This study was performed to examine the main characteristics of the French Romulus twin population: zygosity, chorionicity, sex, term and birthweight. A sample of 104 pairs of twins was distinguished by zygosity, chorionicity and sex, and divided into concordant and discordant birthweight groups. Fifty-three % (n = 55) of the fetus pairs studied were born at “ideal term” (35-38 weeks), and 25% (n = 26) were delivered at “preterm” (28-34 weeks). The very preterm (< 28 weeks), and “postterm” (> 38 weeks) represented altogether 22% (n = 23) of the sample. Of the 104 twin pairs, 68% (n = 71) differ by less than 15% in birthweight, and 32% (n = 33) have a birthweight difference higher than 15%. In dizygotic (DZ) pairs females had more tendency to be in the discordant group (p = 0.01) while in monochorionic-monozygotic (MC-MZ) pairs males were more discordant (p = 0.07). We found a significant interaction between sex and zygosity type (p = 0.02). Males had a birthweight difference significantly weaker than that of females in dichorionic-monozygotic (DC-MZ) and DZ twins whereas it was higher than that of females in MC-MZ twins. There were no MZ twin pairs with DC placentation over than 15% birthweight difference. Log linear analysis demonstrated a three-way interaction (p < 0.05) between term type, zygosity type and hypotrophy. Our data indicate that in the group of twins born between 35 and 38 weeks' gestation the crucial question still remains unsettled on how term and birhweight are related to zygotism and/or chorionicity.

We attempted to define parental anxiety in a population of parents of high-risk premature twins (mean birth weight 1.493 ± 227 kg; mean gestational age 33 ± 3.5 weeks), admitted to III level NICU. We specifically examined the following factors: gestational age of the twins, whether or not the twins had ventilatory support, pulmonary sequelae, major malformations or intra-ventricular hemorrhage, parental gender and highest level of education obtained by the parent. In the immediate pre-discharge period and a month later, a questionnaire (State-Trait Anxiety Inventory) was given to all parents of premature twins presenting for the discharge. The parents of 30 twins entered the study twice, at the discharge of their first twin (mean postnatal age 40 ± 32 days), and one month later. They included 15 mothers and 11 fathers, aged 33 ± 5.5 and 33 ± 4.2 years, and at the second evaluation 11 mothers and 10 fathers, respectively. As case-controls we examined parental anxiety of fifteen consecutive singleton high-risk prematures, with equal gestational age, discharged immediately after. Our results indicate that the parents of high-risk twin and singleton prematures present an elevated, lasting state-trait anxiety level. Pre- and post-discharge parental anxiety is more elevated (not significant) in twinning with respect to the prematurity alone. When assessed separately by parental gender, in both these groups an increased (not significant) anxiety was persistently found in the mothers. We recommend that, although neonatologists generally define the discharge of the high-risk premature based upon the acquired stabilization of vital parameters, they pay special attention to the twin group we have identified which is at increased risk for predischarge parental anxiety.

The stillbirth rates decreased to 2/3 for MZ male twins, 1/2 for MZ female twins, and under 1/2 for DZ twins for both sexes during the 19-year period from 1975 in Japan. The stillbirth rate was significantly higher in MZ males than MZ females in each year, whereas stillbirth rates of DZ twins for both sexes indicated similar values during that period. After 1986, stillbirth rates were more than 2 times higher in MZ twins than in singletons and in DZ twins. The higher stillbirth rate of MZ twins as opposed to DZ twins could be related to monochorionic twin pairs in MZ twins. The stillbirth rate decreased more drastically in twins for both zygosities than in singleton births during the 34-year period from 1960. However, declining rates of stillbirths may be attributed to medical care during twin pregnancies. Recommendation of an optimum day to give birth for twin pregnancy is 37-38 weeks for Japanese women.

Race, sex, nutritional status and cultural factors affect craniofacial morphogenesis. Out of these, sex is a major factor in craniofacial differentiation, because it can be stronger in one ethnic group and weaker in another. In this study, sex differences in genetic variance and heritability of 13 craniofacial traits are investigated. The study is based on a sample of 45 MZ and 101 DZ twin pairs and their 125 singleton siblings, 104 fathers and 103 mothers in 146 families drawn from an urban population of Chandigarh. Results of t'-tests for equality of the means reveal association of zygosity with the mean value of bigonial diameter in female twins and for none in males. Heterogeneity of variance is observed in about 50% traits in females as compared to 15% in males. This invalidates conventional within-pair genetic variance estimates for these traits. The revised genetic variance ratios are higher on an average in males than in females. However, there is greater MZ environmental covariance in male twins than their female counterparts. Family data indicate higher maternal effect for ear height, nasal height and frontal breadth, while greater paternal effect is seen in cranial traits. Sex-wise midparent-child regression coefficients show greater heritability in daughters for nasal traits and bigonial breadth, while sons show higher genetic component for head size measures.

It is generally held that there are genetic factors for dizygotic (DZ) twinning, but the pattern of inheritance is far from clear.

We report on a rare pedigree with three sets of spontaneous DZ female twin births in three successive generations. To our knowledge no similar pedigrees have been reported in literature.

Zygosity determination in three pairs of twins was performed with ABO, MN and Rh blood groups from erythrocytes and with STR analysys from samples of saliva.

In our pedigree, the direct trasmission of the DZ twinning through the maternal line seems show an autosomal dominant pattern of inheritance. We believe that the inheritance of DZ twinning appears to be recessive in most case and autosomal dominant only in rare instances. It is plausible with the hypothesis that the expression of the dizygotic twinning trait in a mother shows a genetic heterogeneity.

A case of monoamniotic monochorionic (MAMC) female twins, with one twin being anencephalic, and the co-twin being normal, is reported. Twin to twin transfusion syndrome was also noted. The reasons for anencephaly in association with monozygotic (MZ) twinning are discussed. The management of such a case is presented.

Il termine LISREL e l'acronimo di LInear Structural RELationship ed è nato inizialmente come nome di un software messo a punto dallo svedese Karl Joreskog e dai suoi collaboratori nei primi anni '70 per stimare, col metodo della massima verosimiglianza, i coefficienti strutturali dei modelli basati su sistemi di equazioni strutturali.

Tali modelli, nella elaborazione tramite il LISREL, rappresentano la sistemazione logica, prima ancora che statistica o computeristica, di tecniche di analisi multivariata le cui prime proposte risalgono all'ininzio del secolo; riconducendo ad un unico modello che ne costituisce una geniale sintesi, approcci ed itinerari scientifici fino ad allora distinti e non comunicanti, quali l'analisi fattoriale, i modelli causali e i modelli di misurazione. In particolare rappresentano in questo momento la più completa e sistematica risposta al problema di operazionalizzare in termini di ricerca e di verifica empirica, nel campo delle scienze sociali, la controversa, ma non per questo meno fondamentale, nozione di causalità. Essi sono quindi la reinterpretazione, sistemazione e soprattutto generalizzazione di quelli che negli anni '60 venivano chiamati i modelli causali e che nella prima metà degli anni '70 avevano conosciuto una notevole popolarità fra i sociologi soprattutto attraverso la tecnica della path analysis.