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PubMed1988

Diabetes mellitus in twins: a cooperative study in Japan. Committee on Diabetic Twins, Japan Diabetes Society.

In 1984, the Japan Diabetes Society organized a committee to collect data on diabetic twins in Japan. Within 3 years, through correspondence with Society members and hospitals, the Committee had contacted 87 pairs of twins, one or both of which had diabetes mellitus or glucose intolerance. Sixty-three pairs were monozygotic and 24 dizygotic. The probands, who had been diagnosed as diabetic or glucose-intolerant earlier, included 21 patients with insulin-dependent diabetes mellitus (IDDM), 56 with non-insulin-dependent diabetes (NIDDM), one with an unknown type of diabetes, and nine with glucose intolerance. Concordance between monozygotic twins was 45% for IDDM and 83% for NIDDM; between dizygotic twins, concordance was 0% (0/10) for IDDM and 40% (4/10) for NIDDM. Concordance was significantly greater in NIDDM than in IDDM, and in monozygotic than in dizygotic twins. Concordance was greater among twins in which one twin had developed diabetes after the age of 20 than among twins in which the age of onset had been earlier. There was no evidence that the period of discordance was shorter in the discordant pairs than in the concordant pairs. About 90% of the IDDM twin pairs lived together, against 20% of the NIDDM pairs, probably due to the later age of onset of NIDDM. The frequency of diabetes in family members other than the twins was higher in NIDDM than in IDDM regardless of concordance. In concordant pairs the presence or absence of various complications agreed in 68-97%; a few pairs were discordant for the severity of retinopathy, which may have resulted from differences in duration and hyperglycemic degree. A 75-g glucose tolerance test administered to the 'normal' discordant twins revealed borderline glucose intolerance in two of six IDDM co-twins and six of eight NIDDM co-twins. The early-phase insulin response was low in two of six IDDM co-twins and four of six NIDDM co-twins. These results are generally consistent with previous reports of diabetic twins in Western countries, reinforcing the importance of genetic factors in the pathogenesis of diabetes. Heredity has a particularly strong influence in NIDDM.

Adolescent↗
PubMed1995

Birth order, delivery route, and concordance in the transmission of human immunodeficiency virus type 1 from mothers to twins. International Registry of HIV-Exposed Twins.

BACKGROUND: We evaluated data from prospectively identified twins to understand better the mechanisms and covariates of mother-to-infant transmission of human immunodeficiency virus (HIV). METHODS: Using data obtained from an international collaboration and multivariate quasilikelihood modeling, we assessed concordance, birth order, route of delivery, and other factors for HIV infection in 115 prospectively studied twin pairs born to HIV-infected women. Actuarial methods were used to evaluate overall survival and survival free of acquired immunodeficiency syndrome for HIV-infected twins. RESULTS: Infection with HIV occurred in 35% of vaginally delivered firstborn (A) twins, 16% of cesarean-delivered A twins, 15% of vaginally delivered second-born (B) twins, and 8% of cesarean-delivered B twins. In a multivariate model, the adjusted odds ratios for HIV infection were 11.8 (confidence interval: 3.1 to 45.3) for concordance of infection with the co-twin, 2.8 (confidence interval: 1.6 to 5.0) for A versus B twins, and 2.7 (confidence interval: 1.1 to 6.6) for vaginally delivered versus cesarean-delivered twins. Among A twins, 52% (lower confidence limit: 6%) of the transmission risk was related to vaginal delivery. Comparing vaginally delivered A twins (infants most exposed to vaginal mucus and blood) to cesarean-delivered B twins (infants least exposed), 76% (lower confidence limit: 48%) of the transmission risk was related to vaginal exposure. Infected B twins had slightly reduced Quetelet indexes and more rapid development of illnesses related to acquired immunodeficiency syndrome. CONCLUSIONS: These results indicate that HIV infection of B twins occurs predominantly in utero, whereas infection of A twins (and, by implication, singletons) occurs predominantly intrapartum. We propose that intrapartum transmission is responsible for the majority of pediatric HIV infections and that reducing exposure to HIV in the birth canal may reduce transmission of the virus from mother to infant.

