Early amniocentesis: alphafetoprotein levels in amniotic fluid, extraembryonic coelomic fluid and maternal serum between 8 and 13 weeks.

OBJECTIVE--The aim was to establish a normal range of alphafetoprotein (AFP) concentrations in amniotic fluid from 8 to 12 weeks gestation, and to determine any difference between AFP levels in amniotic fluid and extraembryonic coelomic fluid. DESIGN AND SUBJECTS--150 women had a transvaginal ultrasound guided amniocentesis before termination of an apparently normal first trimester pregnancy. Separately identified samples of amniotic fluid and extraembryonic coelomic fluid were obtained and assayed by radioimmunoassay for AFP. RESULTS--In amniotic fluid, very high levels of AFP were present at 8 weeks, levels falling rapidly up to 10 weeks after which there was a slight rise. Thus over the period 8 to 10 weeks, there was a significant inverse correlation between amniotic fluid AFP and gestational age (r = 0.67; P less than 0.001). In extraembryonic coelomic fluid, by contrast there was no trend in AFP relative to gestational age. CONCLUSIONS--The rapidly changing levels of AFP from 8 to 10 weeks as well as the small volume of the amniotic cavity makes the use of amniocentesis impracticable before 11 weeks gestation. The lack of any relation between AFP levels in amniotic fluid and extraembryonic coelomic fluid emphasises the importance of identifying the site of amniocentesis in the first trimester.     

Microvillar enzyme activity in amniotic fluid, extraembryonic coelomic fluid and maternal serum in the first trimester of pregnancy.

The activities of two microvillar enzymes, gamma-glutamyl transpeptidase and total alkaline phosphatase, have been measured in samples of amniotic fluid and extraembryonic coelomic fluid obtained by high-resolution transvaginal ultrasound-guided amniocentesis from 40 women between 7 and 12 weeks of gestation. There was a highly significant difference between gamma-glutamyl transpeptidase activity in amniotic fluid (median level 31 U/l; range 2-409 U/l) and extraembryonic coelomic fluid (median level 2 U/l; range less than 2-16 U/l) (P less than 0.001; Mann-Whitney U-test). Alkaline phosphatase activity was not detected in 84% of amniotic fluid samples and 97% of extraembryonic coelomic fluid samples. No difference was found between total alkaline phosphatase activity in these fluids (P = 0.14; Mann-Whitney U-test). Enzyme activities in amniotic fluid increased with gestational age. A significant linear correlation was found between amniotic fluid gamma-glutamyl transpeptidase activity and stage of gestation (r = 0.86; P less than 0.001) and total alkaline phosphatase activity in amniotic fluid and stage of gestation (r = 0.66; P less than 0.001).     

Origin of amniotic fluid alpha-fetoprotein in normal and defective pregnancies.

Alpha-fetoprotein was determined by electroimmunodiffusion and radioimmunoassay in 109 neonatal urine samples and 94 amniotic fluid samples. The samples were obtained from newborns and from pregnancies ranging in gestational age from 20 to 40 weeks. When alpha-fetoprotein values of neonatal urine and amniotic fluid were correspondingly correlated with gestational age, almost identical declining curves could be drawn. Twenty-one cerebrospinal fluid samples from newborns ranging from 25 to 40 weeks of gestation were similarly determined. No correlation between cerebrospinal fluid alpha-fetoprotein and gestational age could be demonstrated. It is concluded that fetal urine is the major source of alpha-fetoprotein in the amniotic fluid of normal pregnancy. In pregnancies associated with neural tube defects, alpha-fetoprotein elevation is probably not due to the leakage of cerebrospinal fluid into the amniotic cavity.     

