Placental transport rather than maternal concentration of amino acids regulates fetal growth in monochorionic twins: implications for fetal origin hypothesis

Oxidative stress biomarkers for fetal growth restriction in umbilical cord blood: A scoping review

Fetal growth restriction and underlying placental insufficiency are associated with increased oxidative stress. Current diagnostics fail to identify all growth restricted fetuses and newborns, due to focus on small size. This scoping review aims to summarize the available evidence on usefulness of cord blood oxidative stress biomarkers for identification of growth restricted newborns in need of monitoring and support because of associated health risks. MEDLINE and EMBASE were searched from inception to May 2024. Studies were included if oxidative stress biomarkers were measured in cord blood collected immediately after delivery in newborns suspected to be growth restricted. Biomarkers were categorized based on the origin and/or biological function and their interrelationships. Oxidative stress was determined for each individual biomarker and category. Literature search identified 78 studies on 39 different biomarkers, with a total of 2707 newborns with suspected growth restriction, and 4568 controls. Total oxidant/antioxidant status, catalase, glutathione, ischemia-modified albumin, and nucleated red blood cells were most consistently associated with suspected growth restriction. Reactive oxygen species/reactive nitrogen species, factors in their production, antioxidant enzymes, non-enzymatic antioxidants, and products of oxidative stress were not consistently associated. This review collates the evidence of associations between cord blood oxidative stress biomarkers and growth restriction. Total oxidant/antioxidant status, catalase, glutathione, ischemia-modified albumin, and nucleated red blood cells could potentially be candidates for developing a cord blood diagnostic tool for future clinical use.

Unraveling the Molecular Mechanisms of the Neurodevelopmental Consequences of Fetal Protein Deficiency: Insights From Rodent Models and Public Health Implications

Fetal brain development requires increased maternal protein intake to ensure that offspring reach their optimal cognitive potential in infancy and adulthood. While protein deficiency remains a prevalent issue in developing countries, it is also reemerging in Western societies due to the growing adoption of plant-based diets, some of which are monotonous and may fail to provide sufficient amino acids crucial for the brain's critical developmental phase. Confounding variables in human nutritional research have impeded our understanding of the precise impact of protein deficiency on fetal neurodevelopment, as well as its implications for childhood neurocognitive performance. Moreover, it remains unclear whether such deficiency could predispose to mental health problems in adulthood, mirroring observations in individuals exposed to prenatal famine. In this review, we sought to evaluate mechanistic data derived from rodent models, placing special emphasis on the involvement of neuroendocrine axes, the influence of sex and timing, epigenetic modifications, and cellular metabolism. Despite notable progress, critical knowledge gaps remain, including understanding the long-term reversibility of effects due to fetal protein restriction and the interplay between genetic predisposition and environmental factors. Enhancing our understanding of the precise mechanisms that connect prenatal nutrition to brain development in future research endeavors can be significantly advanced by integrating multiomics approaches and utilizing additional alternative models such as nonhuman primates. Furthermore, it is crucial to investigate potential interventions aimed at alleviating adverse outcomes. Ultimately, this research has profound implications for guiding public health strategies aimed at raising awareness about the crucial role of optimal maternal nutrition in supporting fetal neurodevelopment.

Amniotic fluid metabolic fingerprinting contributes to shaping the unfavourable intrauterine environment in monochorionic diamniotic twins

BACKGROUND & AIMS

Amniotic fluid (AF) is the primary intrauterine environment for fetal growth throughout gestation. Selective fetal growth restriction (sFGR) is an adverse complication characterized by unequal growth in twins with nearly identical genetic makeup. However, the influence of AF-mediated intrauterine environment on the development and progression of sFGR remains unexplored.

METHODS

High-throughput targeted metabolomics analysis (G350) was performed on AF samples collected from sFGR (n = 18) and MCDA twins with birth weight concordance (MCDA-C, n = 20) cases. Weighted correlation network analysis (WGCNA) was used to identify clinical features that may influence the metabolite composition in AF. Subsequently, partial least-squares discriminant analysis (PLS-DA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to compare the different types of sFGR and MCDA-C twins. Receiver operating characteristic (ROC) and multivariate ROC curves were utilized to explore potential AF markers in twins with sFGR.

RESULTS

In our study, 182 metabolites were quantified in 76 AF samples. WGCNA indicated that the metabolite composition in late AF may not be influenced by gestational age. PLSDA demonstrated distinct variations between the metabolite profiles of AF in the sFGR and MCDA-C twins, with a significant emphasis on amino acids as the primary differential metabolite. The dissimilarities observed in sFGR twins were predominantly attributed to lipid metabolism-related metabolites. In particular, the KEGG enrichment metabolic pathway analysis revealed significant associations of both types of sFGR twins with central carbon metabolism in cancer. The multivariate ROC curves indicated that the combination of carnosine, sarcosine, l-alanine, beta-alanine, and alpha-n-phenylacetylglutamine significantly improved the AUC to 0.928. Notably, the ROC curves highlighted creatine (AUC:0.934) may be a potential biomarker for severe sFGR.

CONCLUSION

The data presented in this study offer a comprehensive metabolic map of the AF in cases of sFGR, shedding light on potential biomarkers associated with fetal growth and development in MCDA twins.

Associations between serum taurine concentrations in mothers and neonates and the children's anthropometrics and early neurodevelopment: Results from the Seychelles Child Development Study, Nutrition Cohort 2

BACKGROUND

High concentrations of taurine are present in the developing human brain and maternal breast milk. Taurine is thought to influence fetal growth and brain development based on experimental rodent studies. As fish is an important dietary source of taurine, we investigated associations between taurine concentrations and child outcomes in a high fish consuming population.

OBJECTIVE

To examine associations between maternal and cord serum taurine concentrations and birth anthropometric measures and cognitive development in children at 20 months of age.

METHODS

Pregnant women were recruited between 2008 and 2011 as part of Nutrition Cohort 2 (NC2) of the Seychelles Child Development Study (SCDS). Maternal taurine serum concentrations were measured at 28 week's gestation and in cord serum. Child weight, length and head circumference were measured at birth and neurodevelopment was assessed using Bayley Scales of Infant Development II (BSID-II) at 20 months of age. Associations between taurine status, birth measures and neurodevelopmental outcomes were examined (n = 300) using regression models and adjusted for relevant covariates.

RESULTS

Mean (SD) maternal and cord taurine concentrations were 124.9 (39.2) µmol/L (range 28.2-253.9 µmol/L) and 187.6 (60.0) µmol/L (range 55.0-417.4 µmol/L) respectively. We found no associations between maternal taurine concentrations and child anthropometric and neurodevelopmental measures (weight β = -0.001, SE=0.001; length β = -0.006, SE=0.006; head circumference β = -0.002, SE=0.002; MDI β = -0.005, SE=0.015; PDI β = -0.004, SE=0.016; all P > 0.05), or between cord taurine concentrations and outcomes (weight β = -0.001, SE<0.000; length β = -0.001, SE=0.004; head circumference β < 0.000, SE=0.002; MDI β = 0.004, SE=0.010; PDI β = -0.015, SE=0.012; all P > 0.05).

CONCLUSION

The Seychellois population have high maternal and cord taurine concentrations owing to their high fish intake and may be considered taurine replete compared to individuals who consume a Westernised diet. This high taurine status may explain why there were no significant associations between maternal and cord taurine concentrations and outcomes after adjusting for covariates.

