Amniotic fluid volumes in normal pregnancies

Normal amniotic fluid volume changes throughout pregnancy

The purpose of this study was to provide a quantitative characterization of the changes in amniotic fluid volume that occur throughout gestation. From 705 published amniotic volumes for normal pregnancies, we found that after log transformation, amniotic fluid volume had a uniform variability over 8 to 43 weeks' gestation. Thus the 95% confidence interval covered the range of 1/2.57 to 2.57 times the mean volume at any given gestational age. Contrary to expected trends, mean amniotic fluid volume did not change significantly between 22 and 39 weeks and averaged 777 ml, with the 95% confidence interval ranging from 302 to 1997 ml. The data are summarized in nomograms covering 8 to 43 weeks' gestation.

The relationship of increased amniotic fluid volume to perinatal outcome

We studied a group of 135 patients with polyhydramnios diagnosed on the basis of ultrasonic findings (greatest vertical diameter of the liquor column greater than or equal to 8.0 cm) between 32 and 36 weeks gestation (study group). We compared the obstetric characteristics and perinatal outcome of the study group with a similar number who constituted our control group. The incidence of women aged 20 years or less was higher in the study group (8.9%) compared with 4.5% in the control group. Of the 135 patients who were diagnosed to have polyhydramnios ultrasonically, the clinical diagnoses prior to referral for ultrasonic scanning, were, suspected large for date fetuses in 34 patients (25.2%), clinically suspected polyhydramnios in 28 (20.7%), gestational diabetes in 21 (15.6%) and insulin dependent diabetes in 6 (4.4%) compared with 13.3%, 5.2%, 3.0% and 0.7%, respectively in the control group (P less than 0.05). Preterm delivery occurred in 11.1% in the study group compared with the incidence of 6.7% in the control group. The incidence of fetal distress, low Apgar Score, macrosomic infants, major fetal anomalies, gross and corrected perinatal mortality rate and admission to special/intensive care nursery was significantly higher in the study group compared with that of the control (P less than 0.01). We found ultrasonic examination is a reliable technique to assess the amount of amniotic fluid volume and it alerts the clinician to possible future problems in pregnancy, labor and neonatal period.

Continuous-wave Doppler ultrasound and decreased amniotic fluid volume in pregnant women with intact or ruptured membranes

The cause(s) of decreased amniotic fluid in the absence of fetal anomalies and intrauterine growth retardation is not clear. A prospective study was performed to evaluate umbilical and uterine artery Doppler velocimetric results in pregnancies complicated by decreased amniotic fluid. Three medically high-risk groups were studied: women with (1) normal fluid and intact membranes, (2) decreased fluid and intact membranes, and (3) decreased fluid and ruptured membranes. The decreased fluid/intact membranes group had a significantly increased incidence of abnormal uterine artery waveforms (diastolic notching or absence of end-diastolic velocity); however, uterine systolic/diastolic ratios were not significantly different. The umbilical systolic/diastolic ratios were marginally higher in the intact membranes/decreased fluid group when compared with the ruptured membranes group. This study suggests that problems with maternal blood supply to the placenta may be related to decreased amniotic fluid when membranes are intact.

Theoretical effects of amniotic fluid volume changes on surfactant concentration measurements

A baseline model for consideration of the theoretical effects of amniotic fluid volume changes on surfactant concentration measurements has been constructed. The baseline data include: a polynomial equation that best fits experimental data comparing amniotic fluid lecithin concentration measurements to gestational age, inflow of 0.450 L of surfactant-poor fluid into the amniotic fluid per day, outflow of 0.450 L of surfactant-rich fluid per day, and volume of 1.0 L of amniotic fluid between 30 to 31 and 38 to 39 weeks' gestation. With this model the incremental amounts of lecithin necessary to achieve the concentration levels derived from the polynomial equation have been calculated. The quantity of lecithin needed was calculated at intervals of 0.1 day for 56 days. Polyhydramnios and oligohydramnios were then allowed to develop hypothetically by modifying the inflow or outflow of fluid while keeping the quantity of lecithin added exactly the same as was determined from the baseline data. Chronic polyhydramnios or oligohydramnios had minimal effects on the concentration measurements. The effects of acute polyhydramnios (or oligohydramnios) were greater when the change in volume was due to an increased (or decreased) volume of inflow as compared to a decreased (or increased) volume of outflow.

