Amniotic fluid volume dynamics

Single-cell guided prenatal derivation of primary fetal epithelial organoids from human amniotic and tracheal fluids

Isolation of tissue-specific fetal stem cells and derivation of primary organoids is limited to samples obtained from termination of pregnancies, hampering prenatal investigation of fetal development and congenital diseases. Therefore, new patient-specific in vitro models are needed. To this aim, isolation and expansion of fetal stem cells during pregnancy, without the need for tissue samples or reprogramming, would be advantageous. Amniotic fluid (AF) is a source of cells from multiple developing organs. Using single-cell analysis, we characterized the cellular identities present in human AF. We identified and isolated viable epithelial stem/progenitor cells of fetal gastrointestinal, renal and pulmonary origin. Upon culture, these cells formed clonal epithelial organoids, manifesting small intestine, kidney tubule and lung identity. AF organoids exhibit transcriptomic, protein expression and functional features of their tissue of origin. With relevance for prenatal disease modeling, we derived lung organoids from AF and tracheal fluid cells of congenital diaphragmatic hernia fetuses, recapitulating some features of the disease. AF organoids are derived in a timeline compatible with prenatal intervention, potentially allowing investigation of therapeutic tools and regenerative medicine strategies personalized to the fetus at clinically relevant developmental stages.

Infection of the maternal-fetal interface and vertical transmission following low-dose inoculation of pregnant rhesus macaques (Macaca mulatta) with an African-lineage Zika virus

BACKGROUND

Congenital Zika virus (ZIKV) infection can result in birth defects, including malformations in the fetal brain and visual system. There are two distinct genetic lineages of ZIKV: African and Asian. Asian-lineage ZIKVs have been associated with adverse pregnancy outcomes in humans; however, recent evidence from experimental models suggests that African-lineage viruses can also be vertically transmitted and cause fetal harm.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the pathway of vertical transmission of African-lineage ZIKV, we inoculated nine pregnant rhesus macaques (Macaca mulatta) subcutaneously with 44 plaque-forming units of a ZIKV strain from Senegal, (ZIKV-DAK). Dams were inoculated either at gestational day 30 or 45. Following maternal inoculation, pregnancies were surgically terminated seven or 14 days later and fetal and maternal-fetal interface tissues were collected and evaluated. Infection in the dams was evaluated via plasma viremia and neutralizing antibody titers pre- and post- ZIKV inoculation. All dams became productively infected and developed strong neutralizing antibody responses. ZIKV RNA was detected in maternal-fetal interface tissues (placenta, decidua, and fetal membranes) by RT-qPCR and in situ hybridization. In situ hybridization detected ZIKV predominantly in the decidua and revealed that the fetal membranes may play a role in ZIKV vertical transmission. Infectious ZIKV was detected in the amniotic fluid of three pregnancies and one fetus had ZIKV RNA detected in multiple tissues. No significant pathology was observed in any fetus; and ZIKV did not have a substantial effect on the placenta.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates that a very low dose of African-lineage ZIKV can be vertically transmitted to the macaque fetus during pregnancy. The low inoculating dose used in this study suggests a low minimal infectious dose for rhesus macaques. Vertical transmission with a low dose in macaques further supports the high epidemic potential of African ZIKV strains.

A review of pregnancy-induced changes in opioid pharmacokinetics, placental transfer, and fetal exposure: Towards fetomaternal physiologically-based pharmacokinetic modeling to improve the treatment of neonatal opioid withdrawal syndrome