Birth Order↗
PubMed2002

[Epidemiology of twin and twin with birth defects in China].

OBJECTIVE: To investigate the incidence of twin and twin with birth defect (BD) and with neural tube defect (NTD) in China. METHODS: A prospective monitoring was conducted among the perinatal infants born in 945 hospitals in 20 provinces/municipalities/autonomous regions in China during the period from 1 October 1986 to 30 September 1987 to count up the numbers of twins and of twins with BD or NTD. RESULTS: 1 243 284 infants were born during this period. Among these perinatal infants there were 12 715 pairs of twins with an incidence of 10.23%. The incidence rates of twin with BD and of twin with NTD were 36.81% and 5.27% respectively. There was no difference in incidence rate of twin among different parts of the country and between urban area and rural area. The incidence rate of twin was the highest among the women aged 20 approximately 39, among primipara, and in October and November. The incidence rate of twin with BD showed no difference among different seasons, parities, and parts of the country and between urban area and rural area. Most of twin with BD occurred at the age 20 approximately 39. Most twins with NTD were born in the northern provinces and rural area. The incidence rate of twin with NTD was correlated with season, most twins with NTD being born in November, and was no correlated with age and parity of the mother. CONCLUSION: The incidence of BD, especially the incidence of NTD, among twins is significantly higher than that among total perinatal infants in China. Prenatal monitoring is important for twin pregnancy.

Birth Order↗
PubMed1994

Twin resemblance in somatotype and comparisons with other twin studies.

Twin resemblance in somatotype components was considered in 28 male and 34 female monozygotic (MZ) twin pairs and 19 male and 21 female dizygotic (DZ) twin pairs, 9.3-23.5 years of age. The Heath-Carter anthropometric somatotype method was used. Mean somatotypes of male twins and female twins did not differ, whereas male twins were significantly more mesomorphic than female twins. Twin resemblance was evaluated in two ways: first, treating each somatotype component independently of the other two (as in earlier twin studies), and, second, looking at resemblance in each somatotype component after statistically controlling for the other two components (thus treating the somatotype as a composite). Intraclass correlations were consistently higher in MZ than in DZ twins of both sexes, and within-pair variances were consistently lower in MZ than in DZ twins of both sexes. However, after controlling for the effects of the other two somatotype components, within-pair variances of male MZ and DZ twins for each somatotype component did not differ. In general, Heath-Carter anthropometric somatotype components show (1) significant resemblance in MZ and DZ twins within each sex, although the degree of resemblance is altered in male twins when a different analytic strategy is used, (2) no sex difference in degree of resemblance, and (3) greater resemblance within MZ twin pairs than within DZ twin pairs. These results are compatible with the presence of genetic variation affecting physique in adolescents and young adults.

Adolescent↗
PubMed1995

The new Danish Twin Register: establishment and analysis of twinning rates.

BACKGROUND: Twin registers provide a valuable source for research into disease causation. The existing population-based registers comprise mostly old twins. In order to be able to study diseases which occur in childhood and youth a new Danish twin register has been established. METHODS: The register is based on the Danish Civil Registration, with information on number of twin births from the Danish Vital Statistics Office as the source of validation. All twins resident in Denmark at 1 March 1991 were sent a one-side questionnaire asking about diabetes, willingness to participate in other research projects and similarity in the twins. RESULTS: The register, comprising 20,888 twin pairs, covers 74.4% of all twin pairs born 1953-1967 (incl.) and 97.4% of those born 1968-1982 (incl.). The response rate to the questionnaire study was 92.3%. The responders represented 19,180 twin pairs distributed as 5304 monozygotic pairs, 6861 same-sex dizygotic pairs, 6244 opposite-sex dizygotic pairs and 771 pairs of unknown zygosity. Of the respondent twins, 96% declared their willingness to participate in additional studies. An analysis of trends in the twinning rates for the years 1968-1982 showed that the rate of monozygotic twinning is increasing and the twinning rate of opposite-sex twin pairs is decreasing. CONCLUSIONS: Earlier estimated trends in twinning rates have been confirmed. Due to the high response rate and opportunities for linkage with other Danish registers, the present material provides a valuable resource for twin studies in diseases and human traits.

