-
BMJ (Clinical Research Ed.) Sep 2016To determine the risks of stillbirth and neonatal complications by gestational age in uncomplicated monochorionic and dichorionic twin pregnancies. (Meta-Analysis)
Meta-Analysis Review
OBJECTIVE
To determine the risks of stillbirth and neonatal complications by gestational age in uncomplicated monochorionic and dichorionic twin pregnancies.
DESIGN
Systematic review and meta-analysis.
DATA SOURCES
Medline, Embase, and Cochrane databases (until December 2015).
REVIEW METHODS
Databases were searched without language restrictions for studies of women with uncomplicated twin pregnancies that reported rates of stillbirth and neonatal outcomes at various gestational ages. Pregnancies with unclear chorionicity, monoamnionicity, and twin to twin transfusion syndrome were excluded. Meta-analyses of observational studies and cohorts nested within randomised studies were undertaken. Prospective risk of stillbirth was computed for each study at a given week of gestation and compared with the risk of neonatal death among deliveries in the same week. Gestational age specific differences in risk were estimated for stillbirths and neonatal deaths in monochorionic and dichorionic twin pregnancies after 34 weeks' gestation.
RESULTS
32 studies (29 685 dichorionic, 5486 monochorionic pregnancies) were included. In dichorionic twin pregnancies beyond 34 weeks (15 studies, 17 830 pregnancies), the prospective weekly risk of stillbirths from expectant management and the risk of neonatal death from delivery were balanced at 37 weeks' gestation (risk difference 1.2/1000, 95% confidence interval -1.3 to 3.6; I(2)=0%). Delay in delivery by a week (to 38 weeks) led to an additional 8.8 perinatal deaths per 1000 pregnancies (95% confidence interval 3.6 to 14.0/1000; I(2)=0%) compared with the previous week. In monochorionic pregnancies beyond 34 weeks (13 studies, 2149 pregnancies), there was a trend towards an increase in stillbirths compared with neonatal deaths after 36 weeks, with an additional 2.5 per 1000 perinatal deaths, which was not significant (-12.4 to 17.4/1000; I(2)=0%). The rates of neonatal morbidity showed a consistent reduction with increasing gestational age in monochorionic and dichorionic pregnancies, and admission to the neonatal intensive care unit was the commonest neonatal complication. The actual risk of stillbirth near term might be higher than reported estimates because of the policy of planned delivery in twin pregnancies.
CONCLUSIONS
To minimise perinatal deaths, in uncomplicated dichorionic twin pregnancies delivery should be considered at 37 weeks' gestation; in monochorionic pregnancies delivery should be considered at 36 weeks.
SYSTEMATIC REVIEW REGISTRATION
PROSPERO CRD42014007538.
Topics: Female; Gestational Age; Humans; Infant, Newborn; Infant, Newborn, Diseases; Intensive Care, Neonatal; Perinatal Death; Pregnancy; Pregnancy, Twin; Prospective Studies; Risk Factors; Stillbirth; Twins, Dizygotic; Twins, Monozygotic
PubMed: 27599496
DOI: 10.1136/bmj.i4353 -
Journal of Child Psychology and... May 2016The etiology of Autism Spectrum Disorder (ASD) has been recently debated due to emerging findings on the importance of shared environmental influences. However, two... (Meta-Analysis)
Meta-Analysis Review
BACKGROUND
The etiology of Autism Spectrum Disorder (ASD) has been recently debated due to emerging findings on the importance of shared environmental influences. However, two recent twin studies do not support this and instead re-affirm strong genetic effects on the liability to ASD, a finding consistent with previous reports. This study conducts a systematic review and meta-analysis of all twin studies of ASD published to date and explores the etiology along the continuum of a quantitative measure of ASD.
METHODS
A PubMed Central, Science Direct, Google Scholar, Web of Knowledge structured search conducted online, to identify all twin studies on ASD published to date. Thirteen primary twin studies were identified, seven were included in the meta-analysis by meeting Systematic Recruitment criterion; correction for selection and ascertainment strategies, and applied prevalences were assessed for these studies. In addition, a quantile DF extremes analysis was carried out on Childhood Autism Spectrum Test scores measured in a population sample of 6,413 twin pairs including affected twins.
RESULTS
The meta-analysis correlations for monozygotic twins (MZ) were almost perfect at .98 (95% Confidence Interval, .96-.99). The dizygotic (DZ) correlation, however, was .53 (95% CI .44-.60) when ASD prevalence rate was set at 5% (in line with the Broad Phenotype of ASD) and increased to .67 (95% CI .61-.72) when applying a prevalence rate of 1%. The meta-analytic heritability estimates were substantial: 64-91%. Shared environmental effects became significant as the prevalence rate decreased from 5-1%: 07-35%. The DF analyses show that for the most part, there is no departure from linearity in heritability.
