Twin's Birth-Order Differences in Height and Body Mass Index From Birth to Old Age: A Pooled Study of 26 Twin Cohorts Participating in the CODATwins Project

A Pregnancy and Childhood Epigenetics Consortium (PACE) meta-analysis highlights potential relationships between birth order and neonatal blood DNA methylation

Higher birth order is associated with altered risk of many disease states. Changes in placentation and exposures to in utero growth factors with successive pregnancies may impact later life disease risk via persistent DNA methylation alterations. We investigated birth order with Illumina DNA methylation array data in each of 16 birth cohorts (8164 newborns) with European, African, and Latino ancestries from the Pregnancy and Childhood Epigenetics Consortium. Meta-analyzed data demonstrated systematic DNA methylation variation in 341 CpGs (FDR adjusted P < 0.05) and 1107 regions. Forty CpGs were located within known quantitative trait loci for gene expression traits in blood, and trait enrichment analysis suggested a strong association with immune-related, transcriptional control, and blood pressure regulation phenotypes. Decreasing fertility rates worldwide with the concomitant increased proportion of first-born children highlights a potential reflection of birth order-related epigenomic states on changing disease incidence trends.

Evidence for ethnicity and location as regulators of the newborn blood metabolome: a monozygous twin study

Introduction

Monochorionic, diamniotic (MCDA) monozygotic twins share nearly all genetic variation and a common placenta in utero. Despite this, MCDA twins are often discordant for a range of common phenotypes, including early growth and birth weight. As such, MCDA twins represent a unique model to explore variation in early growth attributable primarily to in utero environmental factors.

Methods

MCDA twins with a range of within-pair birth weight discordance were sampled from the peri/postnatal epigenetic twin study (PETS, Melbourne; n = 26 pairs), Beijing twin study (BTS, Beijing; n = 25), and the Chongqing longitudinal twin study (LoTiS, Chongqing; n = 22). All PETS participants were of European-Australian ancestry, while all Chinese participants had Han ancestry. The average of the birth weight difference between the larger and smaller co-twins for all twin pairs was determined and metabolomic profiles of amino acids, TCA cycle intermediates, fatty acids, organic acids, and their derivatives generated from cord blood plasma by gas chromatograph mass spectrometry. Within and between co-twin pair analyses were performed to identify metabolites specifically associated with discordance in birth weight. Multivariable regression and pathway enrichment analyses between different regions were performed to evaluate the geographical effects on the metabolism of MCDA twin pairs.

Results

PETS twins showed a markedly different metabolic profile at birth compared to the two Chinese samples. Within-pair analysis revealed an association of glutathione, creatinine, and levulinic acid with birth weight discordance. Caffeine, phenylalanine, and several saturated fatty acid levels were uniquely elevated in PETS twins and were associated with maternal BMI and average within pair birth weight, in addition to birth weight discordance. LoTiS twins had higher levels of glutathione, tyrosine, and gamma-linolenic acid relative to PETS and BTS twins, potentially associated with eating habits.

Conclusion

This study highlights the potential role of underlying genetic variation (shared by MZ twins), in utero (non-shared by MZ twins) and location-specific (shared by MZ twins) environmental factors, in regulating the cord blood metabolome of uncomplicated MCDA twins. Future research is needed to unravel these complex relationships that may play a key role in phenotypic metabolic alterations of twins independent of genetic diversity.

Genetic and Environmental Effects on the Early Motor Development as a Function of Parental Educational Attainment

INTRODUCTION

The contribution of genetic and environmental factors to individual differences in early motor development is still largely uncharted. This large-scale twin study establishes the genetic and environmental influences on the timing of motor milestones achievement, and it further tests whether the influences are moderated by parental education.

METHODS

The twins came from families registered in the Netherlands Twin Register (NTR) from 1986 to 2016. In 30,256 complete twin pairs, mother-reported ages at which each twin was able to first-time roll from back to belly, sit unassisted, hands-and-knees crawl, stand up unaided, and walk independently were used to extract an early motor development factor. Parental education was dichotomized ("both parents with low/average education" vs "at least one parent with high education" with university degree as a threshold).

