How frequently should the amniotic fluid index be repeated?

OBJECTIVE

Our objective was to determine the most appropriate interval for assessing amniotic fluid volume with amniotic fluid index.

STUDY DESIGN

In a retrospective analysis amniotic fluid indexes performed every 3 to 4 days in antepartum testing patients were compared with their follow-up values. Of 10,742 amniotic fluid indexes there were 7393 with follow-up values within 4 days. The results were stratified by current amniotic fluid index, gestational age, and concurrent nonstress test results. The groups were compared with chi 2 analysis.

RESULTS

Patients with normal amniotic fluid index (> or = 8 cm) had a 0.54% chance of oligohydramnios developing in the next 4 days. Those patients with low normal amniotic fluid indexes (5 to 8 cm) had a 5% chance of oligohydramnios developing within the next 4 days, and patients with low amniotic fluid indexes (< or = 5 cm) had a 59% chance of persistent oligohydramnios 4 days after the index examination. Subdividing by gestational age demonstrated that patients > or = 41 weeks' gestation had a 2.6% chance of oligohydramnios developing within 4 days if current amniotic fluid index was between 8 and 15 cm. Results of concurrent fetal heart rate findings did not appear to change the risk for development of oligohydramnios.

CONCLUSION

In patients < 41 weeks' gestation with normal amniotic fluid indexes, a repeat amniotic fluid index is not necessary for 7 days.

Decreased amniotic fluid index in term pregnancy. Clinical significance

In a study of 331 term pregnancies a four-quadrant technique was used to obtain amniotic fluid index measurements, and the results were compared with the current widely used single-pocket measurement. In contrast to the "2-cm rule," the amniotic fluid index measurements consistently demonstrated higher sensitivity in predicting poor fetal outcome with no decrease in specificity. It was noted that pregnancies with an index of < or = 8 cm showed higher incidences of meconium staining, cesarean delivery for fetal distress, abnormal fetal heart rate monitoring and Apgar scores of < or = 7 or less at one minute.

Effects of acute oligohydramnios on respiratory system of fetal sheep

Prolonged oligohydramnios, or a lack of amniotic fluid, is associated with pulmonary hypoplasia and subsequent perinatal morbidity, but it is unclear whether short-term or acute oligohydramnios has any effect on the fetal respiratory system. To investigate the acute effects of removal of amniotic fluid, we studied nine chronically catheterized fetal sheep at 122-127 days gestation. During a control period, we measured the volume of fluid in the fetal potential airways and air spaces (VL), production rate of that fluid, incidence and amplitude of fetal breathing movements, tracheal pressures, and fetal plasma concentrations of cortisol, epinephrine, and norepinephrine. We then drained the amniotic fluid for a short period of time [24-48 h, 30.0 +/- 4.0 (SE) h] and repeated the above measurements. The volume of fluid drained for the initial studies was 1,004 +/- 236 ml. Acute oligohydramnios decreased VL from 35.4 +/- 2.9 ml/kg during control to 22.0 +/- 1.6 after oligohydramnios (P less than 0.004). Acute oligohydramnios did not affect the fetal lung fluid production rate, fetal breathing movements, or any of the other measured variables. Seven repeat studies were performed in six of the fetuses after reaccumulation of the amniotic fluid at 130-138 days, and in four of these studies the lung volume also decreased, although the overall mean for the repeat studies was not significantly different (27.0 +/- 5.2 ml/kg for control vs. 25.5 +/- 5.5 ml/kg for oligohydramnios). Again, none of the other measured variables were altered by oligohydramnios in the repeat studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary hemodynamics in fetal lambs during development at normal and increased oxygen tension

