Long-term memory (LTM) problems are associated with many psychiatric and neurological illnesses and are commonly measured using free and cued recall tasks. Although LTM has been linked with biologic mechanisms, the etiology of distinct LTM tasks is unknown. We studied LTM in 95 healthy female twin pairs identified through birth records in the state of Missouri. Performance on tasks of free recall of unrelated words, free and cued recall of categorized words, and the vocabulary section of the Wechsler Adult Intelligence Scale (WAIS-R) were examined using structural equation modeling. Additive genetic and unique environmental factors influenced LTM and intelligence. Free recall of unrelated and categorized words, and cued recall of categorized words, were moderately heritable (55%, 38%, and 37%). WAIS-R vocabulary score was highly heritable (77%). Controlling for verbal intelligence in multivariate analyses of recall, two components of genetic influence on LTM were found; one for all three recall scores and one for free and cued categorized word recall. Recall of unrelated and categorized words is influenced by different genetic and environmental factors indicating heterogeneity in LTM. Verbal intelligence is etiologically different from LTM indicating that these two abilities utilize different brain functions.

Diagnosis of a major depressive episode by the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association requires 5 out of 9 symptoms to be present. Therefore, individuals may differ in the specific symptoms they experience and reach a diagnosis of depression via different pathways. It has been suggested that depressed women more often report symptoms of sleep disturbance, appetite or weight disturbance, fatigue, feelings of guilt/worthlessness and psychomotor retardation than depressed men. In the current study, we investigate whether depressed men and women differ in the symptoms they report. Two samples were selected from a sample of Dutch and Australian twins and siblings. First, Dutch and Australian unrelated depressed individuals were selected. Second, a matched epidemiological sample was created consisting of opposite-sex twin and sibling pairs in which both members were depressed. No sex differences in prevalence rates for symptoms were found, with the exception of decreased weight in women in the sample of unrelated individuals. In general, the similarities in symptoms seem to far outweigh the differences in symptoms between men and women. This signifies that men and women are alike in their symptom profiles for major depression and genes for depression are probably expressed in the same way in the two sexes.

Hostility has been shown to be a vulnerability marker for various health problems. The present study examined genetic and environmental contributions to individual differences in hostility in South Korean adolescent and young adult twins. Seven hundred and nineteen same- and opposite-sex twin pairs aged from 13 to 23 years completed a hostility scale. The scalar sex-limitation model was applied to the data. The best fitting model indicated that 34% of the total variation of hostility was attributable to genetic factors operating in a nonadditive manner. The remaining 66% of the variance was associated with nonshared environmental influences and measurement error. These findings were largely consistent with results from previous twin studies of personality based on Caucasian twins, rendering support for the pervasive influence of genetic non-additivity on human personality traits and the generalization of the heritability of personality across human populations.

Recent research has provided strong support for the existence of a familial risk for suicide, and efforts have been made to separate genetic from enviromental risk factors. Twin studies have played a major role in the identification of genetic factors, and the results indicate that the concordance rate for suicide is higher in identical than in fraternal twins (Baldessarini & Hennen, 2004). Moreover, Segal and Roy (1995) reported a significantly higher frequency of nonfatal suicidal attempts by monozygotic (MZ) than by dyzygotic (DZ) twins whose co-twins had committed suicide. However, doubts remain as to whether the increased risk of suicide in MZ twins is a response to the intense grief over the loss of a close relative, or whether a common genotype is associated with suicidal behavior. Sudden loss, which may carry a stigma in the case of a suicide, has been linked to increased persistent emotional stress and physiological changes (Epstein, 1993; Martin & Dean, 1993). A number of researchers have reported greater suicidal ideation among bereaved MZ twins as compared to DZ twins, suggesting that a loss due to suicide may increase the risk of suicidal behavior in the surviving co-twin (Segal & Bouchard, 1993; Segal & Roy, 1995; Segal et al., 1995). The aim of the present article is to address the issue of the intense grief experienced by twins after the co-twin suicide.

The aim of this study is to examine causes of individual differences in height, weight and body mass index (BMI) in 5-year-old children registered with the Netherlands Twin Register. In addition, we examine whether the results of twin studies can be expanded to the singleton population by comparing the data from twins to Dutch reference growth data and by looking at the twins' target height, which was derived from parental height. For 2996 5-year-old twin pairs, information on height and weight and on parental height was available. Univariate and bivariate genetic analyses of height and weight and univariate analyses of BMI were conducted. In order to compare the twins to the singleton population, standard deviation scores (SDS) for height, BMI and target height were calculated based on Dutch reference growth charts for the general population from 1997. Genetic influences were an important source of variation in height, weight and BMI and the main source of covariation between height and weight. Additive genetic factors accounted for 69% and 66% of the individual differences in height in boys and girls, respectively. For weight, heritability estimates were 59% in boys and 78% in girls and for BMI 34% and 74%. The influence of common environment on height was 25% and 27%, on weight 24% and 10% and on BMI 44% and 12% in boys and girls. The bivariate model showed a large overlap between the genes influencing height and weight. Genes explain 78% (in boys) and 76% (in girls) of the covariance between weight and height. At the age of 5 years, female twins were as tall as singleton children, while male twins were shorter than singletons. For both boys and girls, however, mean height SDS was 0.6 standard deviation scores below the mean target height. All twins had lower BMI than singletons. Twins grow fairly well compared to singletons, but they grow below their target height. This may be due to the above average height of twin parents.