RESULTS

Additive genetics explained 52% of the variance in motor development, the remaining 39% and 9% were explained by shared and nonshared environment separately. Mean age of achieving motor milestones tended to be higher in infants with high educated parents, and a moderation of parental education on the genetic and environmental variance in motor development was seen in female twins with larger heritability in the high educated parents group (64% vs 43%) paired to a lower shared environmental influence (28% vs 48%). Only 7%-8% of the variance was accounted for nonshared environmental factors, including measurement error. The pattern of results did not change when the degree of urbanicity, a correlate of parental education, was additionally considered.

CONCLUSIONS

Genetic factors explain most of the individual differences in the timing of motor milestone achievement, but factors related to the shared home environment also play an important role in early motor development.

Predicting risks of low birth weight in Bangladesh with machine learning

Background and objective

Low birth weight is one of the primary causes of child mortality and several diseases of future life in developing countries, especially in Southern Asia. The main objective of this study is to determine the risk factors of low birth weight and predict low birth weight babies based on machine learning algorithms.

Materials and methods

Low birth weight data has been taken from the Bangladesh Demographic and Health Survey, 2017–18, which had 2351 respondents. The risk factors associated with low birth weight were investigated using binary logistic regression. Two machine learning-based classifiers (logistic regression and decision tree) were adopted to characterize and predict low birth weight. The model performances were evaluated by accuracy, sensitivity, specificity, positive predictive value, negative predictive value, and area under the curve.

Results

The average percentage of low birth weight in Bangladesh was 16.2%. The respondent’s region, education, wealth index, height, twin child, and alive child were statistically significant risk factors for low birth weight babies. The logistic regression-based classifier performed 87.6% accuracy and 0.59 area under the curve for holdout (90:10) cross-validation, whereas the decision tree performed 85.4% accuracy and 0.55 area under the curve.

Conclusions

Logistic regression-based classifier provided the most accurate classification of low birth weight babies and has the highest accuracy. This study’s findings indicate the necessity for an efficient, cost-effective, and integrated complementary approach to reduce and correctly predict low birth weight babies in Bangladesh.

Should twin-specific growth charts be used to assess fetal growth in twin pregnancies?

One of the hallmarks of twin pregnancies is the slower rate of fetal growth when compared with singleton pregnancies during the third trimester. The mechanisms underlying this phenomenon and whether it represents pathology or benign physiological adaptation are currently unclear. One important implication of these questions relates to the type growth charts that should be used by care providers to monitor growth of twin fetuses. If the slower growth represents pathology (ie, intrauterine growth restriction caused uteroplacental insufficiency), it would be preferable to use a singleton growth chart to identify a small twin fetus that is at risk for perinatal mortality and morbidity. If, however, the relative smallness of twins is the result of benign adaptive mechanisms, it is likely preferable to use a twin-based charts to avoid overdiagnosis of intrauterine growth restriction in twin pregnancies. In the current review, we addressed this question by describing the differences in fetal growth between twin and singleton pregnancies, reviewing the current knowledge regarding the mechanisms responsible for slower fetal growth in twins, summarizing available empirical evidence on the diagnostic accuracy of the 2 types of charts for intrauterine growth restriction in twin pregnancies, and addressing the question of whether uncomplicated dichorionic twins are at an increased risk for fetal death when compared with singleton fetuses. We identified a growing body of evidence that shows that the use of twin charts can reduce the proportion of twin fetuses identified with suspected intrauterine growth restriction by up to 8-fold and can lead to a diagnosis of intrauterine growth restriction that is more strongly associated with adverse perinatal outcomes and hypertensive disorders than a diagnosis of intrauterine growth restriction based on a singleton-based chart without compromising the detection of twin fetuses at risk for adverse outcomes caused by uteroplacental insufficiency. We further found that small for gestational age twins are less likely to experience adverse perinatal outcomes or to have evidence of uteroplacental insufficiency than small for gestational age singletons and that recent data question the longstanding view that uncomplicated dichorionic twins are at an increased risk for fetal death caused by placental insufficiency. Overall, it seems that, based on existing evidence, the of use twin charts is reasonable and may be preferred over the use of singleton charts when monitoring the growth of twin fetuses. Still, it is important to note that the available data have considerable limitations and are primarily derived from observational studies. Therefore, adequately-powered trials are likely needed to confirm the benefit of twin charts before their use is adopted by professional societies.