During the latter third of gestation, the number of resistance vessels in the lungs of the fetal sheep increases by 10-fold even after correction for lung growth. We measured pulmonary arterial pressure and blood flow directly and calculated total pulmonary resistance (pressure divided by flow) in intrauterine fetal lambs at 93-95 days and at 136 days of gestation (term is 145-148 days). In addition, we used a hyperbaric chamber to increase oxygen tension in the fetuses and measured the effect on the pulmonary circulation. When corrected for wet weight of the lungs, pulmonary blood flow did not change with advancing gestation (139 +/- 42 to 103 +/- 45 ml.100 g-1.min-1). Pulmonary arterial pressure increased (42 +/- 5 to 49 +/- 3 mmHg); thus total pulmonary resistance increased with advancing gestation from 0.32 +/- 0.12 to 0.55 +/- 0.21 mmHg.100 g.min.ml-1. If the blood flow is corrected for dry weight of the lungs, neither pulmonary blood flow nor total pulmonary resistance changed with advancing gestation. Increasing oxygen tension increased pulmonary blood flow 10-fold in the more mature fetuses but only 0.2-fold in the less mature fetuses. At the normal low oxygen tension of the fetus, pulmonary blood flow does not increase between these two points of gestation in the fetal lamb despite the increase in vessel density in the lungs. However, during elevated oxygen tension, pulmonary blood flow does increase in proportion to the increase in vessel density.

Ultrastructural anomalies in the fetal small intestine indicate that fetal swallowing is important for normal development: an experimental study

Fetal swallowing is established early in development and if fetal ingestion is prevented, the gastrointestinal (GI) tract fails to grow normally. In this article we describe the ultrastructural features of GI tissues developing in the absence of swallowing, in the fetal sheep. We have noted a number of defects in enterocyte morphology. These include abnormal or absence of microvilli, inappropriate cell extrusion, glycogen accumulation and altered lysosomal morphology. Many of these changes resemble those seen in malnourished infants. It is possible that fetal ingestion provides a significant source of nutrients, ensuring adequate GI tract growth in utero, in addition to specific growth factors which may be present in ingested fluid.

Purification, characterization and cDNA cloning of human lung surfactant protein D

Human pulmonary surfactant protein D (SP-D) was identified in lung lavage by its similarity to rat SP-D in both its molecular mass and its Ca(2+)-dependent-binding affinity for maltose [Persson, Chang & Crouch (1990) J. Biol. Chem. 265, 5755-5760]. For structural studies, human SP-D was isolated from amniotic fluid by affinity chromatography on maltose-Sepharose followed by f.p.l.c. on Superose 6, which showed it to have a molecular mass of approx. 620 kDa in non-dissociating conditions. On SDS/PAGE the human SP-D behaved as a single band of 150 kDa or 43 kDa in non-reducing or reducing conditions respectively. The presence of a high concentration of glycine (22%), hydroxyproline and hydroxylysine in the amino acid composition of human SP-D indicated that it contained collagen-like structure. Collagenase digestion yielded a 20 kDa collagenase-resistant globular fragment which retained affinity for maltose. Use of maltosyl-BSA as a neoglycoprotein ligand in a solid-phase binding assay showed that human SP-D has a similar carbohydrate-binding specificity to rat SP-D, but a clearly distinct specificity from that of other lectins, such as conglutinin, for a range of simple saccharides. Amino acid sequence analysis established the presence of collagen-like Gly-Xaa-Yaa triplets in human SP-D and also provided sequence data from the globular region of the molecule which was used in the synthesis of oligonucleotide probes. Screening of a human lung cDNA library with the oligonucleotide probes, and also with rabbit anti-(human SP-D), allowed the isolation of two cDNA clones which overlap to give the full coding sequence of human SP-D. The derived amino acid sequence indicates that the mature human SP-D polypeptide chain is 355 residues long, having a short non-collagen-like N-terminal section of 25 residues, followed by a collagen-like region of 177 residues and a C-terminal C-type lectin domain of 153 residues. Comparison of the human SP-D and bovine serum conglutinin amino acid sequences indicated that they showed 66% identity despite their marked differences in carbohydrate specificity.