Metabolic dynamics and prediction of sFGR and adverse fetal outcomes: a prospective longitudinal cohort study

BACKGROUND

Selective fetal growth restriction (sFGR) is an extreme complication that significantly increases the risk of perinatal mortality and long-term adverse neurological outcomes in offspring, affecting approximately 15% of monochorionic diamniotic (MCDA) twin pregnancies. The lack of longitudinal cohort studies hinders the early prediction and intervention of sFGR.

METHODS

We constructed a prospective longitudinal cohort study of sFGR, and quantified 25 key metabolites in 337 samples from maternal plasma in the first, second, and third trimester and from cord plasma. In particular, our study examined fetal growth and brain injury data from ultrasonography and used the Ages and Stages Questionnaire-third edition subscale (ASQ-3) to evaluate the long-term neurocognitive behavioral development of infants aged 2-3 years. Furthermore, we correlated metabolite levels with ultrasound data, including physical development and brain injury indicators, and ASQ-3 data using Spearman's-based correlation tests. In addition, special combinations of differential metabolites were used to construct predictive models for the occurrence of sFGR and fetal brain injury.

RESULTS

Our findings revealed various dynamic patterns for these metabolites during pregnancy and a maximum of differential metabolites between sFGR and MCDA in the second trimester (n = 8). The combination of L-phenylalanine, L-leucine, and L-isoleucine in the second trimester, which were closely related to fetal growth indicators, was highly predictive of sFGR occurrence (area under the curve [AUC]: 0.878). The combination of L-serine, L-histidine, and L-arginine in the first trimester and creatinine in the second trimester was correlated with long-term neurocognitive behavioral development and showed the capacity to identify fetal brain injury with high accuracy (AUC: 0.94).

CONCLUSIONS

The performance of maternal plasma metabolites from the first and second trimester is superior to those from the third trimester and cord plasma in discerning sFGR and fetal brain injury. These metabolites may serve as useful biomarkers for early prediction and promising targets for early intervention in clinical settings.

Prediction of maternal complications and neonatal outcome in dichorionic diamniotic twins with fetal weight discordancy measured by ultrasonography

This study aimed to determine the relationship between estimated fetal weight discordance by ultrasonography and maternal and neonatal outcomes in dichorionic diamniotic twin pregnancies. We conducted a retrospective review of the medical records of 106 twin pregnancies delivered at a single tertiary center between January 2011 and February 2020. At 20–24 and 28–32 weeks of gestation, participants were divided into two groups: discordant twins with an estimated fetal weight difference of more than 20% and concordant twins with a weight difference of less than 20%. Maternal complications and neonatal outcomes were compared between the two groups. Although the incidences of preeclampsia and placenta previa were significantly higher in discordant twins measured between 20 and 24 weeks, no statistical significance was found in neonatal outcomes. Delivery times were earlier, and neonatal weights were lower in discordant twins measured between 28 and 32 weeks. Neonatal outcomes such as ventilator use and neurodevelopment were also significantly different. Discordance in estimated fetal weight measured using ultrasonography between 20 and 24 weeks can be a risk factor for maternal preeclampsia and placenta previa, whereas discordance at 28–32 weeks may predict poor neonatal outcomes.

Placental dysfunction: The core mechanism for poor neurodevelopmental outcomes in the offspring of preeclampsia pregnancies

Preeclampsia (PE) is a leading condition threatening pregnant women and their offspring. The offspring of PE pregnancies have a high risk of poor neurodevelopmental outcomes and neuropsychological diseases later in life. However, the pathophysiology and pathogenesis of poor neurodevelopment remain undetermined. Abnormal placental functions are at the core of most PE cases, and recent research evidence supports that the placenta plays an important role in fetal brain development. Here, we summarize the relationship between abnormal fetal brain development and placental dysfunction in PE conditions, which include the dysfunction of nutrient and gas-waste exchange, impaired angiogenesis stimulation, abnormal neurotransmitter regulation, disrupted special protectors, and immune disorders. All these factors could lead to poor neurodevelopmental outcomes.

Monocytes and macrophages in pregnancy: The good, the bad, and the ugly

A successful human pregnancy requires precisely timed adaptations by the maternal immune system to support fetal growth while simultaneously protecting mother and fetus against microbial challenges. The first trimester of pregnancy is characterized by a robust increase in innate immune activity that promotes successful implantation of the blastocyst and placental development. Moreover, early pregnancy is also a state of increased vulnerability to vertically transmitted pathogens notably, human immunodeficiency virus (HIV), Zika virus (ZIKV), SARS-CoV-2, and Listeria monocytogenes. As gestation progresses, the second trimester is marked by the establishment of an immunosuppressive environment that promotes fetal tolerance and growth while preventing preterm birth, spontaneous abortion, and other gestational complications. Finally, the period leading up to labor and parturition is characterized by the reinstatement of an inflammatory milieu triggering childbirth. These dynamic waves of carefully orchestrated changes have been dubbed the "immune clock of pregnancy." Monocytes in maternal circulation and tissue-resident macrophages at the maternal-fetal interface play a critical role in this delicate balance. This review will summarize the current data describing the longitudinal changes in the phenotype and function of monocyte and macrophage populations in healthy and complicated pregnancies.

The Metabolic Signatures of Surviving Cotwins in Cases of Single Intrauterine Fetal Death During Monochorionic Diamniotic Pregnancy: A Prospective Case-Control Study

Introduction: Single intrauterine fetal death (sIUFD) in monochorionic diamniotic (MCDA) twin pregnancy may be associated with adverse clinical outcomes and possible metabolic changes in the surviving co-twin. Metabolomic profiling has not been undertaken before in these complex twin pregnancies.

Methods: In this prospectively collected case-control study, three cross-cohort comparisons were made between sIUFD MCDA (n = 16), uncomplicated MCDA (n = 16, eight pairs), and uncomplicated singleton pregnancies (n = 8). To identify major sources of variation within the sIUFD MCDA cohort, a secondary comparison was conducted between spontaneous sIUFD (n = 8) and sIUFD in MCDA twins due to selective termination of a single abnormal fetus by radiofrequency ablation (RFA) (n = 8). Metabolomics analysis of placental tissue and umbilical cord plasma was performed using LC-MS profiling. The underlying metabolic networks and pathways were analyzed by web-based platforms. Associations and statistical correlations of all identified differential metabolites with neonatal birthweight and birth length were assessed by multivariable linear regression, adjusted for maternal age and gestation.

Results: Across four comparisons, 131 and 111 differential metabolites were identified in placental tissue and cord plasma, respectively, with the highest variation seen between the spontaneous vs. single-induced IUFD in MCDA twins by RFA in the cord plasma. Conversely, the number of viable fetuses and the presence of sIUFD in MCDA twins had the highest impact on metabolite variation in placental tissue. Compounds correlated with fetal growth including placental acylcarnitines and gangliosides, along with specific amino acids (e.g., histidinyl-hydroxyproline), xenobiotics and biliverdin in cord plasma.

Conclusion: sIUFD in MCDA twin pregnancy correlates with distinctive metabolic signatures, mostly in fatty acyls and complex lipids, in placental tissue and cord plasma of the surviving cotwin. Some metabolites are also associated with fetal growth.

