There were 150 deliveries of twin pregnancies over 26 weeks in our hospital. The incidence of twin pregnancies was 1.0% in a population consisting of Greek nationals. Seventy five (50%) were term at delivery whereas 75 (50%) were premature (mean gestational age at delivery 36.5 weeks). The birth weight at delivery ranged from 350 grs to 4,050 grs with mean birth weight for the 1st and 2nd twin of 2,404 grs and 2,384 grs, respectively. One hundred and forty four (48%) neonates had weights between 1,501 to 2,500 grs. Twenty two (9.57%) neonates had weights between 1,501 grs to 2,500 grs. The perinatal mortality when birth weights exceeded 1,500 grs was 7.32%. In total, 186 (62%) newborns were delivered vaginally and 114 (38%) by cesarean section. Forceps were used in 4.33% of the cases and breech extraction was performed in 2.33%. The mode of delivery and perinatal mortality rates were not correlated for both twins (p>0.05). The most common causes of death were hyaline membrane disease (48.5%), immaturity (18.2%), congenital abnormalities (15.1%), septicemia (12.1%) and asphyxia (6.06%). Prematurity seems to constitute the most common cause of perinatal deaths while the mode of delivery found to be irrelevant to perinatal mortality.

The polymorphisms of constitutive heterochromatin regions, present on chromosomes 1, 9, 16 and Y, are inherited in a Mendelian fashion. The C-band heteromorphism has been reported to be associated with various types of cancer. Heterochromatin is considered to play a role in protecting genome against the mutagens. Changes in the quantity and proportion of the different types of satellite DNA might increase the genetic susceptibility in people with heterochromatic variations, which in turn cause chromosome instability and predispose the individual to cancer. We report a case of bilateral retinoblastoma with complete absence of pericentromeric heterochromatin on one of the chromosomes number 9. A similar deficiency of pericentromeric heterochromatin on chromosome number 9 and 16 has been reported in a phenotypically normal individual and a Down syndrome case, respectively. This deficiency was found to be inherited from the father in all the three cases. Complete absence of pericentromeric heterochromatin of chromosome 9 is not being reported in association with cancer syndromes. Further studies are necessary to understand the role of this factor in normals and in those with cancer susceptibility, specially with retinoblastoma and the paternal origin of this deficiency.

Objective. To test the hypothesis that the (case) twin later to succumb in utero has biparietal diameter measurements (by ultrasound) different from those (control) twins surviving the perinatal period.

Material and methods. Information from the Medical Birth Registry, National Board of Health and Welfare, Stockholm, was used to identify all births in a defined population in southern Sweden with about 20,000 deliveries each year. In 3,019 twin pregnancies between 1973 and 1989, one or both twins were stillborn in 47 cases (gestational duration ≥28 weeks, birthweight ≥500g.). For each case pregnancy, two control pregnancies were selected, the matching criteria being: same delivery unit, same parity (0, I, II, III+), similar year of delivery (± 1 year) and maternal age (± 5 years). Data on ultrasound examinations were extracted from the original medical records. Screening in early second trimester started at one of the units as early as 1973 and at the latest of 12 units in 1982.

Results. There was no obvious difference between cases and controls in intra-pair discordant biparietal diameter (BPD) measured in early second trimester. Nor was there any evident difference in the rate of deviant BPD between cases and controls. In all, 8% of dead male and 24% of dead female fetuses were by definition small-for-gestational age (<-2 standard deviations).

Conclusions. No significant difference was seen between cases and controls regarding deviating biparietal diameters. Abdominal diameter may be a better predictor of subsequent fetal death (not analysed in this study), though only about 15% of all dead twins were deemed small-for-gestational age.

