The aim of this study was to investigate the prevalence of anemia in twin pregnancies and the influence of anemia on maternal and neonatal outcomes. This retrospective study included twin pregnant women who delivered in a tertiary hospital in China from January 2018 to December 2018. Patients were divided by WHO criteria (hemoglobin <11.0 g/dL): the anemic and nonanemic groups. Patients with anemia were further classified as recovered or unrecovered subgroup after oral iron therapy. Maternal and neonatal outcomes in women carrying twins were compared using Student’s t test and the chi-squared test or the Fisher exact test. Univariable and multivariable logistic regression models were used to determine the association of maternal and neonatal characteristics with anemia. Linear regression analysis was used to estimate mean birth weight and gestational week. The prevalence of anemia was 42.6% (182/427) in twin pregnancies. The anemic group had higher rates of low 1-minute Apgar score (4.4% vs. 1.8%, p = .028), perinatal death (1.9% vs. 0.2%, p = .012) and neonatal intensive care unit (NICU) admission (27.2% vs. 20.2%, p = .017; adjusted OR, 1.478; 95% CI [1.07, 2.044]). The recovered subgroup had lower NICU admission rate (13.5% vs. 30.3%, p = .006; OR, 0.388; 95% CI [0.186, 0.809]), higher gestational week and birth weight (β, 0.954 week; 95% CI [0.114, 1.794] and β, 171.01 g; 95% CI [9.894, 332.126] respectively). The prevalence of anemia in twin gestation is high. Anemia is associated with adverse neonatal outcomes, and correction of anemia significantly improved the pregnancy outcomes.

The expansion of genetic and genomic testing in clinical practice and research, and the growing market for direct-to-consumer genomic testing has led to increased awareness about the impact of this form of testing on insurance. Genetic or genomic information can be requested by providers of mutually rated insurance products, who may then use it when setting premiums or determining eligibility for cover under a particular product. Australian insurers are subject to relevant legislation and an industry led standard that was updated in 2019 to introduce a moratorium on the use of genetic test results in life insurance underwriting for policies <AU$500K. The Human Genetics Society of Australasia has updated its position statement on genetic testing and life insurance to account for these changes and to increase the scope of the statement to include a wider range of personally-rated insurance products, such as life, critical care, and income protection products. Recommendations include that: providers of professional education involving genetics should include ethical, legal, and social aspects of insurance discrimination in their curricula; the Australian Government take a more active role in regulating use of genetic information in personal insurance; that information obtained in the course of a research project be excluded; insurers seek expert advice when making underwriting decisions regarding genetic testing; and engagement between the insurance industry, regulators, and the genetics profession be improved.

The aim of this study was to determine the pregnancy loss rate of amniocentesis with double-needle insertions in twin pregnancies. This was a retrospective study of twin pregnancies who underwent amniocentesis with double-needle insertion between 2010 and 2019 at a single center. The pregnancy loss rates were recorded as single or double fetal loss before 24 weeks’ gestation and within 4 weeks after the procedure. Risk factors for pregnancy loss after amniocentesis were also assessed. A total of 678 twin pregnancies with amniocentesis were finally included. The pregnancy loss rates before 24 weeks’ gestation and within 4 weeks after the procedure were 0.9% and 1.9%, respectively. Only one fetal loss was presumed to be a direct result of the procedure. All other cases were complicated by structural or chromosomal anomalies. Twin pregnancies with abnormal ultrasound findings had a significantly higher rate of pregnancy loss with a relative risk of 4.81 (95% CI [1.03, 22.2]). Our study showed a low pregnancy loss rate after amniocentesis in twin pregnancies with double-needle insertions technique of sampling, which can help decision making in prenatal screening and diagnosis for twin pregnancies.

Some legal and social complications that arise when identical twins have children are examined. The specific case presented concerns assignment of paternity. This section is followed by a review of recent studies of multiple birth pregnancy risk factors, namely mother to infant HIV transmission and congenital hypothyroidism. Honors given to recently recognized twin researchers are noted, as is the birth of twins to an older mother in the United States.

Commentary on Cherkas et al. (2004). Genetic Influences on Female Infidelity and Number of Sexual Partners in Humans: A Linkage and Association Study on the Role of the Vasopressin Receptor Gene (AVPR1A). Twin Research, 7, 649–658.