Intergenerational health mobility: Evidence from Danish registers

This paper is one of the first to investigate mobility in overall health using high-quality administrative data. The attractiveness of this approach lies in objective health measures and large sample sizes allowing twin analyses. I operationalize health mobility by a variety of statistics: rank-rank slopes, intergenerational correlations (IGCs) and sibling and identical twin correlations. I find rank-rank slopes and IGCs in the range 0.11-0.15 and sibling correlations in the range 0.14-0.20. Mobility in health is thus relatively high, both when compared to similar US-based studies, and when contrasted with outcomes such as educational attainment and income. Comparing sibling and identical twin correlations with parent-child associations confirms earlier findings in the literature on equality of opportunity, namely that sibling correlations capture far more variation than traditional IGCs. I conclude that 14%-38% of the variation in individual health outcomes can be attributed to family background and genes, factors which the individual cannot be held accountable for. This finding suggests that simple parent-child associations may be a poor metric for measuring health mobility.

Brachial Plexus Birth Injury in the Preterm Infant: Suspecting the Unsuspected

BACKGROUND

Prematurity is usually considered as a protective factor for brachial plexus birth injury (BPBI). However, BPBI can occur in the preterm infant, and can cause significant dysfunction and morbidity. There is scant literature regarding this subgroup of patients with BPBI.

METHODS

Patients were identified through a retrospective search of a prospective BPBI registry at a single tertiary pediatric referral center. Prematurity was defined as birth at or before gestational age of 36 (6/7) weeks. Thirty-six arms in 34 patients were included in this study. Data were obtained from patient charts documenting standardized brachial plexus clinical examinations at each visit, medical imaging, questionnaires for parents, and outside perinatal records brought in by parents.

RESULTS

The youngest infant identified with BPBI was born at 23 weeks' gestation. Median birth weight was 3005 g (range: 580 to 4600 g). Twenty-nine arms in 28 patients were categorized into the "late preterm group" [34 to 36 (6/7) weeks gestation], and 7 arms in 6 patients were categorized into the "early preterm group" (<34 wk). Four of 6 (67%) subjects in the early preterm group were delivered vaginally in the breech position, compared with 4 of 28 subjects (14%) in the late preterm group (P=0.02). All 3 twin gestation infants with BPBI were the younger twin and born vaginally in the breech position. Delayed diagnosis (>7 d) occurred in 11 arms in 10 subjects (31%). Median delay in diagnosis was 73 days (range: 10 to 1340 d). Spontaneous recovery of antigravity elbow flexion occurred in 65% of arms (at median 5 mo, range: 1 to 17 mo). Overall, 89% (32/36) of arms with BPBI had residual neurological deficit and 53% (19/36) of arms underwent at least 1 surgical intervention at latest follow-up (median age at latest follow-up: 60 mo, range: 1 to 237 mo).

CONCLUSIONS

BPBI in preterm infants is rare but does occur and can cause significant morbidity. Delayed diagnosis of BPBI is common in preterm infants. A high index of suspicion should be maintained to avoid delayed diagnosis that may jeopardize treatment options. Preterm infants may be more susceptible to birth trauma from breech deliveries and shoulder dystocia, as evidenced by far higher incidence of these factors compared with term infants with BPBI in literature.

LEVEL OF EVIDENCE

Level IV-case series.