Counter-directed leucine gradient promotes amino acid transfer across the human placenta

The developing fetus is highly vulnerable to imbalances in the supply of essential amino acids (AA). Transplacental AA transfer depends on complex interactions between accumulative transporters, exchangers and facilitators, which maintain both intra-extracellular and materno-fetal substrate gradients. We determined physiological AA gradients between maternal and fetal blood and assessed their importance by studying maternal-fetal leucine transfer in human trophoblasts. Maternal-venous and corresponding fetal-arterial/fetal-venous sera were collected from 22 healthy patients at partum. The acquisition of the full AA spectra in serum was performed by ion exchange chromatography. Physiological materno-fetal AA levels were evaluated using paired two-way ANOVA with Tukey's correction. AA concentrations and gradients were tested for associations with anthropometric data by Spearman correlation analysis. Functional effects of a physiological leucine gradient versus equimolar concentrations were tested in BeWo cells using L-[³H]-leucine in conventional and Transwell-based uptake and transfer experiments. The LAT1/SLC7A5-specific inhibitor JPH203 was used to evaluate LAT1-transporter-mediated leucine transport. Maternal AA concentrations correlated with preconceptional and maternal weights at partum. Interestingly, low materno-fetal AA gradients were associated with maternal weight, BMI and gestational weight gain. Leucine uptake was promoted by increased extracellular substrate concentrations. Materno-fetal leucine transfer was significantly increased against a 137µM leucine gradient demonstrating that transplacental leucine transport is stimulated by a counter-directed gradient. Moreover, leucine transfer was inhibited by 10µM JPH203 confirming that Leu transport across the trophoblast monolayer is LAT1-dependent. This study demonstrates a currently underestimated effect of transplacental AA gradients on efficient leucine transfer which could severely affect fetal development.

Impact of growth discordance in twins on preeclampsia based on chorionicity

BACKGROUND

Despite extensive investigations over the last decade, preeclampsia remains an unpredictable pregnancy complication causing perinatal morbidity and mortality worldwide, particularly in twin pregnancies.

OBJECTIVE

This study aimed to determine the relationship between growth discordance in twin pregnancies and the risk for preeclampsia based on chorionicity.

STUDY DESIGN

This was a retrospective single-center study that included 2122 women with twin pregnancies who were admitted to a tertiary hospital between January 2013 and June 2016. Growth discordance was defined as twin birthweight difference ≥20%. Logistic regression models were used to analyze the association between growth discordance and risk for gestational hypertension-preeclampsia in all subjects. Stratified sampling by twin chorionicity (dichorionic and monochorionic) was also conducted. Further analysis was performed to estimate the association between the degree of growth discordance and gestational hypertension-preeclampsia risk in monochorionic and dichorionic twin pregnancies.

RESULTS

The prevalence of growth discordance was 17.6%. In all subjects, growth discordance was associated with increased risk for gestational hypertension-preeclampsia. After stratification by twin chorionicity, growth discordance was associated with an increased risk for gestational hypertension preeclampsia (adjusted odds ratio [AOR], 1.84; 95% confidence interval [CI], 1.26-2.67) and preeclampsia (AOR, 1.82; 95% CI, 1.21-2.73), including mild preeclampsia (AOR, 1.86; 95% CI, 1.02-3.37), severe preeclampsia (AOR, 1.78; 95% CI, 1.06-2.97; P<.05), and early-onset preeclampsia (AOR, 2.98; 95% CI, 1.40-6.32), in the dichorionic twin pregnancy group; however, no significant association was found in the monochorionic twin pregnancy group. A 10% increment of growth discordance in the dichorionic twin pregnancy group was associated with an elevated risk for gestational hypertension preeclampsia (AOR, 1.20; 95% CI, 1.02-1.41) and preeclampsia (AOR, 1.24; 95% CI, 1.04-1.48), including severe preeclampsia (AOR, 1.28; 95% CI, 1.04-1.59) and early-onset preeclampsia (AOR, 1.47; 95% CI, 1.08-2.00), but no significant association was found in the monochorionic twin pregnancy group.

CONCLUSION

Growth discordance is associated with an increased risk for preeclampsia in dichorionic but not in monochorionic twin pregnancy. In addition, the prevalence of preeclampsia increases significantly with increasing degree of growth discordance, reflecting a dose-response relationship in dichorionic twin pregnancy.

Twins are more different than commonly believed, but made less different by compensating behaviors

Twin studies are popular, because twins are believed to be the same/similar in genes and environmental exposures. It is well documented, however, that the firstborns are healthier at birth. We use the entire U.S. record of twin births during 1995-2000 to show that the survival duration parameters differ between twins depending on the birth order. We also find that wiser (i.e., older or educated) or married (i.e., resource-richer) mothers take more care of the weaker, which is a "compensating" behavior reducing the twin difference, as opposed to "reinforcing (the twin difference)" behavior. The systematic survival pattern difference and the mother's intervention against nature send cautions to twin studies that regard twins homogeneous to interpret their findings accordingly. Since the survival duration in our data is 97% right-censored in one year, we devise a quantile-based 'fixed-effect' semiparametric estimator that can handle heavy censoring, which is our methodological contribution.

How much does birth weight matter for child health in developing countries? Estimates from siblings and twins

About 200 million children globally are not meeting their growth potential, and as a result will suffer the consequences in terms of future outcomes. I examine the effects of birth weight on child health and growth using information from 66 countries. I account for missing data and measurement error using instrumental variables and adopt an identification strategy based on siblings and twins. I find a consistent effect of birth weight on mortality risk, stunting, wasting, and coughing, with some evidence for fever, diarrhoea, and anaemia. Bounds analysis indicates that coefficients may be substantially underestimated due to mortality selection. Improving the pre-natal environment is likely to be important for helping children reach their full potential.

Metabolic Biomarkers of Monochorionic Twins Complicated With Selective Intrauterine Growth Restriction in Cord Plasma and Placental Tissue

The selective intrauterine growth restriction (sIUGR) of monochorionic diamniotic (MCDC) twins causes phenotypic growth discordance, which is correlated with metabolomic pertubations. A global, untargeted identification of the metabolic fingerprint may help elucidate the etiology of sIUGR. Umbilical cord blood and placentas collected from 15 pairs of sIUGR monochorionic twins, 24 pairs of uncomplicated twins, and 14 singletons diagnosed with intrauterine growth restriction (IUGR) were subjected to gas chromatography-mass spectrometry based metabolomic analyses. Supervised multivariate regression analysis and pathway analysis were performed to compare control twins with sIUGR twins. A generalized estimating equation (GEE) model was utilized to explore metabolic differences within sIUGR co-twins. Linear logistic regression was applied to screen metabolites that significantly differed in concentration between control twins and sIUGR twins or IUGR singletons. Umbilical cord blood demonstrated better global metabolomic separation of sIUGR and control twins compared to the placenta. Disrupted amino acid and fatty acid metabolism as well as high levels of exposure to environmental xenobiotics were associated with sIUGR. The metabolic abnormalities in MCDA twins suggested that in utero growth discordance is caused by intrauterine and extrauterine environmental factors, rather than genetics. Thus, this study provides new therapeutic targets and strategies for sIUGR management and prevention.

Adverse maternal outcomes and birth weight discordance in twin gestation: British Columbia, Canadian data

Objective

The aim of this study was to determine whether twin pregnancies with birth weight discordance were associated with higher rates of maternal morbidities.

Study design

A large retrospective population-based cohort study of twins born in British Columbia, Canada, from 2000 to 2010 was performed. Maternal morbidities and growth discordant were evaluated.

Results

There were 6,328 twin deliveries during the study period. Pregnancies carrying growth-discordant twins had higher frequencies of hypertension disorders, preterm labor, and cesarean delivery compared with growth-concordant twins. They also stayed longer than 3 days in hospital. Multivariate generalized estimating equation modeling found higher odds of preeclampsia, pregnancy-induced hypertension, preterm delivery, and cesarean delivery in mothers carrying growth-discordant twins compared with those carrying growth-concordant category. The modeling also resulted in higher odds in the length of stay longer than 3 days in mothers carrying growth-discordant twins compared with those carrying growth-concordant twins after adjustment for chorionicity.

