Infants from 22 pairs of appropriate-for-gestational-age/small-for-gestational-age (AGA/SGA) same-sex twins were assessed for temperament stability between the neonatal period and 30 months of age. The evaluation of neonatal temperament included observers' ratings of irritability, resistance to soothing, activity level while awake, activity level during sleep, reactivity, and reinforcement value. At 6, 9, 12, 18, 24, and 30 months mothers rated their infants' temperament on standardized questionnaires which yielded nine temperament categories: activity level, rhythmicity, approach or withdrawal, adaptability, intensity of reaction, quality of mood, attention span, distractibility, and threshold of responsiveness. The Bayley Scales of Infant Development were administered at 6, 9, 12, 18, 24, and 30 months to assess mental development. The results of longitudinal correlational analyses indicated that, for the AGA infants, there was a pattern of significant predictive relations between the neonatal ratings of temperament and maternal ratings of temperament at 6, 9, 12, 18, 24, and 30 months. The SGA infants did not demonstrate similar behavioral stability from the lying-in period up to 30 months of age. Furthermore, for AGA infants there was a consistent trend for both reactivity and neonatal activity during sleep to predict mental development scores between 6 and 30 months. A similar pattern was not observed for the SGA cotwins. The results indicated that temperament stability is an additional area of risk for SGA twins, and that the developmental function of the underlying processes in the neonatal measures is different for AGA and SGA infants.

Data on five tests of general and specific cognitive abilities, cognitive styles, and creativity, obtained from members of 60 identical and 63 fraternal Russian adolescent twin pairs, are presented. All tests are adaptations of standardized instruments widely used outside of the Soviet Union. Identical and fraternal twin correlations for general cognitive ability yielded a lower estimate of heritability (0.29) than generally found in other countries worldwide (0.52) although the twin correlations themselves are fairly comparable to figures from other countries and cultures — 0.83 and 0.69 for Russian identical and fraternal twin pairs, respectively, vs 0.86 and 0.60 for non-Russian identical, and fraternal twin pairs. Twin correlations for other cognitive-related abilities assessed were also comparable to correlations obtained outside the Soviet Union with the exception of creativity which yielded higher within-pair resemblance than reported in previous twin studies.

In vaginally delivered births (including a few cases where the mothers were under epidural anesthesia), differences between first and second born twins were compared according to presentation at delivery. Of twins with vertex/vertex presentation in 15 primipara cases and in 14 multipara cases, pO2 levels for the second born were significantly lower (both being p < 0.05) than for the first born. Of twins vertex/non-vertex presentation, the second born in 9 primipara cases showed significantly lower pH, pO2 and HCO3 levels (p<0.05). Also for multipara twins, the second born had significantly lower pH (p<0.05) and significantly higher pCO2 (p<0.05) values. Umbilical cord blood gas value findings indicate unfavourable conditions for second born twins.

The present study compared two different types of English-language teaching approaches, the grammatical approach (GA) and the communicative approach (CA), by the cotwin control method. This study has two purposes: to study the effects of teaching approaches and to estimate genetic influences upon learning aptitudes. Seven pairs of identical twins (MZ) and 4 pairs of fraternal twins (DZ) participated in the experiment along with 68 other nontwin fifth graders. Each cotwin was assigned to the GA and CA respectively and received 20 hours of lessons over a 10-day period. The behavioral similarities between MZ cotwins were statistically and descriptively depicted. No major effect of either teaching approach was noted, but the genetic influence upon individual differences of learning achievement was obvious. Furthermore, an interesting interaction between the teaching approaches and intelligence was found, that is, that the GA capitalises on and CA compensates for intelligence. This interactional pattern could be interpreted as an example of genotype-environment interaction. The relationship between genetic factors and learning aptitudes is discussed.

The theory of r selection, favoring population growth, as opposed to K selection, favoring more efficient utilization of resources, has in recent years been applied by Rushton to contrast human ethnic groups in terms of their r/K reproductive strategies, suggesting the existence of a continuum from r groups, producing many offspring but providing little parental care, to K groups, producing few offspring but providing much parental care. Rushton's theory, which is largely based on ethnic differences in twinning rates, is here critically examined. It is pointed out that twinning rate differences are not necessarily genetic in origin since various environmental factors clearly play a role, and also that twinning, as a mode of reproduction, is not necessarily an r strategy, considering the high prenatal and perinatal selection to which it has been, and still is, associated. Moreover, Rushton misinterprets a number of relevant aspects related to the biology of twinning. The claim that ethnic differences in twinning rates provide evidence for an r/K typology in human populations with respect to reproductive strategies does not appear to be warranted.

