Gestation-adjusted Birthweight Research Articles

Slow Development of a Day 5 Fresh Transferred Embryo Leads to Reduced Live Birth Rate but Not Birthweight: A Multicenter Retrospective Cohort Study

Objective: This study aims to investigate the impact of slow embryo development on the subsequent live birth rate and birthweight outcomes following a fresh day 5 transfer. Study design: This retrospective multicenter cohort study included 1,213 consecutive patients undergoing autologous oocyte in vitro fertilization (IVF) treatment at four associated private clinics during 2016–2019. Only fresh single day 5 transfers were included for analysis. Results: No implantation was achieved by embryos that failed to reach the early blastocyst stage on day 5 ([Formula: see text]). After adjusting for potential confounding factors, multivariate logistic regression (expressed as adjusted odds ratio or aOR and [Formula: see text] confidence interval) showed a significantly reduced live birth rate in early blastocysts ([Formula: see text]) in reference to those at the expanding (aOR = 0.584, [Formula: see text], [Formula: see text], [Formula: see text]), expanded (aOR = 0.322, [Formula: see text], [Formula: see text], [Formula: see text]), or hatching/hatched stages (aOR = 0.255, [Formula: see text], [Formula: see text], [Formula: see text]). However, early blastocysts led to similar birthweights ([Formula: see text], [Formula: see text]) in comparison to those at the expanding ([Formula: see text], [Formula: see text], [Formula: see text]), expanded ([Formula: see text], [Formula: see text], [Formula: see text]), or hatching/hatched stages ([Formula: see text], [Formula: see text], [Formula: see text]). This was further confirmed by linear regression analysis using either birthweight or [Formula: see text] score (gestation-adjusted birthweight). Conclusion: Slow day 5 development is associated with reduced live birth rate when transferred fresh, however, subsequent birthweight is not impacted once pregnancy is initiated.

Glyphosate exposure in early pregnancy and reduced fetal growth: a prospective observational study of high-risk pregnancies

BackgroundPrenatal glyphosate (GLY) exposure is associated with adverse reproductive outcomes in animal studies. Little is known about the effects of GLY exposure during pregnancy in the human population. This study aims to establish baseline urine GLY levels in a high-risk and racially diverse pregnancy cohort and to assess the relationship between prenatal GLY exposure and fetal development and birth outcomes.MethodsRandom first trimester urine specimens were collected from high risk pregnant women between 2013 and 2016 as part of the Indiana Pregnancy Environmental Exposures Study (PEES). Demographic and clinical data were abstracted from mother and infant medical records. Urine glyphosate levels were measured as a proxy for GLY exposure and quantified using liquid chromatography-tandem mass spectrometry. Primary outcome variables included gestation-adjusted birth weight percentile (BWT%ile) and neonatal intensive care unit (NICU) admission. Relationships between primary outcome variables and GLY exposure were assessed using univariate and multivariate linear and logistic regression models.ResultsUrine GLY levels above the limit of detection (0.1 ng/mL) were found in 186 of 187 (99%) pregnant women. Further analyses were limited to 155 pregnant women with singleton live births. The mean age of participants was 29 years, and the majority were non-Hispanic white (70%) or non-Hispanic Black (21%). The mean (± SD) urine GLY level was 3.33 ± 1.67 ng/mL. Newborn BWT%iles were negatively related to GLY (adjusted slope ± SE = -0.032 + 0.014, p = 0.023). Infants born to women living outside of Indiana’s large central metropolitan area were more likely to have a lower BWT%ile associated with mother’s first trimester GLY levels (slope ± SE = -0.064 ± 0.024, p = 0.007). The adjusted odds ratio for NICU admission and maternal GLY levels was 1.16 (95% CI: 0.90, 1.67, p = 0.233).ConclusionGLY was found in 99% of pregnant women in this Midwestern cohort. Higher maternal GLY levels in the first trimester were associated with lower BWT%iles and higher NICU admission risk. The results warrant further investigation on the effects of GLY exposure in human pregnancies in larger population studies.