Physiologically-based pharmacokinetic (PBPK) modeling has emerged as a useful tool to study pharmacokinetics (PK) in special populations, such as pregnant women, fetuses, and newborns, where practical hurdles severely limit the study of drug behavior. PK in pregnant women is variable and everchanging, differing greatly from that in their nonpregnant female and male counterparts typically enrolled in clinical trials. PBPK models can accommodate pregnancy-induced physiological and metabolic changes, thereby providing mechanistic insights into maternal drug disposition and fetal exposure. Fueled by the soaring opioid epidemic in the United States, opioid use during pregnancy continues to rise, leading to an increased incidence of neonatal opioid withdrawal syndrome (NOWS). The severity of NOWS is influenced by a complex interplay of extrinsic and intrinsic factors, and varies substantially between newborns, but the extent of prenatal opioid exposure is likely the primary driver. Fetomaternal PBPK modeling is an attractive approach to predict in utero opioid exposure. To facilitate the development of fetomaternal PBPK models of opioids, this review provides a detailed overview of pregnancy-induced changes affecting the PK of commonly used opioids during gestation. Moreover, the placental transfer of these opioids is described, along with their disposition in the fetus. Lastly, the implementation of these factors into PBPK models is discussed. Fetomaternal PBPK modeling of opioids is expected to provide improved insights in fetal opioid exposure, which allows for prediction of postnatal NOWS severity, thereby opening the way for precision postnatal treatment of these vulnerable infants.

Association between amniotic fluid evaluation and fetal biometry: a prospective French "Flash" study

We aimed to study the association between three different methods of assessing the amount of amniotic fluid (subjective method (SM), deepest vertical pocket (DVP) and amniotic fluid index (AFI)) and estimated fetal weight (EFW) (in percentile or Z-score) after adjustment on maternal-fetal parameters. We performed a nationwide cross-sectional study through the French network of obstetric sonographers using the "flash" study method and including low-risk singleton pregnancies from 18-40 weeks. Crude and adjusted odds ratio were computed after stratification upon 2nd and 3rd trimester of pregnancy. 1667 ultrasound scans performed by 65 operators were included. Only Z-score of EFW was significantly associated with SM in both trimesters. For DVP and AFI, Z-score of EFW and male fetal gender was significantly associated with them in 2nd trimester. In the 3rd trimester, both Z-score of EFW and large (LGA) or small for gestational age (SGA) fetus were significantly associated with AFI. and DVP. Overweight woman and class I obesity women were also significantly associated with DVP modification. In conclusion, all three methods of amniotic fluid evaluation are significantly associated to estimated fetal weight. DVP and AFI appeared equivalent except that maternal-fetal factors seemed to have a higher impact in DVP than AFI.

Relationship of amniotic fluid index (AFI) in third trimester with fetal weight and gender in a southeast Nigerian population

BACKGROUND

Amniotic fluid (AF) is one of the major determinants of fetal biophysical profile and can predict pregnancy outcome. Abnormal value of amniotic fluid index (AFI) may indicate fetal and maternal disorders.

PURPOSE

To establish reference standards for AFI for this population after 28 weeks of pregnancy and evaluate the relationship between AFI, the estimated fetal weight (EFWT), and fetal gender.

MATERIAL AND METHODS

A prospective cross-sectional estimation of AFI and FWT was done in 385 apparently healthy pregnant women in the gestational age range of 28-42 weeks. General scanning in longitudinal, transverse, and oblique directions of the abdomen was done to assess the fetal wellbeing and determine the fetal gender for each participant. AF was measured in each of the quadrants of the abdomen. The four values of the AF were summed to get the AFI. Measurement of the head circumference, biparietal diameter, abdominal circumference, and femoral length of the fetus were obtained. The EFWT was calculated using Hadlock's formula. The data were divided into five groups: 28-30 weeks 6 days; 31-33 weeks 6 days; 34-36 weeks 6 days; 37-39 weeks 6 days; and 40-42 weeks. AFI for the different gestational age group studied and their percentiles were obtained.

RESULTS

AFI normogram for the local population was established. Positive and significant correlations of AF and EFWT were seen in all the gestational age groups of the women. No significant correlations between AF and EFWT was seen in male fetuses. Regression equations of EFWT and AFI were obtained for female fetuses.

CONCLUSION

The normal range for AFI values for the third trimester was established and could be used to evaluate AFI in the studied population. Established fetal weight should be taken into account when interpreting AFI for female fetuses but this need not be applied for male fetuses.