Multiple pregnancy is NEVER planned. A few years ago one could categorically make such a statement. Perhaps nowadays one cannot be so sure. Although parents are still unlikely to be able to plan such an event, it does seem that current infertility treatments may allow or even encourage practitioners to use methods which predispose to a multiple pregnancy. The practice of returning several fertilised embryos to the uterus in the hope of achieving a successful result has meant that many parents who longed for a baby have had to adjust to the realisation of a multiple pregnancy with all the effects such an occurrence has on family physical, social and emotional resources.

The Study of Triplets and Higher Order Births by the Office of Population Censuses and Surveys [1] highlighted the striking increase in Multiple Births in recent years. This was particularly evident in the case of triplets and higher order births. (Fig. 1) Care of these high-risk infants is costly in resources and no increased funding has been given to the National Health Service or Social Services budgets to provide care and support for the families.

This study endeavours to ascertain the needs of such families preconceptually, antenatally, intra-partum, postnatally and in the early months following the birth. It also tries to assess how appropriate current practice is in meeting these needs.

Findings from an earlier phase of this research project clearly pointed to the mother's psycological adaptation inherent to the specificities of triadic interaction. Mothers' attitudes were classified in a typology ranging from “early twinness” where the two babies are treated as though they were a single unit, to attempts to create two dyadic relationships. The current program deals with the effects of the type of parent-child relationship at one year on the emergence of twin bonding. Sixty-eight families of twins (26MZ, 24DZ same sex, 18DZ different sex) are followed up from birth to the age of 3 using a method based on clinical interviews, videotaped observations, and questionnaires. The data cover mothers' rearing attitudes towards organization of babycare and outward signs of twinness, maternal representations of the relationship between the twins and observation of the children's interaction in a standardized game situation. The findings are discussed in terms of zygosity, and parental SCS.

Of 104 cases, 38 (ie, 36.53%) experienced premature delivery (controls: 4.32%). In instances of threatened premature delivery, 28 cases (26.92%) underwent ligation of the cervix. EPH gestosis occurred in 62 cases - a high incidence rate of 59.61% (controls: 12.9%). Forty-nine cases (47.11%) were complicated by anemia (controls: 8.36%). There were 57 cases of SFD infants, again a high 27.40% incidence rate (controls: 5.94%). Apgar scores of 7 or less at 1 minute after birth indicated that of the 208 neonates, the second-born twin only in 20 cases (9.61%); both infants in 14 cases (6.73%); and, the first-born only in 3 cases (1.44%), developed asphyxia neonatorum. Given the high incidence of premature and immature infants in cases of twins, caution should be employed against threatened premature delivery from around the 28th week of gestation onwards. Ligation of the cervix with ritodrine administration should be performed following admission to hospital, and EPH gestosis, anemia and IUGR should be carefully monitored.

This study is based on 145 pairs of twins included in a longitudinal study of a cohort of singletons born in 1953 and living in the Stockholm metropolitan area in 1963. Of these 145 pairs, 28 were classified as MZ, 103 as DZ and 14 pairs could not be classified. School achievement and ability test results have been collected for this group as well as data for the boys from physical and mental examinations on enrollment to military service. The purpose of this study was to compare within-pair similarity for MZ and DZ twins from birth onwards. There seems to be a divergent trend over time for MZ twin pairs to become more similar and DZ twin pairs to become less similar in height growth, school achievement and verbal ability. This is in accordance with previous research in this field. In relating similarity within pairs to birthweight, we found a drop in within-pair similarity for low birthweight MZ and DZ twin pairs (both twins ≤2.500 g), but not for normal weight twin pairs. A discussion is initiated concerning methodological implications of these results.

