There are sex-dependent differences in hematological and biochemical variables in adulthood attributed to the predominant effects of testosterone in males and estrogen in females. The Twin Testosterone Transfer (TTT) hypothesis proposes that opposite-sex females may develop male-typical traits due to exposure to relatively higher levels of prenatal testosterone than same-sex females. Additionally, prenatal testosterone exposure has been suggested as a correlate of current circulating testosterone levels. Consequently, opposite-sex females might exhibit male-typical patterns in their hematological and biochemical variables. Despite this hypothesis, routine laboratory investigations assign the same reference range to all females. Our cross-sectional study, conducted in Tamale from January to September 2022, included 40 twins, comprising 10 opposite-sex (OS) males (25%), 10 OS females (25%), and 20 same-sex (SS) females (50%), all aged between 18 and 27 years. Fasting venous blood samples were collected and analyzed using automated hematology and biochemistry laboratory analyzers. Results indicated that levels of hemoglobin, serum creatinine, gamma-glutamyl transferase, total protein, globulins, and total testosterone were significantly higher in OS males than OS females. Conversely, total cholesterol and low-density lipoprotein cholesterol were significantly higher in OS females than OS males. Unexpectedly, levels of low-density lipoprotein cholesterol and total testosterone were significantly higher in SS females than OS females. Contrary to expectations, opposite-sex females did not exhibit male-typical patterns in their hematological and biochemical variables. This suggests that the TTT effect may not occur or may not be strong enough to markedly affect hematological and biochemical variables in OS females.

The current study was motivated by an interest in deepening understanding of Brazilian twin research, which is underrepresented internationally, in an effort to rectify this situation. Our aim was threefold: (1) to carry out a comprehensive investigation of Brazilian research on twins according to the area of knowledge; (2) to evaluate the representation of research in the field of psychology in comparison with other areas; (3) to evaluate characteristics of the research that may have contributed to its exclusion from the comprehensive meta-analysis of 50 years of twin research. A scoping review was performed according to PRISMA guidelines. Titles and abstracts were searched up to 2022 in six databases: CAPES, BDLTD, PePSIC, PubMed, Google Scholar, and SciELO, using selected keywords both in Portuguese and in English (e.g., ‘twins’ and ‘Brazil’; ‘twinning’ and ‘Brazil’; ‘gemelaridade’ [twinning], and ‘gêmeos’ [twins]). Three hundred and forty publications were included in the review. Approximately half (53.8‰) used the classic twin design to investigate the heritability of several traits, and the other half (46.2%) used other research designs. The scoping review showed that the number of publications doubled approximately every 10 years. Most publications were from the health area, with medicine accounting for approximately half of the studies, followed by psychology, odontology, and biology. We found that the interest in studying twins among Brazilian scientists is increasing over the years and there are reasons to be enthusiastic about the potential impact of this trend in the global scenario.

We evaluated the prevalence and risk factors for child maltreatment in multiples aged 3 years and compared them to singletons in Japanese population-based data. Records on child maltreatment and health check-ups at 3 years of age from 17,125 singletons, 488 twins and 18 triplets were collected from a Public Health Center between April 2007 and March 2011. The associations of child maltreatment with potential risk factors were analyzed using the logistic regression model. Out of all children, 76 (4.31 per 1000) children had documented maltreatment including 69 (4.03 per 1000) singletons and seven (14.31 per 1000) twins. All of the cases in twins were physical abuse (100%) and nearly half of the cases (43%) included emotional abuse. Among twins, 86% of the biological mothers were suspected. The alleged perpetrators of twins showed a significantly higher rate of maternal depression compared to those of singletons. After adjusting the results for a number of potential biological and social risk factors, twins or triplets had a higher risk for maltreatment than singletons (OR 3.39, 95% CI [1.17, 9.83]). Healthcare providers should be aware that a multiple birth can place considerable stress on a family leading to child maltreatment and should provide appropriate support and intervention for mothers with multiples.

Immunity activation and inflammation are the main characteristics of rheumatoid arthritis and clonal hematopoiesis. However, it remains unclear whether rheumatoid arthritis increase the risk of clonal hematopoiesis. Here, a Mendelian randomization (MR) analysis was conduct to explore the causal effects of rheumatoid arthritis on clonal hematopoiesis. Summary statistics data of rheumatoid arthritis (13,838 cases and 33,742 controls) and clonal hematopoiesis (10,203 cases and 173,918 controls) derived from a genomewide association study were selected to analyze. We selected inverse-variance weighted, MR-Egger, weighted median, simple mode, and weighted mode to evaluate the causal effect of rheumatoid arthritis on clonal hematopoiesis. The two-sample MR analysis suggested a strong causal relationship between rheumatoid arthritis and clonal hematopoiesis by inverse-variance weighted (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039706) and weighted median (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039518447) methods. No significant pleiotropy or heterogeneity was found in the sensitivity analysis. These results supported a potentially causal relationship between rheumatoid arthritis and clonal hematopoiesis, and the exposure of rheumatoid arthritis increased the risks of clonal hematopoiesis. Our findings highlight the importance of how chronic inflammation and immune activation induced rheumatoid arthritis enhances the risks of clonal hematopoiesis, and that early intervention with rheumatoid arthritis patients might reduce the clonal hematopoiesis risks in rheumatoid arthritis patients. Moreover, our study provides clues for prediction of risk factors and potential mechanisms of clonal hematopoiesis.