Regulation of amniotic fluid volume: mathematical model based on intramembranous transport mechanisms

Experimentation in late-gestation fetal sheep has suggested that regulation of amniotic fluid (AF) volume occurs primarily by modulating the rate of intramembranous transport of water and solutes across the amnion into underlying fetal blood vessels. In order to gain insight into intramembranous transport mechanisms, we developed a computer model that allows simulation of experimentally measured changes in AF volume and composition over time. The model included fetal urine excretion and lung liquid secretion as inflows into the amniotic compartment plus fetal swallowing and intramembranous absorption as outflows. By using experimental flows and solute concentrations for urine, lung liquid, and swallowed fluid in combination with the passive and active transport mechanisms of the intramembranous pathway, we simulated AF responses to basal conditions, intra-amniotic fluid infusions, fetal intravascular infusions, urine replacement, and tracheoesophageal occlusion. The experimental data are consistent with four intramembranous transport mechanisms acting in concert: 1) an active unidirectional bulk transport of AF with all dissolved solutes out of AF into fetal blood presumably by vesicles; 2) passive bidirectional diffusion of solutes, such as sodium and chloride, between fetal blood and AF; 3) passive bidirectional water movement between AF and fetal blood; and 4) unidirectional transport of lactate into the AF. Further, only unidirectional bulk transport is dynamically regulated. The simulations also identified areas for future study: 1) identifying intramembranous stimulators and inhibitors, 2) determining the semipermeability characteristics of the intramembranous pathway, and 3) characterizing the vesicles that are the primary mediators of intramembranous transport.

Relationship between amniotic fluid index and ultrasound estimated fetal weight in healthy pregnant african women

Introduction:

Fetal weight (FW) estimation in late pregnancy is an important guide in obstetric care. Amniotic fluid protects the fetus against traumatic and infective insults. There possibly exists a relationship between FW and amniotic fluid index (AFI) that can be estimated by ultrasonography.

Materials and Methods:

Two hundred and fifty-eight low-risk pregnancies were prospectively studied by means of ultrasound over a 12-month period. FW was estimated using a combination of fetal parameters; bi-parietal diameter, fetal trunk cross sectional area, and femur length. AFI was assessed using the 4-quadrant method. Spearman's correlation was used to test possible relationship between amniotic fluid indices and estimated FW pairs. The level of statistical significance was set at P ≤ 0.05.

Results:

The mean AF1 and estimated fetal weight (EFW) pairs were as follows: at 27-29 weeks the values were 172.1 mm and 1,250.2 g; at 30-32 weeks AF1 and EFW values were 170.3 mm and 1,648.0 g; at 33-35 weeks values were 162.3 mm and 2,273.5 g; at 36-38 weeks values were 144.09 mm and 2,906.1 g; at 39-40 weeks AF1 and EFW values were 125.0 mm and 3,222.6 g. Overall, there was no statistically significant relationship between AFI and EFW (P > 0.05; r = 0.241).

Conclusion:

While FW calculations and amniotic index showed variations in value in late pregnancy, there does not appear to be a linear relationship between ultrasound estimate of FW and amniotic index. The implication of this is that fetal size need not be taken into cognizance when alterations in amniotic fluid values are noted.

Differences in amniotic fluid patterns and fetal biometric parameters in third trimester pregnancies with and without diabetes

OBJECTIVE

The amniotic fluid index (AFI) has been increasingly used in the assessment of fetal well-being. We conducted the study to evaluate and compare the amniotic fluid index in third trimester normal and diabetic human pregnancy and to assess the correlation between the AFI and the fetal biometric parameters.

METHODS

Real-time ultrasound was performed to evaluate the AFI (four-quadrant technique), and to measure the biparietal diameter, head circumference, abdominal circumference, and femur length in 225 normal and 120 diabetic pregnant women from 27 to 42 weeks of gestation. Each patient was studied only once.