We tested the hypothesis that energy intake among women with twin pregnancies decreases in late gestation, as the uterus enlarges and they become increasingly uncomfortable. We asked women to recall dietary intake for the previous 24 hours, every 2 weeks from around 29 weeks of gestation, using a photographic atlas and other strategies to estimate portion size. Eighty women provided data at around 29, 31, 33 and 35 weeks of gestation. We calculated total energy intake, and energy intake from carbohydrate, fat and protein. Data were log transformed to reduce skewness. Using mixed effects linear regression models, we found minimal evidence that total energy intake changed over this time period, either before or after adjustment for potential confounding factors (95% confidence interval for relative change per week: −1.4%, 0.6%). There was weak evidence of a small decline in carbohydrate intake over time, both before and after controlling for energy intake. We cannot exclude change in energy intake or diet composition before 29 weeks or after 35 weeks of twin gestation.

Twin pregnancies are becoming common as a result of increased assisted reproduction. Studies have shown that the smaller twin of a pair is at greater risk of morbidity and mortality. Our aim was to determine if there is a relation between birth-weight discordancy and neonatal morbidity and mortality and to test the occurrence of respiratory distress syndrome (RDS) in discordant twins. For 5 years all twins admitted to our intensive care unit were included in the study. Discordance was calculated as the difference between twins' weights divided by the heavier weight. Diagnosis of RDS was made by typical clinical and radiographic methods. Multiple logistic regression was performed with gender, weight order and birth order as the independent variables and RDS as the dependent variable. Two hundred and sixty-six twin pairs with a mean gestation of 33 weeks and a mean birthweight of 1890 g were evaluated. Multiple logistic regression revealed that being the heavier twin was a more important risk factor for RDS (odds ratio 4.5; 95% confidence interval 2.2–9.2) than being the male or second-born twin. Based on neonatal outcomes a birthweight discordance equal or greater than 20% in twin pairs was accepted as the discordance criterion. Discordant and concordant groups were statistically different in neonatal mortality, necrotizing enterocolitis, polycytemia and hypoglycemia. Our data demonstrated that being the heavier twin is a risk factor for RDS and a birth-weight difference of 20% or more in twin pairs should be accepted as discordance.

The purpose of this study is to present curves of estimated placental growth in twins and to evaluate the relative contribution of gestational age, zygosity, chorionicity, fusion of the placentas, sex of the individual and of the twin pair, site of the umbilical cord insertion, birth order, maternal age, and parity. Perinatal data and placental data were obtained from 6315 live-born twin pairs from the East Flanders Prospective Twin Survey. Of 4318 twin pairs, with no missing values, the placental weights of different gestational ages were analyzed using a nonlinear multivariate Gaussian regression. Two groups were distinguished: (1) twins with two separate placentas, and (2) twins with only one placental mass (one placenta in case of monochorionic twins or two fused placentas in case of dichorionic placentas). Overall, placental weight was influenced by gestational age, fusion of the placentas, and parity. In the case of one placental mass, monozygotic dichorionic twins had the lowest weights. If two separate placentas were present, birth order played a role in favor of the first-born twin. For parity and zygosity, the differences were most pronounced between 27 and 29 weeks, whereas the difference for birth order was most pronounced between 33 and 37 weeks. In conclusion, basic physiological characteristics, routinely examined at birth, influence placental weight. Taking these covariates into account allows a better evaluation of the placental weight given a gestational age, as an indicator of growth.

We sought to estimate levels of risk for stillbirth subtypes associated with twin gestations among pediatric mothers (10–14 years). Analysis was on twin pregnancies covering the period 1989 to 2000 in the United States. We classified stillbirth as term, preterm, small-for-gestational-age (SGA) or preterm-SGA. We then assessed the risks of these stillbirth subtypes in pediatric mothers using two comparison groups consisting of women aged 15 to 19 years old (adolescent mothers) and 20 to 24 years old (mature mothers). Adjusted risk estimates were by means of hazard ratios generated from a Cox proportional hazards regression model. We adjusted for dependence of observations within twin clusters using the robust sandwich estimator. The rate of stillbirth was highest among pediatric mothers (56/1000), followed by adolescent gravidas (29/1000) and lowest in mature mothers (20/1000; p for trend < .01). Overall, preterm stillbirth was the most frequent stillbirth phenotype while term stillbirth was the least frequent. Not a single case of term stillbirth was recorded in pediatric mothers. Among pediatric gravidas, the risk for preterm stillbirth was more than tripled (adjusted hazard ratio [AHR] = 3.4; 95% confidence interval [CI] = 2.5–4.6), and that of preterm-SGA stillbirth more than doubled (AHR = 2.6; 95% CI = 1.8–3.7) that of mature mothers respectively. The 30% risk elevation for SGA stillbirth among pediatric mothers was not found to be statistically significant (AHR = 1.1; 95% CI = 0.3–4.3). Pediatric motherhood is a risk factor for stillbirth in twin gestation, especially, preterm and preterm-SGA stillbirth phenotypes. Prevention of stillbirth among this category of mothers should target the period preceding full term.

