A healthy 23-year-old woman with amenorrhea was examined at the Mendel Institute. She had been amenorrheic for 4 years, and had not responded to hormone treatment. We therefore decided to study her family tree and karyotype. We describe the results of our study here: the patient was found to have gonadal dysgenesis, caused by translocation of a fragment of the X to a 12 chromosome, resulting from a break at q21, at the end of the q-arm.

I would like to reply here to a number of criticisms concerning the stance taken by Pope John Paul II on the rights of the unborn child in his book Crossing the Threshold of Hope, made by Dr John Godfrey of the University of Edinburgh in a recent article entitled “The Pope and the Ontogeny of Persons” (Nature, 12 January, 1995).

The accusation levelled against John Paul II is contained in the subheading of John Godfrey's article: “In the recent book… Pope John Paul II airs his views on human reproduction. The pity is that he ignores most of modern genetics and embryology”. Dr Godfrey quotes the following passages written by the Pope in Crossing the Threshold of Hope: “The concept of a ‘person’ is not only a marvellous theory; it is at the centre of the human ethos… in this field more than in any other, collaboration among pastors, biologists and physicians is indispensable”.

All of the recorded twin live births in Washington State birth certificates between 1984 and 1988 were used a retrospective cohort study to determine the risk of zygosity on pregnancy complications and birth outcomes (n = 3458). Relative risks comparing different sex (DS) twins to same sex (SS) twins were corrected to relative risks relating dizygotic (DZ) to monozygotic (MZ) twins, using the Weinberg rule. A higher proportion of DS twin pregnancies (3.5%) than SS pregnancies (1.6%) were complicated by gestational diabetes, resulting in an estimated risk for DZ twin pregnancies relative to MZ pregnancies of 8.6 (95% CI = 3.5-21.0). DZ twin pregnancies were at a lower risk for complications of polyhydraminios (RRDZ∣MZ = 0.2, 95% CI = 0.1-0.4) and of pyelonephritis, (RRDZ∣MZ = 0.3, 95% 0 = 0.1-0.8). MZ twins were more likely to have low birthweight and to have shorter gestations. The proportion of first-born babies of MZ twin pairs who died during their first year was similar to that of first twins of DZ pairs; however, the second-born of MZ twins were more likely to die in infancy than were second-born DZ pairs. First twins of DZ pairs were more likely to die of SIDS (sudden infant death syndrome) than the first of MZ twins (RRDZ∣MZ = 1.5, 95% CI = 0.4-5.1). In contrast, DZ second-born were less likely to die of SIDS than were MZ second-born twins (RRDZ∣MZ = 0.1, 95%CI = 0.1-0.7). DZ twins were less likely to have adverse newborn conditions or malformations. The high risk for gestational diabetes for DZ twin mothers is possibly due to the presence of two placentas which may support the development of greater insulin antagonism than the single placenta in the mother of MZ twins. The reduced risk of DZ relative to MZ twins for selected adverse birth outcomes may result from the increased tendency of MZ twins to be premature.

Precision of zygosity determination in twins can be improved by the use of modern methods of DNA analysis. The clinical application of 4 single- (SLS) and 2 multi-locus (MLS), and 6 PCR (polymerase chain reaction) systems for zygosity determination in 12 twin pairs with oral clefts was compared with regard to the quality and quantity of sample material required and the probability of error in monozygosity determination. PCR systems proved to be superior to SLS or MLS, as DNA sampling is much more convenient, while its level of accuracy still fulfils clinical requirements. For this reason, PCR systems should be considered a basic method in modern clinical twin research.

This study investigates the influence of hypertensive disorders on twin pregnancies for an unselected, population-based series. Between 1986 and 1991, out of a total of 56,381, 766 (1.3%) were twin deliveries at our institution, the only tertiary care hospital serving a population of about 400, 000 inhabitants. The incidence of hypertensive disorders was significantly higher in twin gestations than in singleton pregnancies, at 3437/55,615 (6.2%) vs 85/766 (11.1%) (p<0.001, OR=1.8, 95% CI =1.4-2.3). Hypertensive disorders were significantly higher in twin as compared to singleton pregnancies, regardless of parity, and even after adjusting for maternal age. More instrumentai or surgical deliveries were needed when pregnancies were complicated by hypertension, in twin as well as singleton gestations. Despite the association between prematurity and hypertensive disorders, and prematurity and perinatal mortality, no significant difference was found in perinatal mortality between hypertensive and nor-motensive twin pregnancies. The neonatal death-rate in normotensive and hypertensive twin pregnancies (3.7% and 3.5% respectively) was higher than that of stillbirths (respectively 2.3% and 0%).

Numerous reports in the literature suggest that hormones may transfer from one fetus to another, in humans as in animals. In a large sample of over seven thousand Australian adult twins, it was found that opposite-sex females showed a statistically significant tendency to hold more masculine attitudes than did same-sex female twins. This may be due to post-natal social interaction, but could also be caused by the transfer of testosterone from the male to the female fetus in opposite-sex twins.

The acute form of twin-to-twin transfusion syndrome is caused by rapid transfer of blood from one of the twins to another via placental anastomoses. Usually, this only occurs during the second stage of labour as a result of a sudden relative rise of blood pressure in one of the fetal circulations. This can result in the sudden intrauterine death of a fetus (or both, as in our case). Currently, there is no reliable means of identifying such an at-risk pregnancy by means of ultrasound antenatally. We would classify this as TTTS Type III.