RESULTS

AFI in normal pregnancies was less than that in diabetic pregnancies throughout the gestational ages studied (27-42 weeks). In normal pregnancy, the mean AFI was 14.0 cm at 27 weeks and decreased to 11.4 cm at 42 weeks (r = 0.25, p = 0.0005), whereas in diabetic pregnancies, the values remained stable throughout the gestational ages studied. There exist significant differences in AFI, estimated fetal weight, estimated fetal weight %, abdominal circumference, abdominal circumference %, and head circumference to abdominal circumference ratio between the two groups. In both normal and diabetic pregnancies, there is a positive correlation between the AFI and the percentile of abdominal circumference (p < 0.0001), and between the AFI and the percentile of estimated fetal weight (p < 0.0001).

CONCLUSION

This study provides gestational age-specific values of the AFI in normal and diabetic pregnancies. Diabetic pregnancy has greater AFI values than normal pregnancy between 27 and 42 weeks. The AFI correlates to the percentile of the estimated fetal weight and the abdominal circumference in both groups, suggesting that there may be a relationship between increased AFI and large for gestational age fetus independent of diabetes.

Combined analysis with amniotic fluid index and estimated fetal weight for prediction of severe macrosomia at birth

OBJECTIVE

To evaluate combined analysis with amniotic fluid index (AFI) and estimated fetal weight (EFW) for prediction of severe macrosomia at birth.

STUDY DESIGN

In this retrospective case-control study, 50 term severe macrosomic newborns (birthweight [BW] > or = 97th percentile) were included in the study group and 100 appropriate for gestational age newborns served as controls. All pregnancies underwent a third-trimester sonographic evaluation in which AFI and EFW were measured. The association between BW and AFI and EFW percentiles was examined. The statistical analysis included Student t test, simple regression and receiver-operating curve analyses, and 2x2 tables.

RESULTS

The mean mid-third-trimester AFI percentile and EFW percentile in severe macrosomic infants were 72.4 +/- 22.5 and 83 +/- 12, respectively, which was significantly higher than in controls (P < .0001). Significant correlations were detected between BW and AFI and EFW percentiles (r = 0.44 and r = 0.72, respectively; P < .0001). Receiver-operating characteristic analysis identified AFI > or = 60th percentile and EFW > or = 71st percentile as best predictors of severe macrosomia. The combined analysis with AFI > or = 60th percentile and EFW > or = 71st percentile resulted in a positive predictive value of 85%.

CONCLUSION

There is a significant correlation between mid-third-trimester AFI and BW. AFI > or = 60th percentile and EFW > or = 71st percentile during the mid third trimester are useful predictors of severe macrosomia at birth.

False diagnosis of renal agenesis on fetal MRI

We report a twin pregnancy in which prenatal ultrasound revealed anhydramnios and bilateral absence of the kidneys in both fetuses. To overcome the difficulties faced in obtaining accurate information on fetal ultrasound in cases with oligohydramnios, an attempt was made to use fetal magnetic resonance imaging (MRI) to confirm the renal status. However, while the fetal MRI showed renal agenesis in both twins, postnatal follow-up revealed that one twin, which survived, had a small unilateral kidney not seen antenatally on fetal ultrasound or MRI. The second twin had bilateral renal agenesis and died of pulmonary hypoplasia. Care should be taken when using fetal MRI to replace fetal ultrasound in cases with poor visibility.

Association of amniotic fluid index with estimated fetal weight

OBJECTIVE

The relationship between amniotic fluid volume and gestational age has been described previously. The association of body weight and urine output has been observed in human neonates. Our goal was to assess the correlation of the amniotic fluid index (AFI) with estimated fetal weight (EFW) in the third trimester.

METHODS

We conducted a retrospective observational study on 426 pregnant women with singleton gestations who were referred to our unit for sonographic evaluation in the third trimester. The AFI, EFW, and EFW percentile corrected for gestational age were evaluated. The sonographic examinations were stratified into 3 gestational age categories: 28 through 33.9 weeks, 34 through 37.9 weeks, and 38 weeks and later. Maternal and fetal outcome variables were collected from medical records. Linear regression, Mann-Whitney U, and Kruskal-Wallis tests were used for statistical analysis.