This present study investigated the parental characteristics of multiple births using national birth data in Japan. This study included birth data from Vital Statistics: Occupational and Industrial Aspects every five fiscal years from 1995 to 2020. The multiple birth rates were defined as the number of live-birth deliveries with multiple fetuses (e.g., twins, triplets) per total live-birth deliveries. Parental ages, nationalities, occupations and household occupation (occupation of the top earner of the household) were considered as parental characteristics. The multiple birth rates were calculated based on parental characteristics for each year, and a log-binomial regression model was used to assess the association between parental characteristics and multiple births. The multiple birth rate for Japanese mothers consistently exceeded that for non-Japanese mothers over the years, and the rate increased progressively from manual workers to lower non-manual workers and then to upper non-manual workers for both maternal and paternal occupations. The regression results indicated that the risk ratio (RR) for multiple births among non-Japanese mothers was significantly lower than that among Japanese mothers. Moreover, concerning household occupation, the RRs of self-employed individuals, full-time employees at smaller companies, others, and the unemployed were significantly lower than those of full-time employees at larger companies. Furthermore, the RRs of lower non-manual and manual workers were significantly lower than those of upper non-manual workers in maternal and paternal occupations. The results suggested an association between multiple births and parental socioeconomic status in Japan.

Fetuses undergo major surgical stress as well as fluid shifts secondary to both twin-twin transfusion (TTTS) as well as the fetoscopic surgery for treatment of TTTS. While the pathophysiology of TTTS is understood, the acute metabolic changes that fetuses experience from fetoscopic surgery are not. We sought to evaluate the changes in recipient metabolomic profile secondary to TTTS surgery. Amniotic fluid was collected at the beginning and end of four TTTS surgical cases performed from 12/2022−2/2023. Samples were immediately processed and evaluated via NMR-based Metabolomics Facility protocol. In univariate analysis, 12 metabolites (glucose, lactate, and 10 key amino acids) showed statistically significant changes between the beginning and end of the surgery. Among these, 11 metabolites decreased at the end, while only lactate increased. Supervised oPLS-DA modeling revealed pyruvate and lactate as the two metabolites most impact on the variance between cases, and that 40% of metabolomic changes could be attributed directly to the timing that the sample was taken (i.e., if pre- or postoperatively). These results indicate significant metabolic changes in the recipient twin during fetoscopic surgery for TTTS. These findings of decreased glucose, increased lactate, and decreased amnio acids would indicate increased catabolism during surgery. This study raises questions regarding optimal maternal and fetal nutrition during surgery and if nutritional status could be optimized to further improve twin survival during fetoscopic surgery.

The objective of this study was to investigate the genetic link between the age at first birth (AFB) and the occurrence of preterm labor and delivery, utilizing Mendelian randomization (MR) data alongside genomewide association analysis (GWAS). We obtained AFB-related GWAS summary data from the European Bioinformatics Institute database and preterm labor and delivery data was sourced from the FinnGen Consortium. The study considered AFB as exposure variables, with the incidence of preterm labor and delivery serving as the outcome variable. Several MR analysis methods, such as inverse-variance weighted (IVW), MR Egger, weighted median, simple, and weighted mode were utilized. Besides MR-Egger intercepts, Cochrane’s Q test evaluated heterogeneity in the MR data, while MR-PRESSO test checked for horizontal pleiotropy. To assess the association’s sensitivity, A leave-one-out approach was utilized to evaluate the sensitivity of the association. The IVW analysis validated that AFB is an independent risk factor for preterm labor and delivery (p < .001). Horizontal pleiotropy was unlikely to bias causality (p > .05). The likelihood of horizontal pleiotropy affecting causality was low (p > .05), and there was no indication of heterogeneity among the genetic variants (p > .05). Ultimately, a leave-one-out analysis confirmed the stability and reliability of this correlation. Our research indicated that AFB is a protective factor for preterm labor and delivery. Further research is required to clarify the possible mechanisms.