AFP transport across the fetal membranes in the human

In this investigation the original observation of a correlation between the concentration of amniotic fluid albumin and maternal serum alpha fetoprotein (AFP), as a proof for amniotic fluid-derived AFP in the maternal compartment is confirmed at 15 and 16 weeks of gestation. In contrast to the earlier reported highly significant relation in this study the correlation is only weak, especially at 15 weeks. This might be in agreement with a more frequent absence of raised maternal serum AFP levels in cases of raised amniotic fluid AFP levels prior to 16 weeks of gestation. Transamniotic AFP transport contributes a minor part of the AFP present in the maternal compartment, as also indicated by the lack of correlation between AFP concentrations in amniotic fluid and maternal serum.

Prolonged pregnancy. I. Observations concerning the causes of fetal distress

During a 2-year prospective investigation of prolonged pregnancy in 727 women, 59 (8%) were delivered by cesarean section for fetal distress. This condition was diagnosed by means of electronic fetal heart rate monitoring in 47 of the women, and the patterns were unexpectedly characteristic of umbilical cord compression rather than uteroplacental insufficiency. Blinded sonar examinations were performed in 213 women, and the incidence of cesarean section for fetal distress as now described was significantly increased in those with oligohydramnios (two or fewer 1 cm pockets of amniotic fluid). We conclude that the pathophysiology of fetal distress in prolonged pregnancy is typically oligohydramnios that leads to compromised umbilical cord perfusion, rather than uteroplacental insufficiency.

Predominance of L-dopa in fetal plasma and the amniotic fluid during late gestation in the rat

The purpose of this study was to reevaluate catecholamine distribution in fetal and maternal compartments during late gestation in the rat. Fetal and maternal plasma and amniotic fluid were collected from anesthetized rats on consecutive days from day 17 to day 22, the day of parturition. The fluid was analyzed for dihydroxyphenylalanine (L-dopa), dopamine, norepinephrine, and epinephrine by radioenzymatic assays. Amniotic fluid volume was determined by a direct weighing method. L-Dopa concentrations constituted approximately 50% of total fetal plasma catecholamines and were significantly higher in fetal than in maternal circulation. Dopamine concentrations in fetal plasma were tenfold lower than those of L-dopa but were also significantly higher in fetal than in maternal plasma; norepinephrine levels were similar in both. Maternal plasma epinephrine levels remained relatively constant, whereas fetal epinephrine levels increased fiftyfold from day 17 to day 22. L-Dopa concentrations in the amniotic fluid were tenfold higher than those of dopamine, and the concentrations of both increased markedly during the last 2 days of gestation. However, this apparent rise could be attributed to the concomitant fivefold reduction in the amniotic fluid volume observed at this time. It is concluded that L-dopa is the predominant catecholamine in both the fetal plasma and the amniotic fluid during late gestation in the rat. At the present time, neither the source nor the possible physiologic functions of L-dopa during fetal life are known.

A survey of pregnancies complicated by decreased amniotic fluid

Four hundred seventy-one patients undergoing diagnostic ultrasonography were identified as having moderately decreased amniotic fluid or oligohydramnios, and 339 of these cases were reviewed. Ninety-two of the patients were excluded from further statistical analysis because their decreased fluid was attributed to rupture of the membranes only. Of the remaining patients there was a 7% neonatal malformation rate. Decreased amniotic fluid before 27 weeks of gestation was associated with a significantly poor outcome. Of all the live births, infants of patients with oligohydramnios had lower Apgar scores at 1 minute and 5 minutes than did infants of patients with moderately decreased amniotic fluid. Of cases of patients with decreased fluid, 10% involved fetal distress during labor and in 17% meconium was present. Decreased levels of fluid were associated with an increased rate of abdominal deliveries. Preeclampsia was present in 24.7% of patients with decreased fluid. There was no correlation between the quantitative fluid amounts and the severity of the disease. In view of normative data and clinical experience, these observations suggest that the diagnosis of decreased amniotic fluid on routine ultrasonography requires a fetal scan to rule out anomalies, close antepartum observation to detect complications that may arise in the pregnancy, and delivery under conditions that allow appropriate support and intervention on behalf of the fetus.