Dizygotic Twin Infants: Controversial Case Study Series/Twin Research Reviews: Twin and Non-twin ICSI Conceptions; Emory University Twin Study; Labor in Multiple Pregnancy After Previous C-Section Delivery; Cell-Free DNA Fetal Fraction in Twin Pregnancies/News Reports: Twin Survivor of Auschwitz; Twins Trading Places; Identical Twin Foals; Twins Born in Different Decades; Twins Ambulette Service

This article describes a 1930s case study series involving dizygotic female twin infants. The twins' development was evaluated following periods of intentionally restricted practice and minimal social stimulation. In the opinion of the author of the current article, the study is very unsettling and unacceptable, despite the lack of institutional review boards at that time. This discussion is followed by twin research reviews of recent papers concerning twin and non-twin intracytoplasmic sperm injection conceptions, the Emory University Twin Study of cardiac and brain functions, labor trials in multiple pregnancies after previous C-section delivery and cell-free DNA fetal fraction in twin pregnancies. The article concludes with news items of a twin survivor of Auschwitz, a situation in which twins traded places, the rare birth of identical twin foals, the novel delivery of co-twins in different decades and the Twins Ambulette Service.

Personalized Nutrition for Inflammatory Bowel Disease

A person’s diet may impact inflammatory bowel disease (IBD) risk. IBD is an inflammatory condition. We explore how certain foods may trigger, or indeed attenuate, inflammation in some IBD patients, but not others. Greater knowledge is needed underpinning personalized nutrition within effective medical management.

The Value of Twins for Health and Medical Research: A Third of a Century of Progress

In 1984, Hrubec and Robinette published what was arguably the first review of the role of twins in medical research. The authors acknowledged a growing distinction between two categories of twin studies: those aimed at assessing genetic contributions to disease and those aimed at assessing environmental contributions while controlling for genetic variation. They concluded with a brief section on recently founded twin registries that had begun to provide unprecedented access to twins for medical research. Here we offer an overview of the twin research that, in our estimation, best represents the field has progress since 1984. We start by summarizing what we know about twinning. We then focus on the value of twin study designs to differentiate between genetic and environmental influences on health and on emerging applications of twins in multiple areas of medical research. We finish by describing how twin registries and networks are accelerating twin research worldwide.

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.

The New West Japan Twins and Higher Order Multiple Births Registry

The new West Japan Twins and Higher Order Multiple Births Registry was established by recruiting young twins and multiple births and by referrals from public health centers in the 1990s. The participants included in the survey comprised over 7800 twins and 4241 higher order multiples, and their families. Specifically, the present registry contains one of the largest triplet samples in the world. For these twins and multiples, data on year of delivery, mode of delivery, gestational age, intrapartum complications, longitudinal physical measures, motor milestones, cerebral palsy and feeding methods were obtained from records in the Maternal and Child Health Handbooks and schools. Participating mothers were asked to indicate family structure, parental educational history, maternal sleeping time, maternal health condition, maternal and paternal age at multiple delivery, complications during pregnancy, handedness of multiples and age at menarche of multiples. However, the zygosity differed among the various collaborating public health centers according to factors such as the time of investigation. Follow-up questionnaires have been mailed out every 3-4 years for longitudinal studies. This article describes the goals of this registry, recruitment of multiples and the focus of the study. The goals of this registry are not only to conduct research on human genetics and maternal and child health, but also to contribute to providing appropriate information for families with multiples.

[Obesity in childhood: What are the respiratory risks?]

In childhood and adolescence overweight is defined as a body mass index (BMI) above the 97th percentile for age and sex, according to the curves established by the International Obesity Task Force (IOTF). In France, it is estimated that 25 % of children under 18 years old are overweight. Overweight and obesity in this population are multifactorial, with an important influence of genetic factors, modulated by pre and post-natal (maternal smoking), societal and psychological determinants. The impact of obesity on respiratory function in children is mostly characterized by a decreased FEV1/FCV. Moreover, several studies have shown an association between asthma and overweight/obesity, with a pejorative impact of BMI on asthma control. However, asthma is still poorly characterized in this population, and the determinants of bronchial obstruction seem to differ from non-obese children, with less eosinophilic inflammation. Obstructive sleep apnea syndrome (OSAS) is a frequent complication of obesity, affecting up to 80% of obese children and adolescents. It has a specific polysomnographic definition in children. Symptoms are similar to adult OSAS, but with cognitive and neurobehavioral alterations often more important in adolescents. The treatment consists in ENT surgery when indicated (with systematic post-operative polysomnography), and nocturnal continuous positive airway pressure (CPAP). The obesity-hypoventilation syndrome (OHS) has the same definition in children as in adults and affects up to 20% of obese patients. Treatment consists in nocturnal ventilation using bilevel positive airway pressure (BiPAP). Finally, in some extreme cases, bariatric surgery can be performed. The indication should be discussed in a specialised paediatric reference centre.

