Twin–twin transfusion syndrome is a major complication of monochorionic twin pregnancies. In foetuses from monochorionic twinning the presence of increased nuchal translucency thickness (NT) has been associated with an increased risk of developing this syndrome. One of the presumed mechanisms of increased NT is early cardiac failure, indirectly indicated by abnormal blood flow in the ductus venosus. We present eleven cases of monochorionic twin pregnancies in which nuchal translucency thickness and ductus venosus blood flow evaluation was performed at 11–14 weeks. In the two cases presenting with nuchal translucency discrepancy between the two foetuses along with anomalous ductus venosus blood flow in the foetus with increased nuchal translucency, twin–twin transfusion syndrome (TTTS) eventually developed. In none of the twins displaying no inter-twin difference in NT measurements and in those with discrepant NT but normal flow in both ductus venosus, was the progression to TTTS observed. In the two cases which developed TTTS, foetoscopic laser coagulation of the vascular anastomosis was successfully carried out at 18 weeks and normalisation of the venous return was registered. These findings suggest that the association of increased NT and abnormal flow in the ductus venosus in monochorionic twins may be an early manifestation of haemodynamic imbalance between the donor and the recipient eventually manifested as twin–twin transfusion syndrome. Further studies, however, are necessary to establish the potential role of the combination of NT and ductus venosus blood flow assessment as a screening method for TTTS. Twin Research (2000) 3, 65–70.

This paper intends to demonstrate that the conservative management of triplet pregnancy after delivery of one foetus is a feasible and reasonable approach. Three cases of triplet pregnancy with successful conservative management after miscarriage of one foetus, are presented and compared with cases in the literature. The route of delivery, as well as the role of tocolysis, cerclage, prophylactic antibiotic therapy and corticosteroids are discussed. Guidelines for conservative treatment are proposed. The deliveries of our three pregnancies were delayed by 63, 44 and 22 days respectively. Foetal and neonatal evolution are normal in five of the remaining foetuses. Only one intrauterine death is observed. No maternal complications with sequelae are reported. After abortion of the first triplet, contractions often persist and the birth of the two remaining foetuses may be unavoidable. Nevertheless, in our experience, confirmed by some reports in the literature, prolongation of the pregnancy after expulsion of the first foetus is possible. It can be achieved by cervical cerclage associated with tocolytic and antibiotic therapy. This management is not associated with significantly increased foetal-maternal morbidity. Twin Research (2000) 3, 71–75.

A case is presented of pregnancy and delivery of triplets following intracytoplasmic sperm injection (ICSI) therapy. Although the outcome was satisfactory, with the birth of normal children free from any malformation, most of the obstetric and particularly the neonatal complications that can be associated with this therapy are illustrated in this case. In addition, from point of view of medical costs, concerns are raised about the current policy of multiple embryo transfer which is directly responsible for the high rate of multiple gestations observed in the IVF/ICSI programme. The authors consequently recommend a policy of transferring not more than two embryos per treatment cycle. Twin Research (2000) 3, 76–79.

We investigated possible genetic influences on women's liability to preterm birth, using data from a large sample of Australian female twin pairs. In a 1988–90 questionnaire survey, both members of 905 parous twin pairs (579 monozygotic and 326 dizygotic) reported on whether deliveries had been more than two weeks preterm. Tetrachoric twin pair correlations for first birth were rMZ = 0.20 ± 0.11 and rDZ = −0.03 ± 0.14, and for any birth were rMZ = 0.30 ± 0.08 and rDZ = 0.03 ± 0.11. Best-fitting models to data contained only additive genetic influences and individual environmental effects. Heritability was 17% for preterm delivery in first pregnancy, and 27% for preterm delivery in any pregnancy. In the former case, however, we could not reject a model without genetic influences. Although our data did not allow for differentiation of the varying aetiologies of premature parturition, results from this exploratory analysis suggest that further investigation of genetic influences on specific reasons for preterm birth is warranted. Twin Research (2000) 3, 80–82.

