The small size of most reported triplet series has resulted in conflicting statements about the influence of several clinical variables on triplet birth weight. Therefore, obstetrical and neonatal data were collected on 196 mothers and their 580 infants (8 stillbirths excluded). Gestational age was based on the date of fertilization in 13 IVF triplets and on the date of ovulation in 90 medically induced triplets. Obstetrical and ultrasonic criteria were used to estimate the date of confinement in 93 spontaneous triplets. Birth weight appeared to be higher in males and with higher maternal parity, independent of gestational age. The apparent effect of medical technologies such as ovulation induction or IVF on combined triplet birth weight disappeared when maternal parity and fetal gender were controlled. Preeclampsia, maternal race and zygosity were not significantly associated with birth weight. While birth order did not significantly effect ultimate birth weight, the heaviest triplet did present first more often than would be expected by chance alone. Future evaluation of neonatal outcome data in multifetal gestations should control for gestational age, fetal gender and maternal parity. It appears that triplet birth weight is not affected by etiology, which is important given the significant impact of medical technologies.

As an extension of previous work on the risk of prematurity in singletons and on the social cost of twin births, an analysis has been carried out into the cost effectiveness of preventing premature delivery in twin pregnancies. The cost of prevention is assessed in terms of early diagnosis through ultrasound screening and of an extra 11 weeks of work leave to expectant mothers. When this cost is compared to the social cost involved in the transfer of newborns to neonatal intensity care units and in supporting handicapped children, it is concluded that the total cost of prevention corresponds to one-third of the long-term costs associated to lack of prevention.

For 173 pairs of like-sex adult twins, self-assessment of zygosity was verified by laboratory diagnosis. Seventeen percent of twins who were very likely monozygous (MZ) believed themselves dizygous (DZ), frequently citing two placentas at their delivery as “evidence.” We suggest that twins be asked what leads them to their assessment of their own zygosity. For 93% of Caucasian and 89% of American Black like-sex twins in our sample, DZ twins could be differentiated based on six polymorphic markers retrievable from frozen sera. MZ twins who believe themselves DZ can be considered “environmentally DZ, genetically MZ” twins, and might be used to study genetic and environmental influences on the treatment of twins and on twins' choices of social characteristics.

Biometrical genetical techniques have been applied to the analysis of certain anthropometric characters measured in 134 pairs of adult twins. After allowing for assortative mating it appears that there is a family environment (E2) component for variation in height larger than previously reported. “Fatness” traits – weight, ponderal index, and skinfold thickness – all show higher heritabilities in males and substantial E2 components in females, and reasons for this are discussed. The same is true for cephalic index and forearm length but the reason for these differences is not so obvious. Head length shows a much higher heritability than head breadth. A larger sample of DZ opposite-sex pairs would allow more powerful discrimination, but the variety of patterns of variation revealed by the model-fitting approach used here justify its use over more traditional techniques.

Delivery records of public hospitals and local health centers were analyzed to investigate the secular trend of multiple births from 1955 to 1990 in Taiwan. Twinning rates decreased gradually from the late 1950s to 1973, slightly increased and remained stable from 1974 to 1980, and then increased strikingly from 1981 to 1990. During the study period, MZ rates were consistently higher than DZ rates except in 1986 when a higher DZ rate was observed. The highest MZ rate of 7.7 per 1,000 deliveries was observed in 1985, while the highest DZ rate of 4.6 per 1,000 deliveries was observed in 1986. The triplet incidence rate also declined from the early 1960s to 1973 and then increased markedly from 1974 to 1990. A case-control study including 482 MZ and 252 DZ twin pairs and 1,496 singletons was carried out in four teaching hospitals in Taipei City between October 1985 and June 1989 to examine factors related to twinning. The zygosity of twin pairs was determined by sex, placentation and red blood cell antigens. Multiple logistic regression analysis showed that the higher the maternal age, the lower the MZ and DZ rates, while the higher the parity, the higher the rates. There was no association of paternal age or of maternal educational level with twinning rates

Selective feticide by fetoscopic air embolism was carried out in six twin pregnancies complicated by discordance for a severe abnormality. In three, a previous diagnostic fetoscopy had been performed. The procedure was effective and uncomplicated in all cases. One patient is undelivered and five have delivered healthy babies, three at term and two preterm. One of the latter, delivered at 28 weeks, died of complications in the neonatal period.