Slow Development of Day 5 Embryo Leads to Compromised Live Birth But Not Birthweight Outcomes

Background: There is currently no consensus regarding developmental cutoff for fresh transfer of slow developing day 5 embryos on. Literature is sparse regarding true prognosis of such embryos. Aim: To investigate live birth and birthweight outcomes of slow developing day 5 transferred embryos. Method: This retrospective multi-center study included 1213 consecutive autologous-oocyte single fresh day 5 transfers performed at 4 Monash IVF clinics during 2016-2019. Repeat cycles by same patients were excluded to avoid clustering effects. Live birth and birthweight were followed up in all pregnancies. Multiple regression was performed to investigate associations between slow day 5 development (defined as ≤ early blastocyst) and (a) live birth, (b) birthweight, and (c) gestation-adjusted birthweight (Z score) to account for gestational age and gender. Results were expressed as adjusted odds ratio (aOR) with 95% confidence interval (CI). Results: No implantation was achieved when day 5 embryo failed to reach early blastocyst stage (i.e. ≤morula, n=76). Live birth rate was significantly lower following transfer of early blastocysts (n=237, 16%), in comparison to expanding (n=329, 27%, P=0.001), expanded (n=392, 41%, P=0.000), and ≥hatching blastocysts (n=169, 44%, P=0.000). After adjusting for maternal age, hours post insemination at day 5 assessment, number of oocytes collected, number of 2PNs, and number of embryos frozen; multiple logistic regression showed a significantly reduced likelihood of live birth resulting from early blastocysts in reference to expanding (aOR=0.584, 0.371-0.917, P=0.020), expanded (aOR=0.322, 0.208-0.501, P=0.000), or ≥hatching stages (aOR=0.255, 0.147-0.443, P=0.000). However, early blastocysts resulting in live birth (n=39) did not alter birthweight or Z score in reference to expanding (n=90, P>0.05 respectively), expanded (n=160, P>0.05 respectively), or ≥hatching (n=75, P>0.05 respectively). Conclusion: There is no clinical value of fresh transferring day 5 embryos at ≤morula stage. Fresh early blastocysts lead to a reduced live birth rate but not birthweight outcomes.

O-213 Slow day 5 development affects implantation potential of fresh transferred embryos but not birthweight once pregnancy occurs: A multi-center retrospective cohort study