The twin method has been criticised for its alleged non-generalisability. When population parameters of intellectual abilities are estimated from a twin sample, critics point to the twin–singleton differences in intrauterine and family environments. These differences are suggested to lead to suboptimal cognitive development in twins. Although previous studies have reported twin–singleton differences in intelligence, these studies had two major drawbacks: they tested young twins, and twins were compared with (genetically) unrelated singletons. To test accurately whether twin–singleton differences in intelligence exist, a group of adult twins and their non-twin siblings were administered the Dutch WAIS-III. The group was large enough to detect twin–singleton differences of magnitudes reported in earlier investigations. The data were analysed using maximum likelihood model fitting. No evidence of differences between adult twins and their non-twin siblings on cognitive performance was found. It is concluded that twin studies provide reliable estimates of heritabilities of intellectual abilities which can be generalised to the singleton population. Twin Research (2000) 3, 83–87.

Parents of 323 twin pairs with reading disability (RD) reported significantly more problems learning to read (16% of mothers and 33% of fathers) than parents of 309 twin pairs without reading difficulties (6% of mothers and 9% of fathers). These rates of self-reported reading problems in parents of twins are highly similar to those previously obtained in parents of non-twin children with RD and controls, suggesting that the etiology of reading deficits in twin and non-twin children may also be highly similar. Moreover, within both the RD and control samples, twins whose parents self-reported a positive history of reading problems had lower reading performance test scores, on average, than those whose parents reported no reading problems. Therefore, results of the present twin study support those of previous studies with non-twin children in which parental self-reports have been found to provide a valid index of family history status for reading difficulties. Twin Research (2000) 3, 88–91.

A mathematical model based on queuing theory is used to study the dynamics of environmental influence on twin pairs. The model takes into consideration genetic factors and effects of non-shared environment. Histograms are exploited as base analysed characteristics, with the method of minimum chi-square yielding estimated characteristics. The proposed technique was applied to analysis of longitudinal data for MZ and DZ twins. It was shown that the same environment impact may yield different contributions to final variances of the IQ parameters under investigation. Magnitudes of these contributions depend on the genetic factor represented by distributions of an analysed parameter at the point of birth. Twin Research (2000) 3, 92–98.

This study explores the use of an individual's genetic (IGFS) and environmental factor score (IEFS), constructed using genetic model fitting of a multivariate strength phenotype. Maximal isometric and dynamic strength measures, one maximal repetition load (1RM) and muscle cross-sectional area (MCSA) were measured in 25 monozygotic and 16 dizygotic twin pairs. The use of IGFS and IEFS in predicting the sensitivity to environmental stress was evaluated by the association of the scores with strength training gains after a 10-week high resistance strength training programme. Results show a high contribution of genetic factors to the covariation between maximal strength and muscle cross-sectional area (84–97%) at pre-training evaluation. Individual factor scores explained the largest part of the variation in 1RM and other strength measures at pre-training and post-training evaluation respectively. Genes that are switched on due to training stress (gene–environment interaction) could explain the decrease in explained variation over time. A negative correlation was found between IGFS and strength training gains (−0.24 to −0.51, P < 0.05); individuals with a high IGFS tend to gain less strength than individuals with low IGFS. Individual environmental factor scores have lower differential power. The predictive value of the IGFS has potential utility in identifying an individual's susceptibility to environmental stress in a variety of multifactorial characteristics, eg diseases and impairments, and for selection of sib pairs for QTL analyses. Twin Research (2000) 3, 99–108.

We report abnormal maternal laboratory parameters in twin-to-twin transfusion syndrome (TTTS) at mid-pregnancy. A retrospective chart review was undertaken of 109 patients with TTTS evaluated for placental laser surgery. Complete blood count (CBC), blood type and Rh factor, urine analysis and serum chemistry panel were obtained preoperatively, with the CBC and serum albumin repeated on the first postoperative day. The mean gestational age was 21.2 ± 1.7 weeks. Initial abnormal values included hematocrit (32.1 ± 3.0%), hemoglobin (11.0 ± 1.03 g/dl), serum magnesium (1.71 ± 0.17 mg/dl), total protein (6.08 ± 0.55 g/dl) and albumin (3.06 ± 0.34 g/dl). Despite minimal blood loss and conservative fluid replacement mean hematocrit, hemoglobin, and albumin were 27.3 ± 2.74%, 9.3 ± 0.94 g/dl and 2.56 ± 0.23 g/dl, respectively on postoperative day one. Weight gain (8.0 ± 5.5 lb.) and low urinary output were characteristic peri-operative events. Maternal hypoproteinemia and anemia occur in TTTS at mid-pregnancy. This may contribute independently to amniotic fluid production rates in the fetuses, and explain in part the maternal sensitivity to intravenous fluids in multiple pregnancy. Twin Research (2000) 3, 113–117.