A review of 62 cases of leukemia in twins reveals most cases occurred in MZ twins, although diagnosis of zygosity was at times admittedly questionable. Concordance was clearly highest in MZ twins of the perinatal-congenital period. This tendency was not maintained at later stages of life.

The older concept of a human placental barrier has been greatly modified. Tracer substances have demonstrated that leukemic cells pass the placental barrier. Materno-fetal transmission of leukemia is well known; all forms of murine leukemia can be transmitted similarly from generation to generation. Certain requisites effect the transmission of neoplastic-hematopoietic disease during pregnancy. Rare cases are reported of pregnant women with leukemia who bear children in whom clinical leukemia subsequently develops. The maternal diagnosis was made at the time of, or shortly after, delivery, suggesting an evolution of the maternal disease late in pregnancy.

That both partners of a pair of twins, either MZ or DZ, can become ill with leukemia within days or months of each other, appears more than coincidental. Chromosomal defects, common environmental factors, and conjoined intrauterine circulations may be important in the transmission of leukemia from one twin to another, a theory supported by the frequent concordance during the first year of life.

After having examined the literature on the subject, the A. presents the study he has carried on 60 twin-pairs with one or both twins suffering from neurosis or psychosis.

In 50 pairs a psychic suffering of neurotic type was present: out of the 20 MZ pairs, 18 were concordant with a percentage of 90%; out the 30 DZ pairs, 13 were concordant 43%.

Although discriminating the various forms and admitting the interference of environmental factors and other somato-psychic and psychogenetic causes, in 50% of the cases an undoubted psychotic and neurotic heredity was ascertained.

In the four pairs suffering from dysthymic psychosis the 3 MZ were concordant and the DZ discordant.

In the four pairs suffering from schizophrenia the MZ pair was concordant while the 3 DZ pairs were discordant.

In the two pairs of uncertain zygosity the concordance could not be extimated due to the death of the cotwin.

Dysthymia seems to be trasmitted as a dominant character and schizophrenia as a recessive.

Both dystymia and schizophrenia may undergo changes of expressivity with phenotypical characters which can be clinically mistaken as psychoneurotic forms.

The Swedish Twin Registry of the Karolinska Institute comprises about 10 000 sets of twins, and was built up in 1961-1962. It covers about 95% of all Swedish same-sexed twins that were born in the country in 1886-192 5 and were still living as unbroken pairs at the time of compilation.

The compilation procedure has been presented in detail by Cederlöf (1966a), and will be summarized as follows. Since the middle of the last century, a rather unique system for population registration has existed in Sweden. It is based not only on birth records, but also on migration records. As soon as an individual moves away from the place he lives, he has to notify the authorities as to where he moves. This system made it possible for us to follow-up any individual from his place of birth to his next place of living, and so on, until we found his current address or had to discard him as deceased. We started, in that way, with about 41 000 multiple birth records, handscreened from about 3½ million birth records from all Sweden during the period in question, and ended with a series of about 12 000 located sets of twins. Of the remainder, about 26 000 had to be discarded, due to death of one or both partners; 1 000, due to emigration to foreign countries; and 100, due to hospitalization in mental asylums, or home for aged people, etc. In the compilation procedure we lost track of about 1 100 individuals, or 1.5%.

The zygosity of the twins has been determined with the aid of some similarity questions contained in a questionnaire, mailed to all the twins in the registry. Out of several questions, one proved to be of high reliability, namely the very simple question whether the twins as children were as alike as two peas in a pod, or of family likeness only. We assumed that if both twins in a set agreed in saying that they had been as alike as two peas in a pod, the pair was MZ. If they, on the other hand, agreed in saying that they had been of family likeness only, we regarded the pair as DZ. We validated this questionnaire diagnosis by analyzing the outcome from a subsample of 200 pairs who had also been examined serologically in regard to five markers, A1A2BO, MN, Rh, Hp, and Gm. The results were reported here in Rome in 1961 and showed an agreement in diagnoses of 95% for MZ and 90% for DZ (Cederlöf et al, 1061).

