This project sought to examine 2 competing hypotheses: first, that twins are likely to be more prosocial by virtue of growing up with another same-age peer in the home, or second, that they are less prosocial because they have become more comfortable interacting with a same-age peer who is both genetically and environmentally similar to themselves and therefore they are less comfortable with other children who are dissimilar. Two studies were conducted to compare twins to singletons on measures of prosocial and aggressive behaviors. In Study 1, 5-year-olds (N = 91 twins and N = 152 singletons) engaged in a peer play situation with an unfamiliar, same-age, same-sex peer, and they were rated on items assessing prosocial and aggressive behaviors. Results showed that twins were less prosocial but not more aggressive than were singletons. In Study 2, which was a supplemented follow-up study of twins in Study 1, 10- to 15-year-old twins (N = 98) and singletons (N = 84) were rated by their parents on prosocial and aggressive behaviors. No significant differences were found between the groups on prosocial behavior, but twins were rated as more aggressive than singletons. Thus, in early childhood twins appear to exhibit fewer prosocial behaviors with unfamiliar peers, but this prosocial deficit was not aligned with parent-reported prosocial behaviors in adolescence. In adolescence, twins were rated by parents as more aggressive. These studies suggest that twins may be at risk for poorer social interactions in early and middle childhood.

The aim of this tertiary hospital–based cohort study was to determine and compare perinatal outcome and neonatal morbidities of pregnancies with twin–twin transfusion syndrome (TTTS) before and after the introduction of a treatment program with laser ablation of placental communicating vessels. Twenty-seven pregnancies with Stage II–IV TTTS treated with amnioreduction were identified (amnioreduction group). The data were compared with that obtained from the first 31 pregnancies with Stage II–IV TTTS managed with laser ablation of placental communicating vessels (laser group). Comparisons were made for perinatal survival and neonatal morbidities including abnormalities on brain imaging. The median gestation at therapy was similar between the two groups (20 vs. 21 weeks, p = .24), while the median gestation at delivery was significantly greater in the laser treated group (34 vs. 28 weeks, p = .002). The perinatal survival rate was higher in the laser group (77.4% vs. 59.3%, p = .03). Neonatal morbidities including acute respiratory distress, chronic lung disease, requirement for ventilatory assistance, patent ductus arteriosus, hypotension, and oliguric renal failure had a lower incidence in the laser group. On brain imaging, ischemic brain injury was seen in 12% of the amnioreduction group and none of the laser group of infants (p = .01). In conclusion, these findings indicate that perinatal outcomes are improved with less neonatal morbidity for monochorionic pregnancies with severe TTTS treated by laser ablation of communicating placental vessels when compared to treatment by amnioreduction.

Trends in the civil registration of fetal death in multiple gestations that has occurred before, but expelled from the womb after, 24 weeks' gestation are examined using England and Wales 1993–2004 registration obtained from the Office for National Statistics. Count was made of fetal death registrations in which fetus papyraceous, fetal death before 24 weeks' gestation or fetocide before 24 weeks' gestation was recorded. There were 3700 fetal death registrations among 217,595 twin, triplet and higher order multiple births in England and Wales between 1993 and 2004. In 354 (9.6%) of these fetal deaths, death was recorded as having occurred before 24 weeks' gestation. There has been a threefold increase in such fetal death registrations. It is a legal requirement of parents to register a fetal death. The definition of a fetal death that meets formal registration criteria is that the fetus is expelled from the womb after 24 weeks' gestation. However, if the fetal death occurs before 24 weeks, there is confusion, nationally and internationally, whether or not registration is legally required. Fetal death in a multiple gestation has serious clinical implications for a surviving co-conceptus and failure to inform parents of an early death in a multiple gestation may have important repercussions. Legal definition for the registration of fetal death requires international agreement and application.

Pregnancy outcome and characteristics of women who conceive following subfertility treatment remains a subject of great interest. We analyzed these variables among 199 women who delivered a registerable twin birth compared with 1773 women who delivered a naturally conceived twin birth in a population-based obstetric cohort drawn from around Oxford, England. Treatment was restricted to conceptions involving simple ovulation induction only. Treated mothers were of significantly higher social class and older, more likely to deliver girls and to be delivered by cesarean section, and significantly less likely to be smokers at the time of antenatal booking and to have delivered previous pregnancies. Pregnancy outcome was similar between the two groups for most measures, with the exception of birthweight which was lower in treated twins, though not significantly so. Overall the results are reassuring with respect to outcome in twin pregnancies following simple ovulation induction.