Conclusion

Maternal complications are associated with growth discordance. Screening for birth weight discordance during pregnancy may alert clinicians to predict subclinical maternal conditions.

Persistent Pulmonary Hypertension of the Newborn in Twin-Twin Transfusion Syndrome: A Case-Control Study

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is associated with severe morbidity and mortality. Twin-twin transfusion syndrome (TTTS) is suggested to increase the risk of PPHN.

OBJECTIVES

To describe the incidence of PPHN in TTTS twins and to identify risk factors in TTTS twins for the development of severe PPHN.

METHODS

Cases with severe PPHN were extracted from our monochorionic twin database (2002-2016). Severe PPHN was defined as severe hypoxaemia requiring mechanical ventilation and inhaled nitric oxide (iNO) treatment, confirmed by strict echocardiographic criteria. A case-control comparison within TTTS survivors was conducted to identify risk factors for PPHN.

RESULTS

The incidence of PPHN in TTTS twins was 4% (24/598, 95% confidence interval [CI] 2.7-5.9%) and 0.4% (2/493, 95% CI 0.1-1.5%) in uncomplicated monochorionic twins (odds ratio [OR] 10.3, 95% CI 2.4-43.9; p = 0.002). Two risk factors were independently associated with PPHN: severe prematurity (OR 3.3, 95% CI 1.0-11.4) and recipient status (OR 3.9, 95% CI 1.4-11.0). In TTTS recipients, another risk factor for PPHN is anaemia at birth (OR 7.2, 95% CI 1.8-29.6).

CONCLUSION

Clinicians caring for neonates with TTTS should be aware of the 10-fold increased risk of PPHN compared to uncomplicated monochorionic twins. PPHN occurs more often in case of premature delivery and in recipient twins, particularly in the presence of anaemia at birth. As the development of severe PPHN is difficult to predict, we advise that all TTTS twins should be delivered in a tertiary care centre with iNO treatment options.

Nutrition for Multiples

In 2012 there were 135,943 infants of multiple pregnancies born in the United States, nearly a 2-fold increase since 1980, with twins accounting for 96% of all multiple births. To date, most perinatal morbidities associated with multiple births have proven resistant to technological or pharmaceutical interventions. Maternal nutrition can have a profound effect on the course and outcome of multiple pregnancy, with the goal of achieving optimal intrauterine growth and birthweights, and minimizing prenatal and perinatal complications for the mother and her children.

The Prenatal Environment in Twin Studies: A Review on Chorionicity

A literature search was conducted to identify articles examining the association of chorionicity (e.g., whether twins share a single chorion and thus placenta or have separate chorions/placentas) and genetics, psychiatry/behavior, and neurological manifestations in humans twins and higher-order multiples. The main aim was to assess how frequently chorionicity has been examined in relation to heritability estimates, and to assess which phenotypes may be most sensitive to, or affected by, bias in heritability estimates because of chorionicity. Consistent with the theory that some chorionicity effects could lead to overestimation and others to underestimation of heritability, there were instances of each across the many phenotypes reviewed. However, firm conclusions should not be drawn since some of the outcomes were only examined in one or few studies and often sample sizes were small. While the evidence for bias due to chorionicity was mixed or null for many outcomes, results do, however, consistently suggest that heritability estimates are underestimated for measures of birth weight and early growth when chorionicity is not taken into account.

Effect of protein or energy restriction during late gestation on hormonal and metabolic status in pregnant goats and postnatal male offspring

The objective of this study was to investigate the effects of maternal protein or energy restriction on hormonal and metabolic status of pregnant goats during late gestation and their postnatal male kids. Forty-five pregnant goats were fed a control (CON), 40% protein-restricted (PR) or 40% energy-restricted (ER) diet from 90 days of gestation until parturition. Plasma of mothers (90, 125 and 145 days of gestation) and kids (6 weeks of age) were sampled to determine metabolites and hormones. Glucose concentration for pregnant goats subjected to PR or ER was less (P < 0.001) than that of CON goats at 125 and 145 days of gestation. However, plasma nonesterified fatty acids concentration was greater (P < 0.01) at 125 and 145 days for PR and ER than CON. Protein restriction increased (P < 0.01) maternal cortisol concentration by 145 days of gestation, and ER decreased (P < 0.01) maternal insulin concentration at 125 days of gestation. Moreover, maternal amino acid (AA) concentrations were affected by nutritional restriction, with greater (P < 0.05) total AA (TAA) and nonessential AA (NEAA) for PR goats but less (P < 0.05) TAA and NEAA for ER goats at 125 days of gestation. After 6 weeks of nutritional recovery, plasma concentrations of most metabolic and hormonal parameters in restricted kids were similar to CON kids, except for reduced (P < 0.05) insulin concentration in ER, and reduced (P < 0.05) Asp concentration in PR and ER kids. These results provide information on potential metabolic mechanisms responsible for fetal programming.

Influence of prenatal exposure to environmental pollutants on human cord blood levels of glutamate

Some chemicals released into the environment, including mercury and some organochlorine compounds (OCs), are suspected to have a key role on subclinical brain dysfunction in childhood. Alteration of the glutamatergic system may be one mechanistic pathway. We aimed to determine whether mercury and seven OCs, including PCBs 138, 153, and 180, DDT and DDE, hexachlorobenzene (HCB), and beta-hexachlorocyclohexane (β-HCH) influence the cord levels of two excitatory amino acids, glutamate and aspartate. Second, we evaluated if this association was mediated by glutamate uptake measured in human placental membranes. The study sample included 40 newborns from a Spanish cohort selected according to cord mercury levels. We determined the content of both amino acids in cord blood samples by means of HPLC and assessed their associations with the contaminants using linear regression analyses, and the effect of the contaminants on glutamate uptake by means of [(3)H]-aspartate binding in human placenta samples. PCB138, β-HCH, and the sum of the three PCBs and seven OCs showed a significant negative association with glutamate levels (decrease of 51, 24, 56 and 54%, respectively, in glutamate levels for each 10-fold increase in the contaminant concentration). Mercury did not show a significant correlation neither with glutamate nor aspartate levels in cord blood, however a compensatory effect between T-Hg and both PCB138, and 4,4'-DDE was observed. The organo-metallic derivative methylmercury completely inhibited glutamate uptake in placenta while PCB138 and β-HCH partially inhibited it (IC50 values: 4.9±0.8 μM, 14.2±1.2 nM and 6.9±2.9 nM, respectively). We conclude that some environmental toxicants may alter the glutamate content in the umbilical cord blood, which might underlie alterations in human development.

Selective intrauterine growth restriction in monochorionic twin pregnancies: markers of endothelial damage and metabolomic profile

The aim of this study was to assess the aorta-intima thickness (aIT) and serum metabolomic profile in selective intrauterine growth-restricted (sIUGR) monochorionic diamniotic (MCDA) twin fetuses presenting Doppler velocimetry alterations. Fetal abdominal aIT was measured by ultrasound at 32 weeks of gestation, enrolling 24 MCDA twin fetuses (8 sIUGR and 16 controls). sIUGR twin fetuses were classified into two groups: Group 1 consisted of sIUGR with abnormal umbilical artery (UA) Doppler waveforms and Group 2 included sIUGR with normal UA Doppler. Group 3 were control fetuses appropriate for gestational age (AGA). Fetal blood samples were obtained from the umbilical vein immediately after fetal extraction. A non-targeted metabolomic profiling investigated fetal metabolism alterations by using liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Median fetal aIT was significantly larger in Group 1 (median value = 0.9 mm; range = 0.8-1.0 mm; p < .002) and Group 2 (median value = 0.8 mm; range = 0.7-0.8 mm; p < .002) than in AGA Group 3 (median value = 0.5 mm; range = 0.4-0.6 mm; p < .002). Metabolomic analyses, performed on four sIUGR cases (Group 1) compared with four AGA co-twins, showed an upregulation of phenylalanine, sphingosine, glycerophosphocholine, and choline, and a downregulation of valine, tryptophan, isoleucine, and proline sIUGR Group 1 compared with AGA. Although for metabolomics data only a statistical tendency (and not a statistical significance) was reached due to the small sample size, we believe that our results represent a valid starting point for further in-depth metabolomic and proteomic investigations of sIUGR in MCDA fetuses.

