Separately identified samples of amniotic fluid and extraembryonic coelomic fluid obtained by high resolution transvaginal ultrasound-guided amniocentesis from 32 women between 7 and 12 weeks of pregnancy were analysed for human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP). There was a highly significant difference between the hCG levels in amniotic fluid (median level 6.3 U/ml; range 1.6-310.0 U/ml) and those in extraembryonic coelomic fluid (median level 400.0 U/ml; range 135.0-2250.0 U/ml) (p less than 0.001; Mann-Whitney U-test). The levels of AFP were very similar in amniotic fluid (median 26.0 kU/ml; range 10.0-116.5 kU/ml) and extraembryonic coelomic fluid (median level 24.1 kU/ml; range 12.4-94.4 kU/ml).

Objective To determine the biochemical composition of amniotic fluid and extra‐embryonic coelomic fluid between 8 and 12 weeks gestation. Design Prospective observational study. Subjects 40 women with a normal pregnancy between 7 and 12 weeks gestation having termination of pregnancy. Interventions Before termination the women had a transvaginal ultrasound guided amniocentesis. Pure samples of amniotic fluid and extraembryonic coelomic fluid were obtained from each woman and standard biochemical variables were measured in each fluid sample immediately after collection. Results Levels of sodium, potassium and bicarbonate were significantly higher in amniotic fluid whilst chloride, urea, bilirubin, protein, albumin, glucose, creatinine, calcium and phosphate were present in higher concentrations in extraembryonic coelomic fluid. All differences in concentration were significant (P <0.05; unpaired Mest). No relation was demonstrated between electrolyte concentrations in amniotic fluid or coelomic fluid and stage of gestation. Conclusions Amniotic fluid and extraembryonic coelomic fluid have a widely differing biochemical composition. The biological significance of these differences remains unexplained.

Objective-The aim was to establish a normal range of alphafetoprotein (AFP) concentrations in amniotic fluid from 8 to 12 wecks gestation, and to determinc any difference between AFP lcvels in amniotic fluid and extraembryonic coclomic fluid. Design and subjects-150 women had a transvaginal ultrasound guided amniocentesis before termination of an apparently normal first trimester prcgnancy.Separately identified samples of amniotic fluid and extraembryonic coclomic fluid wcrc obtained and assayed by radioimmunoassay for AFP. Results-In amniotic fluid, very high levcls of AFP werc present at 8 weeks, lcvels falling rapidly up to 10 wccks after which there was a slight rise. Thus over the pcriod 8 to 10 weeks, there was a significant invcrse corrclation between amniotic fluid AFP and gestational age (r = 0-67; P < 0.001). In extraembryonic coelomic fluid, by contrast there was no trend in AFP rclative to gestational age. Conclusions-Thc rapidly changing levels of AFP from 8 to 10 weeks as well as the small volumc of the amniotic cavity makes the usc of amniocentesis impracticable bcfore 11 weeks gestation. The lack of any relation between AFP lcvels in amniotic fluid and extraembryonic coelomic fluid cmphasises the importance of identifying the site of amniocentesis in the first trimestcr.The measurcrnent of alpha-fetoprotein (AFP) or acetylcholinesterase (AChE) in amniotic fluid is an established method of diagnosis of neural tube defects in the sccond trimester of preg-Combined Academic

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