire on size at birth and subsequent growth, milk production and fertility in dairy heifers

Genetic selection has resulted in larger cows with high milk production potential but a tendency for poor fertility. In multiparous cows fetal development competes for nutrients with concurrent milk production. This study tested the hypotheses that (a) maternal age and milk yield during pregnancy alter calf birth size and (b) birth weight influences subsequent productivity and fertility. Concurrently born Holstein-Friesian heifers (n=65) with multiparous dams and three sires were monitored from birth to the end of their first lactation to assess effects of birth weight on growth, milk production and fertility. Calves were analyzed as three subgroups: low (L), average (A) and high (H) birth weight (BW) calves (n=21-22 per group). LBW calves were born 10 kg lighter than HBW calves and remained significantly lighter throughout the study. They were generally smaller in other measured indices (length, height, girth, ponderal index) between birth and 9 months and were more likely to have older dams (lactations 3-6) with higher peak yields (>42 kg/day). Milk production parameters were indistinguishable between the 3 birthweight groups and metabolic parameters (IGF-I, insulin, glucose) measured around first calving were unaffected. HBW offspring were more likely to have persistent corpora lutea following their first calving and other fertility parameters also tended to be worse. Sire influenced gestation length but not birth size. Sire heritability estimates showed that weight, IGF-I and insulin concentrations after first calving and fertility in the first lactation were all heritable. The results support the hypothesis that high milk production in the dam may predispose to birth of a smaller calf. Smaller birth size did not, however, have any subsequent adverse effects on productivity or fertility in the first lactation and sire was more influential at this stage.