Genetic, environmental and stochastic factors in monozygotic twin discordance with a focus on epigenetic differences

Genetic-epidemiological studies on monozygotic (MZ) twins have been used for decades to tease out the relative contributions of genes and the environment to a trait. Phenotypic discordance in MZ twins has traditionally been ascribed to non-shared environmental factors acting after birth, however recent data indicate that this explanation is far too simple. In this paper, we review other reasons for discordance, including differences in the in utero environment, genetic mosaicism, and stochastic factors, focusing particularly on epigenetic discordance. Epigenetic differences are gaining increasing recognition. Although it is clear that in specific cases epigenetic alterations provide a causal factor in disease etiology, the overall significance of epigenetics in twin discordance remains unclear. It is also challenging to determine the causality and relative contributions of environmental, genetic, and stochastic factors to epigenetic variability. Epigenomic profiling studies have recently shed more light on the dynamics of temporal methylation change and methylome heritability, yet have not given a definite answer regarding their relevance to disease, because of limitations in establishing causality. Here, we explore the subject of epigenetics as another component in human phenotypic variability and its links to disease focusing particularly on evidence from MZ twin studies.

Parenteral administration of L-arginine enhances fetal survival and growth in sheep carrying multiple fetuses

The frequency of multiple fetuses has increased in human pregnancies due to assisted reproductive technologies. This translates into a greater proportion of premature and low-birth weight infants in the United States and worldwide. In addition, improvements in sheep breeding have resulted in new breeds with increased litter size but reduced fetal survival and birth weight. Currently, there are no treatments for preventing fetal growth restriction in humans or sheep (an established model for studying human fetal physiology) carrying multiple fetuses. In this work, Booroola Rambouillet ewes (FecB+/-) with 2-4 fetuses were fed a diet providing 100% of NRC-recommended nutrient requirements. Between d 100 and 121 of gestation, ewes received an i.v. bolus injection of either saline solution or 345 μmol arginine-HCl/kg body weight 3 times daily. The arginine treatment reduced (P < 0.05) the percentage of lambs born dead by 23% while increasing (P = 0.05) the percentage of lambs born alive by 59%. The i.v. administration of arginine enhanced (P < 0.05) the birth weights of quadruplets by 23% without affecting maternal body weight. The improved pregnancy outcome was associated with an increase in maternal plasma concentrations of arginine, ornithine, cysteine, and proline, as well as a decrease in circulating levels of ammonia and β-hydroxybutyrate. These novel results indicate that parenteral administration of arginine to prolific ewes ameliorated fetal mortality and growth retardation. Our findings provide support for experiments to assess the clinical use of arginine to enhance fetal growth and survival in women gestating multiple fetuses.

Changes in the metabolic footprint of placental explant-conditioned medium cultured in different oxygen tensions from placentas of small for gestational age and normal pregnancies

Being born small for gestational age (SGA) confers significantly increased risks of perinatal morbidity and mortality. Accumulating evidence suggests that an SGA fetus results from a poorly perfused and abnormally developed placenta. Some of the placental features seen in SGA, such as abnormal cell turnover and impaired nutrient transport, can be reproduced by culture of placental explants in hypoxic conditions. Metabolic footprinting offers a hypothesis-generating strategy to investigate factors absorbed by and released from this tissue in vitro. Previously, metabolic footprinting of the conditioned culture media has identified differences in placental explants cultured under normoxic and hypoxic conditions and between normal pregnancies and those complicated by pre-eclampsia. In this study we aimed to examine the differences in the metabolic footprint of placental villous explants cultured at different oxygen (O(2)) tensions between women who deliver an SGA baby (n = 9) and those from normal controls (n = 8). Placental villous explants from cases and controls were cultured for 96 h in 1% (hypoxic), 6% (normoxic) and 20% (hyperoxic) O(2). Metabolic footprints were analysed by Ultra Performance Liquid Chromatography coupled to an electrospray hybrid LTQ-Orbitrap Mass Spectrometry (UPLC-MS). 574 metabolite features showed significant difference between SGA and normal at one or more of the oxygen tensions. SGA explant media cultured under hypoxic conditions was observed, on a univariate level, to exhibit the same metabolic signature as controls cultured under normoxic conditions in 49% of the metabolites of interest, suggesting that SGA tissue is acclimatised to hypoxic conditions in vivo. No such behaviour was observed under hyperoxic culture conditions. Glycerophospholipid and tryptophan metabolism were highlighted as areas of particular interest.

Leptin affects system A amino acid transport activity in the human placenta: evidence for STAT3 dependent mechanisms

BACKGROUND

Amino acids are important nutrients during fetal development, and the activity of placental amino acid transporters is crucial in the regulation of fetal growth. Leptin, an adipocyte- and placenta-derived hormone, has been proposed to act as a peripheral signal in reproduction in humans. Leptin is elevated during pregnancy and elevated further in pathologic pregnancies such as preeclampsia. However, the role of leptin in placental function has not been fully elucidated. We hypothesize that leptin plays a role in the regulation of placental amino acid transport by activation of the JAK-STAT pathway.

METHODS

Placental amino acid transport, specifically system A transport was studied in placental villous fragments using the amino acid analog, methylaminoisobutyric acid (MeAIB). Specific inhibitors of the JAK-STAT signal transduction pathway were used to further elucidate their role in leptin-mediated effects on amino acid transport activity. Western blotting was performed to identify STAT3 phosphorylation as a measure of leptin receptor activation.

RESULTS

Leptin significantly increased system A amino acid transporter activity by 22-42% after 1h of incubation. Leptin activated JAK-STAT signaling pathway as evidenced by STAT3 phosphorylation, and inhibition of STAT3 or JAK2 resulted in 36-45% reduction in system A amino acid transporter activity. Furthermore, blocking endogenously produced leptin also decreased system A transport by 45% comparable to STAT3 inhibition.

CONCLUSIONS

These data demonstrate that leptin stimulates system A by JAK-STAT dependent pathway in placental villous fragments. Our findings support the autocrine/paracrine role of leptin in regulating amino acid transport in the human placenta.

Left ventricular isovolumic relaxation and renin-angiotensin system in the growth restricted fetus

OBJECTIVE

To determine left ventricular isovolumic relaxation time (LV IRT) in normally developing and growth restricted fetuses (FGR) as an indicator of fetal cardiac afterload and neonatal systolic blood pressure.

STUDY DESIGN

A prospective longitudinal study in 124 normally developing and 47 growth restricted fetuses (FGR). LV IRT, fetal heart rate (FHR) and umbilical artery pulsatility index (PI) were determined at 2-3 week intervals starting at 22-26 weeks of gestation until delivery. Renin and angiotensin I levels were measured by radioimmunoassay in umbilical venous blood after delivery. Systolic blood pressure was measured at day 1 and day 5 of postnatal life. To evaluate the association between LV IRT, gestational age and FHR, bivariate regression analyses were performed.