Studies concerning twins with a sociological focus are scarce in Hungary as well as international research, although the number of twin births has increased dramatically worldwide. The raising and education of twins are tasks demanding special attention from both the family and institutions. In our study we examine these aspects, looking back from adulthood, using the narrow scope of the available data from research based on the ‘Hungarostudy 2021’ database (N total: 7000; n twins: 106). Our results, corresponding to the hypotheses of educational sociology, demonstrate how the relationships between family size and school career and increasing number of siblings reduces the chances of high educational attainment. A regression analysis confirmed that both the number of siblings and a later position in the birth order reduces the chance of obtaining a higher education. For the second child in a family, the chance of earning a university degree is reduced to to 0.743. The role of a large family concerning higher education showed a stronger relationship in the case of twins compared to nontwins. For twins, the sibling pattern has a decisive effect in educational attainment. Twins themselves have a 1.449 times higher chance of obtaining a higher education compared to nontwins (p = 0.101), and fraternal twins have half (0.517) the chance of obtaining a higher education compared to identical twins; but both results are not significant (p = 0.156).

This study starts with a simple model by which Hardy-Weinberg proportions are attained in a single generation while maintaining gene frequencies. The question of differentiating between random and non-random mating is explored by simulation. Sample mating proportions are generated using the model as base. The difficulty of differentiating between random and non-random mating is illustrated.

Between 2006 and 2021, the Hungarian Twin Registry (HTR) operated a volunteer twin registry of all age groups (50% monozygotic [MZ], 50% dizygotic [DZ], 70% female, average age 34 ± 22 years), including 1044 twin pairs, 24 triplets and one quadruplet set. In 2021, the HTR transformed from a volunteer registry into a population-based one, and it was established in the Medical Imaging Centre of Semmelweis University in Budapest. Semmelweis University’s innovation fund supported the development of information technology, a phone bank and voicemail infrastructure, administrative materials, and a new website was established where twins and their relatives (parent, foster parent or caregiver) can register. The HTR’s biobank was also established: 157,751 individuals with a likely twin-sibling living in Hungary (77,042 twins, 1194 triplets, 20 quadruplets, and one quintuplet) were contacted between February and March of 2021 via sealed letters. Until November 20, 2022, 12,001 twin individuals and their parents or guardians (6724 adult twins, 3009 parents/guardians and 5277 minor twins) registered, mostly online. Based on simple self-reports, 37.6% of the registered adults were MZ twins and 56.8% were DZ; 1.12% were triplets and 4.5% were unidentified. Of the registered children, 22.3% were MZ, 72.7% were DZ, 1.93% were triplets, and 3.05% were unidentified. Of the registered twins, 59.9% were female (including both the adult and minor twins). The registration questionnaire consists of eight parts, including socio-demographic and anthropometric data, smoking habits and medical questions (diseases, operations, therapies). Hungary’s twin registry has become the sole and largest population-based twin registry in Central Eastern Europe. This new resource will facilitate performing world-class modern genetic research.

This Position Statement provides guidelines for health professionals who work with individuals and families seeking predictive genetic testing and laboratory staff conducting the tests. It presents the major practical, psychosocial and ethical considerations associated with presymptomatic and predictive genetic testing in adults who have the capacity to make a decision, children and young people who lack capacity, and adults living with reduced or fluctuating cognitive capacity.

Predictive Testing Recommendations: (1) Predictive testing in adults, young people and children should only be offered with pretest genetic counseling, and the option of post-test genetic counseling. (2) An individual considering whether to have a predictive test should be supported to make an autonomous and informed decision. Regarding Children and Young People: (1) Predictive testing should only be offered to children and young people for conditions where there is likely to be a direct medical benefit to them through surveillance, use of prevention strategies, or other medical interventions in the immediate future. (2) Where symptoms are likely to develop in childhood, in the absence of direct medical benefit from this knowledge, genetic health professionals and parents/guardians should discuss whether undertaking predictive testing is the best course of action for the child and the family as a whole. (3) Where symptoms are likely to develop in adulthood, the default position should be to postpone predictive testing until the young person achieves the capacity to make an autonomous and informed decision. This is applicable regardless of whether there is some action that can be taken in adulthood.

Dr H. Keith Sigmundson co-authored a seminal article (with the late Dr Milton Diamond) that revealed the truth about a highly controversial twin case. Specifically, the genitals of an infant male monozygotic twin were accidentally destroyed during a medical procedure performed to alleviate his difficult urination. The child’s parents were advised to physically and psychologically transform their twin son into a girl. Occasional reports about the case indicated that the plan was successful, but some members of the medical community were doubtful. An interview with Dr H. Keith Sigmundson, for the purpose of obtaining his unique perspective on this case, is presented. The interview is followed by a tribute to our late twin research colleague, Dr John L. Hopper, of Melbourne, Australia. A review of research on nonhuman primate twinning, an overview of a 2024 documentary film, The Accidental Twins, and a story of different looking identical twin newborns are also provided.