New rapid test for prenatal detection of trisomy 21 (Down's syndrome): preliminary report

OBJECTIVE

To devise and evaluate a rapid screening method for detecting trisomy 21 (Down's syndrome) in samples of uncultured amniotic fluid cells.

DESIGN

Non-radioactive in situ hybridisation with HY128, a 500,000 base pair yeast artificial chromosome probe specific for chromosome 21. Blinded study of 12 karyotypically normal amniotic fluid samples and eight samples trisomic for chromosome 21.

SETTING

Cytogenetic and obstetric services at a tertiary referral centre, Copenhagen.

MAIN OUTCOME MEASURES

Time necessary to complete the test. Proportion of cell nuclei containing two and three hybridisation signals in karyotypically normal and abnormal amniotic fluid samples.

RESULTS

The test could be completed within three to four days after amniocentesis. In the normal samples a mean of 73% (range 61-82%) of the amniotic cell nuclei showed two hybridisation signals and 6% (0-18%) showed three signals. By contrast, among the trisomic samples 29% (19-38%) of the nuclei exhibited two signals and 48% (31-60%) showed three signals.

CONCLUSION

The technique clearly distinguished between normal and trisomic samples. Prenatal diagnosis with in situ hybridisation with chromosome specific probes was fast and may make it possible to screen for selected, aneuploidies. However, the technique is still at a preliminary stage and needs further evaluation and refinement.

Arachidonic acid metabolites: effects on inflammation of fetal rabbit excisional wounds

Uncovered fetal rabbit excisional wounds do not exhibit any classic signs of healing; wounds covered with an impermeable cover do contract, reepithelialize, and exhibit inflammation. Prostaglandin E2 (PGE2) is elevated in amniotic fluid, acting as an immunosuppressant at the maternal-fetal interface. Full-thickness excisional wounds were made on 25-day gestational age rabbit fetuses. Half the wounds were covered with an impermeable cover. Tissue from covered, uncovered, and nonwounded fetuses was examined 72 h after wounding for arachidonic acid metabolites. Uncovered wounds had significantly (P less than or equal to 0.05) elevated levels of PGE2, PGF2 alpha, and 12-HETE versus covered wounds and control tissue. Covered wounds had significantly elevated levels of 15-HETE compared to uncovered and control tissue. The elevated PGE2 in uncovered wounds may act as a fetal immunosuppressant; covered wounds (lower PGE2) developed cellular inflammation. Further investigations of these interactions may permit modulation of adult inflammation.

The physiologic mechanisms of variable decelerations

OBJECTIVES

The purpose of this study was to determine the cause and physiologic consequences of variable decelerations.

STUDY DESIGN

Previous studies of heart rate changes in human and experimental animals were critically reviewed with respect to the autonomic nervous system component, the cause of the increased vagal activity, and the role of cord compression or other stimuli in these heart rate changes.

RESULTS

There is abundant evidence from experimental and human studies that variable decelerations can be reproduced by either cord compression or head compression. The vagal reflex produced is probably caused by a combination of chemoreflex (earlier in the deceleration) and baroreflex (later). The variable deceleration is accompanied by an acidosis, primarily respiratory, and probably hypoxemia. Cord compression results in decreased umbilical blood flow.

CONCLUSIONS

Recent Doppler velocimetry studies suggest that even though the variable decelerations may be similar in duration and depth, the reduction of umbilical blood flow may be greater when the prime cause is cord compression than when the prime cause is vagal reflex from another source.

[Water-salt metabolism in the maternal and fetal organisms during hydration at different periods of the pregnancy]

The water surplus in the organism of a pregnant rat was found to cause an increase in the diuretic and ionouretic responses. The hyperhydration, particularly in the beginning of the pregnancy, was found to cause a high percentage of the foetus reabsorption.