CONCLUSIONS
We demonstrate that: (a) ASD is due to strong genetic effects; (b) shared environmental effects become significant as a function of lower prevalence rate; (c) previously reported significant shared environmental influences are likely a statistical artefact of overinclusion of concordant DZ twins.
Topics: Autism Spectrum Disorder; Diseases in Twins; Genetic Predisposition to Disease; Humans
PubMed: 26709141
DOI: 10.1111/jcpp.12499 -
BMC Psychology Jan 2022In the general population, 10.6% of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-,... (Meta-Analysis)
Meta-Analysis
BACKGROUND
In the general population, 10.6% of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-, or non-right-) handedness in (i) twins compared to singletons, and in (ii) monozygotic compared to dizygotic twins. Moreover, (iii) studies have shown a higher rate of handedness concordance in monozygotic compared to dizygotic twins, in line with genetic factors playing a role for handedness.
METHODS
By means of a systematic review, we identified 59 studies from previous literature and performed three sets of random effects meta-analyses on (i) twin-to-singleton Odds Ratios (21 studies, n = 189,422 individuals) and (ii) monozygotic-to-dizygotic twin Odds Ratios (48 studies, n = 63,295 individuals), both times for prevalence of left-, mixed-, and non-right-handedness. For monozygotic and dizygotic twin pairs we compared (iii) handedness concordance Odds Ratios (44 studies, n = 36,217 twin pairs). We also tested for potential effects of moderating variables, such as sex, age, the method used to assess handedness, and the twins' zygosity.
RESULTS
We found (i) evidence for higher prevalence of left- (Odds Ratio = 1.40, 95% Confidence Interval = [1.26, 1.57]) and non-right- (Odds Ratio = 1.36, 95% Confidence Interval = [1.22, 1.52]), but not mixed-handedness (Odds Ratio = 1.08, 95% Confidence Interval = [0.52, 2.27]) among twins compared to singletons. We further showed a decrease in Odds Ratios in more recent studies (post-1975: Odds Ratio = 1.30, 95% Confidence Interval = [1.17, 1.45]) compared to earlier studies (pre-1975: Odds Ratio = 1.90, 95% Confidence Interval = [1.59-2.27]). While there was (ii) no difference between monozygotic and dizygotic twins regarding prevalence of left- (Odds Ratio = 0.98, 95% Confidence Interval = [0.89, 1.07]), mixed- (Odds Ratio = 0.96, 95% Confidence Interval = [0.46, 1.99]), or non-right-handedness (Odds Ratio = 1.01, 95% Confidence Interval = [0.91, 1.12]), we found that (iii) handedness concordance was elevated among monozygotic compared to dizygotic twin pairs (Odds Ratio = 1.11, 95% Confidence Interval = [1.06, 1.18]). By means of moderator analyses, we did not find evidence for effects of potentially confounding variables.
CONCLUSION
We provide the largest and most comprehensive meta-analysis on handedness in twins. Although a raw, unadjusted analysis found a higher prevalence of left- and non-right-, but not mixed-handedness among twins compared to singletons, left-handedness was substantially more prevalent in earlier than in more recent studies. The single large, recent study which included birth weight, Apgar score and gestational age as covariates found no twin-singleton difference in handedness rate, but these covariates could not be included in the present meta-analysis. Together, the secular shift and the influence of covariates probably make it unsafe to conclude that twinning has a genuine relationship to handedness.
Topics: Birth Weight; Functional Laterality; Humans; Prevalence; Twins, Dizygotic; Twins, Monozygotic
PubMed: 35033205
DOI: 10.1186/s40359-021-00695-3 -
JCPP Advances Jul 2021Non-shared environment (NSE) effects account for around one-third of the etiology of autism spectrum disorder (ASD). However, the knowledge of mechanisms and phenotypic...
BACKGROUND
Non-shared environment (NSE) effects account for around one-third of the etiology of autism spectrum disorder (ASD). However, the knowledge of mechanisms and phenotypic profiles associated with NSE in ASD is scarce.
METHODS
A systematic search was conducted using Embase, MEDLINE, and PsycINFO for studies published in English between 1990 and August 2020 using co-twin control design to compare behavioral and biological phenotypes among monozygotic (MZ) twin pairs concordant/discordant for ASD, clinical autism symptoms, or autistic traits. Risk of bias was assessed through a modified Newcastle-Ottawa Scale.