Elevated amniotic fluid leptin levels in early second trimester are associated with earlier delivery and lower birthweight in twin pregnancy

OBJECTIVE: To explore the possibility of using early second trimester amniotic fluid leptin levels as a predictor of pregnancy outcome in twin pregnancy. STUDY DESIGN: Amniotic fluid leptin levels from 18 twin-pregnant women in early second trimester were analyzed for their correlation with gestational age at delivery and fetal birthweight. Leptin levels in 16 amniotic fluid samples collected from small for gestational age (SGA) twin pregnancies were compared with those in 20 amniotic fluid samples collected from non-SGA twin pregnancies. RESULTS: A significant correlation was observed between amniotic fluid leptin levels and gestational age at delivery (r = 0.71, p < 0.001) as well as fetal birthweight (r = 0.72, p < 0.001). There was also a significant correlation between gestational age at delivery and fetal birthweight (r = 0.92, p < 0.001). The average gestational age at delivery was 30.4 +/- 1.4 weeks in the SGA group, with a mean birthweight of 1552 +/- 200 g at delivery. For the non-SGA group, the values were 37.3 +/- 0.5 weeks and 2759 +/- 115 g ( p < 0.001), respectively. Amniotic fluid leptin levels were found to be significantly higher ( p < 0.001) for women in the SGA group (11.4 +/- 1.5 ng/mL) than for those in the non-SGA group (5.4 +/- 0.5 ng/mL). CONCLUSION: Higher amniotic fluid leptin levels in early second trimester were associated with both lower gestational age at delivery and lower birthweight. Our results suggest that amniotic fluid leptin levels in early second trimester may be a good marker for the prediction of perinatal complications in twin pregnancy.     

In vivo investigation of placental transfer early in human pregnancy

The use of coelocentesis to study placental drug transfer in the first trimester has required the adaptation of existing pharmacologic models to the changing anatomical structures present before and after 12 weeks of gestation. The biochemical properties of the coelomic and amniotic fluids are important parameters in evaluating the pharmacokinetics of drugs and toxins in early pregnancy. In particular, the protein concentration and pH of these fluids are significantly different and vary widely with gestational age. These biochemical variations are less likely to influence the distribution of inert substances such as inulin inside the first trimester conception cavities than the distribution of drugs such as diazepam or propofol. This can explain why they are not all accumulating inside the exocoelomic cavity. It has been demonstrated that the permeability of the placenta is greater in early pregnancy than at term. Furthermore, because of the slow turn-over of the coelomic fluid, substances such as nicotine to which the mother is chronically exposed accumulate inside the exocoelomic cavity. This prolonged fetal exposure to tobacco carcinogens has important teratogenic implications and should be further explored.     

Selenium status in pregnancy: studies in amniotic fluid from normal pregnant women

Selenium concentrations were determined in amniotic fluid samples obtained from 111 healthy normal pregnant women (median age, 27.5 years) between 12 and 42 weeks of gestation using hydride generation technique coupled with atomic absorption spectroscopy. There was a gradual decrease in the amniotic fluid selenium concentration with the progress of pregnancy. The negative correlation between the gestational age and amniotic fluid selenium concentration was highly significant (p less than 0.001). The implications of these findings in normal pregnancy are discussed.     

Correlation of subjective assessment of amniotic fluid with amniotic fluid index.

We assessed the correlation between abnormal amniotic fluid volumes as defined by the two techniques of (1) subjective evaluation and (2) the amniotic fluid index. Ultrasound evaluation of amniotic fluid volume was conducted on 420 pregnant women with known gestational age greater than twenty weeks but less than 42 weeks. Amniotic fluid was evaluated subjectively and placed into one of three categories: normal, oligohydramnios or polyhydramnios. After fetal biometry was performed, the amniotic fluid volume was assessed semi-quantitatively by the amniotic fluid index technique and assigned to similar categories. We analyzed the data with 2 x 2 contingency tables, using amniotic fluid index as the 'gold standard test'. Our study demonstrates that there was moderate agreement (kappa.5) between both amniotic fluid techniques in the identification of oligohydramnios. However, agreement between the techniques was poor for the identification of polyhydramnios (kappa.16).     

Normal values for human umbilical venous and amniotic fluid pressures and their alteration by fetal disease

Umbilical venous and amniotic fluid pressures were measured in 68 human pregnancies at the time that cordocentesis was performed. Normal umbilical venous pressure was unrelated to gestational age and remained within a tight range (5.3 +/- 2.3 mm Hg, mean +/- SD). Fetuses with an elevated umbilical venous pressure had disorders consistent with either hepatomegaly or congestive heart failure. Umbilical venous pressure was significantly increased before treatment in two fetuses with immune hydrops; it rapidly declined with treatment. Neither gestational age nor umbilical venous pressure was significantly different in the groups that received and did not receive pancuronium. There was a strong relationship between amniotic fluid pressure and gestational age in normal pregnancy (r = 0.54, p less than 0.0001). Women with hydramnios had amniotic fluid pressures greater than control subjects (p = 0.0007). This investigation documents normal human amniotic fluid and fetal umbilical venous pressures. These measurements are altered by disease and may prove to be of diagnostic and therapeutic value in the future.     