RESULTS

There was no significant relationship between the AFI and EFW in the entire group of patients (R = 0.08; P = .096). There was a significant relationship between the AFI and EFW after 38 weeks' gestation (R = 0.30; P = .003). In addition, in female fetuses the EFW percentile correlated with higher AFI values at all gestational ages (R = 0.31; P < .001); this, however, was not observed in male fetuses.

CONCLUSIONS

There is no relationship between the AFI and EFW during the third trimester, although a positive relationship between the AFI and EFW was noted late in gestation. In pregnancies with female fetuses, the AFI was positively associated with EFW percentile before 38 weeks' gestation.

Elimination kinetics of ethanol in pregnant women

To evaluate the pharmacokinetics of ethanol in the early second trimester of pregnancy, ethanol concentrations simultaneously measured in the maternal blood (EtOH-MB) and in the amniotic fluid (EtOH-AF) of six pregnant women were obtained from a previous study in which a single ethanol dose of 300mgkg(-1) body weight was administered orally. For maternal blood ethanol concentration, the kinetic equation was: [Formula: see text] where k(12) and k(21) are, respectively, the rate constant of ethanol transfer from either the central compartment to the peripheral compartment or vice versa; V(max)(EtOH)is the maximal velocity for ethanol oxidation; and K(m)(EtOH) is the concentration at which half of the maximal rate of ethanol elimination is reached. The maximum concentration of EtOH in AF was 60% lower than in MB (P=0.36). However, the AUC(0-3.5h) in AF was only 16% lower than the value for MB (P=0.059). The k(12) (0.20 =/- 0.26 h(-1)) was almost twice faster than k(21) (0, h(-1)). The V(max)(EtOH) was 237.6 +/- 71.5 microgml(-1)h(-1) and K(m)(EtOH) was 3.7 +/- 4.7 microgml(-1). Our results imply that in the early second trimester, ethanol metabolism is fast. However, ethanol clearance from the AF is slower than ethanol clearance in MB. This process is widely variable, and our findings may partially explain the wide variability of ethanol's toxic effects on the fetus.

Mechanisms responsible for postnatal middle ear amniotic fluid clearance

Neonatal guinea pigs show signs of a temporary conductive hearing loss during the first few days after birth. It has been suggested that this is due mainly to the presence of amniotic fluid in the middle ear (ME) cavity at birth and its subsequent clearance. This study was designed to try to identify the mechanisms responsible for the amniotic fluid clearance from the ME after birth by means of several experiments in guinea pigs. The osmolarity of the blood, amniotic fluid and the fluid in the ME cavity of guinea pig fetuses was measured. Serum and normal saline were introduced into the ME of older animals and fluid clearance was monitored short- and long-term by microscopic observation, tympanometry and estimation of residual fluid. Following instillation of 1/5 normal saline and normal saline into the ME cavity, the osmolarity of the remaining fluid was determined, short- and long-term. Clear osmotic pressure gradients were found between amniotic fluid (low pressure), fetal blood (higher pressure) and the fluid in the fetal ME (intermediate between them). The MEs into which normal saline had been introduced developed negative pressure and, over several days, were cleared of fluid. When serum was applied, ME pressure remained close to atmospheric and the fluid was not cleared. Hypotonic saline application led to an increase in the osmotic pressure in the fluid remaining in the ME. It is concluded that most of the amniotic fluid is cleared from the neonatal ME cavity by water outflow into the blood due to osmotic pressure gradients.

Is there a relationship between fetal weight and amniotic fluid index?

OBJECTIVE

To establish whether there is a relationship between the amniotic fluid index and estimated fetal weight in the third trimester. The presence of a relationship would require adjustment of amniotic fluid index to take account of estimated fetal weight with potential improvement in its prediction of adverse perinatal outcomes.