Chorion type is an important variable that can affect the prenatal environment of monozygotic (MZ) twin pairs, leading to differences in growth and development. In particular, vascular anastomoses between monochorionic (MC) MZ twin pairs can lead to an imbalance in nutrition between co-twins. One objective of this study was to determine whether maternal reports, hospital records or birthweight discordances found in MZ co-twins provide reliable indications of monochorionicity. The other objective was to test the hypotheses that in MZ twin pairs of known chorion type, MC twin pairs would show greater birthweight differences and greater within-pair variability in permanent tooth size than dichorionic (DC) twin pairs, reflecting greater differences in intrauterine environment between MC MZ pairs. Birthweights and tooth size data were recorded for 170 pairs of MZ Australian twins enrolled in an ongoing study of dentofacial growth and development. Chorion type based on maternal reports was compared with that based on hospital records for a subsample of 68 pairs of these MZ twins. Maternal reports were found to be unreliable for determining chorion type and hospital records often did not provide enough information to be certain about chorionicity. For 27 twin pairs with confirmed chorion type, associations were tested between birthweight discordances in MZ twin pairs and chorion type, and also between intrapair variances for tooth size and chorion type. A significant association was noted between birthweight discordance and chorion type (p <.05), with greater discordances occurring more often in MC twin pairs. Although significant heterogeneity of intrapair variances for tooth size was found in only 5 of 48 comparisons, intrapair variances for crown dimensions were greater significantly more often in MC pairs than DC pairs (p <.05). Our findings indicated that neither maternal reports nor often hospital records can be relied upon for information on chorion type. However, when analyses were performed on data for MZ twin pairs of known chorion type, we found evidence of a significant association between intrapair birthweight differences and chorion type and also between intrapair variances of dental crown measurements and chorion type. Consistent with our hypotheses, large birthweight discordances were found to occur more often in MC twin pairs than DC twin pairs, and intrapair variances for tooth size in MC twin pairs exceeded those in DC twin pairs more often than expected due to chance.

Temporal variations in the stillbirth rate among singletons, twins and triplets in Sweden between 1869 and 1967 were studied. Both among single and multiple births there were marked secular decreasing trends in the stillbirth rates. Based on our long time series since 1869, this study confirms that among twins and triplets the stillbirth rate was higher among same-sexed than among opposite-sexed sets. Comparisons between the stillbirth rates among twin births in urban and rural regions indicate higher stillbirth rates in rural areas. In addition, the stillbirth rates among twins of unmarried mothers were higher than those of twins of married mothers. These findings also hold for both same-sexed and opposite-sexed twin pairs. Analyses of the stillbirth rates for singletons and for different types of twins indicate that up to 1950 the risk of stillbirth among males was almost constantly between 15% to 20% higher than among females. After that the difference in the risk decreased. Comparisons with other populations were performed.

The Jena Twin Registry focuses on identifying twins in eastern Germany. It is based in part on registers of multiple births and data from registration offices, and in part on a volunteer sample approached by media calls and twin clubs. The Jena Twin Study of Social Attitudes (JeTSSA) is the first study based on the Jena Twin Registry. In a sample of 226 monozygotic and 168 dizygotic adult twin pairs, self- and independent reports of significant others (peers, spouses, parents) are collected to estimate genetic and environmental effects on social attitudes and the covariation of genetic influences on personality traits and social attitudes. In addition, the effects of measured environmental variables on attitude formation are examined.