RESULTS
Twenty six articles were included. Differential DNA methylation and gene expression were found among ASD discordant twins; however, genetic results were inconsistent. Neurological disorders and early medical events were associated with ASD and autistic traits, while no within pair differences were found for minor physical anomalies or head circumference. Structural and functional brain imaging studies and research on social and other cognitive/behavioral functions were inconclusive. Risk of bias assessment found that all studies used the same exposure (or outcome) measures to collect data for participants and most used either secure health-related records or structured interviews for ascertainment of exposure; however, only a handful of studies representative of the population from which they were drawn. Formal assessment of risk of publication bias (i.e., funnel plot) was not possible.
CONCLUSIONS
Our results suggest that NSE in ASD could be associated with heterogeneous postzygotic genetic mechanisms and manifest as a range of biological and behavioral phenotypes. Extant findings were limited by relatively few studies, small sample sizes, and methodological diversity. More research is needed on co-occurring biological and behavioral phenotypes using a consistent format for designing, analyzing, and reporting MZ ASD discordant twin studies in order to further examine the role of NSE in the etiology of ASD.
PubMed: 37431470
DOI: 10.1111/jcv2.12017 -
EFORT Open Reviews May 2022Idiopathic scoliosis is the most common spinal deformity and affects 1-3% of children and adolescents. Idiopathic scoliosis may run in families and the purpose of this... (Review)
Review
PURPOSE
Idiopathic scoliosis is the most common spinal deformity and affects 1-3% of children and adolescents. Idiopathic scoliosis may run in families and the purpose of this systematic review was to describe the degree of heritability.
METHODS
We searched Medline, Web of Science and EMBASE for family and twin studies reporting heritability estimates for idiopathic scoliosis, or studies from which heritability estimates could be calculated. Reference lists were screened for additional papers. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The protocol was registered at PROSPERO (registration number: CRD42022307329).
RESULTS
The literature search identified 1134 reports. After full-text screening, nine eligible reports were included for data extraction. Seven were twin studies containing between 5 and 526 pairs, and two were family studies with 1149 and 2732 individuals, respectively. Quality was 'good' in four studies and 'fair' in five studies. In general, studies with radiograph-confirmed diagnosis reported higher heritability estimates than studies with self-reported diagnosis. Population-based twin studies reported lower heritability estimates than clinic-based twin studies. Family-based studies reported higher heritability estimates than twin studies. Pairwise concordance for scoliosis ranged from 0.11 to 1.00 in monozygotic twins and from 0 to 1.0 in dizygotic twins. A meta-analysis of three studies resulted in a narrow sense heritability estimate of 0.57 (95% CI: 0.29-0.86).
CONCLUSION
Twin and family studies indicate a hereditary component in idiopathic scoliosis, but study heterogeneity is large, and the degree of the heritability is uncertain. Nevertheless, known genetic variants associated with idiopathic scoliosis can still only explain a minor part of heritability.
PubMed: 35638601
DOI: 10.1530/EOR-22-0026 -
Ultrasound in Obstetrics & Gynecology :... Aug 2014The aim of this systematic review was to explore the relationship between crown-rump length (CRL) discordance detected at 11-14 weeks of gestation and adverse outcome in... (Meta-Analysis)
Meta-Analysis Review
OBJECTIVE
The aim of this systematic review was to explore the relationship between crown-rump length (CRL) discordance detected at 11-14 weeks of gestation and adverse outcome in twin pregnancy and to assess its predictive accuracy.
METHODS
A protocol designed a priori following MOOSE guidelines and recommended for systematic review and meta-analysis was used. The outcomes observed were: total fetal and perinatal loss, fetal loss at <24 weeks, fetal loss at ≥ 24 weeks, birth-weight (BW) discordance, preterm delivery (PTD) at < 34 weeks and fetal anomalies. The analysis was performed for all twins and for dichorionic (DC) and monochorionic (MC) twins separately.
RESULTS
A total of 2008 articles were identified and 17 studies were included in the systematic review. Twin pregnancies with CRL discordance ≥ 10% were at significantly higher risk of perinatal loss (RR, 2.80; 95% CI, 1.25-6.27; P = 0.012), fetal loss at ≥ 24 weeks (RR, 4.07; 95% CI, 1.47-11.23; P = 0.006), BW discordance (RR, 2.24; 95% CI, 1.89-2.64; P < 0.001) and PTD at < 34 weeks (RR, 1.49; 95% CI, 1.23-1.80; P < 0.001) but not of fetal loss at < 24 weeks (P = 0.130). A meta-analysis of fetal anomalies was not possible because fewer than two studies explored this outcome. However, when used alone to screen for adverse pregnancy outcome, the predictive accuracy of CRL discordance was low for each of the outcomes explored.