Many studies of human behavior and psychological constructs rely on subjects' willingness to disclose information about themselves. This is problematic for phenotypes that require the disclosure of sensitive information, such as sexual behavior or illicit drug use, which are likely to be underreported. We describe a method for evaluating how sensitive variance component estimates are to underreporting. The method involves estimating, by maximum likelihood, the original population proportions of the response classes, and adjusting them for a set of hypothesized underreporting parameters. If the true values of the underreporting parameters were known, the researcher could estimate the variance components based on these values. Usually, underreporting levels are not known with certainty. However, it is possible to assume a specific value for the underreporting rate, obtain response pattern proportions adjusted for this rate, and then to conduct the analyses on these revised estimates. By repeating the procedure across the range of plausible underreporting values, the researcher can assess how sensitive the variance component estimates are to variation in underreporting. We apply this method to a sample of male-male twin pairs who reported on themselves and their co-twins for illicit drug abuse and dependence (DAD). We show how underreporting influences estimates of additive genetic, common environment, and specific environment variance components (A, C, and E) obtained for DAD in a classical twin design.

Following the Derom et al. paper recently published in Twin Research (2003, 6, 19–21), we investigated our French sample, studying the retrospective validity of information given by parents to determine the chorion type of their monozygotic twins. The sample included 44 MZ pairs of known chorion type. Chorion type was established by a pathologist specialising in the study of placenta and zygosity diagnosis using molecular genetic techniques. Results show that of the parents who had information, there was a high level of uncertainty of the chorion type. It therefore seems impossible to obtain valid retrospective determination from parents and the only solution is to have accurate information in the birth records.

Health is a multidimensional and continual concept. Traditional latent analytic approaches have inherent deficits in capturing the complex nature of the concept; however, the Grade of Membership (GoM) model is well suited for this problem. We applied the GoM method to a set of 31 indicators to construct ideal profiles of health status based on physical, mental and social support items among 848 adult twins from Qingdao, China. Four profiles were identified: healthy individuals (pure type I), individuals with personality disorders (pure type II), individuals with mental impairments (pure type III) and individuals with physical impairments (pure type IV). The most frequently occurring combination in this population was profiles I, II, IV (14.74%), followed by profiles I, II, III, IV (13.44%), and then type I (11.08%). Only 13.56% of subjects fell completely into one single pure type, most individuals exhibited some of the characteristics of two or more pure types. Our results indicated that, compared to conventional statistical methods, the GoM model was more suited to capture the complex concept of health, reflecting its multidimensionality and continuity, while also exhibiting preferable reliability. This study also made an important contribution to research on GoM application in non-independent samples.

In this article we present the protocol of the Birmingham Registry for Twin Heritability Studies (BiRTHS), which aims to establish a long-term prospective twin registry with twins identified from the antenatal period and subjected to detailed follow-up. We plan to investigate the concordance in anthropo-metrics and early childhood phenotypes between 66 monozygotic and 154 dizygotic twin pairs in the first 2 years of recruitment. In this project we plan to determine the relative contributions of heritability and environment to fetal growth, birth size, growth in infancy and development up to 2 years of age in an ethnically mixed population. Twins will be assessed with the Griffitth's Mental Development Scales, which will enable us to obtain detailed information on development. As maternal depression may have an effect on the twins' neurodevelopment, the Edinburgh Postnatal Depression Scale will be used at various stages during pregnancy and after delivery to assess maternal depressive symptoms. The increasing prevalence of obesity in both adults and children has raised concerns about the effect of maternal obesity in pregnancy on fetal growth. The prospective study design gives us the opportunity to obtain data on maternal nutrition (reflected by body mass index) and ante- and postnatal growth and development of twins.

Twins are not a homogeneous group. According to zygosity and chorionicity essential differences exist. The lower sex proportion at birth is due to the monozygotic twins, especially the monoamnionic variety. X-inactivation patterns in monozygotic twin girls are totally symmetrical in monoamnionic pairs, almost symmetrical in monochorionic diamnionic pairs and can be very asymmetrical in the dichorionic variety.