This article conceptualizes the child as having active agency in the constructions of their social worlds, and reports on a study that understands the twin experiences from the perspectives of the twins. It examines how twins account for their relationships with their co-twins. The study drew on accounts of 60 twin children — 10 monozygotic (MZ), 10 dizygotic (DZ) same-sex, 10 DZ opposite-sex pairs — aged 5 to 10 years and their parent (n = 30). The children engaged in a sticker activity in which they represented their friendships, including their friendship with their co-twin. Using the task as a resource, the children were asked about their friends, the attributes of friendship and examples of everyday friendships encounters. These were audio-recorded and transcribed. Further, parents completed a questionnaire that provided demographic information and asked parents about the children's social experiences including twin children's time spent together, shared interests and their co-twin relationship. Using data from the pictorial representation from the sticker task and parent questionnaires, differences in relationship between MZ, DZ same-sex and DZ opposite-sex twins were examined and used to select a smaller sample for detailed study. DZ same-sex twins tended to view their co-twin less favorably and there was a nonsignificant trend in which conflict was elevated, compared to the other two groups. Based on these findings, the transcripts selected for analysis focuses on the DZ same-sex girls. The girls reported that they had differences of thought, activity and self-presentation. Conflict, competition and challenge as types of social interaction were described, suggesting that the everyday relationship of the twin with her co-twin is always being negotiated and realigned. Evident here is the complexity of social interactions in which the twins engaged everyday with each other.

The rapid increase in twinning rates in developed countries has increased interest in the question as to whether twin mothers have higher mortality and more health problems than mothers of singletons. Here we use a national survey, the Office for National Statistics Longitudinal Study of England & Wales, and a linkage between the Danish Twin Registry and the Danish population register to examine mortality patterns after age 45 (50 for fathers) for twin parents and the whole population born from 1911 to 1950. For England and Wales, presence of limiting long-term illnesses and self-rated health status was also investigated. Overall similar health and mortality was found for twin parents and the whole population although both life table methods and survival analysis suggested a slight excess mortality among older cohorts of twin mothers in England and Wales.

The combination of an onphalocele, an anterior thoracic wall defect and an anterior diaphragmatic defect constitutes classical Cantrell's pentalogy. We present a case of Cantrell's pentalogy diagnosed prenataly in twins with conventional and three-dimensional sonography.

After briefly recapitulating two earlier German twin studies (BiLSAT and GOSAT), we present two new German twin studies with a longitudinal perspective: CoSMoS and TwinPaW. The twin study on Cognitive ability, Self-reported Motivation and School performance (CoSMoS) aims to investigate predictors and influences of school performance in a genetically sensitive design, beginning with children in late elementary school. The Twin study on Personality And Wellbeing (TwinPaW) focuses on adult personality and its relation to physical health as well as health-related behavior in an adult sample of twins. Both studies are characterized by an effort to recruit new large twin samples through a novel recruitment procedure aimed at reducing self-selective sampling. In two German federal states, contact information on persons born on the same day and with the same name was retrieved from record sections. From the resulting pool of more than 36,000 addresses we contacted approximately 2000 parents of twins aged 9 and 10 for CoSMoS, as well as 2000 adult twin pairs for TwinPaW by telephone and mail. Personal contact by telephone proved to be more efficient with agreement rates of 63% in the children sample and 65% in the adult sample. In this article we briefly describe the rationale and the study aims of CoSMoS and TwinPaW as well as the characteristics of the sample we have recruited so far.

This study aimed to evaluate the prevalence of birth-weight discordance among twins, to determine the risk cut-off point for birthweight discordance, and to clarify whether perinatal deaths are aggravated by birthweight discordance or by low birthweight itself. A population-based analysis of all twins born between 1995 and 1999 in Japan was conducted using data collected from national birth, death and stillbirth certificates. Birthweight discordance was determined as: higher birthweight minus lower birthweight divided by higher birthweight multiplied by 100. Among twins with a birthweight discordance of more than 15%, the fetal and perinatal mortality rate was higher than that of twins with a discordance of less than 15%. Ninety per cent of the relative cumulative frequency of twin live-births were within 25% of the birthweight discordance. Logistic regression analysis showed that the stillbirth of at least one of the twins is associated with the birthweight of the larger twin and birthweight discordance. It also showed that the stillbirth of both twins in the twin pair is associated with the birth-weight of larger twins and the gestational weeks. It was clarified that birthweight discordance was associated with the stillbirth of only one twin in the twin pair, and the stillbirth of both twins in the twin pair was associated with low birthweight itself.

