The comparison of 622 twin and 622 singleton births allowed us to confirm the association of dizygotic twinning with maternal age, parity, and maternal weight and height, as well as the occurrence of unlike-sex twins in the mother's family. It was also shown that none of these associations, except for maternal height, can be explained by the others. Dizygotic twinning was also found to be negatively correlated with previous use of oral contraceptives and with irregularity of menstrual cycle. Finally, the relationship between spontaneous abortion in previous pregnancies and maternal exposure to medical irradiation was investigated.

Out of a total of 1025 twin births occurring in 11 South Moravian districts from 1972 to 1976, 638 occurred in the same time and space interval (P = 0.00037). The observed clustering suggests the existence of environmental factors influencing twinning rates.

The dizygotic twinning rate in Western Nigeria is the highest on record (45—50 per mil maternities). It is suggested that, rather than to peculiarities in the population structure or to genetic factors, such a high incidence might be due to the presence in the diet of estrogen-like substances.

A follow-up of 78 twin pregnancies diagnosed in the first trimester indicated that early ovular resorption occurred in 63% of spontaneous and 64% of Clomiphene-induced gestations, so that singletons were born. No failure was observed in the 12 twin conceptions following administration of gonadotropins or Cyclofenil.

A series of 978 repeated ultrasonic measurements of the fetal biparietal diameter (BPD) assessed the growth of 119 twin pairs during the second half of pregnancy. The mean BPD values for each gestational week were close to the mean values for singletons. From the 32nd week, the BPD growth curves for twins deviated from that for singletons. The second twins' growth curve ran consistently below that of the first and fell away more from the 32nd week on. In 80% of the measurements, the first twin (defined as the twin in, or close to, the pelvic inlet) was the one with the largest BPD. The intrapair difference in BPD had no correlation to the intrapair difference in body length, head circumference, or birth weight. In 91 of the 119 twin pairs, zygosity was settled by sex, histological examination of placenta, or blood grouping. The longitudinally compiled BPD growth curves (678 BPD determinations) showed the curve for dizygotic twins consistently running above that of the monozygotic twins. The BPD differences between the first and the second twin remained also within mono- and dizygotic groups of twins.

A total of 123 twin pregnancies were studied, 68 by records analysis only, and 55 by serial haematological assessment in detail. The incidence of low haemoglobin levels is found to be greater than in singleton pregnancy; evidence of iron and folic acid deficiency is common in sternal marrow aspirates but not in peripheral blood films. Routine haematinic prophylaxis in twin pregnancy is not advocated.

The hypothesis of a slower rate of glucose disappearance after intravenous glucose injection has been tested and proved in a sample of 54 women with twin pregnancies. Different standards for glucose tolerance being therefore required for these women, care should be taken before labelling them as diabetic.

The urinary nitrogen output appears to be related to both protein and energy intake, so that women having heavier babies probably eat more, although this may simply mean that they are larger women. Women with twin pregnancies have been found to have a lesser urinary nitrogen output, but it seems unlikely that this be due to lower intakes. They might simply utilize their diet more efficiently — a hypothesis that is now being tested.

Biparietal diameter growth differs considerably in the twin gestation compared to the singleton gestation; thus the use of a specific standard is recommended. A shift toward lower values is noticed in monochorial twins. In the case of the abdominal diameter growth, instead, no significant difference is found between twins and singletons.

A continuous series of 483 twin deliveries was studied. In 30% of cases, intravenous oxytocic treatment was given for labour induction or to accelerate the first stage. In 13% of twin deliveries this treatment was applied only after the first twin's birth. In the group perfused during cervix dilatation, foetal mortality rate was significantly lower than in the nontreated group. In order to understand the reason(s) for this difference, the following factors were studied in relation to oxytocic treatment: parity, obstetrical complications, second stage duration, abnormal presentations, obstetrical maneuvers, and birth weight. Contrasting with mortality data, Apgar scores of first twins were significantly lower in the oxytocin-treated group. In summary, several variables indirectly linked to oxytocic treatment could have favoured or hampered foetal outcome in the treated group. Therefore, it is difficult to ascertain if the use of oxytocics is helpful in twin pregnancy management. In the majority of cases, however, it may at least be considered harmless.