Scarless wound healing in the mammalian fetus

Fetal wound healing is a remarkable process that is fundamentally different than postnatal healing. Healing of primarily closed, linear wounds occurs rapidly and without scarring. In late gestational age fetal sheep, a transition to adult-like healing occurs as evidenced by minimal scar formation. Acute inflammation is not involved, fibroblast recruitment and proliferation is minimal, the matrix of the wounds is enriched with HA and collagen deposition is highly organized so that scarring is minimal or nonexistent. Open wounds in several species do not contract, an observation that may be because of an inhibitor of contraction in amniotic fluid. The underlying mechanisms that regulate fetal wound repair are currently not well understood. An altered supply or activity of growth factors may be instrumental. Fibroblasts may preferentially produce HA secondary to a factor present within the fetal system, and HA may influence cellular and matrix events within the wound. As greater knowledge of the biologic factors of scarless healing in the fetus is gained, applications to abnormal adult healing may be developed. As the age of fetal surgery is approaching, it is essential to understand the injury response in these new patients.

Exposure of human amnion to amniotic fluid obtained before labor causes a decrease in chorion/decidual prostaglandin release

Prostaglandin (PG) production by fetal membranes has been implicated in the initiation of human parturition, but its regulation is not well understood. We used an in vitro system to study paracrine control of term, fetal membrane PG production. Using a modified Ussing chamber, full thickness fetal membranes with attached decidua were sealed into a chamber so that each hemichamber was a compartment for either the fetal (amnion) or maternal (chorion/decidua) side. Released PGs from maternal and fetal sides were then measured after exposure of the amnion to either buffer or amniotic fluid. We found that basal release of PGs from both the fetal and maternal sides was 2- to 3-fold higher in membranes obtained after labor compared to those obtained before labor. When amnion obtained after labor was exposed to amniotic fluid, we found a 3- to 5-fold increase in the net release of PGE2 from the amnion; however, the maternal side showed an unexpected relative decrease in PGE2 and PGF2 alpha release. This was a paracrine effect, since direct exposure of chorion/decidua to amniotic fluid caused increased release of the PG precursor, arachidonic acid. Direct transfer of radiolabeled PG from fetal to maternal side was minimal.

Amniotic fluid index and prolonged antepartum fetal heart rate decelerations

Both prolonged fetal heart rate (FHR) decelerations and decreased amounts of amniotic fluid (AF) have been associated with adverse fetal outcome. To determine whether adverse outcome could be predicted by a quantitative assessment of AF in patients with prolonged FHR decelerations, we identified 97 consecutive pregnancies found during antepartum testing to have prolonged FHR decelerations. A four-quadrant AF index was measured concurrently in 92 of these 97 patients. Women with an AF index less than 2 cm had operative intervention for fetal distress in seven of 11 cases (64%), compared with 17 of 81 (21%) who had an index of 2 cm or more (P = .005). We conclude that in patients with a prolonged FHR deceleration during antepartum testing, the need for operative intervention for fetal distress is increased when oligohydramnios is present.

Mimicking low amniotic pressure by chronic pharyngeal drainage does not impair lung development in fetal sheep

OBJECTIVE

The etiology of oligohydramnios-related pulmonary hypoplasia is not understood but is known to involve chronic lung liquid loss. We tested the hypothesis that low amniotic pressure in oligohydramnios disturbs the normal tracheal-amniotic pressure gradient to increase lung liquid loss and impair lung development.

STUDY DESIGN

Chronic pharyngeal catheterization with drainage to the exterior was used in 15 fetal sheep to mimic reduced amniotic pressure at the upper airway in the presence of normal amniotic fluid volume.

RESULTS

Pharyngeal pressures relative to amniotic pressures were negative in all drained fetuses (mean +/- SE -3.0 +/- 0.6 mm Hg), in contrast to positive pressures in controls (0.7 +/- 0.1 mm Hg). There was no significant difference in lung weight or deoxyribonucleic acid relative to body weight, or in lung morphometry, between 10 fetuses drained for 10 to 21 days and their control cotwins.