The global rise in twinning rates poses health challenges due to increased risks for infants and mothers. Despite the benefits, breastfeeding rates among multiples are low, with exclusive breastfeeding (EBF) particularly scarce compared to singletons. Our study focuses on the mothers of twins in a unique population in Kodinhi village, Kerala, India, known for its high twinning rates, which aims to contribute to existing knowledge of breastfeeding practices and perspectives in a high twinning environment and offer valuable insights to promote optimal breastfeeding among mothers of twins. A retrospective cross-sectional survey was adopted. Seventy-five mothers with twins under 3 years of age from Kodinhi and neighboring areas were interviewed face to face using structured validated tools. Data collection focused on quantitative data supplemented by narrative descriptions. Most women delivered preterm (57.3%), operative delivery (58.7%), and had a late initiation of breastfeeding (32.9% within 24 hours). Colostrum feed was common (86.7%). The EBF rate was 4%, with 47.9% initiating nonexclusive breastfeeding before 3 months, and most of the twins (46.6%) were breastfed for 1−2 years. Fatigue (69.9%) and low milk supply (38.7%) were chief concerns. While 16.4% of mothers opted for a tandem breastfeeding technique, many preferred consecutive feeding as tandem was challenging. Mothers in Kodinhi demonstrated commendable efforts in breastfeeding twins; despite the low rate of EBF, breastfeeding extended to 1−2 years. Evidence-based interventions and personalized support, primarily focusing on maternal perspectives of milk insufficiency, fatigue and breastfeeding techniques, are crucial for sustaining optimal breastfeeding practices among mothers of twins.

This study assessed the trends in twin births and their survival in Bangladesh by analyzing over a quarter million live births during 1970–2018, pooled from all eight rounds of the Bangladesh Demographic and Health Survey. In these five decades, the twinning rate increased by 1.5 times, from 5.8 to 8.6 twins per 1000 maternities. The decadal twinning rates varied across maternal age, parity, body mass index, household wealth index, and geographic region. The gap in decadal neonatal, infant, and under-five cumulative survival probability between singleton and multiple births was found to be closing, using Kaplan-Meier curves. Child mortality decreased by 80% and 60% in singleton and multiple births respectively. However, the absolute size of child mortality in multiple births remained six times higher than in singletons and was concentrated in the neonatal period. The share of multiple births surged in all types of child mortality. We predict a further and faster rise in multiple births in the coming decades in the face of upward trends in maternal age overlapping with higher parities, education, career prospects, contraceptive use, and the future demand-supply of assisted reproductive technology. A particular focus on the improvement of perinatal and neonatal care with wider availability is warranted. Otherwise, increased multiple births might raise child mortality and create public health challenges.

This article begins with an overview of twin research in Brazil, initiated by the University of São Paulo Panel of Twins. I met with many new research collaborators and students while on a fall 2023 four-city lecture tour in that country. A meeting with a world-famous surgeon who recently separated craniopagus conjoined twin pairs is also described. This overview is followed by summaries of twin research on binge eating, twins’ physical outcomes linked to different diets, working conditions and sickness absence in Swedish Twins and facial morphology differences in monozygotic twins. The final section of this article provides a sampling of human interest stories with important implications. They include a Michigan family forced to adopt their own twins, ethical issues surrounding the hiring of a surrogate to bear twins; twin survivors of the Israel-Hamas war, a twin pregnancy with a double uterus, and three twin pairs on the same women’s soccer team.

Placental vascular anastomoses are traditionally thought to exist exclusively in monochorionic pregnancies. However, they have been reported in dichorionic twin pregnancies as well. In turn, twin to twin transfusion syndrome (TTTS) and twin anemia polycythemia sequence (TAPS) have also been noted to impact some of these gestations. Through discussion of one such case at our institution along with a review of the available literature, we review the proposed pathophysiology of placental vascular anastamoses in dichorionic twin gestations, and aim to raise awareness of the possibility of associated pathologies in dichorionic gestations. This is an emerging area of literature that will require future study to guide prenatal surveillance and mitigate morbidity.

An overview of circumstances in which twins take the place of their co-twin is presented. Various explanations and speculations are proposed for understanding twins’ willingness to do so in certain situations. This section is followed by reviews of timely twin research, namely single versus multiple embryo transfer; neurimaging of twins with periventricular nodular heterotopia; a twin dietary comparison; and a new book of twin-related readings from Hungary. The final portion of this article concerns human interest stories that both inform and entertain. They involve valedictorian and salutatorian twins; a mother delivering twins at age seventy; twins reunited by TikTok; a new film about twins with selective mutism; and twins becoming doctors.