Evolution of the amniotic sac and extracelomic space as seen by early ultrasound examination

OBJECTIVE: Amniotic sac and extracelomic space changes occurring from 5 to 14 weeks of pregnancy were observed with transvaginal ultrasound to gain new insights into their normal relationships during this time period. STUDY DESIGN: Ninety-seven women from 5 to 15 weeks' gestation were enrolled in the study. Gestational age was determined by measuring embryonic crown-rump length. The embryo, amniotic sac, and gestational sac areas were measured using the best-fitted computer-generated elliptical view. The embryonic heart rate was measured using the M-mode function of the ultrasound equipment. Associations were determined using the least-squares method and Pearson's correlation coefficient. RESULTS: Mean (range) gestational age calculated from CRL was 9.6 (5.3-14.6) weeks, embryonic heart rate 153 (100-188) beats per minute, embryonic surface 699.6 (5-2,199) mm(2), amniotic sac surface 1,383 (5-5,335) mm(2) and gestational sac surface was 1,517 (110-5,335) mm(2). Significant correlations between gestational sac surface, amniotic sac surface, embryonic surface, heart rate and gestational age were noted (p < 0.01). Changes in the amniotic sac surface correlated with embryonic surface but not with heart rate even when multiple regression analysis was attempted. CONCLUSION: These data describe the normal relationships between the embryonic, amniotic sac, extracelomic space, and gestational sac surface, suggesting that increases in embryonic surface area is a determining factor for early expansion of the amniotic sac at these gestational ages.     

Standardized measurement of amniotic fluid volume by correlation of sonography with dye dilution technique

Amniotic fluid volume was measured in two ways in 23 subjects admitted for interruption of pregnancy at gestational ages 16-24 weeks. The amniotic fluid volume calculated from sonographic measurements was plotted against the "true" amniotic fluid volume obtained by a dye dilution technique. Linear regression analysis showed a good correlation between the two methods (r = 0.815; P less than .001) and yielded a factor that may be used on a general basis to derive the true amniotic fluid volume from the value obtained by sonography. This approach thus offers a standardized procedure for amniotic fluid volume estimation in the second trimester based on the technical simplicity of ultrasonography with the relative accuracy of the dye dilution technique.     

Total antioxidant capacity and reactive oxygen species in amniotic fluid

OBJECTIVE: To identify the presence and/or absence of reactive oxygen species and total antioxidant capacity in amniotic fluid and to determine changes in the levels of reactive oxygen species and total antioxidant capacity with advancing gestational age of pregnancy and fetal or neonatal weights. METHODS: Amniotic fluid was collected from a total of 26 nonsmoking patients. Nine specimens were collected in the third trimester of pregnancy, and 17 specimens were collected in the second trimester. Amniotic fluid reactive oxygen species and total antioxidant capacity levels were determined by chemiluminescence and spectrophotometric assays, respectively. Reactive oxygen species and total antioxidant capacity levels were established and then compared for advancing gestational ages and estimated fetal weights or neonatal weights. RESULTS: Reactive oxygen species levels were present in some but not all specimens, and total antioxidant capacity was present in all specimens. Total antioxidant capacity but not reactive oxygen species levels increased from the second to the third trimester (347.0 mmol/L versus 776.0 mmol/L, P <.001). There was a positive Spearman correlation between total antioxidant capacity and gestational age (r = 0.72, 95% confidence interval 0.43, 1.0, P <.001) and between total antioxidant capacity and estimated fetal weights or neonatal birth weights (r = 0.70, 95% confidence interval 0.40, 1.0, P <.001). There was no correlation between reactive oxygen species and advancing gestational age or weight. CONCLUSION: Total antioxidant capacity levels are present in amniotic fluid at least as early as the second trimester and increase with advancing gestational age and fetal or neonatal weights. Reactive oxygen species levels are not necessarily present in amniotic fluid, and they do not appear to be influenced by gestational age or estimated fetal or neonatal weights.     