Adolescent↗
PubMed1994

Funipuncture for evaluation of hematologic and coagulation indices in the surviving twin following co-twin's death.

OBJECTIVE: To examine the changes in hematologic and coagulation indices in the surviving twin when the co-twin dies because of the twin-twin transfusion syndrome. METHODS: Fetal blood was obtained by funipuncture in seven surviving twins upon the death of their co-twins. Five of them were monochorionic. In one case at 32 weeks' gestation, two repeated funipunctures were done in both twins before and in the surviving twin after the death of the co-twin. Fetal blood was examined for blood coagulation factors as well as complete blood counts. RESULTS: Although coagulation factors were not abnormal, three of the five monochorionic surviving twins had cerebral abnormalities postnatally. The fetal blood profile revealed anemia in the surviving twin, especially in the cases in which funipunctures were performed within 24 hours after the co-twin's death. This demonstrates that acute anemia in the surviving twin was induced by hemorrhage from the larger to the smaller twin at the time of death. CONCLUSION: Following the death of one twin, morbidity in the surviving twin can be produced by hypotensive ischemia of the brain due to hemorrhage through placental vascular anastomoses.

Blood Coagulation↗
PubMed2003

Communication between identical twins: health behavior and social factors are associated with longevity that is greater among identical than fraternal U.S. World War II veteran twins.

BACKGROUND: Longevity is greater for identical twins than for fraternal twins from the same population. Factors that are explanatory for this difference are not known. METHODS: Multivariate survival analysis is applied to current mortality data for 26,974 male twins with known zygosities of the National Academy of Science-National Research Council World War II Veteran Twins Registry, and this analysis is applied to their health and social behavior and personal histories, as collected from two survey questionnaires distributed in 1967 and 1983 (with 14,300 and 9475 responses received, respectively). To explain this difference in longevity, social, health, and personal history factors are evaluated for associations with longevity. RESULTS: Survival functions of identical and fraternal twins differed significantly (p<.0001). Median lifetimes were 82 years for identical and 80.5 years for fraternal twins. The correlation between lifetimes of identical twin partners was greater than that of fraternal twins. For identical but not for fraternal twins, the risk of mortality was significantly lower for twin partners who communicated 1 or more times per month, compared with those who communicated less frequently (relative risk.80, 95% confidence interval 0.68-0.94, p=.008, with control for other factors associated with longevity: smoking, exercise, a current marriage, living with both parents until age 15 or older, and having a live co-twin). Distributions of communication, exercise level, and smoking prevalence were more beneficial with regard to longevity for identical than for fraternal twins as a group. CONCLUSIONS: Frequent communication between identical but not fraternal twin partners, and both level of exercise and prevalence of smoking, distributed more beneficially in terms of longevity for identical compared with fraternal twins, are explanatory for the greater longevity of identical than fraternal twins.

Aged↗
PubMed1993

North-American twins with IDDM. Genetic, etiological, and clinical significance of disease concordance according to age, zygosity, and the interval after diagnosis in first twin.

In 224 twin pairs (132 monozygotic, 86 dizygotic, and 6 of uncertain zygosity) in whom the index twin had developed IDDM before 30 yr of age, 51 of the co-twins (38 monozygotic, 10 dizygotic, and 3 of uncertain zygosity) subsequently became diabetic. On the basis of concordance ratios, which were significantly discrepant (P < 0.01) between monozygotic and dizygotic twins, the substantial genetic role in IDDM etiology is confirmed. For the monozygotic co-twin of an IDDM case, the relative risk is significantly related to an early age at proband diagnosis (P < 0.01 for 0-4 vs. 5-9 yr of age). However, among monozygotic co-twins at any age, IDDM risk decreases as time passes after the proband diagnosis (P < 0.01 for 0-23 vs. > or = 24 mo after a proband diagnosis at 5-9 yr of age). Moreover, a structural-equation analysis suggests a profound contribution to liability (as much as 79%) from the twins' shared environment. Risk to like-sex male dizygotic co-twins is as high as that to monozygotic co-twins, significantly higher than that to like-sex female dizygotic co-twins (P < 0.005), and even higher than that to male co-twins in unlike-sex dizygotic pairs (P < 0.05). Overall, the risk to the dizygotic co-twin of a case is significantly higher (P < 0.001) than that to a non-twin sibling, as reported in the literature. The observed male excess is consistent with reported patterns of IDDM in experimental animals, and in certain circumstances in humans. Taken together, these observations suggest an important early acquired determinant of IDDM, independent of genetic determinants. On the basis of Kaplan-Meier IDDM-free survival curves, if the proband is diagnosed before 15 yr of age, the long-term risk to the co-twin is estimated at 44% (monozygotic) and 19% (dizygotic); it reaches 65% for the co-twin of a monozygotic proband diagnosed before 5 yr of age. An IDDM discordant period of no more than 3 yr was observed in 60% of the pairs destined to become concordant, offering a very brief window for intervention following the recognition of high risk.