CONCLUSION

Mimicking low amniotic pressure in the upper airway by chronic fetal pharyngeal drainage does not impair lung development in fetal sheep.

Acceleration of alveolar type II cell differentiation in fetal rhesus monkey lung by administration of EGF

To examine the effect of epidermal growth factor (EGF) on lung parenchymal maturation in fetal rhesus monkey, recombinant human EGF was administered intraperitoneally (IP) at 66 mg/kg body wt over a 7-day period into the fetal peritoneal cavity alone or IP and into the amniotic fluid (AF) simultaneously. The saline carrier was injected IP and AF into control (CO) fetuses. The body weights of the IP + AF group were significantly larger than CO. Overall lung growth, measured as wet lung weight or fixed volume of the right cranial lobe, was unchanged. Fixed lung volume per gram body weight was significantly lower for both IP + AF and IP compared with CO. Morphogenesis of lung parenchyma, measured as percent parenchymal airspace or airspace size, was unchanged. Alveolar type II cell ultrastructure was significantly altered by EGF treatment; volume fraction of cytoplasmic glycogen was 50% less and lamellar bodies threefold greater for IP + AF and IP groups compared with CO. Total phospholipid content of AF was not altered, but relative percentages of different phospholipids were changed by EGF treatments; phosphatidylinositol was significantly reduced, and phosphatidylglycerol was significantly elevated. The lecithin-to-sphingomyelin ratio was unchanged. Surfactant apoprotein A concentration in AF was significantly elevated and was detected by immunoperoxidase in more cuboidal alveolar cells in EGF-treated animals when compared with CO. We conclude that exogenous EGF administered in the last trimester of pregnancy accelerates structural and functional cytodifferentiation of the alveolar type II cell in fetal primates. These maturational changes occur in the absence of significant alterations in overall lung growth or morphogenesis of the gas exchange area.

The accuracy of the assessment of normal fetal intestinal echogenicity--electro-optical densitometry versus the ultrasonographer's eye

Ten plates of normal fetal ultrasonography (at 16-20 weeks' gestation) showing fluid, liver, lung, bone and intestine were submitted to electro-optical transmission surface densitometry. A distinct echogenic gradient has been found and used as an 'internal standard' to evaluate intestinal echogenicity. Intestine had significantly different echogenic properties from bone, liver and fluid but similar to that of lung. Using this echogenicity scale for fetal bowel, observers were correct in 46%, overscored in 32.6% and underscored in 21.4%. These poor results may be due to the significant inconsistency in the interpretation of each plate compared to other plates (about 65%). Although the densitometry-derived grading scale seems valid at these gestational ages, interobserver variation is too large and precludes a simple ultrasonic diagnosis of the hyperechogenic fetal intestine. Densitometric evaluation may be indicated in suspected cases when fetal bowel seems to have increased echogenicity.

[The effect of amniotic fluid taken from women in labor on the morphofunctional development of fetal and newborn rats]

Amniotic fluid from women was injected intra-amniotically to rats at the 14th day of pregnancy in a dose 0.3 ml. Morphological and functional parameters of embryonic development of rats and EMG activity of rat puppies at the age of 30-34 days differed from control ones with respect to the degree of maturity and motor disturbances of newborn babies. The data obtained reveal not only evident but also masked forms of motor pathology which was observed in children later, namely to 6-9 months. Chronic motor pathology in rat puppies was unilateral with central motor disturbances in babies being directly related to the degree of these disturbances.