Abstract Study question Does slow development of fresh transferred day 5 embryos lead to decreased implantation potential and birthweight? Summary answer Slow day 5 development was associated with reduced implantation potential when transferred fresh but the subsequent birthweight of the resulting baby was not impacted. What is known already Slow development of in vitro cultured cleavage stage embryos is associated with reduced blastocyst development and implantation rates. There is no current consensus regarding whether to transfer fresh slow developing day 5 embryos or to extend culture for a subsequent day with potential for cryopreservation. It is therefore important to understand the true prognosis of fresh transferred day 5 embryos at less advanced developmental stages. This would provide evidence based guidelines for the decision making process in regard to embryo transfer. Study design, size, duration This is a retrospective multi-center cohort study, including 1213 consecutive patients undergoing autologous oocyte in vitro fertilization (IVF) treatment during 2016-2019,with fresh transfer of a single day 5 embryo (selection based on developmental stage and inner cell mass and trophectoderm morphology if blastocyst was at the ≥expanding stage). Cycle data were collected from 4 associated private clinics, with repeat cycles of same patients excluded to avoid clustering effect at statistical analysis. Participants/materials, setting, methods Live birth and birthweight were followed up in all 1213 fresh day 5 SETs. Multiple regression (logistic or linear) was performed to investigate association between slow day 5 development (defined as ≤ early blastocyst) and (a)live birth, (b) birthweight, and (c) gestation-adjusted birthweight (Z score) to account for gestational age, gender and compared to embryos at ≥ expanded stage. Results were expressed as adjusted odds ratio (aOR) with 95% confidence interval (CI)or coefficients (β). Main results and the role of chance No implantation was achieved following single fresh transfer of day 5 embryos that failed to reach early blastocyst stage (n = 76) and were transferred as ≤ morula stage. Live birth rate was significantly lower following single day 5 fresh transfer of an early blastocyst (n = 237, 16%), in comparison to expanding (n = 329, 27%, P = 0.001), expanded(n = 392, 41%, P = 0.000), and hatching/hatched blastocysts (n = 169, 44%, P = 0.000). After adjusting for potential confounding factors including; maternal age, hours post insemination at day 5 assessment, number of oocytes collected, number of 2PN embryos, and number of embryos frozen; multiple logistic regression showed significantly reduced likelihood of live birth resulting from early blastocysts in reference to those at the expanding (aOR=0.584, 0.371-0.917, P = 0.020), expanded (aOR=0.322, 0.208-0.501, P = 0.000), or hatching/hatched stages (aOR=0.255, 0.147-0.443, P = 0.000). However, multivariate linear regression indicated that early blastocysts resulting in a live birth (n = 39) did not lead to altered birthweight (β=-9.091, P = 0.904; β=-34.960, P = 0.343; β=-26.074, P = 0.414; respectively) or Z score (β = 0.045, P = 0.706; β=-0.051, P = 0.426; β=-0.028, P = 0.506; respectively) in reference to the expanding (n = 90), expanded (n = 160), or hatching/hatched stages (n = 75). Limitations, reasons for caution The retrospective nature of this study does not allow controlling of unknown confounders. The 4 participating clinics are associated within the same network with shared protocols, therefore, results may not be generalized to other clinics with different settings. Wider implications of the findings The findings suggest no clinical value of fresh day 5 transfer of embryos ≤morula stage. Although early blastocysts implant at reduced rate, assuring birthweight outcomes suggest clinical value. Future studies intend to investigate slow growing day 5 fresh transfers versus embryos that were slow growing but transferred after day 6. Trial registration number NA

Associations of IVF singleton birthweight and gestation with clinical treatment and laboratory factors: a multicentre cohort study.

Do IVF treatment and laboratory factors affect singleton birthweight (BW)? BWs of IVF-conceived singleton babies are increasing with time, but we cannot identify the specific treatment factors responsible. IVF-conceived singleton babies from fresh transfers have slightly lower BW than those conceived naturally, whilst those from frozen embryo transfer (FET) cycles are heavier and comparable to naturally conceived offspring. Our recent studies have shown that BW varies significantly between different IVF centres, and in a single centre, is also increasing with time, without a corresponding change in BWs of naturally conceived infants. Although it is likely that factors in the IVF treatment cycle, such as hormonal stimulation or embryo laboratory culture conditions, are associated with BW differences, our previous study designs were not able to confirm this. Data relating to BW outcomes, IVF treatment and laboratory parameters were collated from pre-existing electronic records in five participating centres for all singleton babies conceived between August 2007 and December 2014. Seven thousand, five hundred and eighty-eight births, 6207 from fresh and 1381 from FET. Infants with severe congenital abnormalities were excluded. The primary outcome of gestation-adjusted BW and secondary outcomes of unadjusted BW and gestation were analysed using multivariable regression models with robust standard errors to allow for the correlation between infants with the same mother. The models tested treatment factors allowing for confounding by centre, time and patient characteristics. A similar matched analysis of a subgroup of 379 sibling pairs was also performed. No significant associations of birth outcomes with IVF embryo culture parameters were seen independent of clinic or time, including embryo culture medium, incubator type or oxygen level, although small differences cannot be ruled out. We did not detect any significant differences associated with hormonal stimulation in fresh cycles or hormonal synchronization in FET cycles. Gestation-adjusted BW increased by 13.4 (95% CI 0.6-26.1) g per year over the period of the study, and babies born following FET were 92 (95% CI 57-128) g heavier on average than those from the fresh transfer. Although no specific relationships have been identified independent of clinic and time, the confidence intervals remain large and do not exclude clinically relevant effect sizes. As this is an observational study, residual confounding may still be present. This study demonstrates the potential for large scale analysis of routine data to address critical questions concerning the long-term implications of IVF treatment, in accordance with the Developmental Origins of Health and Disease hypothesis. However, much larger studies, at a national scale with sufficiently detailed data, are required to identify the treatment parameters associated with differences in BW or other relevant outcomes. This work was supported by the EU FP7 project grant, EpiHealthNet (FP7-PEOPLE-2012-ITN-317146). No competing interests were identified. N/A.