Water distribution in the foetus and newborn infant

A short survey is given over changes in water metabolism from early foetal life to infancy. The close connection between water metabolism and body composition is described as well as the changes taking place after birth. The impact of intrauterine malnutrition, delivery and postnatal nutrition is discussed.

Hydramnios: ultrasound diagnosis and its impact on perinatal management and pregnancy outcome

Ultrasonographic technique allows for noninvasive quantification of amniotic fluid volume in pregnancy. A series of 12 pregnancies with ultrasonographically confirmed hydramnios is presented in detail. Following the diagnosis of hydramnios an intensive system-by-system evaluation of the fetal structures was performed. Developmental defects known to be associated with the production of hydramnios were detected in 83% of these pregnancies. Anomalies detected included abdominal wall defects, abnormalities of the central nervous system, pleural effusions, obstructions of the fetal gastrointestinal tract, and others. The early definition of hydramnios and the subsequent discovery of anomalies associated with increased amniotic fluid volume may lead to alteration in prenatal care, in intrapartum management, and in postdelivery resuscitative measures in these complicated pregnancies. In this series, despite early diagnosis of hydramnios and associated fetal developmental anomalies, complications of the pregnancies directly resultant from hydramnios resulted in a high perinatal mortality rate.

Sonographic detection of polyhydramnios: a five-year experience

Between 1975 and 1980, 16,586 sonograms, including repeat scans, were obtained on pregnant women for various obstetric indications. The diagnosis of polyhydramnios was made 78 times by an experienced sonographer as a simple observer judgment of an excess amount of amniotic fluid. In pregnancies thus diagnosed, the fetus was then carefully scanned for anomalies, and repeat scans were done. Major clinical problems encountered are discussed.

Body water metabolism in early infancy

A short survey is given over water metabolism from early fetal life to infancy. The close connection between water metabolism and body composition is described as well as the changes taking place during growth. The impact of intrauterine malnutrition, delivery and postnatal nutrition is discussed, and it is pointed out how the premature infant differs from the full-term infant.

Methods of evaluating fetal lung maturity

Respiratory distress syndrome occurs in infants born with immature lungs. The immature fetal lung lacks an adequate supply of surfactant, a phospholipid-rich substance which is produced in the type II cells of the alveolar epithelium. In the fetus, surfactant is secreted into the potential air spaces of the lung and passes into the amniotic fluid as gestation proceeds. It is now clear that most methods currently in use for assessing fetal lung maturity depend on the detection of a sudden release of surfactant into the amniotic fluid as the lung reaches a critical stage of maturity. These methods, which include the lecithin/sphingomyelin ratio, the lung profile, total phospholipid or lecithin concentration, fluorescence depolarization, lamellar body phospholipid concentration, and the "shake" test, are reviewed in the light of recent understanding of the nature of surfactant. In assessing each method, we have examined possible sources of error in performing the test in the laboratory, factors which could theoretically limit its ability to reflect the state of fetal lung maturity and current information regarding its reliability, in terms of clinical performance. Guidelines for future research in this area are also suggested.

Congealed amniotic fluid in the alveoli of lungs of aborted foals

The alveoli of the lungs of 2 aborted foals contained elongated, dense bodies when examined histologically and by transmission and scanning electron microscopy. By light microscopy, the bodies (10 to 40 micrometers in size) stained intensely with the Gram stain, and up to 10 were present within an alveolus. Electron microscopy determined that such bodies were not cellular in origin but appeared to be a congealed fluid product composed of layers of fibrillar-like material. From the human literature, it was concluded that these intraalveolar bodies were probably congealed amniotic fluid.

Analysis of amniotic fluid, maternal plasma, and cord blood for a human breast gross cystic disease fluid protein

Amniotic fluid was analyzed for the presence of the 15,000 monomer molecular size glycoprotein found in human breast gross cystic disease fluid (GCDFP-15). From 24 weeks' gestation a log-linear increase in levels of GCDFP-15 was noted. The levels of GCDFP-15 doubled every 16 to 28 days, and the highest value recorded was 7,200 ng/ml. At delivery, levels of GCDFP-15 in cord blood plasma were in a background range (mean, 8 ng/ml). Maternal plasma levels of GCDFP-15 were one to tenfold higher in the third trimester of pregnancy when compared to those in nonpregnant women. Since saliva is known to contain high concentrations of GCDFP-15 (10 to 70 micrograms/ml), it is proposed that the levels in amniotic fluid originate from saliva and tracheobronchial secretions.