Age Factors↗
PubMed2005

The long term neurologic outcome of children from pregnancies complicated by twin-to-twin transfusion syndrome.

OBJECTIVE: To assess long term outcomes of children from pregnancies complicated by twin-to-twin transfusion syndrome. DESIGN: Comparison of children from pregnancies with twin-to-twin transfusion syndrome in Western Australia with a contemporaneous regional comparison cohort of preterm and term infants studied using an identical assessment procedure. POPULATION AND SETTING: All infants aged > or =18 months were identified from a geographically based longitudinal cohort of monochorionic twin pregnancies with an antenatal diagnosis of twin-to-twin transfusion syndrome conducted prospectively since 1992. METHODS: Children were evaluated using age-specific developmental and behavioural assessments. Cerebral palsy was diagnosed clinically and ascertainment confirmed through the Western Australian Cerebral Palsy Register. MAIN OUTCOME MEASURES: Intellectual disability, cerebral palsy, behavioural and cognitive function. RESULTS: Fifty-two children were identified as eligible for study and assessments were performed on 49 (94%). Three surviving children had a diagnosis of cerebral palsy (5.8%). The mean IQ score was 8 points lower in twin-to-twin transfusion syndrome children compared with the comparison cohort although this was mainly due to a decrement of 13 points in those born before 33 weeks of gestation. There was no difference between the donor and the recipient twin in terms of IQ scores (median difference -3, 95% CI -9 to 6). There was no relationship of IQ score to the worst stage of the twin-to-twin transfusion syndrome. Child Behavior Check List and Vineland Adaptive Behavior Scale scores did not differ between twin-to-twin transfusion syndrome children and the comparison group. CONCLUSIONS: Twin-to-twin transfusion syndrome is associated with a significant reduction in IQ score in very preterm survivors. There seems to be no increase in the prevalence of cerebral palsy. Overall behaviour and adaptive behaviour scale scores are similar to a comparison group.

Cerebral Palsy↗
PubMed2005

Increasing cardiac output and decreasing oxygenation sequence in pump twins of acardiac twin pregnancies.

An acardiac twin pregnancy is a rare but serious complication of monochorionic twinning and consists of an acardiac twin and a pump twin. The acardiac twin is a severely malformed fetus that lacks most organs, particularly a heart, but grows during pregnancy because it is perfused by the developmentally normal pump twin via a set of arterioarterial and venovenous placental anastomoses. Pump twins die intrauterine or neonatally in about 50% of the cases. Because the effects of an acardiac mass on the pump twin's development are incompletely known, methods for outcome prognosis are currently not available. We sought to derive simple relations for the pump twin's excess cardiac output and decreased oxygenation and to use available clinical cases for a preliminary test of the model. As a method, we used a theoretical flow model to represent the fetoplacental circulation of an acardiac twin pregnancy and estimated blood deoxygenation and reoxygenation following perfusion of the two bodies and placentas, respectively. The results show the pump twin's excess cardiac output and decrease of venous oxygen saturation to depend on the ratio of pump twin to acardiac twin umbilical blood flow, whose ratio can be measured by ultrasonography. The clinical cases show a decreasing umbilical flow ratio with gestation. In conclusion, prospective serial study is necessary to test whether measurement of umbilical flow ratios allows monitoring the pump twin's pathophysiologic development, possibly resulting in a guideline for prognosis of pump twin survival.

