Since the discovery that major histocompatibility complex (MHC) proteins provide a barrier to tissue transplantation between individuals it has been a paradox that, during pregnancy, the mother is able to retain a fetus that expresses MHC antigens from the father without rejection. The nature of this materno-fetal tolerance is not well understood and may involve multiple mechanisms. However since a major mechanism of histo-incompatible tissue rejection involves T lymphocytes, it seems plausible that controlling T cell responses is likely to be important. Recently, there has been considerable research activity focusing on the role of a sub-set of CD4+ T cells that express the interleukin-2 receptor chain CD25+. These CD4+CD25+ cells are termed regulatory T cells (Treg) based on their ability to prevent autoimmune tissue damage. In this review we discuss recent evidence that may link Treg to materno-fetal tolerance during pregnancy.

Preterm delivery occurs in less than 10% of pregnancies but accounts for more than 70% of all neonatal deaths. Approximately one third of preterm deliveries are associated with preterm prelabour amniorrhexis. In those with infection, labour frequently ensues and survival depends on gestational age at amniorrhexis. In those without infection the pregnancy continues and death is then dependent on the development of pulmonary hypoplasia (PH).

Ultrasound has been used in cardiac diagnosis since the 1960s. The original modality used was M-mode, which recorded the movement of heart structures relative to a single line of sound passed through the heart and was displayed as a paper tracing. During the 1970s, a two-dimensional image became possible, but it was a static image, which had limited value for cardiac evaluation. However, by the end of the 1970s, advances in ultrasound equipment allowed the heart to be displayed in real-time. This technology was applied initially in the adult and subsequently in the child. Echocardiography proved particularly suitable for children, partly because it is non-invasive and repeatable, but also because most heart disease in children is due to malformation of anatomical structure, which ultrasound can ideally display. At the same time, obstetric ultrasound was progressing rapidly and descriptions of the appearances of malformations in most fetal systems began to be published by the end of the 1970s. It was not until real-time equipment became generally available in obstetrics that the fetal heart could be satisfactorily evaluated. This led to descriptions by several authors of normal fetal cardiac anatomy as seen echocardiographically in 1980. The appearances of the echocardiogram in different forms of congenital heart disease (CHD) in children were published in the late 1970's, setting the stage for diagnosis in fetal life. As a result, by the mid-1980's, most major forms of CHD had been detected prenatally.

Isolated case reports of the prenatal detection of urinary tract malformations first appeared in the literature in the late 1970s and by the mid 1980s prenatal diagnosis had already become a firmly established feature of paediatric urological practice throughout the developed world. The rapid development of prenatal diagnosis of urinary tract malformations can be attributed to the relatively high incidence of congenital anomalies within this system and the fact that the common anomalies are usually associated with dilatation or cystic pathology which is readily visualised by ultrasound. Although many aspects of prenatal diagnosis have been clarified by studies undertaken over the last twenty years some important questions have yet to be fully resolved – for example the long term natural history of asymptomatic uropathies such as pelvi ureteric obstruction and the benefit (if any) of prenatal diagnosis in reducing long term burden of chronic renal failure associated with posterior urethral valves.