Relief of presumed compression in oligohydramnios: amnioinfusion does not affect umbilical artery Doppler waveforms

The suggestion that amnioinfusion improves umbilical artery Doppler indices of downstream resistance in oligohydramnios by relieving cord compression was investigated by obtaining waveforms before and immediately after amnioinfusion in 16 pregnancies with severe oligohydramnios. There was no significant difference in the change in umbilical artery pulsatility index (PI) between 11 pregnancies in which amniotic fluid volume was restored (mean delta PI = -0.07, 95% confidence interval -0.17 to +0.07), and 5 pregnancies in which immediate vaginal leakage of infused fluid prevented restitution of amniotic fluid volume. Fetal heart rate did not change significantly in either group. End-diastolic frequencies did not return with restitution of amniotic fluid volume in the 2 pregnancies in which they were absent before infusion (absent in 1, reverse in 1). This study suggests that restitution of amniotic fluid volume in human pregnancies complicated by severe oligohydramnios does not acutely alter the umbilical artery PI.

[Role of the amniotic fluid in gastroschisis. An experimental study]

The short and thick bowel found in gastroschisis has been attributed to contact with amniotic fluid, among other factors. We designed an original animal model in order to isolate the effect of amniotic fluid on the fetal bowel. We created experimental gastroschisis in fetal rabbits. Extruded bowel was kept out of the amniotic sac in half of the operated fetuses. At term, seven days after surgery, 21 surviving fetuses--12 intra-amniotic (GIA) and nine extra-amniotic (GEA)--and 16 control littermates were harvested for study. Five parameters were measured in each animal: body weight, intestinal weight, intestinal length, bowel diameter and bowel wall thickness. We found no statistically significant difference in body weight, intestinal weight or bowel wall thickness. An enormous difference was found in intestinal length among the three groups. Bowel diameter was significantly different in the extreme groups (GIA and controls), with the intestine being more dilated in GIA than in GEA and controls. Gastroschisis in the absence of amniotic fluid has not been as damaging to the fetal intestine as "natural" intraamniotic gastroschisis.

Normal amniotic pressure throughout gestation

OBJECTIVE

To characterize amniotic pressure (AP) in pregnancies with normal amniotic fluid volume.

DESIGN

Observational study, mainly cross-sectional.

SETTING

Fetal medicine unit within a tertiary referral hospital.

SUBJECTS

Patients undergoing transamniotic invasive procedures in whom amniotic fluid volume was subjectively assessed as normal on ultrasound. Those beyond 16 weeks with a deepest vertical pool on ultrasound less than 3.0 or greater than 8.0 cm were excluded. Overall 194 pregnancies were studied on 232 occasions between 7 and 38 weeks gestation.

INTERVENTIONS

Manometry readings referenced to the top of the maternal abdomen were obtained via a fluid-filled line from the needle hub and either connected to a pressure transducer (n = 190) or held vertically against a ruler (n = 42).

MAIN OUTCOME MEASURES

AP in mm Hg, AP corrected for gestational age (z scores), semi-quantitative ultrasonic indices of amniotic fluid volume, clinical variables.

RESULTS

AP in singleton pregnancies increased with advancing gestation (P less than 0.001), and the sigmoid-shaped regression curve plateaued in the mid-trimester. AP z scores were not influenced by volume-related phenomena such as twin gestation, the deepest vertical pool, or amniotic fluid index, nor by maternal age, parity, gravidity, fetal sex, or subsequent spontaneous preterm delivery.

CONCLUSIONS

These findings suggest that AP is not principally determined by intrauterine volume. We speculate that AP, which reflects change in uterine tension as a function of radius, may instead be determined by gestation-specific anatomical and hormonal influences on gravid uterine musculature. A reference range for AP has been constructed for use in amnioinfusion and amnioreduction procedures.