CONCLUSION
CRL discordance is associated with an increased risk of adverse pregnancy outcome. However, the accuracy of CRL discordance in predicting adverse outcome is poor and thus limits its routine use in clinical practice.
Topics: Birth Weight; Crown-Rump Length; Female; Fetus; Humans; Infant, Newborn; Pregnancy; Pregnancy Outcome; Pregnancy, Twin; Twins, Dizygotic; Twins, Monozygotic; Ultrasonography, Prenatal
PubMed: 24585501
DOI: 10.1002/uog.13335 -
Translational Psychiatry Jun 2023The first systematic review and meta-analysis of obsessive-compulsive disorder (OCD) genetic epidemiology was published approximately 20 years ago. Considering the... (Meta-Analysis)
Meta-Analysis
The first systematic review and meta-analysis of obsessive-compulsive disorder (OCD) genetic epidemiology was published approximately 20 years ago. Considering the relevance of all the studies published since 2001, the current study aimed to update the state-of-art knowledge on the field. All published data concerning the genetic epidemiology of OCD from the CENTRAL, MEDLINE, EMBASE, BVS, and OpenGrey databases were searched by two independent researchers until September 30, 2021. To be included, the articles had to fulfill the following criteria: OCD diagnosis provided by standardized and validated instruments; or medical records; inclusion of a control group for comparison and case-control, cohort or twin study designs. The analysis units were the first-degree relatives (FDRs) of OCD or control probands and the co-twins in twin pairs. The outcomes of interest were the familial recurrence rates of OCD and the correlations of OCS in monozygotic compared with dizygotic twins. Nineteen family, twenty-nine twin, and six population-based studies were included. The main findings were that OCD is a prevalent and highly familial disorder, especially among the relatives of children and adolescent probands, that OCD has a phenotypic heritability of around 50%; and that the higher OCS correlations between MZ twins were mainly due to additive genetic or to non-shared environmental components.
Topics: Adolescent; Child; Humans; Molecular Epidemiology; Twins, Dizygotic; Databases, Factual; Research Design
PubMed: 37380645
DOI: 10.1038/s41398-023-02433-2 -
Sports Medicine - Open Dec 2017There is evidence for considerable heterogeneity in the responsiveness to regular physical activity (PA) which might reflect the influence of genetic factors. The aim of... (Review)
Review
BACKGROUND
There is evidence for considerable heterogeneity in the responsiveness to regular physical activity (PA) which might reflect the influence of genetic factors. The aim of this systematic review was to assess whether the response to a PA intervention for measures of body composition and cardiorespiratory fitness is (i) correlated within twin pairs and/or families and (ii) more correlated in monozygotic twins (MZ) compared to dizygotic twins (DZ), which would be consistent with genetic effects.
METHODS
We performed electronic database searches, combining key words relating to "physical activity" and "genetics", in MEDLINE, CINAHL, EMBASE, SPORTS Discuss, AMED, PsycINFO, WEB OF SCIENCE, and SCOPUS from the earliest records to March 2016. Twin and family studies were included if they assessed body composition and/or cardiorespiratory fitness following a PA intervention, and provided a heritability estimate, maximal heritability estimate, or within MZ twin pair correlation (r). Data on heritability (twin studies), maximal heritability (family studies), and the r were extracted from included studies, although heritability estimates were not reported as small sample sizes made them uninformative.
RESULTS
After screening 224 full texts, nine twin and five family studies were included in this review. The pooled r in response to PA was significant for body mass index (r = 0.69, n = 58), fat mass (r = 0.58, n = 48), body fat percentage (r = 0.55, n = 72), waist circumference (r = 0.50, n = 27), and VOmax (r = 0.39, n = 48), where "n" represents the total number of twin pairs from all studies. Maximal heritability estimates ranged from 0-21% for measures of body composition, and 22-57% for cardiorespiratory fitness. Twin studies differed in sample age, baseline values, and PA intervention, although the exclusion of any one study did not affect the results.
CONCLUSIONS
Shared familial factors, including genetics, are likely to be a significant contributor to the response of body composition and cardiorespiratory fitness following PA. Genetic factors may explain individual variation in the response to PA.
TRIAL REGISTRATIONS
PROSPERO Registration No CRD42015020056 .