RESULTS

Mean LV IRT (62+/-8 ms) was 29 percent longer in FGR as compared to the normal subset (47+/-6 ms) at all gestational ages (p<0.001). Mean postnatal active plasma renin level (7.78+/-S.D. 1.03 ng/ml) and postnatal angiotensin I level (4.21+/-0.70 ng/ml) in the FGR subset were significantly higher (p<0.001) than in the normal subset (4.81+/-1.04 ng/ml, renin and 2.69+/-0.44 ng/ml, angiotensin I). There was a significant difference (p<0.01) in systolic blood pressure between the two subsets on postnatal day 1 (FGR 52+/-6 mmHg vs. normal 46+/-4 mmHg) and day 5 (FGR 76+/-5 mmHg vs. normal 60+/-6 mmHg).

CONCLUSION

Left ventricular isovolumic relaxation time may act as a sensitive index of increased arterial afterload in the growth retarded fetus and may herald raised systolic blood pressure in the early neonatal period.

Birth weight and attention-deficit/hyperactivity symptoms in childhood and early adolescence: a prospective Swedish twin study

OBJECTIVE

To determine whether low birth weight increases the risk of attention-deficit/hyperactivity disorder (ADHD) in childhood and early adolescence.

METHOD

In a population-based sample of 1,480 twin pairs born in the period 1985-1986 ascertained from the Swedish Twin Registry, birth weight was collected prospectively through the Medical Birth Registry. ADHD symptoms were measured with a 14-item checklist covering DSM-III-R criteria (parental rating) at age 8 to 9 years and 13 to 14 years. We used both a dichotomous approach for birth weight (>400 g or 15% weight difference) and ADHD (eight or more symptoms) and continuous measures to investigate between- and within-twin pair effects.

RESULTS

Our results showed that low birth weight was a risk factor for symptoms of ADHD and the associations did not diminish when we controlled for genetic influence. The lighter twin in birth weight-discordant pairs had on average 13% higher ADHD symptom score at age 8 to 9 years (p = .006) and 12% higher ADHD score at age 13 to 14 years (p = .018) compared with the heavier twin. The genetic correlations suggest modest or no genetic overlap between birth weight and ADHD.

CONCLUSIONS

The hypothesis that low birth weight is associated with the development of ADHD symptoms was supported in this prospective twin study. Fetal growth restriction seems to represent a modest but fairly consistent environmental influence on the development of ADHD symptoms.

Prenatal diagnosis in monozygotic twins with Down syndrome who had different phenotypes

We report the case of monozygotic (MZ) male twin fetuses with different Down syndrome (DS) phenotypes. Prenatal fetal sonography showed a bichorial biamniotic pregnancy with increased nuchal translucency in twin A and a cervical cystic hygroma and heart defect in twin B. Cytogenetic analysis performed after double amniocentesis showed free and homogeneous trisomy 21 in both twins. Monozygosity was confirmed by molecular analysis. The pregnancy was terminated at 17 weeks of gestation (WG). Postmortem analysis confirmed the phenotypic discordance. To our knowledge, this is the first reported prenatal diagnosis of MZ male twins with different Down syndrome phenotypes but identical karyotypes. We discuss the mechanisms involved in phenotypic discordance of monozygotic twins and particularly the role of environmental factors.

Perinatal outcome of quadruplet pregnancies in relation to chorionicity

OBJECTIVE

To compare the perinatal outcome of quadruplets in relation to chorionicity.

PATIENTS AND METHODS

In this retrospective study, the maternal, neonatal and chorionicity data were collected from 24 sets of quadruplet pregnancies delivered between January 1985 and December 2001. Perinatal and neonatal data were evaluated in relation to chorionicity.

RESULTS

Sixteen pregnancies were quadra-chorionic quadramniotic (QC) and eight had at least one monochorionic pair (TC). The median gestational age at delivery was 31 weeks (23 to 34 weeks) with overall perinatal mortality rate of 177 per 1000 total birth. Delivery before 30 weeks (OR 89; 95% CI 9 to 607; P<0.01) and discordant birth weight of >25% (OR 7.6; 95% CI 2 to 29; P<0.01) had independent effects on perinatal loss rate. The perinatal loss was five fold higher in TC quadruplets than those of QC (OR 5.1; 95% CI 1.7 to 15.4; P<0.001). This was attributed to higher risk of very low birth weight (69 vs 13%; P<0.01), delivery before 30 weeks (63 vs 13%; P<0.001) in TC quadruplets compared to QC gestation.

CONCLUSIONS

The quadruplets with MC pair have 5 times higher perinatal mortality than quadra-chorionic quadruplet pregnancies owing to preterm delivery and discordant birth weight.

Risk of persistent pulmonary hypertension of the neonate in twin-to-twin transfusion syndrome

BACKGROUND

Chronic twin-to-twin transfusion syndrome (TTTS) is a complication of monochorionic twin gestations and is associated with high perinatal mortality and increased neurological, cardiovascular and renal morbidity.

OBJECTIVE

To report the risk of severe persistent pulmonary hypertension of the newborn (PPHN) in TTTS and discuss the possible association between severe PPHN and TTTS.

METHODS

All cases of monochorionic twins with severe PPHN at birth admitted to our nursery between June 2002 and July 2006 were reviewed retrospectively. We compared the incidence of severe PPHN in monochorionic twins with and without TTTS. Severe PPHN was diagnosed according to clinical and ultrasound criteria when an infant with a structurally normal heart had (1) severe hypoxemia and (2) evidence of a right-to-left shunt on persistent ductus arteriosus or foramen ovale, requiring treatment with inhaled nitric oxide (iNO).

RESULTS

In a consecutive series of 73 twin pregnancies with TTTS, 4 of the 135 live-born twins (3%) were affected by severe PPHN. All reacted promptly to treatment with iNO. The incidence of severe PPHN in monochorionic twins without TTTS was 0% (0/161).

CONCLUSION

In view of the severe clinical course in PPHN and need for adequate and prompt treatment with iNO, perinatologists should be aware of the increased risk of severe PPHN in TTTS.

Type 1 collagen marker of bone turnover, insulin-like growth factor, and leptin in dichorionic twins with discordant birth weight

OBJECTIVE

We investigated the relationship between IGF-I-IGF binding protein (IGFBP)-1 and leptin levels with type 1 collagen markers of bone turnover in dichorionic twins with or without discordant birth weight of 20% or greater.

METHODS

Maternal and cord bloods were collected from gestational age-matched dichorionic twins with (n = 16) or without (n = 16) discordant birth weight. The samples were assayed for cross-linked carboxyl terminal telopeptide (ICTP, a marker of bone resorption) and propeptide (PICP, a marker of bone formation) of type I collagen, leptin, IGF-I, and IGFBP-1 by RIA.

RESULTS

The intrauterine growth-restricted (IUGR) twins of the discordant group had higher fetal ICTP (P < 0.001) and IGFBP-1 (P < 0.001) levels, whereas PICP (P < 0.001), IGF-I (P < 0.001), and leptin (P < 0.001) were lower than the cotwins with normal weight (AGA). In contrast, concentrations of IGF-I, IGFBP-1, ICTP, PICP, and leptin were comparable between concordant twin pairs. Leptin levels were positively correlated with PICP (r = 0.61; P < 0.001) and negatively with ICTP (r = -0.57; P < 0.001) in concordant and AGA twins but not in IUGR twins. In IUGR twins, IGF-I had positive association with PICP (r = 0.76; P < 0.001) and negative association with ICTP (r= -0.76; P < 0.001), whereas IGFBP-1 was negatively correlated with PICP levels (r = -0.65; P < 0.01). No such association was found in concordant and AGA twins.

CONCLUSION

These data suggest that IUGR twins had high bone turnover, which is independent of maternal factors and perhaps may be due to altered IGF axis.

