The discipline of radiology owes its existence today to the discovery of bands of radiation in the electromagnetic spectrum which can penetrate human tissue, and thus can be exploited as windows for imaging. Magnetic resonance (MR) employs radio-frequency radiation and almost certainly represents the final such window in the electromagnetic spectrum for imaging. It is similar to Computerised Tomography (CT) in providing a cross-sectional display of body anatomy with excellent resolution of soft tissue detail. The images are essentially a map of the distribution density of hydrogen nuclei and parameters reflecting their motion in cellular water and lipids. The total avoidance of ionizing radiation, its lack of known hazard and the penetration of bone and air without attenuation, make it a particularly attractive non-invasive imaging technique.

The efficacy of labour is determined by uterine, fetopelvic and cervical factors. Whereas the first two of these are well recognized, acknowledgement of the modulating function of the cervix during labour is relatively new. In particular, clarification of the synthesis and metabolism of prostaglandins has contributed considerably to our understanding of the biological control of the cervix.

The normal thyroid secretes thyroxine (T4) and, to a lesser extent, triiodothyronine (T3). The T4 is transported in the circulation to peripheral tissues largely bound to thyroxine binding globulin (TBG); T3, which is produced in peripheral tissues by deiodination of T4, also binds to TBG. It is, however, the free thyroid hormone concentration which determines the metabolic state, by its action on T3 nuclear receptors in the cells of kidney, heart, liver, anterior pituitary and other tissues.

Multiple pregnancy is associated with a high rate of perinatal loss – mainly due to preterm labour but with important contributions from fetal malformation, intrauterine growth retardation and twin-twin transfusion syndrome. The overall perinatal mortality rate is consistently around six times that of singleton pregnancies but the rate rises progressively with the number of fetuses. Rates of 63,164,200,214 and 416 per 1000 births have been recently reported for twins, triplets, quadruplets, quintuplets and sextuplets respectively. In addition to these alarming figures, it should be emphasized that the restricted concept of perinatal mortality obscures the real extent of loss. If we include late abortion (after 20 weeks), late neonatal deaths and deaths in infancy from perinatal causes, as well as the usual indices of perinatal mortality (stillbirths and early neonatal deaths) we find that the total loss rate from twin pregnancy alone doubles and may be close to 10%. Although the rate of loss from multiple pregnancies is now substantially higher than that associated with the pregnancies of diabetic women, the challenge of multiple pregnancy has not been met with the same commitment or organisation of specialized perinatal services as has diabetes.