Trends of twinning rates were analyzed using vital statistics in Austria, Finland, Norway, Sweden, Canada, Australia, Hong Kong, Israel, Japan, and Singapore during the period from 1972 to 1996. The twinning rates increased significantly year by year in each country. During these periods, the twinning rate increased by twenty percent in Austria and Canada, and by sixty percent in Norway and Sweden. The twinning rate was 1.6 times higher in Sweden than in Hong Kong in 1972 and by eighty percent in Israel in 1995. Twinning rates were higher in European countries, Canada, and Australia than in Asia. The variations of the twinning rates among countries were not only due to biological factors, but also to assisted reproductive techniques. In Australia, the overall twinning rate was 1.3 times higher in the nuptial births (14.1 per 1000 births) than in the ex-nuptial births (10.7) during the period 1994-1996. As for maternal age, twinning rates in Sweden increased year by year for maternal age groups except the youngest and the oldest age groups. In Sweden, the rising twinning rate has been attributed to the higher proportion of mothers (for the 25-39 year old age groups) treated with ovulation-inducing hormones and attributed to in-vitro fertilization.

234 pairs of twins were studied from pregnancy up to 21 years of age on the basis of records from maternity hospitals, neonatal wards and children's health centres and questionnaires filled in by the parents when the twins were aged 2-10 and 12-21 years, and by the twins themselves at age 12-21. 74 twins were personally interviewed about human relationships in their families and with the Present State Examination (PSE) at age 15-21.

When the evaluation of parental preference was made by the parents, the mother's favourites had learned to speak earlier and were more often the psychic leader of the pair, but they more often had sleeping difficulties and other psychosomatic symptoms in adolescence. They were most often scored in class 2-3, non-specific neurotic symptoms in the PSE, but none of them was placed in the higher classes of possible or probable psychiatric disorder. Mothers seem to develop a tighter affectionate bond towards their favourites than do fathers, thus inducing a good basic trust and faster language acquisition in childhood, but probably also transient non-specific neurotic symptoms in adolescence in face of the developmental task of entering autonomous adulthood. The father's favourites were more often the physical leaders of the pair, showed less accident proneness and most often reported tendencies towards autonomy from their co-twins, thus indicating that the fathers' attitudes may be more encouraging towards independence. As the least psychosomatic symptoms were seen in twins in the intermediate position regarding parental preference, it seems reasonable that the division of twins between parents on the grounds of favouritism should not be strict.

I gemelli sono i rappresentanti di un'eccezione biologica della specie umana, di un avvenimento fuori dal consueto, per cui il parto della donna non dà origine ad un nuovo essere, ma a due o più rappresentanti della specie. Questa eccezione è così evidente e caratteristica che non ha mancato, come non manca, di impressionare l'intelligenza e la fantasia dell'uomo presso ogni popolo e in ogni epoca della storia.

Anche il sapere medico, prima ancora che si organizzasse in scienza, ha fermato la sua attenzione sul fenomeno della gemellanza cercandone la causa e le applicazioni.

Secondo la scienza Talmudica la nascita dei gemelli è dovuta al fatto che una goccia di sperma si è divisa in due parti. Del pari Ippocrate ritiene che il concepimento gemellare avvenga per la bipartizione dello sperma e ciascuna parte penetri in una delle due corna dell'utero. Nell'antichità classica il fenomeno della gemellarità fu riportato al caso delle formazioni doppie dovuto, secondo Empedocle, ad un eccesso dello sperma emesso in una sola volta, dovuto invece, secondo Democrito, allo sperma emesso in più volte, ad ognuna delle quali corrisponderebbe un embrione.

Secondo Aristotele invece, le mostruosità doppie «sarebbero originate da un fenomeno di concrescenza per il quale due embrioni, dapprima separati, vengono a fondersi parzialmente, in modo da costituire una sola formazione, nella quale però sono riconoscibili le due componenti».

Galeno sembra accettare l'ipotesi di Empedocle, aggiungendo tuttavia che il calore eccessivo dell'utero possa dividere il seme in più parti, donde originerebbe formazioni doppie, triple, ecc… Plinio non aggiunge nulla di nuovo alle idee dominanti e si limita a fornire descrizioni più o meno esaurienti di gravidanze multiple.

A case of balanced X; autosome translocation 46, X, t (X; 22) (q 24; q 13) in a 25-year-old female with secondary amenorrhea and premature ovarian failure (POF) is described. The relationship between balanced X; autosome translocation [t (X; A)] and varied phenotypic expression observed in these women is discussed. This case highlights the importance of early recognition of these women in order to give them the best chance of conception in their oligohypomenorrhic phase before complete loss of gonadal function.