The CODATwins Project: The Current Status and Recent Findings of COllaborative Project of Development of Anthropometrical Measures in Twins

The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural-geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.

Contributions of birthweight, annualised weight gain and BMI to back pain in adults: a population-based co-twin control study of 2754 Australian twins

PURPOSE

To investigate associations between anthropometric measures (birthweight, weight gain and current BMI) and back pain; and to determine whether these associations differ between those born with low or full birthweight.

METHODS

The cross-sectional associations between the lifetime prevalence of back pain and anthropometric measures (birthweight, weight gain and current BMI) among 2754 adult twins were investigated in three stages: total sample; within-pair case-control for monozygotic and dizygotic twins together; and within-pair case-control analysis separated by dizygotic and monozygotic. Results were expressed as odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

Birthweight was not associated with back pain (OR 0.99; 95% CI 0.99-1.00), but a weak association was found between weight gain (OR 1.01; CI 1.00-1.01) or current BMI (OR 1.02; 95% CI 1.00-1.05) and back pain in the total sample analysis. These associations did not remain significant after adjusting for genetics. The associations did not differ between those whose were born with low or full birthweight.

CONCLUSION

Birthweight was not associated with prevalence of back pain in adulthood. Weight gain and current BMI were weakly associated with back pain prevalence in the total sample analysis but did not differ between those born with low or full birthweight. However, the small-magnitude association only just achieved significance and appeared to be confounded by genetics and the early shared environment. Our results suggest that a direct link between these predictors and back pain in adults is unlikely. These slides can be retrieved under Electronic Supplementary Material.

Associations between birth characteristics and age-related cognitive impairment and dementia: A registry-based cohort study

BACKGROUND

There is evidence for long-lasting effects of birth characteristics on cognitive ability in childhood and adulthood. Further, low cognitive ability throughout the lifetime has been linked to age-related cognitive decline and dementia risk. However, little is known about the effects of birth characteristics on cognitive dysfunction late in life. Here we explore potential associations between birth characteristics (weight, head circumference, length, and gestational age), adjusted and not adjusted for gestational age, and cognitive impairment and dementia late in life.

METHODS AND FINDINGS

Data from twins in the Swedish Twin Registry born 1926-1960 were merged with information from the Swedish birth, patient, and cause of death registries, resulting in a sample of 35,191 individuals. A subsample of 4,000 twins aged 65 years and older also participated in a telephone cognitive screening in 1998-2002. Associations of birth characteristics with registry-based dementia diagnoses and on telephone-assessed cognitive impairment were investigated in the full sample and subsample, respectively. The full sample contained 907 (2.6%) individuals with a dementia diagnosis (an incidence rate of 5.9% per 100,000 person-years), 803 (2.4%) individuals born small for gestational age, and 929 (2.8%) individuals born with a small head for gestational age. The subsample contained 569 (14.2%) individuals with cognitive impairment. Low birth weight for gestational age and being born with a small head for gestational age were significant risk factors for cognitive dysfunction late in life, with an up to 2-fold risk increase (p < 0.001) compared to infants with normal growth and head size, even after controlling for familial factors, childhood socioeconomic status, and education in adulthood. In line with this, each additional 100 g birth weight and each additional millimeter head circumference significantly reduced the risk for dementia (hazard ratio 0.98, 95% confidence interval 0.97 to 0.99, p = 0.004) and cognitive impairment (odds ratio 0.99, 95% confidence interval 0.99 to 1.00, p = 0.004), respectively. Within-pair analyses of identical twins, though hampered by small sample size, suggested that the observed associations between birth characteristics and dementia are likely not due to underlying shared genetic or environmental etiology. A limitation of the present study is that registry-based dementia diagnoses likely miss some of the true dementia cases in the population. Further, a more precise measure of cognitive reserve early in life as well as a date of onset for the cognitive impairment measure in the subsample would have been favorable.