Abnormalities, Severe Teratoid↗
PubMed2003

Twins and non-twin siblings: different estimates of shared environmental influence in early childhood.

Twin studies typically indicate shared environmental influence for cognitive abilities, especially in early childhood. However, across studies, DZ twin correlations tend to be greater than non-twin sibling correlations, suggesting that twin estimates of shared environment are to some extent specific to twins. We tested this hypothesis in a sample of more than 1800 MZ and 1800 same-sex DZ pairs from the Twins Early Development Study (TEDS), a study of twins born in England and Wales in 1994 and 1995. For this analysis, we obtained comparable data from more than 130 same-sex younger siblings of the twins. Twins and their younger siblings were assessed for language, cognitive abilities and behavior problems by their parents at 2 and 3 years of age. For language and cognitive measures at both 2 and 3 years, but not for behavior problems, estimates of shared environment were more than twice as large for twins as compared to non-twin siblings. We conclude that about half of twin study estimates of shared environment for cognitive abilities in early childhood are specific to twins. Although many possibilities exist for explaining the special shared environment effect for twins, we suggest that cognitive-relevant experiences that are not shared by siblings are shared by twins because they are exactly the same age.

Chi-Square Distribution↗
PubMed2005

Co-twin dependence modifies heritability of abstinence and alcohol use: a population-based study of Finnish twins.

The role of co-twin dependence (twins' closeness or reliance on the co-twin) was examined as a moderator of genetic and environmental influences on alcohol use in adolescence and early adulthood in a large longitudinal population-based study of Finnish twins (FinnTwin16). The associations between co-twin dependence and alcohol use were studied first at an individual level in adolescence (n = 3362) and early adulthood (n = 2912). Then, maximum likelihood models were fit to the two waves of data from same-sex twin pairs to assess the differences and changes in genetic and environmental influences on alcohol use (abstinence, drinking frequency, intoxication frequency); N = 1342 pairs in adolescence, and N = 1078 pairs in early adulthood. Overall, no significant associations were found between co-twin dependence and individual alcohol use. However, co-twin dependence importantly modulated genetic effects on drinking habits, especially in adolescence, but also in early adulthood. Co-twin-dependent twins reported greater similarity in their alcohol-related behavior across all alcohol-use measures at both time points, and the role of genes and environments varied according to co-twin dependence. Shared environmental factors explained most of the variation in drinking among co-twin-dependent twins in adolescence and contributed to drinking to intoxication during early adulthood. In contrast, among co-twin-independent twin pairs, genetic variance contributed significantly to all alcohol-use measures at both time-points. An interdependent sibling relationship is an important modifier of drinking habits, and it appears to reduce the impact of inherited liabilities on alcohol-related behavior especially in adolescence.

Adolescent↗
PubMed1996

A population-based study of cancer risk in twins: relationships to birth order and sexes of the twin pair.

One thousand and sixty-three twins with cancer whose co-twin was born alive were identified among patients born since September 1939 with cancers incident in England and Wales during 1971-1984 at childhood and young adult ages. Site-specific risks of cancer were analysed in relation to birth order within the twinship and sexes of the twin pair, using adjusted national birth data to give control distributions of these variables. Risk of leukaemia was increased in first-born twins, risk of testicular cancer was increased in second-born twins with female co-twins but decreased in second-born twins with male co-twins and lung cancer risk was increased in first-born twins with same-sex co-twins. Cutaneous melanoma risk was increased in persons with opposite-sex co-twins, nervous system cancer risk was increased in females with opposite-sex co-twins and Hodgkin's disease risk was increased in persons with same-sex co-twins. For most of the findings, no previous comparable analyses are available, so interpretation of the results must be provisional until the analyses can be repeated on other data. The result for leukaemia would accord with previous suggestions that leukaemia may be of prenatal origin and may sometimes lead to intrauterine death. The Hodgkin's disease result would fit with theories of an infectious aetiology, and this view is strengthened by reanalysis of previous data on paralytic poliomyelitis in twins, which show a pattern similar to that for the Hodgkin's disease patients. Cancer risk in relation to birth order and sex of twins can give novel, objective data relating to prenatal and infectious disease aetiology of cancers.