Current early diagnosis, surveillance and intervention options make it hard to determine the natural course of twin pregnancies, especially regarding spontaneous preterm delivery and perinatal mortality. We studied the natural course in monochorionic (MC) and dichorionic (DC) twin pregnancies in a historical cohort. Twin pregnancies were studied in a unique database of 651 twin pairs born in the period 1907 to 1938. We examined the effect of chorionicity on gestational age, birthweight, peri-natal mortality, intertwin birthweight differences, the incidence of preeclampsia and maternal mortality. Perinatal mortality was 27.7% for MC and 15.8% for DC twins (p < .001). Gestational age and birthweight were stronger predictors of perinatal mortality than chorionicity. Perinatal outcome was poorer for the second twin, especially in DC twins. Delivery before 37 weeks of gestation occurred more often in MC twin pregnancies (48.8% compared to 33.3% in DC twin pregnancies). DC twins were on average 288 g (95% confidence interval 201–376) heavier than MC twins. Severe birthweight discordancy occurred equally in MC and DC twins (18.1%). However, if present, mortality was only increased in MC twins. The birthweight of girls was not affected by the presence of a male co-twin. In this historical cohort MC twin pregnancies had a higher perinatal mortality, caused by a high incidence of low birthweight mainly due to preterm delivery. Mortality did not differ in deliveries after 31 weeks of gestation, which is in contrast to recent data. Apparently, modern obstetrics is more effective in reducing mortality in DC twins.

Two observations suggest a genetic similarity among close friends: (1) the observed similarity among friends in certain traits and behaviors; (2) the evidence that many of these traits and behaviors have a genetic component. This hypothesis is tested using monozygotic (MZ) twins, dizygotic (DZ) twins, full biological siblings, and their best friends from the National Longitudinal Study of Adolescent Health (Add Health). Whether the resemblance between MZ twins' friends is larger than that between friends of DZ twins and full siblings is investigated with respect to 4 individual traits or behaviors: grade point average (GPA), AHPVT (the version Peabody Picture Vocabulary Test [PPVT] designed for Add Health), aggressive behavior, and depression. Our hypothesis is supported in analyses among same-sex friends (not among different-sex friends) for GPA, aggressive behavior, and AHPVT.

Behavioral problems in young children can be assessed by asking their parents or teachers to rate their behaviors. Genetic analyses of parental ratings show relatively large heritabilities for emotional and behavioral problems in young children, but data from teachers for this age group are scarce. Sources of variation in the Teacher's Report Form (TRF) problem scales were examined. The TRF was completed for 211 Dutch 5-year-old twin pairs and 4 single twins. Twins rated by different teachers had higher means and variances than twins rated by the same teacher, in addition twin correlations were lower in this group. In both groups monozygotic (MZ) correlations were generally higher than dizygotic (DZ) correlations. A model for twin resemblance was tested that allowed for these effects. For 5 problem scales (Withdrawn, Social Problems, Aggressive Behavior, Rule Breaking Behavior and Attention Problems) a model with genetic and unique environmental sources of variation fitted best to the data. For 3 problem scales (Anxious/Depressed, Thought Problems and Somatic Complaints) there were familial influences but it was not possible to distinguish between common environmental influences or genetic influences. Heritability was 63% for Attention problems, around 45% for Withdrawn, Social Problems, Aggressive Behavior and Rule Breaking Behavior, and around 30% for Anxious/Depressed, Thought Problems and Somatic Complaints.

The goals, prospects and methods of the Longitudinal Israeli Study of Twins (LIST) are described. This study is interested in children's prosocial development from phenotypic, genetic and environmental perspectives. It focuses on measuring prosociality with a multi-trait multi-method approach, and relating it to children's general cognitive and sociocognitive abilities, and to parenting in the family. Other variables of interest such as children's temperament and parental values are discussed, as are ideas for further research.

This study was performed to determine the rates of breastfeeding among singletons, twins and triplets in Japan, and identify factors associated with the decision to breastfeed or bottle-feed. We analyzed a database of medical check-up of infants aged 3 to 6 months between April 2001 and July 2004 in Nishinomiya City in Japan. This medical check-up is given to almost 100% of infants in Japan and the data of 15,262 infants were analyzed. Among these, 14,963 (98.0%) were singletons, 290 (1.9%) were twins and 9 (0.1%) were triplets. Exclusive breast-feeding was chosen by 6680 (43.8%) mothers, mixed-feeding by 4645 (30.4%) mothers, and bottle-feeding with formula milk only by 3900 (25.6%) mothers. The rate of exclusive breastfeeding among twins or triplets was significantly lower than among singleton babies: 4.1% among twins or triplets, and 44.7% among singletons. Moreover, twins and triplets were independently associated with a higher rate of bottle-feeding: the odds ratio indicated that mothers who had twins or triplets were 2.44 times more likely to choose bottle-feeding with formula milk only than those who had singletons. Sucking ability at birth was associated with a higher rate of bottle-feeding: the odds ratio indicated that mothers who had infants with poor sucking ability at birth were 1.56 times more likely to choose bottle-feeding as those who had infants with normal sucking ability.