The impact of embryo quality on singleton birthweight in vitrified-thawed single blastocyst transfer cycles.

Does the quality of a single transferred blastocyst affect singleton birthweight in frozen-embryo transfer (FET) cycles? The transfer of a poor-quality blastocyst was associated with lower mean birthweight and gestation-adjusted birthweight (Z-scores) when compared with the transfer of an excellent-quality blastocyst during FET cycles. Embryo quality is a strong predictor of IVF success rates. However, very few studies have examined the effect of embryo quality on singleton birthweight. This retrospective study involved singleton live births born to women undergoing frozen-thawed single blastocyst transfers during the period from January 2010 to December 2017 at a tertiary care centre. A total of 1207 women who fulfilled the inclusion criteria were included and were grouped into four groups depending on the blastocyst quality: excellent, good, average and poor. The primary outcome measure was singleton birthweight. The Z-score was employed to calculate the birthweight adjusted for gestational age and newborn gender. Multiple linear regression analysis was performed to investigate the relationship between embryo quality and neonatal birthweight after adjustment for some potential confounders. In the primary multivariable model, singletons from the poor-quality blastocyst group weighed 183.5g less than those from the excellent-quality blastocyst group (95% CI: -295.1 to -71.9g, P = 0.001) in terms of mean birthweight after accounting for patient characteristics, IVF treatment parameters, the year of treatment and newborn gender. Likewise, poor-quality blastocyst transfer was associated with lower gestation-adjusted Z-scores than the transfer of excellent-quality blastocysts (β = -0.35, 95% CI: -0.59 to -0.12, P = 0.003). The current study was limited by its retrospective design and the fact that our analysis was restricted to women with singleton births from single blastocyst transfers. Future prospective studies are required to confirm our findings. Our findings provide new insight into the relationship between embryo quality and neonatal outcomes by showing that poor-quality blastocyst transfer was associated with a decrease in singleton birthweight. This study was supported by the National Key Research and Development Program of China (grant no. 2018YFC1003000), the National Natural Science Foundation of China (grant nos. 81771533, 81571397 and 31770989), and the China Postdoctoral Science Foundation (Grant no. 2018M630456). The authors have no conflicts of interest to declare. Not applicable.

The impact of selected embryo culture conditions on ART treatment cycle outcomes: a UK national study.