Adult↗
PubMed1999

The relation between inter-twin birth weight discordance and total twin birth weight.

OBJECTIVE: We tested the hypothesis that the frequency of growth discordance among twins is not related to the uterine capacity for carrying twins. METHOD: We counted and compared the frequencies of birth weight discordance of more than 25% in an unlike-sexed twin cohort (n = 1244) and in a population-based twin cohort (n = 7570) across the deciles of the total twin birth weight (twin A + twin B) distribution. The birth order of the heavier twin was noted. RESULTS: Similar frequencies of discordant pairs were found in both cohorts (11% and 12%, respectively; Mantel-Haenszel chi2 test: P = .131, odds ratio (OR) 0.9, 99% confidence interval (CI) 0.67, 1.11; Woolf test for heterogeneity: two-tailed P = .472). In the discordant pairs, twin A was considerably more often the heavier twin in all birth weight deciles (unlike-sexed cohort: P < 10(-8), OR 5.9, 99% CI 3.0, 11.7; population-based cohort: P < 10(-8), OR 3.1, 99% CI 2.3, 4.0), and in both cohorts (inter-cohort difference: P = .109, OR 1.4, 99% CI 0.83, 2.32). Both cohorts showed a similar nonlinear trend: given that X = decile order, discordance decreased as a function of 22.0 - 6.54 ln[X] for the unlike-sexed twins cohort and 23.0 - 8.18 ln[X] for the population-based cohort, with r values of 0.967. CONCLUSION: The more favorable the uterine milieu for carrying twins, the smaller the likelihood of discordant twin growth. Birth order of the heavier twin appears to be an integral part of the discordance phenomenon. The similarity of the cohorts suggests that these conclusions are valid for both like and unlike-sexed twins.

Birth Weight↗
PubMed2003

Long-term neurodevelopmental outcome in twin-to-twin transfusion syndrome.

OBJECTIVE: The purpose of this study was to determine the long-term neurodevelopmental outcome in children after twin-to-twin transfusion syndrome. STUDY DESIGN: Maternal and neonatal medical records of all twin-to-twin transfusion syndrome patients who were admitted to our center between 1990 and 1998 were reviewed. Neurologic and mental development at school age was assessed during a home visit in all twin-to-twin transfusion syndrome survivors. RESULTS: A total of 33 pregnancies with twin-to-twin transfusion syndrome were identified. Four couples opted for termination of pregnancy. All other pregnancies were treated conservatively, 18 pregnancies (62%) with serial amnioreductions and 11 pregnancies (38%) without intrauterine interventions. Mean gestational age at delivery was 28.6 weeks (range, 20-37 weeks). The perinatal mortality rate was 50% (29/58 infants). The birth weight of the donor twins was less than the recipient twins (P<.001). Systolic blood pressure at birth was lower in donors than in recipients (P=.023), and donors required inotropic support postnatally more frequently than did recipients (P=.008). The incidence of hypertension at birth was higher in recipients than in donors (P=.038). Abnormal cranial ultrasonographic findings were reported in 41% of the neonates (12/29 neonates). All long-term survivors (n=29 neonates) were assessed during a home visit. Mean gestational age at birth of the surviving twin was 31.6 weeks (range, 25-37 weeks). The mean age at follow-up was 6.2 years (range, 4-11 years). The incidence of cerebral palsy was 21% (6/29 infants). Five of 6 children with cerebral palsy had an abnormal mental development. The incidence of cerebral palsy in the group of survivors who were treated with serial amnioreduction was 26% (5/19 infants). Four children were born after the intrauterine fetal demise of their co-twin, 2 of which had cerebral palsy. CONCLUSION: The incidence of adverse neurodevelopmental outcome in twin-to-twin transfusion syndrome survivors is high, especially after the intrauterine fetal demise of a co-twin.

Brain↗
PubMed2003

Challenges in recruiting older twins for the Sri Lankan twin registry.