CONCLUSIONS

In this study, we found that infants of smaller birth size (i.e., low birth weight or small head circumference adjusted and unadjusted for gestational age) have a significantly higher risk of age-related cognitive dysfunction compared to those with normal growth, highlighting the importance of closely monitoring the cognitive development of such infants and evaluating the potential of early life interventions targeted at enhancing cognitive reserve.

Twins as Participants in Randomized Controlled Trials: A Review of Published Literature

Monozygotic (MZ) and dizygotic (DZ) twins participate in research that partitions variance in health, disease, and behavior into genetic and environmental components. However, there are other innovative roles for twins in medical research. One such way is involving MZ and/or DZ twins in co-twin control-designed randomized controlled trials (RCTs). To our knowledge, no reviews have been conducted that summarizes the involvement of twins in RCTs. Therefore, we conducted a systematic literature search using the U.S. Clinical Trials Database, NHS electronic databases, MEDLINE, EMBASE, and PsychINFO for RCTs on publications involving MZ and/or DZ twins as RCT participants. Out of the 186,027 clinical trials registered in the U.S. clinical trial register ClinicaTrails.gov, only six RCTs used twins as participants. From 1,598 articles identified in our search, 50 peer-reviewed English language publications met our pre-defined inclusion criteria. Sample sizes for RCTs have ranged from a total number of participants from 2 to 1,162; however, 32 (64%) studies had a sample size of 100 or less, and of those, 12 (24%) had fewer than 10. Both MZ and DZ twins have been recruited to the RCTs. In most instances (33/50) each twin from a pair were assigned to different study arms. Most of those studies included MZ twins only. Despite the methodological advantages, the use of MZ and DZ twins as participants in interventional RCTs appeared limited. The continuous development of innovative twin designs, especially RCTs, indicates that twin research can extend beyond the more widely recognized heritability estimates.

Nonpresenting Dichorionic Twins and Placental Vascular Malperfusion

OBJECTIVE

To explore the hypothesis that selective placental pathology affecting the nonpresenting twin is a significant contributory factor mediating the smaller size at birth of nonpresenting dichorionic twins.

METHODS

We conducted a retrospective cohort study of all dichorionic twin deliveries in a single tertiary center between 2002 and 2015 where by departmental policy, all placentas from multifetal gestations are routinely sent for pathologic examination. Maternal charts, neonatal charts, and pathology reports were reviewed. Placental abnormalities were classified into lesions associated with maternal vascular malperfusion, fetal vascular malperfusion, placental hemorrhage, and chronic villitis. Comparison of neonatal outcomes and placental abnormalities was made between all nonpresenting and all presenting twins as well as within twin pairs.

RESULTS

A total of 1,322 women with dichorionic twins were studied. Nonpresenting twins were smaller at birth compared with the presenting cotwin starting at 32 weeks of gestation (birth weight [±standard deviation] 2,224±666 g compared with 2,278±675 g, P=.036). Nonpresenting twins had smaller placentas (361±108 g compared with 492±129 g, P<.001) as early as 24 weeks of gestation. Nonpresenting twins had higher odds for any placental abnormality (adjusted odds ratio [OR] 1.91, 95% confidence interval [95% CI] 1.63-2.23), small placenta (adjusted OR 4.69, 95% CI 3.75-5.88), and maternal vascular malperfusion (OR 2.75, 95% CI 2.32-3.27) compared with their presenting cotwins. In nonpresenting twins, the presence of maternal vascular malperfusion pathology was associated with lower birth weight compared with their presenting cotwin during the third trimester.

CONCLUSION

The lower birth weight of nonpresenting fetuses in dichorionic twin pregnancies is correlated with a higher rate of placental maternal vascular malperfusion pathology.