The case is presented as an unusual example of the benefit of tracheostomy during pregnancy in a patient with obstructive sleep apnoea syndrome.

Of 178 consecutive twin pregnancies, 63 were both monozygotic and also studied prenatally by rcal-time B-scan (and usually Doppler) ultrasound. T h e 48 pregnancies with monochorionic placentas (in which vascular anastomoses are almost universal) were compared with the 1. 5 monozygotic pregnancies having dichorionic placentas. T h e type of placenta found at delivery was predicted with substantial accuracy by ultrasound examination in mid-pregnancy. We were unable to identify any intcr-group difference in fetal growth rate, discordance of fetal growth between twins or pattern of umbilical artery flow velocity waveform. In the absence of the rare florid twin transfusion syndrome, the vascular anastomoses that have been shown t o b e common in monochorionic placentas d o not exert a strong influence on fetal growth or fetoplaccntal blood flow.There is a high rate of fetal loss from twin pregnancies generally (Pate1 et al. 1984) and from monozygotic pregnancies particularly (Naeye et al. 1978). Preterm labour and fetal growth retardation are commonly associated with both types of twinning, and monozygotic pregnancies are thought to be at increased disadvantage because of more frequent fetal malformation (Fogel etal. 1965) and the adverse consequences of monochorionic placentation. Three-quarters of monozygotic pregnancies have monochorionic placentas and, almost always, these contain vascular anastomoses connecting the circulations of each twin (Robertson &L Neer 1Y83). Arteriovenous anastomoses enable the shunting of

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The daily variability of umbilical artery and lateral uterine wall artery velocity-time waveforms recorded by continuous wave Doppler ultrasound was determined by making three observations in each of 97 women on different days within a 7-day period. There were no significant changes in the maxima1:minimal Doppler shift frequency ( N B ratio) or the pulsatility index in either artery over the period of study. Common pregnancy complications did not influence the variability of the recordings. The variability of uterine artery recordings was not affected by gestational age between 17 and 41 weeks but the degree of variability of the umbilical artery recordings was greater before 30 weeks. We conclude that after 30 weeks gestation this technique has an acceptable range of daily variability for clinical and research applications.Fetal and uteroplacental blood flow evaluation using Doppler ultrasound has recently attracted considerable research interest because of the technique's simplicity, apparent safety and possible clinical application. An important factor in determining the usefulness of these measurements will be the reproducibility of the technique used.In vitro, pulsed wave Doppler ultrasonic evaluation of blood volume flow and velocity is highly accurate (Gill 1980;Erskine & Ritchie 1985), but in vivo a number of methodological