An evaluation of the maternal effect on spontaneous abortion and the genetic contribution to various reproductive variables was made using like-sexed twins born between 1915–1946. Health and reproductive questionnaires were sent to 2,365 twin pairs listed in the Norwegian Twin Registry. Zygosity was determined by a questionnaire which proved to be 98% accurate in discriminating between monozygotic (MZ) and dizygotic (DZ) twins. Verification of the zygosity questionnaire was accomplished by blood cell marker zygosity determination in 200 twin pairs. Data from 428 monozygotic twin pairs (174 male pairs and 254 female pairs) were analyzed by a new model for qualitative traits and a striking maternal effect was found. The results suggested that over 54% of all women may belong to a high risk group who have approximately a 13% risk of early fetal loss. The incidence of first trimester abortions and spontaneous abortion reported by a sample of 915 like-sexed twin pairs and spouses was .079 and .089, respectively; there were no significant differences between male and female pairs.

Other reproductive variables were studied in both MZ and DZ twins including the age of menarche and menopause, the age at marriage and birth of the first child, and the interval between marriage and the first birth. These variables were examined for evidence of genetic effects and secular trends. The mean age of menarche had decreased significantly between the years 1915–1935 and 1936–1946. The secular trend appeared to be environmental in nature and accounted for more than 7% of the overall variation in age of menarche. Sixty-five percent of the variation in the age of menarche was attributed to genetic factors. The mean age of marriage and the mean age at the first birth decreased significantly between 1915–1935 and 1936–1946. Twins born between 1936–1946 also reported fewer pregnancies than did twins born between 1915–1946, but this was statistically significant among MZ twins only; no significant difference in the frequency of spontaneous abortions was found between the 1915–1935 and the 1936–1946 groups.

Although there were occasional groups in which differences were statistically significant, no general trends were identified in comparing couples who reported a spontaneous abortion with those who did not. Traits compared were: the age of menarche, age of marriage, age at first birth, the interval between marriage and first birth and the mean present age of the twins and spouses. Couples reporting a first trimester spontaneous abortion had significantly more total pregnancies than those not reporting a spontaneous abortion. Unaffected pregnancies were also significantly more numerous in couples with a spontaneous abortion compared to those without, suggesting over-compensation for fetal loss.

A maternal effect in spontaneous abortion was indicated by the correlation coefficients found; significant positive correlations were found in both MZ and DZ females but not in males. For total pregnancies and unaffected pregnancies, MZ twins, both male and female, had significant correlation coefficients while DZ twins did not.

The objective of this study was to compute yearly neonatal mortality rates (NMRs) in twins and compare these to rates in singletons during the same time period. The focus was on time trends in birthweight-specific twin mortality in the birth population of New York City during the years 1968 to 1986. The study population was all twin livebirths ≥ 500 g birthweight (N = 45,605), with a comparison group of all singleton livebirths in the same birthweight range (N = 2,191,144). Data came from the New York City Department of Health's computerized vital records on livebirths and infant deaths. Between 1968 and 1986 the crude NMR declined 39% in twins and 47% in singletons. In twins there were birthweight-specific declines of 69% to 84% between 1000 g and 2499 g. However, there was only a 19% decline in the twin NMR over 2499 g. This contrasts with a 50% decline in the singleton NMR over 2499 g. In New York City, modern medical care has been remarkably successful in lowering the NMR in low birthweight twins. However, more effort must be made to understand the etiology of perinatal problems in twins with birth weights greater than 2500 g.

Analysis of the statistics of multiple births in England and Wales between July, 1938 and December, 1945 proves that the frequency of monozygotic twin births is virtually constant, at about 3 per 1000 pregnancies, for all ages of mothers. The frequency of dizygotic twinning, however, increases with maternal age from 2 per 1000 pregnancies at 17 to a maximum of 14 per 1000 pregnancies at 38, and then decreases gradually to 5 per 1000 maternities at 45. Comparison of the average numbers of previous children to mothers at each age shows that the twin pregnancies were associated with a greater number of previous children then were the single maternities. While the reasons for this difference cannot be deduced from this data, if the tendency to multiple births is governed entirely by heredity and is independent of a woman’s parity, this greater number of previous children to mothers of twins vould indicate that the probability of repetition of a twin birth is ten times as large as he total population frequency of twins births.