Biochemical composition of amniotic fluid and extraembryonic coelomic fluid in the first trimester of pregnancy.

OBJECTIVE: To determine the biochemical composition of amniotic fluid and extraembryonic 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 less than 0.05; unpaired t-test). 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.     

Biovar diversity of Ureaplasma urealyticum in amniotic fluid: distribution,intrauterine inflammatory response and pregnancy outcomes

OBJECTIVE: The objective of this study was to determine the distribution of two biovars of Ureaplasma urealyticum (parvo and T960) in human amniotic fluid and to examine whether the magnitude of the intrauterine inflammatory response and pregnancy outcomes are different between patients with microbial invasion of the amniotic cavity with "parvo biovar" and those with "T960 biovar". STUDY DESIGN: This cohort included 77 preterm singleton pregnancies (gestational age < 37 weeks) in whom U. urealyticum was detected from amniotic fluid using the polymerase chain reaction (PCR). Amniotic fluid was obtained by transabdominal amniocentesis. Amniotic fluid was cultured for aerobic and anaerobic bacteria as well as mycoplasmas. U. urealyticum was biotyped by PCR methods. Amniotic fluid inflammatory response was determined by amniotic fluid white blood cell count and interleukin-6 concentration. RESULTS: 1) The "parvo biovar" was detected in 82% (63/77) and "T960 biovar" was in 18% (14/77) of cases; 2) U. urealyticum was isolated by conventional culture method from amniotic fluid in 56% (35/63) of cases with positive for "parvo biovar" and in 50% (7/14) of cases with positive for "T960 biovar"; 3) There were no significant differences in the median gestational age at amniocentesis, gestational age at delivery, birth weight, amniotic fluid white blood cell count, amniotic fluid interleukin-6 concentration and the rates of clinical chorioamnionitis, histologic chorioamnionitis, funisitis and neonatal morbidity between patients in the two biovar groups. CONCLUSIONS: 1) The "parvo biovar" is more frequently isolated from amniotic fluid of preterm gestations than the "T960 biovar"; 2) Biovar diversity of U. urealyticum in amniotic fluid was not associated with different pregnancy outcome and magnitude of the intraamniotic inflammatory response.     

First-trimester amniotic fluid and extraembryonic coelomic fluid acetylcholinesterase electrophoresis.

Acetylcholinesterase (AChE) gel electrophoresis was performed on samples of amniotic fluid and extraembryonic coelomic fluid obtained by high resolution transvaginal ultrasound-guided amniocentesis from 38 women between 8 and 12 weeks of pregnancy. AChE was positive in 33 per cent (12/36) of the amniotic fluid samples; the percentage of positive results decreased as gestation advanced. AChE was positive in 32 per cent (9/28) of the extraembryonic coelomic fluid samples. In 81 per cent (21/26) of matched samples, the AChE results were identical in the two fluids. Amniotic fluid and extraembryonic coelomic fluid AChE electrophoresis cannot be used to diagnose neural tube defects prior to 12 weeks of gestation.     

Placental transfer of Zidovudine in first trimester of pregnancy

OBJECTIVE: Zidovudine is one of the most common antiretroviral drugs used to prevent vertical transmission of human immunodeficiency virus. However, it is not recommended for use in the first trimester of pregnancy because of reservations about its potential teratogenicity during the organogenesis phase. The objective of this study was to investigate the placental transfer of zidovudine in the first trimester of human pregnancy. METHODS: Twenty-six pregnant women were given 2 oral doses of zidovudine (200 mg) before first trimester surgical termination of pregnancy. Maternal blood, fetal tissue, and coelomic and amniotic fluid were collected for drug analysis. RESULTS: Zidovudine was detected in all samples of maternal serum and fetal tissue but present in only 7 samples of amniotic and coelomic fluid. Zidovudine concentration in fetal tissue was similar to that of maternal serum. The median fetal/maternal ratio was 0.92 and was not associated with gestational age (r = 0.03, P = .89). CONCLUSION: Zidovudine crossed the first trimester human placenta readily and achieved the level of maternal serum rapidly. Patients who choose to take zidovudine in first trimester of pregnancy should be counseled about the potential fetal effects.     