STUDY QUESTIONAre selected embryo culture conditions namely media, oxygen level, and incubator type, associated with IVF live birth rate (LBR) and the health of singleton offspring at birth?SUMMARY ANSWERThere were statistically significant differences in LBR between the eight culture media systems analysed; however, none of the embryo culture factors showed statistically significant associations with birth weight (BW) in multivariable regression analyses.WHAT IS KNOWN ALREADYIn clinical ART culture media is the initial environment provided for the growth of human embryos. Pre-implantation development is a critical period of developmental plasticity, which could have long-lasting effects on offspring growth and health. Although some studies have shown an impact of culture medium type on BW, the interaction between culture medium type and associated culture conditions on both treatment success rates (LBR) and offspring BW is largely unexplored. This study aimed to examine these factors in a large multicentre national survey capturing the range of clinical practice.STUDY DESIGN, SIZE, DURATIONIn this cross-sectional study, data from a survey circulated to all UK IVF clinics requesting information regarding culture medium type, incubator type, and oxygen level used in ART between January 2011 and December 2013 were merged with routinely recorded treatment and outcome data held in the Human Fertilisation and Embryology Authority Register up to the end of 2014.PARTICIPANTS/MATERIALS, SETTING, METHODSForty-six (62%) UK clinics responded to the survey. A total of 75 287 fresh IVF/ICSI cycles were captured, including 18 693 singleton live births. IVF success (live birth, singleton or multiple; LB), singleton gestation and singleton gestation-adjusted BW were analysed using logistic and linear regression models adjusting for patient/treatment characteristics and clinic-specific effects.MAIN RESULTS AND THE ROLE OF CHANCECulture medium type was shown to have some impact on LBR (multivariable logistic regression, (MRL); post-regression Wald test, P < 0.001), but not on BW (MLR; post-regression Wald test, P = 0.215). However, blastocyst culture had the largest observed effect on odds of LBR (odds ratio (OR) = 1.35, CI: 1.29–1.42), increased the risk of pre-term birth even when controlling for oxygen tension (MLR; OR = 1.42, CI: 1.23–1.63), and gestation-adjusted BW (MLR, β = 38.97 g, CI: 19.42–58.53 g) when compared to cleavage-stage embryo culture. We noted a very strong effect of clinic site on both LBR and BW, thus confounding between treatment practices and clinic site may have masked the effect of culture conditions.LIMITATIONS, REASONS FOR CAUTIONLarger datasets with more inter-centre variation are also needed, with key embryo culture variables comprehensively recorded in national treatment registries.WIDER IMPLICATIONS OF THE FINDINGSThis study is the largest investigation of laboratory environmental effects in IVF on both LBR and singleton BW. Our findings largely agree with the literature, which has failed to show a consistent advantage of one culture media type over another. However, we noted some association of LBR with medium type, and the duration of embryo exposure to laboratory conditions (blastocyst culture) was associated with both LBR and singleton health at birth. Because of the strong effect of clinic site noted, further randomized controlled trials are needed in order to reliably determine the effect of embryo culture on IVF success rates and the growth and health of subsequent offspring.STUDY FUNDING/COMPETING INTEREST(S)This study was funded by the EU FP7 project grant EpiHealthNet (FP7-PEOPLE-2012-ITN -317 146). The authors have no competing interests to declare.

The Importance of Gestation-Adjusted Birthweight Centile in Assessment of Fetal Growth in Metabolic Conditions

The Importance of Gestation-Adjusted Birthweight Centile in Assessment of Fetal Growth in Metabolic Conditions

The relationship between maternal opiate use, amphetamine use and smoking on fetal growth

Opiate and amphetamine use during pregnancy is frequently associated with cigarette smoking. The negative effects on fetal growth from nicotine combined with opiates or amphetamines during pregnancy are not well documented. To investigate the relationship between maternal opiate or amphetamine use and smoking on fetal growth. A retrospective study was performed comparing pregnancies affected with either opiates or amphetamines with individually matched controls. All mothers smoked cigarettes during pregnancy. The outcome measures included changes in fetal abdominal circumference, head circumference and femur length during the second half of pregnancy and weight, length and head circumference at birth. There were 91 opiate- and 37 amphetamine-affected pregnancies. Deviations from normative data only became apparent from the third trimester. The proportion of infants with a gestation-adjusted birthweight below the 10th percentile was not significantly different in the opiate group compared to their controls 35 (38%). However, there was a significant difference in proportions in the amphetamine group and their controls (P < 0.001). We then compared antenatal growth patterns between the amphetamine group and their controls. Amphetamine-exposed fetuses showed comparable growth parameters in the second trimester but significantly larger head and abdominal circumferences and longer femoral lengths in the third trimester than their respective controls (P < 0.05 for all). When combined with cigarette smoking, opiates had no observed independent effect on birth parameters. Unexpectedly, in the amphetamine group, the negative effects of smoking on growth were altered in late pregnancy.