PubMed: 28074345
DOI: 10.1186/s40798-016-0073-9 -
The Cochrane Database of Systematic... Apr 2015Monoamniotic twin pregnancies are formed when a single egg is fertilised and the resulting inner cell mass splits to form twins sharing the same amniotic sac. This... (Review)
Review
BACKGROUND
Monoamniotic twin pregnancies are formed when a single egg is fertilised and the resulting inner cell mass splits to form twins sharing the same amniotic sac. This condition is rare and affects about one in 10,000 pregnancies overall. Monoamniotic twin pregnancies are susceptible to complications including cord entanglement, increased congenital anomalies, intrauterine growth restriction, twin-to-twin transfusion syndrome and increased perinatal mortality. All twin pregnancies also carry additional maternal risks including pre-eclampsia, anaemia, antepartum haemorrhage, postpartum haemorrhage and operative delivery.The optimal timing for the delivery of monoamniotic twins is not known. The options include 'planned early delivery' between 32 and 34 weeks, or alternatively awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation), unless there is a specific indication for earlier delivery.
OBJECTIVES
To assess whether routine early delivery in monoamniotic twin pregnancies improves fetal, neonatal or maternal outcomes compared with 'expectant management'. Expectant management means awaiting spontaneous labour at least up until the usual time of planned delivery for other monochorionic twins (approximately 36 to 38 weeks' gestation in many centres), unless a specific indication for delivery occurs in the meantime, e.g. for non-reassuring antenatal testing.
SEARCH METHODS
We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2015).
SELECTION CRITERIA
Published and unpublished randomised controlled trials (including cluster-randomised trials) comparing outcomes for women and infants who were randomised to planned early delivery of a monoamniotic twin pregnancy with outcomes for women and infants who were randomised to either planned term delivery or expectant management. However, we did not identify any trials for inclusion in this review.Quasi-randomised controlled trials, trials published in abstract form only, and trials using a cross-over design are not eligible for inclusion in this review.
DATA COLLECTION AND ANALYSIS
No trials were identified by the search strategy.
MAIN RESULTS
No trials were identified by the search strategy.
AUTHORS' CONCLUSIONS
Monoamniotic twins are rare, and there is insufficient randomised controlled evidence on which to draw strong conclusions about the best management. In their absence, we can refer to historical case series and expert consensus. Management plans should take into consideration the availability of high-quality neonatal care if early delivery is chosen. Women and their families should be involved in the decision making about these high-risk pregnancies.Ongoing, multicentre audits of maternal and perinatal outcomes for monoamniotic twins are needed in order to inform families and clinicians about up-to-date perinatal outcomes with contemporary obstetric practice. Research should consider the social and economic implications of planned interventions, as well as the perinatal outcomes.
Topics: Delivery, Obstetric; Female; Humans; Pregnancy; Pregnancy, Twin; Twins, Monozygotic; Watchful Waiting
PubMed: 25906204
DOI: 10.1002/14651858.CD008820.pub2 -
Clinical Dysmorphology Oct 2012The VATER/VACTERL association is typically defined by the presence of at least three of the following congenital malformations: vertebral anomalies, anal atresia,... (Review)
Review
The VATER/VACTERL association is typically defined by the presence of at least three of the following congenital malformations: vertebral anomalies, anal atresia, cardiac malformations, tracheo-esophageal fistula, renal anomalies, and limb abnormalities. The identification of 14 twin pairs with an initial diagnosis of VATER/VACTERL association at our clinical centers led to the performance of a classical twin study. This involved a thorough evaluation of these 14 twin pairs and a further 55 twin pairs identified from a systematic review of the literature. The zygosity, concordance, and malformation status of all 69 twin pairs were evaluated. Twenty-four twin pairs fulfilled the criteria for inclusion in a comparison of the concordance rates between monozygous (MZ) and dizygous (DZ) twin pairs. The pairwise concordance rates were 15% [95% confidence interval (CI) 4-42%] for MZ and 18% (95% CI 5-48%) for DZ twin pairs (P=0.53). The probandwise concordance rates were 27% (95% CI 11-52%) for MZ and 31% (95% CI 13-58%) for DZ twin pairs (P=0.40). Although based on a limited number of twin pairs, the findings of the present study are consistent with the low number of familial cases reported to date, and suggest that the role of inherited genetic factors in the majority of VATER/VACTERL cases is limited.
Topics: Anus, Imperforate; Diseases in Twins; Esophagus; Heart Defects, Congenital; Humans; Radius; Spine; Trachea; Twins, Dizygotic; Twins, Monozygotic
PubMed: 22895008
DOI: 10.1097/MCD.0b013e328358243c