Physiological distribution of placental growth factor and soluble Flt-1 in early pregnancy

OBJECTIVE: To examine the distribution of placental growth factor (PlGF), vascular endothelial growth factor (VEGF) and soluble VEGF receptor-1 (sFlt-1) in maternal and embryonic fluid compartments in early pregnancy. METHOD: The concentrations of PlGF, VEGF and sFlt-1 were measured in coelomic fluid and maternal serum from 16 singleton pregnancies at 7.0-9.3 weeks. In six cases, amniotic fluid was also examined. RESULTS: The median concentration of PlGF was 14.1 (range 8.9-27.6) pg/mL in maternal serum, 13.9 (range 9.5-31.4) pg/mL in coelomic fluid and 8.9 (range 3.9-15.3) pg/mL in amniotic fluid. The concentration of PlGF increased between 7.0 and 9.3 weeks in maternal serum (p = 0.001) and decreased in coelomic and amniotic fluid (p = 0.001). The median concentration of sFlt-1 was 8561 (range 6724-10 673) pg/mL in coelomic fluid, 523 (range 244-986) pg/mL in maternal serum, 30 (range 12-83) pg/mL in amniotic fluid (p = 0.0001), and it did not change significantly with gestation. VEGF was undetectable in most of the samples, and therefore, no further analysis was performed. CONCLUSION: PlGF and sFlt-1 are present in the maternal and fetal fluid compartments in very early pregnancy, and their distribution is consistent with their site of production and the local conditions of transport.     

Amniotic fluid volume and in vivo permeability of ovine fetal membranes

Serial measurements of amniotic fluid volume were made using a tracer dilution technique in sheep during the last half of gestation. No consistent trends were observed in amniotic fluid volume changes over this period. Disappearance of tracer-labeled urea and water from the amniotic fluid was observed at various gestational ages during the last half of pregnancy. The rate of disappearance of urea from the amniotic fluid decreased with gestational age. The disappearance rate of water did not change. Relationships between disappearance rates and amniotic fluid volume suggest that the permeability of the fetal membranes may be important in determining amniotic fluid volume.     

Complement factors in fetal and maternal blood and amniotic fluid during the second trimester of normal pregnancy

Summary. Complement factors (C3, C4, C5; Factors B, H and I) were measured in maternal and fetal serum and amniotic fluid obtained from 55 women with singleton pregnancy undergoing diagnostic fetoscopy at 15 to 28 weeks gestation. Maternal serum levels were consistently 10 times higher than fetal levels which in turn were 10 times higher than levels in amniotic fluid. Spearman rank correlation analysis at weeks 20 to 22 (n = 20) revealed a statistically significant correlation between maternal and fetal levels of C3 and Factors B and I, and between maternal and amniotic fluid levels of Factors B and I. A significant increase in fetal levels of C3, C4 and Factor H, and in amniotic fluid levels of C3 and Factor B was seen in relation to advancing gestational age. These differences were not seen in maternal scrum during the short interval of pregnancy studied. These data confirm earlier assumptions of fetal synthesis of complement factors, and provide normal reference ranges of complement factors in fetal blood and amniotic fluid.     

Complement factors in fetal and maternal blood and amniotic fluid during the second trimester of normal pregnancy

Complement factors (C3, C4, C5; Factors B, H and I) were measured in maternal and fetal serum and amniotic fluid obtained from 55 women with singleton pregnancy undergoing diagnostic fetoscopy at 15 to 28 weeks gestation. Maternal serum levels were consistently 10 times higher than fetal levels which in turn were 10 times higher than levels in amniotic fluid. Spearman rank correlation analysis at weeks 20 to 22 (n = 20) revealed a statistically significant correlation between maternal and fetal levels of C3 and Factors B and I, and between maternal and amniotic fluid levels of Factors B and I. A significant increase in fetal levels of C3, C4 and Factor H, and in amniotic fluid levels of C3 and Factor B was seen in relation to advancing gestational age. These differences were not seen in maternal serum during the short interval of pregnancy studied. These data confirm earlier assumptions of fetal synthesis of complement factors, and provide normal reference ranges of complement factors in fetal blood and amniotic fluid.     

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.