We applied a noninvasive prenatal test for the determination of fetal gender in multiple pregnancies by using free fetal DNA circulating in maternal blood in order to evaluate whether the quantification of male DNA could distinguish the fetal gender and the number of male and female fetuses in multiple pregnancies. We enrolled consecutively 44 women with twin pregnancies between 11–14 weeks of gestation. Peripheral maternal blood was collected, and genomic DNA was extracted from maternal plasma and analyzed for the multicopy DYS 14 sequence by using real-time PCR to quantify male DNA. Results showed that male DNA concentration was significantly higher in twin pregnancies with at least one male fetus, compared to twin pregnancies with only female fetuses. Comparing male DNA concentration in pregnancies with two male fetuses versus pregnancies with one female fetus and one male fetus, we did not obtain a significant difference between the two groups due to a slight overlapping of the range values. Therefore, our test correctly predicted fetal gender, distinguishing twin pregnancies with at least one male fetus from twin pregnancies with only female fetuses, with a diagnostic accuracy of 100%. For distinguishing pregnancies with two male fetuses from pregnancies with both female and male fetuses, a diagnostic accuracy of 76.1% was achieved.

Linkage analysis (either parametric or nonparametric) is commonly applied to identify chromosomal regions using related individuals affected by disease. In complex disease the incomplete relationship between phenotype and genotype can be modeled using a phenocopy parameter, the probability that an individual is affected given they do not carry the disease mutation of interest, and a nonpenetrance parameter, the probability that an individual is not affected given they do carry the disease mutation of interest. If the linkage phase between multiple markers and a putative disease locus is known, then haplotypes carrying the mutation can, in principle, be identified by comparing the chromosome segments that are shared identical-by-descent (IBD) across affected individuals. We consider here the effect of a nonzero phenocopy rate on the linkage peak and hence upon the identification of disease haplotypes that are shared IBD between affected individuals. We show, by theory and computer simulation, that in diseases for which there is a nonzero phenocopy rate, the chromosomal regions identified may not include the true disease locus. We utilize a LOD-1 confidence interval for a widely used nonparametric linkage statistic. We find that in small/moderate samples this confidence interval may be inappropriate. We give specific examples where the phenocopy rates are nonnegligible in some complex diseases. The success of further work to identify the causal mutations underlying the linkage peaks in these diseases will depend on researchers allowing for the presence of phenocopies by examining appropriately wide regions around the initial positive linkage finding.

The predictive relation between neonatal reactivity and 12-, 18-, and 24-month temperament was assessed for 22 appropriate-for-gestational-age (AGA)/small-for-gestational-age (SGA) twin pairs. Neonatal reactivity included ratings of visual and auditory orienting responses to a bull's-eye, rattle, bell, voice, and face plus voice combined, as well as alertness. Infant temperament ratings were made of emotional tone, activity, attentiveness, and social orientation to staff during ageappropriate activities in the laboratory. There were no group differences in the neonatal or infant ratings. For AGA twins, a pattern of predictive correlations was obtained between neonatal reactivity and temperament at each age. A similar predictive pattern was not observed for the SGA twins. Group differences in rates of maturation related to stresses associated with intrauterine growth retardation influenced the significance of the neonatal variables for later temperament development.

The second recorded case of sesquizygotic (SQZ) twins is summarized. It is suspected that SQZ twins result from the fertilization of an egg by two separate spermatozoa, followed by division of the fertilized ovum. Next, recent studies examining how differences in parental affection affect co-twins’ personality profiles, the prenatal demise of fetuses during twin pregnancy, a forensic case of heteropaternal superfecundation and selective feticide in dichorionic twins are reviewed. Finally, summaries of newsworthy items featuring an identical twin Oscar winner, a case of ‘superfecundated’ twins born to a gay couple, identical twins who try partly living apart and new molecular techniques to distinguish an innocent identical twin from his or her guilty co-twin are presented.

Stillbirth rates of triplet births in the whole of Japan were analyzed using vital statistics from 1975 to 1998. Stillbirths were registered at 12 weeks gestation or later. The stillbirth rate was significantly higher in like- than in unlike-sex triplets for 1975–1998. During the 23-year period the stillbirth rate decreased from 342 to 49 per 1000 total births for like-sex and from 195 to 54 for unlike-sex triplets. The decrease in the stillbirth rate in the 23-year period was greater in both like- and unlike-sex triplets than in singleton and twin births. Risk factors for stillbirth in triplets were like-sex, youngest or oldest maternal age groups, shorter gestational age and lower birthweight. It is recommended that the optimum period to give birth for triplet pregnancies is 34–35 weeks of gestation for Japanese women.

We describe two cases of delayed delivery in dichorionic, diamniotic pregnancies, where we used an Endoloop ligature to clamp the umbilical cord with excellent maternal and fetal long-term outcome.