Intrapartum amniotic fluid index and its relationship to fetal distress

Amniotic fluid index was measured in 50 consecutive laboring women after membrane rupture. The 10th percentile of the normal range was 6.2 cm. Thirty-three women had a repeat measurement by a second observer. Although there was no systematic bias between the two observers, the limits of agreement were wide: 95% of the measurements by one observer were between 0.59 and 2.07 times those of the second. Closer agreement was observed when amniotic fluid index was low (less than 6.2 cm). The relationship between intrapartum amniotic fluid index and fetal distress was then investigated in a further 60 laboring women. When compared with women with a normal intrapartum amniotic fluid index, women with a low amniotic fluid index had higher incidences of fetal heart rate abnormalities during the first stage of labor (64% vs 20%, p less than 0.01), meconium (grade II or III) at delivery (64% vs 35%, p less than 0.05), and operative delivery for fetal distress (57% vs 17%, p less than 0.01). Umbilical artery pH and Apgar scores were, however, similar for the two groups. Measurement of intrapartum amniotic fluid index may be an appropriate method for selecting women suitable for intrapartum aminoinfusion.

Increased inorganic sulfate concentrations in amniotic fluid

We assayed inorganic sulfate by ion chromatography in 49 amniotic fluid samples from pregnancies of 14 to 38 weeks gestation. In second trimester samples (14 to 26 weeks gestation), amniotic fluid sulfate concentrations (317 +/- 22 mumol/L, mean +/- SE; n = 32) were not different from previously reported maternal serum values but were significantly lower (p < 0.001) than in the third trimester (693 +/- 42 mumol/L; n = 16). In third trimester samples, sulfate concentrations were significantly correlated with creatinine and uric acid but not chloride, suggesting that renal excretion may be the major source of the amniotic fluid sulfate in the late stages of gestation.

On the physiological significance of tumor necrosis factor-alpha in the human amniotic fluid

Tumor Necrosis Factor (TNF)-alpha and Interleukin (IL)-1 beta levels have been measured in 16 weeks gestation amniotic fluids and mother's sera. Detectable levels of TNF-alpha were found in amniotic fluids, while IL-1 beta was absent. No cytokines were detected in mother's sera. The possible role of TNF-alpha as growth factor for fetal hematopoietic cells is discussed.

The amniotic fluid compartment: the fetal habitat

This study begins with a phylogenetic overview of the fetal membranes in terrestrial vertebrates. It is, of course, well known that the human amnion differs very little from that of other recent members of the phylum, although during evolution the development of the placenta has brought about extensive changes in the chorion. Much of the structure and many of the functions of both the amnion and chorion laeve can be interpreted from a comparative point of view (e.g., production of lipids). The next section deals with the ontogeny of the human amniotic sac, and the histogenesis and functional structure of the fetal membranes. It concludes with a structural analysis of the single layers of the fetal membranes at the end of pregnancy. Light and electron microscopy and histochemical examination are combined with experimental investigations; the striking differences and departure from any possible "norm", however, made the interpretation of morphological findings particularly difficult. Explanations for these differences are put forward: the texture of the connective tissue elements is only approximately determined and therefore gives rise to many irregularities; differences in the structure of cells depend upon their functional state; and the cells exist in groups which reciprocally exchange functional activity with each other. It is emphasized that the amniotic epithelium produces lipids which then appear in the same composition in the amniotic fluid. The fibroblasts in the amniotic connective tissue may, when necessary, be transformed into phagocytes (the so-called Hofbauer cells). Within the fetal membranes one can also observe glucose metabolism which, apart from the supply of local energy and the storage of glycogen, is concerned with production of phospholipids, triglycerides, glycoproteins, proteoglycans, and collagen (types I, III, and IV). A similar process of glucose metabolism is found in the trophoblast, especially the building-up of an extracellular matrix (the so-called fibrinoid), which seems to play a part in the formation of an immune barrier. An attempt is made to correlate the various differentiated cells of the trophoblast with particular functions. The vacuolated cells obviously store glucose. Others, as lectin-binding investigations have shown, are concerned with production of the extracellular matrix. They produce a three-dimensional latticework between the cells, and reach out as far as the borders of the chorionic connective tissue. In this regard, the microtexture of the amniotic and chorionic connective tissue provides a basis for a more precise understanding of their mechanical stability.(ABSTRACT TRUNCATED AT 400 WORDS)