Twinning rates in all of Japan for 1951-1968 and 1974-1990 were analyzed using data from vital statistics of Japan. The twinning rate per 1,000 births was 6.43 in 1951 and remained nearly constant until 1968, then decreased to 5.79 in 1974 and gradually increased to 7.00 in 1990. The MZ twinning rate increased slightly up to 1966, but decreased thereafter, whereas the DZ rate declined over the entire period. As for maternal age, the DZ rate increased up to the age group 35-39 and decreased thereafter. The same tendency is seen in the MZ rate, but the maternal age effect is less marked than in DZ twins. The same tendency is also seen in the overall rate for 1975-1985. As for geographical variations, the MZ and DZ rates were computed in each prefecture for 1955-1959 and in 1974. The DZ rate increased from a low level in the southwest of Japan to a high level in the northeast for both periods, whereas the MZ rate was rather constant in 1974 throughout Japan. As for seasonal variation, the highest rates per 1,000 births for MZ(4.56) and DZ(2.20) twins were seen in April, with the lowest rate in September (3.69) for MZ twins and in July (1.71) for DZ twins.

The genetic and environmental contributions to physical aging (hair graying, balding, presbyopia) and longevity (age at death) were examined by within-pair comparison in monozygotic (MZ) and dizygotic (DZ) twins in later adulthood. Physical aging was investigated on 135 pairs of adult twins aged over 50. Hair graying and hair loss (baldness) showed significantly higher rates of concordance in the MZ twins than in the DZ twins. The intrapair difference of the degree of hair graying was negligible in 79%, slight in 15% and striking in 5% among the MZ pairs; while negligible in 40%, slight in 50% and striking in 10% among the DZ pairs. The intrapair difference of the degree of hair loss was negligible in 92%, slight in 8% (and striking in none) among the MZ pairs; while negligible in 69%, slight in 25% and striking in 6% among the DZ pairs. The age at onset of presbyopia showed a slightly higher rate of concordance in the MZ than in the DZ pairs. Longevity (age at death) was surveyed on 184 pairs of twins who died at over 40 years of age. The intrapair difference of longevity was 6.65 ± 5.6 years (maximum 18.0; minimum 0.04) in the MZ pairs, and 8.66 ± 7.2 years (maximum 18.6; minimum 2.9) in the DZ pairs. The MZ pairs showed a slightly smaller within-pair difference of longevity than the DZ pairs.

Monozygotic (MZ) and dizygotic (DZ) twins in later adulthood were studied in order to examine genetic and environmental contributions to the decline of cognitive performance. In this study, 118 twin pairs took a comprehensive medical examination at a university hospital. Cognitive function was measured by the Wechsler Adult Intelligence Scale (WAIS). The intraclass correlation coefficients on Digit Span (D) and Digit Symbol (DS) subtests of the WAIS did not show any significant difference between MZ and DZ twins although Block Design (BD) showed a significant difference. The values of the intraclass correlation coefficients were mostly around 0.5 and showed significant within-pair similarity of test scores. The mean score of D, DS and BD declined with advancing age. The intraclass correlation coefficients for D, DS and BD were around 0.2 in the MZ twins reared apart, and around 0.6 in the MZ twins reared together. These results indicated a significant environmental influence on cognitive aging in later adulthood.

In order to examine perinatal mortality and prevalence of major congenital malformations in twins, deliveries in four teaching hospitals in Taipei City were studied. Among a total of 73,264 deliveries from October 1985 to June 1989, there were 844 pairs of twins. The zygosity of the twin pairs was determined by sex, placentation and 12 red blood cell antigens. There were 482 MZ and 252 DZ twin pairs identified, but the zygosity of a further 110 twin pairs was indeterminable due to lack of information on plancentation and/or blood types. A total of 4,573 singletons delivered in one study hospital from July 1986 to June 1987 were also studied as controls. The perinatal mortality rate was 7.5% for MZ twins, 1.4% for DZ twins, and 0.7% for singletons. The concordance rate of perinatal death was significantly higher in MZ (60%) than in DZ (0%) twins. The prevalence of major congenital malformations was 2.7% for MZ twins, 1.0% for DZ twins, and 0.6% for singletons. The concordance rate of major congenital malformations was 18% for MZ twins, but no DZ pair was concordant in any major congenital malformation. The concordance rate of facial clefts was 29% for MZ twins. There were 2 sets of conjoined twins giving a prevalence rate of 2.7 per 100,000 deliveries. These findings showing the prevalence of perinatal mortality and major congenital malformation to be highest in MZ twins, intermediate in DZ twins and lowest in singletons, suggest the importance of intrauterine environments in the determination of perinatal mortality and congenital malformations.