Consequences of Intrauterine Growth Restriction for the Kidney

Low birth weight due to intrauterine growth restriction is associated with various diseases in adulthood, such as hypertension, cardiovascular disease, insulin resistance and end-stage renal disease. The purpose of this review is to describe the effects of intrauterine growth restriction on the kidney. Nephrogenesis requires a fine balance of many factors that can be disturbed by intrauterine growth restriction, leading to a low nephron endowment. The compensatory hyperfiltration in the remaining nephrons results in glomerular and systemic hypertension. Hyperfiltration is attributed to several factors, including the renin-angiotensin system (RAS), insulin-like growth factor (IGF-I) and nitric oxide. Data from human and animal studies are presented, and suggest a faltering IGF-I and an inhibited RAS in intrauterine growth restriction. Hyperfiltration makes the kidney more vulnerable during additional kidney disease, and is associated with glomerular damage and kidney failure in the long run. Animal studies have provided a possible therapy with blockage of the RAS at an early stage in order to prevent the compensatory glomerular hyperfiltration, but this is far from being applicable to humans. Research is needed to further unravel the effect of intrauterine growth restriction on the kidney.

The late effects of fetal growth patterns

The immediate prenatal and postnatal consequences of reduced fetal growth have long been known. The longer term associations between reduced birth weight and adult disease risk are also now well established. Reduced fetal growth is usually detected late in gestation, and the assumption has been that this is the time when factors regulating fetal growth have their greatest effect. However, recent evidence suggests that both the growth trajectory of the fetus and its adaptive responses to the prenatal and postnatal environment may be determined in the period around the time of conception.

Elevated IGFBP-1 cause high bone turnover in growth-restricted monochorionic twins with discordant birth weight

OBJECTIVE

To test the hypothesis that low birth weight twins have a higher risk of osteoportotic fracture in later life, we investigated the association between fetal IGF axis and type-1 collagen markers of bone turnover in monochorionic (MC) twins with or without discordant birth weight of >or=20%.

METHODS

Maternal and cord bloods were collected from gestational age matched MC twins of discordant (n = 16) and concordant birth weights (n = 16). The samples were assayed for cross linked carboxyl terminal telopeptide (ICTP, a marker of bone resorption) and pro-peptide (PICP, a marker of bone formation) of type I collagen, IGF-1, and IGFBP-1 by radio-immunoassay.

RESULTS

The growth-restricted twins (IUGR) of discordant group had higher fetal IGFBP-1 and ICTP (P < 0.001) levels, while PICP (P < 0.001) was lower than the co-twins with normal weight (AGA). In contrast, cord blood levels of IGF-1, IGFBP-1, ICTP, and PICP in concordant twin pairs were comparable to AGA twins. The concordant and AGA twins had a positive correlation between ICTP and PICP levels (y = 23x - 711; r = 0.84; P < 0.001; n = 48) but no such association was found in IUGR twins. Instead, IGFBP-1 levels in IUGR twins had a negative association with PICP (r = 0.81; P < 0.001; n = 16) and a positive correlation with ICTP (r- = 0.51; P < 0.05; n = 16). No such association was found in concordant and AGA twins.

CONCLUSION

These data suggest that growth-restricted twins had high bone turnover, due to elevated IGFBP-1. This association seems to be independent of maternal and genetic factors.

Perinatal outcome of spontaneously conceived triplet pregnancies in relation to chorionicity

OBJECTIVE

The purpose of this study was to determine the perinatal outcome of spontaneously conceived triplet pregnancies in relation to chorionicity.

STUDY DESIGN

In this retrospective study, maternal, neonatal, and chorionicity data were collected from 88 sets of triplet pregnancies that were delivered at >20 weeks of gestation from 3 tertiary referral centers in the United Kingdom. The data were collected between January 1986 and December 2000. There were 49 sets of trichorionic triamniotic triplet pregnancies and 39 sets of triplet pregnancies with a monochorionic pair (ie, dichorionic triamniotic triplets). The outcome of each pregnancy was assessed in relation to chorionicity.

RESULTS

The overall perinatal mortality rate was 151.5 per 1000 total births, with dichorionic triamniotic triplets having a 5.5-fold higher risk than trichorionic triamniotic gestations (odds ratio, 5.5; 95% CI, 2.5-12.2). The dichorionic triamniotic triplets have a higher risk of delivery at < 30 weeks of gestation (odds ratio, 4.6; 95% CI, 1.6-11.8; P < .05) and birth weight of < 1000 g (odds ratio, 53.6; 95% CI, 17.5-164; P < .05) than those of trichorionic triamniotic pregnancies. The neonatal morbidity in terms of respiratory distress syndrome (P < .001), anemia (P < .01), and intraventricular hemorrhage (P < .001) were higher in dichorionic triamniotic compared with trichorionic triamniotic triplets. The premature rupture of membrane (odds ratio, 7.5; 95% CI, 3.5-15.7) and twin-twin transfusion syndrome (odds ratio, 14.9; 95% CI, 6.6-4) were independent risk factors for perinatal death.

CONCLUSION

In spontaneously conceived triplets, the incidence of dichorionicity was 44%. The dichorionic triamniotic triplets have a 5.5-fold higher risk of adverse perinatal outcome predominantly because of twin-twin transfusion syndrome and premature rupture of membranes.

Trophoblast differentiation during embryo implantation and formation of the maternal-fetal interface

Trophoblasts, the specialized cells of the placenta, play a major role in implantation and formation of the maternal-fetal interface. Through an unusual differentiation process examined in this review, these fetal cells acquire properties of leukocytes and endothelial cells that enable many of their specialized functions. In recent years a great deal has been learned about the regulatory mechanisms, from transcriptional networks to oxygen tension, which control trophoblast differentiation. The challenge is to turn this information into clinically useful tests for monitoring placental function and, hence, pregnancy outcome.

Maternal Nutrient Restriction Reduces Concentrations of Amino Acids and Polyamines in Ovine Maternal and Fetal Plasma and Fetal Fluids1

Amino acids and polyamines are essential for placental and fetal growth, but little is known about their availability in the conceptus in response to maternal undernutrition. We hypothesized that maternal nutrient restriction reduces concentrations of amino acids and polyamines in the ovine conceptus. This hypothesis was tested in nutrient-restricted ewes between Days 28 and 78 (experiment 1) and between Days 28 and 135 (experiment 2) of gestation. In both experiments, ewes were assigned randomly on Day 28 of gestation to a control group fed 100% of National Research Council (NRC) nutrient requirements and to an nutrient-restricted group fed 50% of NRC requirements. Every 7 days beginning on Day 28 of gestation, ewes were weighed and rations adjusted for changes in body weight. On Day 78 of gestation, blood samples were obtained from the uterine artery and umbilical vein for analysis. In experiment 2, nutrient-restricted ewes on Day 78 of gestation either continued to be fed 50% of NRC requirements or were realimented to 100% of NRC requirements until Day 135. Fetal weight was reduced in nutrient-restricted ewes at both Day 78 (32%) and Day 135 (15%) compared with controls. Nutritional restriction markedly reduced (P < 0.05) concentrations of total alpha-amino acids (particularly serine, arginine-family amino acids, and branched-chain amino acids) and polyamines in maternal and fetal plasma and in fetal allantoic and amniotic fluids at both mid and late gestation. Realimentation of nutrient-restricted ewes increased (P < 0.05) concentrations of total alpha-amino acids and polyamines in all the measured compartments and prevented intrauterine growth retardation. These novel findings demonstrate that 50% global nutrient restriction decreases concentrations of amino acids and polyamines in the ovine conceptus that could adversely impact key fetal functions. The results have important implications for understanding the mechanisms responsible for both intrauterine growth retardation and developmental origins of adult disease.

