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The pathological mechanism that causes the transient phenomenon sonographically defined as "nuchal translucency' is still poorly understood. Seven pregnancies in which the fetuses clearly presented this ultrasonic sign at 10-14 weeks' gestation were terminated because of an abnormal fetal karyotype. The pathological specimens, compared by morphometric analysis with normal fetuses of the same gestational age, showed oedema and dilatation of lymphatic capillary vessels. No particular relationship was found with any structural abnormality. We speculate that nuchal oedema is a transient non-specific phenomenon which is probably related to an early disarrangement of lymphatic connections.

The feasibility of fetal renal biopsy has been investigated in order to assess the diagnostic value of the histological specimen. Two fetuses with a severe bilateral renal abnormality (multicystic dysplastic kidney, Meckel-Gruber syndrome with polycystic kidney) and one fetus with Down syndrome (no detectable structural anomaly) were sampled. Histological findings in the biopsy specimens of cases 1 and 2 were diagnostic of an early obstructive renal disease. In case 3, the findings were consistent with normal development for gestational age of the kidney. Fetal renal biopsy is technically feasible; histological examination of the samples showed a good correlation with postnatal findings. Further studies of its diagnostic value are required.

A technique is described for measuring pressure within the amniotic cavity and within fetal vessels and/or body compartments. Two saline-filled catheters were connected at one end to needles inserted during indicated invasive procedures and at the other to silicon strain gauge transducers. In 36 pregnancies with normal liquor volume, stable intra-amniotic pressure (IAP, range 1-14 mmHg) increased with gestation (r = 0.48, p less than 0.01). In pregnancies complicated by severe oligohydramnios, IAP was less than or equal to 1 mm Hg and rose to normal levels with saline amnioinfusion. Raised IAP (range 17-26 mm Hg), found in pregnancies with gross polyhydramnios, fell with drainage of amniotic fluid. Subtraction manometry was used to determine supra-amniotic pressure within the intervillus space, umbilical vein, umbilical artery, abdominal and thoracic cavities, and the urinary tract in normal and/or pathological fetuses. Low intravesical and intrapelvicalyceal pressures (median 6.5, range 2-10 mm Hg) were noted in fetuses with obstructive uropathies. Intrauterine subtraction manometry appears to be a useful tool in the understanding of fetal pathophysiology and may be of clinical benefit in the therapeutic drainage and infusion of amniotic fluid and in the assessment of certain fetal disease states.