METHODS

Paired measurements of amniotic fluid index and estimated fetal weight from 274 low-risk pregnancies enrolled in a longitudinal study of fetal growth. Measurements were made at fortnightly intervals from 30 weeks' gestation until delivery. A relationship between amniotic fluid index and estimated fetal weight was sought at gestational age week intervals of 30-32, 33-35, 36-38 and 39-41.

RESULTS

One thousand and three pairs of measurements of amniotic fluid index and estimated fetal weight were available for analysis. Mean amniotic fluid index decreased towards term as expected. There was no correlation between amniotic fluid index and estimated fetal weight. Furthermore, there was no correlation between amniotic fluid index and estimated fetal weight at any of the gestational age intervals.

CONCLUSIONS

There is no clinically relevant correlation between amniotic fluid index and estimated fetal weight. It should remain clinical practice to take account of gestational age when interpreting amniotic fluid index but it is not necessary to make adjustments for estimated fetal weight.

Prenatal diagnosis and management of abnormalities in the urologic system

We have reviewed the prenatal diagnosis and management of abnormalities in the urologic system. Urologic anomalies may be caused by embryologic aberrations, genetic disease, or a nonrandom association with other structural abnormalities. There is a wide range of prognoses, depending on the cause and the impact of the anomaly on the production of amniotic fluid. Management focuses on obtaining an accurate prenatal diagnosis, providing appropriate counseling, and ensuring the proper surveillance or treatment before and after birth.

Amniotic fluid and the umbilical cord: the fetal milieu and lifeline

Amniotic fluid volume should be routinely assessed in every second and third trimester case. A review of amniotic fluid physiology and techniques for ultrasound evaluation of fluid volume is presented. The causes and significance of oligohydramnios and polyhydramnios are stressed. Umbilical cord abnormalities are often incidently observed at the time of amniotic fluid evaluation. The clinical significance of some common umbilical cord abnormalities such as a two-vessel cord and nuchal cord are discussed. Other, more uncommon entities such as cord mass lesions are also reviewed. Finally, the role of cord Doppler interrogation in determining fetal well-being is discussed.

Clinical assessment of amniotic fluid

Amniotic fluid volume estimation has become an integral part of fetal evaluation. Although the sonographic techniques clinically available are limited in their accuracy and predictive value, the careful performance of AFI measurements provide important and complementary clinical data on which to base management decisions in pregnancies at risk.

Vascularization of the ovine amnion and chorion: a morphometric characterization of the surface area of the intramembranous pathway

OBJECTIVE

The purpose of this study was to characterize the vascularization of the ovine amnion, allantois, and chorion.

STUDY DESIGN

A white silicone vascular casting material was infused into both umbilical arteries of nine fetal sheep ranging in age from 58 to 142 days' gestation. A morphometric analysis of photomicrographs of the membranes was then performed with computerized image analysis techniques.

RESULTS

After removal of the uterus, the fetus was surrounded by a layer of white silicone-filled microvessels in the chorion. The amniotic membrane after separation from the chorion was covered by a fine mesh of microvessels, whereas the allantois was avascular. The amniotic membrane readily separated into an outer vascularized layer and an inner, avascular layer containing the amnion. Approximately 50% of the surface of the chorionic membrane was covered by microvessels; this appeared independent of gestational age. At midgestation 30% of the surface of the amnion was covered by microvessels, and this decreased to 17% at 142 days. Relative to fetal weight, the amniotic and chorionic vascular surface areas decreased from 6 to 0.3 and from 15 to 1.5 cm2/gm fetal weight, respectively, over the last half of gestation.

CONCLUSIONS

There is an extensive network of microscopic fetal blood vessels within the ovine chorion and covering the outer surface of the amnion. These vessels appear to be ideally situated to facilitate a direct exchange of water and solutes between amniotic or allantoic fluids and fetal blood through the intramembranous pathway.