A Decomposition of the Black-White Differential in Birth Outcomes

Substantial racial disparities continue to persist in the prevalence of preterm births and low- birth-weight births. Health policy aimed at reducing these disparities could be better targeted if the differences in birth outcomes are better understood. This study decomposes these racial disparities in birth outcomes to determine the extent to which the disparities are driven by differences in measurable characteristics of black mothers and white mothers as well as the extent to which the gap results from differences in the impact of these characteristics. The analysis is focused on three adverse birth outcomes: preterm, early preterm birth (less than 32 weeks gestation), and low birth weight. The results suggest that differences in covariates accounted for approximately 25 percent of the gap in the incidence of preterm births. The specific characteristics that matter the most are marriage rates, father's characteristics, and prenatal care. For gestation-adjusted birth weight, approximately 16 percent of the racial gap for first births is explained by covariates; for subsequent births this covariate explanation rises to 22 percent of the gap. Furthermore, differences in coefficients explain about another quarter of the gap in preterm birth outcomes but very little of the gap in birth weight. JEL classification: I1

Role of Adiponectin in Matching of Fetal and Placental Weight in Mothers With Type 1 Diabetes

To assess the association of fetal hormones with placental growth and fetal weight-to-placental weight ratio index (FPI) in pregnancies complicated by maternal diabetes. We conducted a prospective study using umbilical venous blood samples taken at birth from 122 offspring of mothers with type 1 diabetes (OT1D) and 46 control subjects. Placental weight (P = 0.009) and gestation-adjusted birth weight (P < 0.001) were increased in OT1D, but FPI was unaltered (P = 0.33). Placental weight correlated with birth weight (P < 0.001) and cord leptin (P < 0.001) in control subjects and OT1D, with further relationships with cord insulin, IGF-1, IGF-binding protein-3 (IGFBP-3), and triceps and subscapular thickness in OT1D. FPI was associated with adiponectin in both groups, even after adjustment for confounders. Placental and fetal growth show a parallel increase in mothers with type 1 diabetes. The possible role of adiponectin in matching of fetal and placental growth merits further study.

Fetal growth and childhood cholesterol levels in the United States

Research has linked fetal environment to subsequent adult disease. This study examines the extent to which infants born small-for-gestational age (SGA) were at risk for high cholesterol levels in early childhood (ages 4-6 years). Data were obtained from 1727 children aged 4-6 years who participated in the cross-sectional third US National Health and Nutrition Examination Survey and had both birth certificates and blood cholesterol information. The odds of having moderately elevated (170-199 mg/dL) or high (> or =200 mg/dL) serum total cholesterol after being born SGA were determined after controlling for sex, race/ethnicity, education of household head, saturated fat intake, parental history of high cholesterol and overweight status. Approximately 11% of participants were SGA. Proportions of children with moderately elevated and high cholesterol levels were approximately 28 and 8%, respectively. SGA children were almost twice as likely (odds ratio 1.97, 95% confidence interval [0.8, 4.8]) to have high cholesterol vs. low cholesterol than non-SGA children, although the result was not statistically significant. Multiple linear regression demonstrated a similar inverse, non-significant relationship between gestation-adjusted birthweight and cholesterol (beta = -2.3, P = 0.33). These data indicate a possible association between reduced fetal growth, represented by birthweight adjusted for gestational age, and increased cholesterol levels in early childhood.

Patterns of fetal and childhood growth and the development of psychosis in young males: a cohort study.