Very-Early-Onset Discordant Growth in Monochorionic Twin Pregnancy

BACKGROUND

The significance of growth restriction in the first trimester in karyotypically normal fetuses is uncertain.

CASE

We report a case of diamniotic monochorionic twin pregnancy with marked growth discordance noted in the first trimester. No major congenital or karyotype abnormalities or ongoing evidence of twin-twin transfusion syndrome were found during gestation. Birth weight discordance in the twins was 49.5%. Histologic examination revealed immature villi, with a shortage of terminal villi and an abundance of intermediate mature villi, as well as hypoxic areas with altered villi in the part of the placenta supplying the smaller twin.

CONCLUSION

The causes underlying discordant growth in karyotypically normal twin pregnancies without evidence of twin-twin transfusion syndrome are not entirely clear. There may be other conditions responsible for discordant growth that occur in the first or early second trimester of pregnancy.

The effect of an elevated maternal lysine concentration on placental lysine transport in pregnant sheep

OBJECTIVES

In a previous study, the coinfusion into the maternal circulation of lysine and several other amino acids failed to increase significantly lysine umbilical uptake. The purpose of this study was to determine whether umbilical lysine uptake can be increased by infusing a lysine solution that does not contain any other amino acid.

STUDY DESIGN

Six late-gestation ewes were studied on 2 consecutive days. Samples were collected in both the control (first day) and experimental (second day) periods simultaneously from the maternal artery, uterine vein, fetal artery, and umbilical vein. In the control period, L-[1-(13)C] lysine was infused into the maternal circulation. During the experimental period, both L-[1-(13)C] lysine and L-(12)C lysine were infused to increase maternal lysine concentration. Uterine and umbilical blood flows were measured by the steady state diffusion technique. Uterine and umbilical uptake of lysine and of alpha-aminoaminoadipic acid (AAD, a biproduct of lysine oxidation) were calculated.

RESULTS

In response to a 2.7-fold increase in maternal lysine concentration (P<.001), fetal lysine concentration increased approximately 70% (P<.05) and umbilical uptake 50% (P<.05). In the experimental period, there was a significant (P<.05) placental uptake of fetal AAD, and the fetal/maternal plasma (13)C-lysine-specific activity ratio increased from 0.221+/-0.026 to 0.294+/-0.029 (P<.05). In response to the increase in maternal lysine concentration, the maternal and fetal concentrations of several other amino acids were significantly decreased.

CONCLUSION

This study establishes that the umbilical uptake of lysine can be increased by infusing lysine in the maternal circulation. However, the lysine infusion is associated with a decrease in the maternal concentration and umbilical uptake of other essential amino acids. These data, compared with the results of previous studies, indicate that attempts to increase the fetal uptake of an amino acid via maternal infusion may decrease the uptake of other amino acids by decreasing their maternal concentration and by inhibition of placental transport.

Monochorionic diamniotic twins: complications and management options

PURPOSE OF REVIEW

Monochorionic compared with dichorionic twins have disproportionately high fetal loss rates, perinatal mortality and morbidity. This is because of the unpredictable vascular anastomoses and the often asymmetrical distribution of the single placenta between both twins.

RECENT FINDINGS

The pathophysiology of twin-to-twin transfusion syndrome is usually explained on an angioarchitectural basis, although certain hemodynamic and hormonal factors also may be involved. The results of the large randomized trials on amnioreduction, fetoscopic laser coagulation and septostomy are still awaited. An update is given on hardware and instruments required for fetoscopic laser. Subsequently, the problem of the monochorionic twin set with severe early discordant growth is addressed. Several etiological mechanisms have been proposed, but little is known of its natural history. Also, umbilical artery Doppler waveforms may not have the same predictive value as in singletons. Prophylactic laser coagulation of the vascular anastomoses to protect against the adverse effects of single intrauterine demise, has so far not been shown to confer any benefit in outcome. Finally, pathophysiology and management of discordant structural and chromosomal anomalies in monochorionic twins are discussed. Laser and monopolar coagulation, which can be introduced through a needle, may be used for selective feticide in early pregnancy or low hemodynamic conditions. Bipolar coagulation seems more effective at later gestational ages and normal hemodynamic conditions.

SUMMARY

Our insight into the complications associated with monochorionic twins has increased in recent years. It is hoped that this will lead to better surveillance and ultimately an improved outcome for these high-risk pregnancies.

Risk factors for intrapair birth weight discordance in twins

OBJECTIVES

To determine the risk factors for birth weight discordance in twins.

METHODS

We used the United States (1995-97) Matched Multiple Birth File (n = 294 568) to assess the association between birth weight discordance and maternal sociodemographic, pregnancy and infant characteristics.

RESULTS

Eighty-four per cent of the twins were 0-19% discordant, 11.1% were 20-29% discordant, 3.4% were 30-39% discordant, and 1.8% were > or = 2 40% discordant. The risk factors for birth weight discordance for same-sex twins were eclampsia (odds ratio (OR) 1.39,95% confidence interval (CI) 1.20, 1.61), pre-eclampsia (OR 1.31, 95% CI 1.24, 1.38), pre-existing hypertension (OR 1.32, 95% CI 1.12, 1.56), diabetes (OR 1.13, 95% CI 1.04, 1.24) and certain congenital anomalies. For opposite-sex twins, the risk factors for birth weight discordance were pre-eclampsia (OR 1.17, 95% CI 1.09, 1.27), pre-existing hypertension (OR 1.59,95% CI 1.32, 1.91), and certain congenital anomalies. Also, smoking and increased maternal age were associated with birth weight discordance in both same-sex and opposite-sex twins.

CONCLUSIONS

Maternal hypertensive disorders, smoking and delayed childbearing were associated with intrapair birth weight discordance. The mechanisms of these associations deserve further investigation.

Epigenetic contributors to the discordance of monozygotic twins

Human monozygotic (MZ) twins estimated to occur once in 250 live births, result from an errant decision by embryonic cell(s) to develop as separate embryos. They are considered genetically identical and any phenotypic discordance between them has been used to implicate the role of environment. More recent literature, however, has questioned these assumptions but the frequency and the nature of any genetic discordance between MZ twins remains poorly understood. We will review published cases of phenotypic and genetic discordance between monozygotic twins to argue that not all discordance between such twins is due to differences in environment. The causes of reduced concordance between MZ twins remains poorly understood. They represent among the challenging aspects of the genetics of complex multi-factorial traits and diseases. A number of questions regarding the published results on MZ twins merit a re-assessment in the light of modern molecular insight of the human genome. Such an assessment is needed in directing future studies on MZ twins. In particular, we will deal with the origin, development, genetic and epigenetic factors that may have implications in discordance of the MZ twin pairs.

Prospective function of placental leptin at maternal-fetal interface

Leptin is an endocrine and a growth factor which is important for regulation of body fat, feeding, and energy homeostasis. The anti-obesity function of leptin has been recently extended to reproduction, puberty and pregnancy as an endocrine signal to the hypothalamus. Leptin controls the functional integrity of the feto-placental unit thereby maintaining pregnancy by virtue of its immunomodulatory property via T lymphocytes or other proto-oncogenes. Dysregulation of autocrine/paracrine function of leptin at feto-placento-maternal interface may be implicated in the pathogenesis of recurrent miscarriage gestational diabetes, pre-eclampsia and intra-uterine fetal growth retardation including disturbance of fetal bone turnover. This review will focus on the role of leptin in normal and abnormal pregnancy and fetal growth.