The "stuck twin" phenomenon in monochorionic diamniotic (MCDA) pregnancies is characterized by marked disparity in both fluid volume and fetal size between the twin gestations. To determine the prevalence, sonographic characteristics, and clinical outcome of this phenomenon, discharge summaries, placental pathologic reports, and prenatal sonograms from 307 twin pregnancies were reviewed. Of 52 cases of MCDA pregnancies, 18 (35%) demonstrated marked disparity in amniotic fluid volume. In 16 of these 18 cases there was discordant twin growth, further suggesting the diagnosis of twin transfusion syndrome. All 16 cases and an additional nine cases supplied by another center demonstrated a small, morphologically normal fetus in an oligohydramniotic sac suspended anteriorly (72%) or laterally (28%) in the uterus. The amniotic membrane separating this twin from the larger twin in the polyhydramniotic sac was thin, closely applied to the smaller fetus, and difficult to detect. Perinatal morbidity was 100% for all twin pairs, and premature labor occurred in all cases. Perinatal mortality ranged from 88% for the larger/poly twin to 96% for the small/oligo twin.

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concern at lowering blood pressure and maintaining proper fluid balance. The randomised study that Dommisse quoted in his letter, along with similar studies being carried out in Durban, suggests that prophylactic anti-convulsant therapy in severe preeclamptic women may not be necessary.The problem with the treatment of patients with established eclampsia is more difficult because of its rarity in the United Kingdom. More consultants will only see a case of eclampsia every few years, and therefore their experience of managing this problem is not great. Despite its rarity eclampsia still contributes to about 50% of the maternal mortalities from severe preeclampsia or eclampsia, and it may be that the role of magnesium sulphate in this area should be more closely assessed by the British obstetricians.I still use phenytoin in my practice because I feel comfortable with it, but I am willing to be convinced by the worldwide multicentre studies if they find magnesium sulphate to be a superior preparation. There has been no previous study, even in North America, that has properly validated magnesium sulphate in this way. J. J. Walker University of Lee&, School of Medicine Division of Obstetrics and Gynaecology Fetal immunological and haematological changes in intrauterine infection Sir,A report in your journal (Vol 101, May 1994) coincided with our paper in the Lancet (Michie et al. 1994) on the fetal response to congenital infection. We have made a similar observation and wish to report new data. Thilaganathan et al. (1994) documented an increased number of natural killer (NK, or CD56+) cells in the circulation of infected fetuses. Using cord blood collected at delivery, in the cohort of patients already described, the NK cells of 25 infants were studied using the previously described methods (Michie et al. 1994). Three infants had congenital infection: one with cytomegalovirus, one with varicella zoster, and one with toxoplasmosis. As reported by Thilaganathan, total numbers of NK cells were increased in those infants with congenital infection (Table l), including a child with a protozoal infection. Double labelling to measure subsets of NK cells, defined by their expression of activation and adhesion molecules, showed that NK cells expressed the longer isoform of the leukocyte common antigen, CD45, (that is, CD45RA) in the majority of patients. This concurs with previous studies (Braakman et al. 1991). However, in the three infected infants a significant proportion of these cells expressed the shorter isoform, CD45RO. These results are shown in Table 1 with the percentage of CD56+ cells expressing CD45 isoforms detailed for each case. Expression of CD45RO in vitro by NK cells represents activation of NK cells (Roth 1994); these data suggest that in cases of congenital infection, there is activation of NK cells in the cord blood.Expression of activation markers on various cells of the fetal or infant immune system suggests that a fetus can mount an immune response to infection similar to that of an adult. In these fe...