The National Twin Registry of Sri Lanka was established in 1997 as a volunteer register. To extend it to a population-based register, we examined the effectiveness of tracing older twins by inspecting birth records and recruiting them by postal invitation and in-person contact. Birth records at a divisional secretariat reported from 2 maternity hospitals between the years of 1954-1970 were scrutinised to identify a random sample of twins. These hospitals had the highest twin delivery rates for the whole country. We identified 620 twins and a questionnaire was mailed to them. Research assistants visited a cohort of non-respondents (71) in the postal survey. These 620 twins were identified after perusing 20700 birth records. The twinning rate was estimated at 29.95 ([620/20700] x 1000) twins per 1000 registered births (CI 27.63-32.27). In the postal survey, 37 (12%) responded and 62 letters were returned (20%). Both twins were still alive in 20 pairs, one was still alive in 15 pairs, and both twins were dead in 2 pairs. During field visits, 42 (59.2%) addresses were located. Information was available on 16 twin pairs. Both twins were alive in 8 pairs, one each in 4 pairs, and both were dead in 4 pairs and at least one twin was traced in 10 pairs (14%). Both the postal and the field survey gave a low yield. This finding is different from tracing younger twins born between 1985-1997 by using the same methods. Migration, urbanization and development in the country might have affected tracing older twins from the birth record addresses, which were decades old.

Birth Certificates↗
PubMed1998

Similarity of social security numbers among twins: data from the Virginia Twin Registry.

At least two twin registries in the United States have been or are being assembled using the similarity of Social Security Numbers in computerized records to help identify possible twin pairs. While the success of such enterprises depends directly on a high probability of twinness given Social Security Numbers, there are theoretical and practical reasons to study the probability of Social Security Number similarity given twinness. For example, the number of twin pairs with similar Social Security Numbers obviously determines the maximum number of twin pairs that can be discovered by similarity algorithms. To study this issue, we examined the similarity of known Social Security Numbers in twin pairs from the Virginia Twin Registry by age, sex, race, and zygosity of the pair. We found that similarity between the Social Security Numbers of twin pairs varies markedly by age, and MZ twin pairs have significantly more similar Social Security Numbers than DZ pairs at all ages. Among older twins, there are also significant differences by sex and race. For younger twins, algorithms that identify putative twin pairs on the basis of the similarity of their Social Security Numbers hold the promise of being able to identify a large proportion of all true twin pairs. Such algorithms will be substantially less successful, however, in identifying a large proportion of older twin pairs.

Adult↗
PubMed1990

Twinning in cattle: III. Effects of twinning on dystocia, reproductive traits, calf survival, calf growth and cow productivity.

An evaluation of natural twinning in beef cattle revealed that cows birthing twins had shorter (P less than .01) gestation lengths, more (P less than .01) retained placentas, more (P less than .01) dystocia, more (P less than .01) days to estrus, lower (P less than .01) conception rates and more (P less than .01) days to pregnancy than cows birthing singles. Days to estrus, conception rate and days to pregnancy were not affected by number of calves reared (1 vs 2) in cows birthing twins. Survival at birth was greater (P less than .01) for single- than for twin-born calves, but twins and singles did not differ (P greater than .05) in postnatal survival. When dystocia was experienced, calf survival at birth was 95% vs 73% for singles vs twins compared with 99% vs 92% when no dystocia was experienced. Calves born twins were lighter (P less than .01) at birth, 100 d and 200 d, but twins and singles did not differ in postweaning gains. Total calf weights at 100 d per cow calving were 12% greater (P less than .01) in cows birthing twins vs singles when twin calves reared by foster dams were excluded. The potential increase in cow productivity for total calf weight at 100 d is 40% if calf survival rates of twins with dystocia relative to survival rates of twins without dystocia were comparable to survival rates of singles with and without dystocia, and if cows birthing twins were fed and managed to obtain conception rates equal to those of cows birthing singles. Identification of cows gestating twins to provide for their higher prepartum nutritive requirements and calving assistance at parturition is necessary to make twinning in cattle an economically viable technology.

Age Factors↗