The stillbirth rate in twins is a more sensitive indicator of environmental hazards than the stillbirth rate in singletons. Medical care or other socioeconomic factors may be more influential for perinatal survival in twin than in single deliveries. Studies have indicated that stillbirths among children in a set of multiple maternities are not independent. Models were considered assuming independent outcomes within a set of multiple maternities. Analyses of the stillbirth rates confirm that the risk of stillbirth among males is almost constantly higher than among females. Any model introduced should assume different stillbirth rates for males and females. The models were tested with both maximum likelihood and minimum χ2 methods. Data was analyzed from Sweden, the Åland Islands, Saxony, England and Wales, and significant discrepancies obtained from the independence models. The same-sexed twin data contain both monozygotic and dizygotic twin sets with apparently different stillbirth rates. Consequently, for same-sexed twins the proposed model could be considered too simple. After improvement by splitting the same-sexed data into monozygotic and dizygotic twin sets, the dependence still remains. The proportion of both same-sexed and opposite-sexed twin pairs that contain two stillborn is greater than what the stillbirth rates and the independence should indicate. Consequently, stillbirth rate estimates based on the relative frequency of twin sets with two stillborn children have a positive bias. When the stillbirth rate decreases, the number of sets with two stillborn children decreases more slowly than would be indicated by independence.

The aim of this study was to compare maternal and neonatal outcome of twin births according to mode of delivery and to isolate the factors predicting a successful vaginal delivery and those predicting a failed trial of labor (TOL) leading to an emergent cesarean section. We reviewed all twin deliveries during the years 1995 to 2004. Parameters studied include maternal age, parity, gestational age, maternal antepartum complications and postpartum complications, fetal presentations, birthweight, mode of delivery of each twin, Apgar scores and cord pH. During the study period there were 40,710 deliveries of which 804 (1.9%) were twin deliveries. Of the 804 twins, 398 (49.5%) had planned cesarean sections (PCS) and 406 (50.5%) entered a TOL. Maternal age and parity were similar among the groups. Neonatal outcomes and postpartum complications did not differ between the groups. Of 406 women who had a TOL, 84.9% eventually delivered both twins vaginally. A significantly higher percentage of antepartum complications were noted among those who failed the TOL compared to those with successful TOL (8.2% vs. 1.7%, p =.01). The number of neonates with pH of less than 7.0 did not differ between the groups although more neonates (2.5% vs. 0.4%, p =.05) among the failed TOL had an Apgar score of less than 7.0 at 5 minutes compared to successful TOL. Vaginal delivery of both twins after TOL occurred in 91% of vertex/vertex compared with 71.8% of vertex/nonvertex presenting twins ( p < .01). Neonatal outcomes did not differ between both groups. Our results indicate that both vaginal and PCS are comparable options for vertex presenting first twin regardless of second twin presentation.

Ovarian hyperstimulation syndrome (OHSS) is a serious complication of assisted reproduction techniques using in vitro fertilization and intracytoplasmic sperm injection (IVF/ICSI). Its etiology has still not yet been fully resolved. Human chorionic gonadotrophin, administered exogenously as well as produced endogenously during pregnancy, is responsible for the onset of OHSS, and high levels of estradiol appear to worsen the condition. In this case series, the course of mild to severe OHSS was evaluated in 19 intact twin pregnancies after IVF/ICSI. Another serious complication associated with OHSS is thromboembolic events. In these cases, the pregnancy can be protected through anticoagulation treatment, but there may be exceptions to this. This series includes a case of bilateral thrombosis of the internal and external jugular veins in the 7th gestational week in a twin pregnancy after OHSS and ICSI, with termination of the pregnancy in the 9th gestational week due to progressive thrombosis during anticoagulation therapy.

Acephalus acardia is among the most severe malformations described in fetuses, with an incidence of about 1 in 35,000 births and is due to twin-to-twin transfusion syndrome, frequently occurring in monochorionic twin pregnancies. The severity of the syndrome depends upon the type of the anastomoses arising between the vascular networks of the two fetuses, usually configuring the ‘twin reverse arterial perfusion syndrome’. No clear and univocal etiological explanation is known, though few cases with chromosomal abnormalities have been reported so far. In some cases the fusion of two or more separate placentae of dizygotic fetuses occurs, leading to monochorionic twinning. Few cases of acardius amorphous with complete autoptical examination have been described so far. We report a case of acephalus acardius amorphus fetus, showing features of extremely severe sistemic immaturity with very few structured organs. Defined external and autoptic examinations have been performed on the dismorphic twin, along with the histological examination of tissue samples. Kariotype analysis showed sex discrepancy between the twins, as a normal female kariotype had been detected in the acephalus acardius while the living co-twin was a normal healthy male. The analysis of the placenta showed the vascular anomalies leading to the twin-to-twin transfusion syndrome.