Early detection is a prerequisite for the active management of twin pregnancy. Detection rate was not, or was only slightly, increased by improved anamnesis or more alert physical examination. General placental lactogen screening selected 95% of the twins but implied a subsequent ultrasonic screening examination of 16% of the pregnant population for the definitive diagnosis. A general screening programme with ultrasound detected 90% of the twin pregnancies (methodological error 1.7%; not participating 8%) in the mid-trimester. Extensive restriction of maternal physical activity from the 29th to the 36th gestational week by bed rest in hospital reduced perinatal mortality to the level of singletons and also decreased the incidence of neurological and mental handicap among the surviving twins. For the supervision of twin pregnancy, urinary estriol estimates predict birth weight rather than fetal distress. Monitoring with repeated ultrasonic biparietal diameter measurements seem limited in value; even large intertwin BPD differences are not indicators of fetal distress in the smallest twin. The decrease of perinatal mortality and morbidity among twins subjected to special antenatal supervision suggests that large gains can be made by early detection and antenatal hospitalization. The earlier finding that impairment of the intrauterine supply line is closely associated with neurological sequelae gives added importance to the reduction of CNS handicap and of growth-retarded fetuses observed during such a programme.

In this study of 53 twin pregnancies, the plasma concentrations of the placental proteins, placental lactogen (hPL), and pregnancy-specific glycoprotein (SP1) were measured. Placental lactogen was found to be of more value than SP1 both in the detection of twins and in assessment of fetal growth. Serial measurement of either protein would seem to be more useful in assessment of fetal growth than single measurements. Preliminary studies of the less well known placental protein, PP5, in a small series of twin pregnancies indicate that it may also prove to be of clinical value in the detection and monitoring of twin pregnancies.

A total of 88 women with a twin pregnancy who had elective cervical suture were compared with 76 women with a twin pregnancy who had cervical assessment between the 13th and the 28th weeks of gestation but received no active treatment. The incidence of spontaneous onset of labour before 36 weeks was higher in the cervical suture group, and 53.4% of them sustained cervical damage.

Early diagnosis and subsequent management of twin pregnancy resulted in a considerable reduction of preterm deliveries (26% vs 61% for late diagnoses).

During 1973/1978, more than 90% of the pregnant women in Malmö, Sweden, were examined by ultrasound to improve the early diagnosis of twin pregnancy. This screening programme detected 90% of the twin pregnancies delivered during this period, 105 were subjected to a preventive treatment with bed rest in hospital, usually from the 29th to the 37th week (mean: 55 days). This study evaluates the outcome of these pregnancies, compared with those not treated with bed rest and with all twin pairs born a decade earlier (1963/1965). All twins of this group born up to 1 May 1977 were also monitored by regular postpartum check-ups until at least 18 months of age. Perinatal mortality was reduced to 0.5% in the group with bed rest, but remained as high (8%) as ten years earlier in the group without bed rest. The bed rest group, compared with the group without bed rest and the group of twins born 1963/1965, also showed a significantly reduced frequency of deliveries before the 37th week; also, the incidence of twins born light-for-gestational age and with birth weight below 1500 g was reduced. The incidence of twins born with cerebral palsy, mental retardation, and late development was 3% in 1973/1977 and 8.1% in 1963/1965. The reduction of mortality and morbidity of twins paralleled the improved obstetric and neonatal care. The fact that perinatal mortality and preterm delivery were reduced only among twins subjected to special antenatal supervision suggests that large gains are to be made by early detection and antenatal hospitalization. The lower CNS morbidity provides evidence of the quality improvement among the twin survivers.