Factors influencing fetal and childhood growth may affect a person's risk of developing schizophrenia. Associations of size at birth and body size in young adulthood with schizophrenia and other nonaffective psychoses were assessed in a cohort of 334,577 Swedish male conscripts born in 1973-1980 for whom linked birth, census, hospital admission, and adult height and weight data were available. Complete data on all study variables were available for 246,655 subjects. Over a mean 3.4-year follow-up beginning at age 18 years, 80 subjects developed schizophrenia and 124 developed other nonaffective psychoses. A reverse J-shaped association was found between gestation-adjusted birth weight and schizophrenia. The hazard ratios were 7.03 (95% confidence interval: 1.59, 31.10) for males of low birth weight (<2.5 kg) and 3.37 (95% confidence interval: 1.68, 6.74) for those of high birth weight (>4.0 kg). Birth weight was not strongly related to other nonaffective psychoses. Taller males had a reduced risk of psychosis. The lowest risks were seen for low birth weight males who became tall adults. The associations with birth weight indicate that fetal exposures, including possible effects of gestational diabetes, are important in the etiology of psychosis. The role of childhood exposures, as indexed by adult height and body mass index, appears to be less strong.

Growth In Utero and During Childhood Among Women Who Develop Coronary Heart Disease: Longitudinal Study

Coronary heart disease (CHD) in Finnish men has been associated with low birth weight and more strongly with thinness at birth, as reflected by a low birth weight/length ratio. Mortality was highest in those who were thin when born but whose body weight caught up by age 7 years. The corresponding cohort of women born in the same hospital during the same years (1924–1933) now has been analyzed. Hazard ratios for hospital admission or death due to CHD were calculated for 3447 women. A total of 247 had been hospitalized for CHD, and 35 had died of it. Another 32 women had died without being admitted to a hospital. The annual death rate among women aged 45 to 64 years was 0.8 per 1000; the corresponding figure among men was 3.9 per 1000. Hazard ratios for CHD declined with increasing birth weight, although not to a significant degree. Adjusting for gestational age strengthened the association. The hazard ratio rose by approximately 10 percent for every centimeter decrease in length at birth (adjusted for length of gestation). Neither the ponderal index nor head circumference was a significant correlate of CHD risk in females. Hazard ratios did correlate with an increasing ratio of placental weight to gestation-adjusted birth weight. Women who developed CHD had grown less in height and weight from age 7 to 15 years. The relationship of shortness at birth and tallness in childhood to CHD was especially strong in women whose own mothers had been relatively tall. Differences between males and females in body size at birth seemed to be small, but differences in proportionate size were more marked. A short body length and high placental weight, the pattern predicting CHD in women, was much more prevalent in girls than in boys. Conversely, boys more often were thin at birth and had a large head circumference, and it was thinness at birth that predicted CHD in men. Sex-related differences in correlates of CHD may reflect differing rates of fetal growth at similar levels of maternal nutrition. Females may have less CHD because they grow more slowly in utero. Br Med J 1999;319:1403–1407

Do standing, lifting, climbing, or long hours of work during pregnancy have an effect on fetal growth?

We assessed prospectively the impact of length of the work week and job activity on fetal growth. Among 575 women who worked during pregnancy, neither prolonged standing, frequent lifting, or climbing at work, nor a high composite activity score showed an association with fetal growth, as measured by birthweight for gestational age. Long hours of work, however, did reduce fetal growth. Infants of women working long hours late in pregnancy showed decreases in gestation-adjusted birthweight of about 80 gm (95% confidence limits = -238, +74 gm), compared with women working 20 hours or less. When long hours (> 40 hours per week) were combined with job activity, the estimated reductions ranged up to 350 gm. At lower weights (< or = 3,000 gm), categorical analyses showed elevated odds ratios (1.1-1.8) for climbing, lifting, and long hours and for the combination of prolonged standing with a lengthy work week. These results indicate that long weeks of physically demanding work could lead to fetal growth reductions that may be clinically significant. Consistent with this suggestion, infants of women who worked part-time had the highest mean birthweights. Hours of work, not only job tasks, may be important for pregnant workers.