Description of a family five members of which, in four generations show the syndrome mentioned in the title. The mode of inheritance is dominant, with a rather strong penetrance and a great variability in the expressivity. The importance of genetic counseling is stressed.

A total of 45 twin pairs (19 MZ and 26 DZ), with one or both members affected by essential Generalized Epileptic Attacks, have been drawn out of the Mendel Institute's twin file. Concordance was observed in 18: 19 MZ, but only in 3: 26 DZ twin pairs.

Analysis of the 18 MZ concordant twin pairs has shown (1) concordance of clinical form in 17 pairs, (2) concordance in the age of onset in 15 pairs, and (3) concordance of expression (frequency of generalized attacks) in 13 pairs.

A study has been carried-out on familial glioma, according to various data, both personal and drawn from the literature. The statistic evaluation indicates, at least in part, a probable hereditary conditioning. Out of 393 cases of glioma, three have been found to be familial, which is much more than it would be expected on the basis of statistical evidence. This should be taken into account in the evaluation of the origin of tumours.

A case is reported of a transfusion syndrome in a triplet pregnancy with intrauterine death of two of the fetuses. This is an exceptional occurrence in a triplet pregnancy and raises the problem of the management of multiple pregnancies associated with the death of one or more of the fetuses. The problem of the method of delivery and the complications arising in triplet dizygotic pregnancies is discussed.

Monozygotic twins are the best witnesses of the existence of a hereditary biological time, because they would not be identical if they had not also inherited the times of appearance and duration of their common hereditary information. The authors gave the name “chronogenetics” to this branch of genetics which concerns the temporal dimension of the gene and the mechanisms of transmission and manifestation of the temporal characteristics. The “Ergon/Chronon System” is suggested as a model to explain chronological heredity in terms of molecular genetics.

An example is offered of a chronogenetic analysis of puberty based on the study of puberty times in 157 female and 154 male twin pairs. This shows the hereditary conditioning of numerous chronogenetic parameters, the extrapolation of conclusions concerning the phenomenon of puberty, and the establishment, in this regard, of a borderline between hereditary and physical times.

A picture is finally drawn exemplifying Normal Hereditary Times (gametic, auxologic, homeostatic, and old-age recession times) and Pathological Hereditary Times (auxologic, cardiovascular, neoplastic, immunitary, metabolic, and antitoxic pathology times).

Provisional chronogenetic developments are indicated, and a possible advancement toward the recycling of the gene is hoped for.

This report is concerned with the twin births which occurred in the Collaborative Study of Cerebral Palsy, Mental Retardation and Other Neurological and Sensory Disorders of Infancy and Childhood. This is a collaborative endeavor of 14 institutions throughout the US and the National Institute of Neurological Diseases and Stroke, to observe and study factors which affect the parents before a child is born and to relate them to the outcome of pregnancy. To this end, we are following approximately 60 000 pregnant women from the first months of their pregnancy, through labor and delivery and up to the seventh year of the study child's life. The Study population is about 46% White, 46% Negro, 7% Puerto Rican, and the rest a variety of other ethnic groups. The prospective nature of the study makes possible the recording of observations with high accuracy and the avoidance of biases inherent in other types of investigations. These advantages should also be reflected in the collection and evaluation of twin data.

This is a follow-up study of twins, including 33 twinpairs from the Stockholm area, aiming to study the cognitive development of twins at eight years of age. The twins have been followed at different ages from birth onwards. All children were tested with the Wechsler Intelligence Scale for Children in a Swedish translation (WISC). The WISC test consists of a Verbal and a Performance Scale. There were no significant differences between twin girls and twin boys on these Scales. On the Performance subtests Block Design, Object Assembly, and Coding, however, the twin girls performed significantly better than the twin boys. In comparing cognitive development for twins and singletons, the twin group had somewhat lower average scores than the singletons. Prematurity and low birth weight continued to be related to cognitive development at eight years of age. Also at this age the school teacher completed a questionnaire about the twins social behaviour and some personality traits. There was a relation between one questionnaire factor, a low score of assertiveness, and the mother's negative or ambivalent expectations concerning the twin pregnancy. The twin group with the mother's negative expectations also had significantly lower results on the subtests Comprehension and Coding. Negative mothers had more premature twins than mothers who were positive toward the twin pregnancy.