Relationship between fetal urine production and amniotic fluid volume in normal pregnancy and pregnancy complicated by diabetes

The hourly fetal urine production rate (HFUPR) was calculated from ultrasonic measurements of fetal bladder volume. A normal HFUPR reference curve, constructed from measurements in 189 normal pregnancies between 24 and 42 weeks gestation, showed a rapid increase of HFUPR from 3-3 to 24-4 ml up to 40 weeks followed by a slight decline. The amniotic fluid volume was estimated by the p-aminohippuric acid method within 12 hours of HFUPR measurements. In 67 normal pregnancies, there was no relationship between HFUPR and amniotic fluid volume measured between 36 and 41 weeks gestation. In 12 patients with fetal growth retardation, a relationship was found between reduced fetal urinary output and low amniotic fluid volume between 36 and 38 weeks gestation. In the 16 diabetic patients studied between 28 and 40 weeks gestation, there was no relationship between HFUPR (within or below normal range) and the high amniotic fluid volume (above 1500 ml in 13 patients). The implication of these findings are discussed.

[Fetal causes of the onset of labour. A kybernetic model (author's transl)]

The question of initiation of labour is not yet solved. A fetal fixing of the date would be ingenious. On the one hand the fet is endangered by prematurity, on the other hand by placental insufficiency in postmaturity. Fetuses with comparatively lighter placenta remain in average shorter in utero until spontaneous initiation of labour than those with comparatively heavier placenta. This fact leads to the assumption of a relative placental insufficiency as a determining factor of the onset of labour. A further inquiry demonstrates, that babies born after premature termination of pregnancy about the term - either by induction of labour or by primary sectio caesarea - are heavier and longer than those born after spontaneous labour. This leads to the assumption of a prenatal weight loss of the infant before spontaneous initiation of labour. This weight loss is caused by diminution of water content and relative placental insufficiency. This relative placental insufficiency also leads to a diminution of amniotic fluid, which is swallowed by the "hungry" fet in a greater amount. Altogether a diminution of uterine volume is resulting, which is accomplished by a diminution of uterine wall tension. The coordination of uterine activity, which precedes delivery, is combined with the ripening of the cervix. The ripening of the cervix also leads to a retraction of myometrium and thus to a further diminution of uterine wall tension. It is concluded, that a diminution of uterine volume, causes by fetal weight loss and diminution of amniotic fluid, leads to a reduction of uterine wall tension, which is supported by the ripening of the cervix. This reduction of uterine wall tension is the precondition of the increasing coordination of activity, which precedes delivery.

Alpha1-antitrypsin in amniotic fluid and cord blood of preterm infants with the respiratory distress syndrome

Total protein, alpha1-antitrypsin, and alpha2-macroglobulin were measured on amniotic fluid in 125 pregnancies between 11 and 42 weeks' gestation, and on the cord blood of 66 newborn infants. Amniotic fluid surface active material was assessed by the foam stability test. Amniotic fluid alpha1-antitrypsin is linearly and directly related to amniotic fluid total protein (r = 0.703, p less than 0.001). The cord alpha1-antitrypsin is also linearly related to cord total protein. Intrapartum complications are associated with a significant lowering of the cord alpha1-antitrypsin. Infants with a negative foam stability test had RDS regardless of the amniotic fluid alpha1-antitrypsin. The cord blood alpha1-antitrypsin value did not appear to be related to amniotic fluid surface active material. There were 23 infants with cord alpha1-antitrypsin of less than 0.2 gm/dl and with an intermediate or positive foam stability test; 19 of them had respiratory difficulties of varying severity. It is conceivable that infants, in spite of apparent adequate prenatal lung surfactant, develop respiratory disturbances on the basis of pulmonary fluid and protein transudation and/or reduction or inhibition of pulmonary surfactant incident to intrapartum complications.