39 Volume 59 November 1966 1127 Section of Obstetrics and Gyn2cology President Professor T N A Jeffcoate FRCSEd FRcoG Meeting March 251966 The Volume and Circulation of the Liquor Amnii [Abridged] Mr G L Bourne presence of many tiny basal processes which (St Bartholomew's Hospital, London) protrude into the basement membrane. A com- plex intercellular canalicular system is present The Anatomy ofthe Human Amnion and Chorion consisting of branching canals, some of which branch as a complex network into the side wall The anatomy, physiology and pathology of the of the cell. Microvilli also protrude into these foetal membranes have received insufficient canals. At higher magnification the electron attention and are, therefore, inadequately under- microscope reveals a complex system of tiny stood. A study of the anatomy reveals that these intracellular canals which connect between the organs are complex and possess a structure which intercellular canalicular system and the base of appears to be capable of transmitting fluid and the cell (Bourne 1962). (2) The basement mem- materials between the fretus and the mother. brane is a narrow layer of connective tissue to The presence of a circulation between the which the cells are firmly adherent. (3) The com- amniotic fluid and the fcetus is now accepted. The pact layer consists of a complicated reticular exact volume of fluid exchanged is subject to network which is responsible for most of the controversy. In theory at least, a large amount of strength of the amnion. (4) The fibroblast layer the fluid-exchange between the foetus and the contains a loose network of fibroblasts; these mother should occur directly across the faotal cells may also be phagocytic. (5) The spongy layer membranes. is a layer of loose connective tissue which enables the amnion to move comparatively freely upon Amnion: The amnion consists of five layers the fixed underlying chorion. (Fig 1): (1) A single layer of epithelial cells forms the innermost layer. These cells are cuboidal and Chorion: The chorion consists of four layers: (1) are surmounted by many microvilli. The base of The cellular layer which is thin and usually the cell is made incredibly complicated by the present only in early pregnancy; it consists of a Fig 1 Section through human amnion and chorion (diagrammatic). (Repro- duced from Bourne, 1960, by kindpermission) 1128 Proceedings ofthe Royal Society ofMedicine 40 fibroblast network. (2) The reticular layer forms of these anomalies is entirely haphazard and un- the bulk of the chorion and contains a loose predictable but the search for them is likely to reticular network. (3) The pseudo-basement stimulate the clinician's acumen - and this surely membrane acts as an anchoring structure for the is the one justification for his engaging in trophoblast. (4) The trophoblast layer in the non- research. placental chorion consists of trophoblast cells My object is to consider the theoretical infor- from two to ten layers in thickness, closely mation obtained from this sort of clinical applied to the maternal decidua and containing approach and to assess how this integrates with obliterated chorionic villi. experimental tracer studies and studies such as Bourne's (1962) to make up as rational an under- Blood supply: The amnion has no blood supply. standing of liquor turnover and volume as is The chorion has no blood supply as such, but possible at the present time. vessels do travel within the reticular layer of the Almost certainly several routes of production chorion to reach the placental villi. These vessels, and disposal exist - and these vary as pregnancy with rare exceptions, atrophy completely in the progresses: if one of these is interfered with, nonplacental chorion as pregnancy advances. partially or completely, then imbalance will occur. The turnover is so rapid that a factor of only 10% Nerve supply: The amnion and the chorion have per volume change will soon result in a significant no demonstrable nerve supply. alteration in the liquor volume - 1 litre in ten days (Hibbard 1962). Lymphatic vessels: The amnion and the chorion The recent work of Tervila (1964) shows that in have no demonstrable lymphatic vessels. cases of feetal death the turnover continues but is Materials such as meconium can be traced from reduced by the order of 50% -suggesting that the amniotic epithelium through the amnion and membrane transfer is responsible for about half the chorion into cells lying adjacent to blood the water exchange. This observation might be vessels in the maternal decidua. Meconium exerts extended to suggest that membrane transfer is a a harmful effect upon the amniotic epithelium more important route for disposal than for pro- resulting in rapid destruction of the epithelial duction of liquor because liquor resorption tends cells. to occur after feetal death, though it must be The structure of the amnion as seen by the accepted that the behaviour of the membranes electron microscope indicates that the epithelial may well alter after death of the baby. This cells at least are capable of transferring large suggestion, however, does correlate with the volumes of fluid between the amniotic and the electron microscopic studies of Bourne & Lacy maternal compartments. The two pathways (1960) which suggested that the appearances were available (intercellular canaliculk and intra- more in keeping with a function which was mainly cellular canals) indicate the possible presence of a absorptive. The idea that 25-50% of the turnover selective mechanism. The presence of meconium occurs through the feetus in late pregnancy is also rapidly destroys this mechanism and may, there- in keeping with the estimate of Gray et al. (1956) fore. be more harmful than hitherto appreciated. and Hutchinson et al. (1959). In considering the clinical evidence it is helpful REFERENCES to review it in relation to polyhydramnios, oligo- Bourne G L (1960) Amer. J. Obstet. Gynec. 79, 1070 hydramnios and also qualitative abnormalities. (1962) The Human Amnion and Chorion. London Observations in Relation to Polyhydramnios Analysis of the association of gross polyhydram- nios recorded clinically in 385 pregnancies Professor James S Scott demonstrates the main correlations which have (Department ofObstetrics and Gynecology, been noted. Gross feetal malformations were University ofLeeds) present in approximately one-third and of these the great majority (90) were anencephalics. In the The Volume and Circulation ofthe Liquor Amnii: same period of time there were 26 other anence- Clinical Observations phalics in which the situation with regard to liquor volume was doubtful and only 6 in which Pregnancy represents an elegant experimental liquor was definitely not present in excessive system of nature. When abnormalities exist it quantity. The only other significant group was would appear theoretically possible, by assessing one of 37 in which there was an upper alimentary the variations in liquor volume, to get information atresia or some lesion which could be expected to as to the routes of production and disposal. It is cause obstruction to deglutition. If an apparently an irritating inconvenience that the programming normal baby is delivered from a hydramniotic sac.