One way to achieve the large sample sizes required for genetic studies of complex traits is to combine samples collected by different groups. It is not often clear, however, whether this practice is reasonable from a genetic perspective. To assess the comparability of samples from the Australian and the Netherlands twin studies, we estimated Fst (the proportion of total genetic variability attributable to genetic differences between cohorts) based on 359 short tandem repeat polymorphisms in 1068 individuals. Fst was estimated to be 0.30% between the Australian and the Netherlands cohorts, a smaller value than between many European groups. We conclude that it is reasonable to combine the Australian and the Netherlands samples for joint genetic analyses.

There are only a few reports of fetal parvovirus infection in the circumstance of a twin pregnancy. We report a case of differential fetal infection following maternal parvovirus B19 infection in a dichorionic twin pregnancy culminating in a dual live-birth. A 32-year-old woman was diagnosed with parvovirus infection following exposure to her infected child at 19 weeks' gestation in a dichorionic twin gestation. Maternal IgG seroconversion was documented and maternal blood parvovirus B19 DNA was detected by PCR testing. Fetal monitoring with serial ultrasound assessment was instituted. At 25 weeks' gestation Twin I (male) displayed minor ascites, small pericardial effusion, placentomegaly and oligohydramnios. Middle cerebral artery peak systolic velocity (MCA PSV) studies were abnormal. Twin II (female) was sonographically unremarkable. A single fetal intravascular transfusion for Twin I was performed (pretransfusion Hb 80 g/L). Twin I fetal blood parvovirus B19 DNA was detected by polymerase chain reaction (PCR) and serum demonstrated both B19 IgG and IgM. Following fetal transfusion the hydrops resolved, although the placentomegaly persisted. Two live infants were delivered at 37 weeks' gestation. Individual neonatal venepuncture detected B19 DNA by PCR in Twin I but not in Twin II. B19 IgM was present in Twin I but not Twin II. Both neonates had B19 IgG antibodies. Placental histopathology demonstrated mild edema for Twin I but no inclusion cells. The placenta of Twin II was unremarkable. This case demonstrates the ability for differential transplacental infection of this virus and the assistance of fetal MCA flow studies to guide therapy in a multiple pregnancy at risk of parvovirus infection.

Population-based studies in twins have been of insufficient size to explore the relationship between risk of cerebral palsy and intrauterine growth. Earlier studies in singletons have suggested an optimum size at birth for minimum cerebral palsy risk between the 75th and 90th percentiles of weight for gestational age. We aggregated data from nine European cerebral palsy registers for 1976 to 1990. Using sex-specific fetal growth standards for twins, a z score of weight-for-gestation was derived for each of the 373 twin cases. The rates of cerebral palsy in each z-score band were compared to the rate in the a priori reference band of 0.67 to less than 1.28 (equivalent to the 75th to less than 90th percentiles). In twins born at 32 weeks' gestation or more (92% of all twins), cerebral palsy rates were higher for both light and heavy-forgestation babies compared to an optimum (i.e., minimum risk) in the reference band. However, the rate ratio for heavy babies (90th percentile or greater) did not reach conventional (95% confidence intervals [CI]) statistical significance (rate ratios = 1.76; 90% CI 1.02–3.03). For twins born at less than 32 weeks, the significantly higher risk for cerebral palsy was observed consistently in all z-score bands less than average compared to the reference band. This multi-center study demonstrates that for twins born at 32 weeks' gestation or more, an increased risk of cerebral palsy is associated with deviations from optimal intrauterine growth at about 1 standard deviation above mean weight, as was earlier reported for singletons. For twins born at less than 32 weeks' gestation, this pattern is only demonstrable for babies weighing below the optimum weight-for-gestation.