The fetuses of nine pregnant ewes were chronically cannulated between 86 and 130 days with cannulae in one carotid artery, one jugular vein, the fetal bladder and the amniotic cavity. The effects of infused AVP on fetal urine flow rate and composition were studied. A dose of 35 pmol . h-' always caused an increase in urine osmolality and a decrease in flow rate and free water clearance without change in blood pressure. Higher doses (140 pmol.h-1) were significantly pressor and caused increased excretion of sodium, chloride, urea and creatinine. Although this dose always caused an increase in urine osmolality, in five experiments the flow rate also rose. It is concluded that the ovine fetus has the ability to control its own urine flow and composition, and possibly also amniotic fluid volume and composition.Although the compositions of ovine fetal urine and amniotic fluid have been studied by several groups of workers [Alexander, Nixon, Widdas and Wohlzogen 1958;Mellor and Slater, 1972], little is known of the mechanisms which control the volumes and compositions of these fluids. Urine formation begins at about the third month of fetal life in the human [Vernier and Smith, 1968] and by the third trimester is thought to be an important source of amniotic fluid. This view is supported by clinical findings that when urine production is impaired in some way, oligohydramnios often results [Jeffcoate and Scott, 1959]. Thus in studying the maintenance of amniotic fluid volume and composition it becomes relevant to investigate possible controlling factors of fetal renal function.Antidiuretic hormone (ADH) is a hormone which affects renal function in the adult. It has been shown to be present in ovine fetal blood [Alexander, Britton, Forsling, Nixon and Ratcliffe, 1974] but a physiological effect has not yet been demonstrated. In the experiments to be described in this paper a chronic preparation in pregnant sheep was used to study the effects of infused antidiuretic hormone on urine composition and flow rate in the ovine fetus. METHODS Surgery. The fetuses of nine cross-bred merino ewes of known mating dates had vascular, bladder and amniotic cannulae inserted at 86-130 days gestational age (term-147 ± 5 days).

Summary Spontaneous fetomaternal haemorrhage at 14 to 20 weeks gestation resulted in raised serum alpha‐fetoprotein (AFP) levels in 13 of 150 patients attending a genetic counselling clinic. In all 13 patients, the placenta was anterior or fundal in position. By allowing for a rise in serum AFP levels of 4 μg/l for each fetal cell seen in 30 high power fields (Kleihauer test), a 62·5 per cent reduction in the number of patients selected for amniocentesis because of raised serum AFP levels would have been achieved. The occurrence of fetomaternal haemorrhages at the time of amniocentesis can be detected by either the Kleihauer technique or the measurement of maternal serum AFP levels.

Summary The lecithin/sphingomyelin (L/S) ratio in the amniotic fluid of 57 patients attending an antenatal diabetic clinic was determined. The L/S ratio in Class A, B and C patients (White, 1965) showed a similar rise with gestation to non‐diabetic patients; 89 per cent in this group had an L/S ratio above 2:1, but of these 27 per cent developed mild or moderate respiratory distress syndrome (RDS). In Class D, F and R diabetic patients there was a little correlation of the L/S ratio with gestational age and in this group 55 per cent of the infants developed some form of RDS. The value of measuring amniotic fluid L/S ratios in the diabetic pregnancy is questioned.

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