POLYHYDRAMNIOS OLIGOHYDRAMNIOS
Category: Child Health
Abstract : Polyhydramnios and Oligohydramnios (too much amniotic fluid, too little
amniotic fluid, oligoamnios, oligamnios, fetal lung development, membrane
rupture, fetal urine, fetal swallowing, Potter syndrome) The amniotic fluid
that bathes the fetus is necessary for its proper growth and development. It
cushions the fetus from physical trauma, permits fetal lung growth, and provides
a barri
Polyhydramnios and Oligohydramnios (too much amniotic fluid, too little
amniotic fluid, oligoamnios, oligamnios, fetal lung development, membrane
rupture, fetal urine, fetal swallowing, Potter syndrome)
The amniotic fluid
that bathes the fetus is necessary for its proper growth and development. It
cushions the fetus from physical trauma, permits fetal lung growth, and provides
a barrier against infection.
Normal amniotic fluid levels vary; however, the
average volume increases with gestational age, peaking at 800-1000 mL, which
coincides with 36-37 weeks' gestation. An abnormally high level of amniotic
fluid, polyhydramnios, alerts the clinician to possible fetal anomalies.
Inadequate levels of amniotic fluid, oligohydramnios, results in poor
development of the lung tissue and can lead to fetal death. In pregnancies
affected by polyhydramnios, approximately 20% of the neonates are born with a
congenital anomaly of some type; therefore, the delivery of these newborns in a
tertiary care setting is preferred. This article presents the causes, outcomes,
and treatments of polyhydramnios and oligohydramnios, as well as their effects
on the developing fetus and neonate.
Pathophysiology:
Rupture of the
membranes is the most common cause of oligohydramnios. However, because the
amniotic fluid is primarily fetal urine in the latter half of the pregnancy, the
absence of fetal urine production or a blockage in fetus' the urinary tract also
can result in oligohydramnios. Fetal swallowing, which occurs physiologically,
reduces the amount of fluid, and an absence of swallowing or a blockage of the
fetus' gastrointestinal tract can lead to
polyhydramnios.
Frequency:
In the US: Oligohydramnios occurs in 4% of
pregnancies, and polyhydramnios occurs in 1% of
pregnancies.
Mortality/Morbidity:
• Chamberlin used ultrasonography to
evaluate the perinatal mortality rate (PMR) in 7562 patients with high-risk
pregnancies. The PMR of patients with normal fluid volumes was 1.97 deaths per
1000 patients. The PMR increased to 4.12 deaths per 1000 patients with
polyhydramnios and 56.5 deaths per 1000 patients with oligohydramnios
•
Preterm labor and delivery occurs in approximately 26% of mothers with
polyhydramnios. Other complications are premature rupture of the membranes
(PROM), abruptio placenta, malpresentation, cesarean delivery, and postpartum
hemorrhage
• Studies show an increased risk of associated fetal anomalies
in more severe forms of polyhydramnios. In series in 1990, 20% of cases of
polyhydramnios involved associated fetal anomalies, including problems of the
gastrointestinal system (40%), central nervous system (26%), cardiovascular
system (22%), or genitourinary system (13%). Among these cases of
polyhydramnios, multiple gestations occurred in 7.5%, 5% were due to maternal
diabetes, and the remaining 8.5% were due to other causes. However, at least 50%
of the patients had no associated risk factors.
• The mortality rate in
oligohydramnios is high. The lack of amniotic fluid allows compression of the
fetal abdomen, which limits movement of its diaphragm. In addition to chest wall
fixation, this limitation leads to pulmonary hypoplasia. Oligohydramnios is also
associated with meconium staining of the amniotic fluid, fetal heart conduction
abnormalities, poor tolerance of labor, lower Apgar scores, and fetal acidosis.
In cases of intrauterine growth restriction (IUGR), the degree of
oligohydramnios is often proportional to growth restriction, and it is
associated with a corresponding increase in the PMR.
• In twin gestation
with twin-to-twin transfusion, polyhydramnios may exist in the recipient twin,
and oligohydramnios may exist in the donor. This complication is associated with
high morbidity and mortality rates. Age: No age variables
exist.
Physical:
• Amniotic fluid o The volume of the amniotic fluid
is evaluated by visually dividing the mother's abdomen into 4 quadrants. The
largest vertical pocket of fluid is measured in centimeters. The total volume is
calculated by multiplying this value by 4.
o Polyhydramnios is usually
defined as an amniotic fluid index (AFI) more than 24 cm or a single pocket of
fluid at least 8 cm in deep that results in more than 2000 mL of fluid.
o
Oligohydramnios is sonographically defined as an AFI less than 7 cm or the
absence of a fluid pocket 2-3 cm in depth.
• Polyhydramnios
o Visual
inspection may reveal a rapidly enlarging uterus in the pregnant mother
o
Multiple gestations are associated with polyhydramnios.
o Fetal abnormalities
associated with polyhydramnios include neonatal macrosomia, fetal or neonatal
hydrops with anasarca, ascites, and pleural or pericardial effusions.
o
Skeletal malformations also can occur; these include congenital hip dislocation,
clubfoot, and limb reduction defect.
o Attempt to identify abnormalities in
fetal movement suggestive of neurologic abnormalities and obstruction of the
gastrointestinal tract.
• Oligohydramnios
o When the oligohydramnios
is associated with renal agenesis, symptoms include a marked deformation of the
fetus due to of intrauterine constraint (Potter syndrome).
o Other
obstructive uropathies cause similar deformations, including external
compression with a flattened facies and epicanthal folds, hypertelorism, low-set
ears, a mongoloid slant of the palpebral fissure, a crease below the lower lip,
and micrognathia. Thoracic compression also may occur.
o Oligohydramnios
adversely affects fetal lung development, resulting in pulmonary hypoplasia that
typically leads to death from severe respiratory insufficiency. Findings
associated with pulmonary hypoplasia include bowed legs, clubbed feet, a single
umbilical artery, gastrointestinal atresias, and a narrow chest secondary to
external compression. Infants are typically small for their stated gestational
age (SGA). When an abdominal mass is found on examination of the infant in this
clinical setting, it often represents multicystic-dysplastic kidney, enlarged
urinary bladder, or prune-belly syndrome.
Causes:
•
Polyhydramnios
o Twin gestation with twin-to-twin transfusion (increased
amniotic fluid in the recipient twin and decreased amniotic fluid in the donor)
or multiple gestations, which can lead to twin-to-twin transfusion syndrome
o
Fetal anomalies, including esophageal atresia (usually associated with a
tracheoesophageal fistula), tracheal agenesis, duodenal atresia, and other
intestinal atresias
o CNS abnormalities and neuromuscular diseases that cause
swallowing dysfunction
o Congenital cardiac-rhythm anomalies associated with
hydrops, fetal-to-maternal hemorrhage, and parvovirus infection
o Maternal
type 2 diabetes mellitus (more often than in oligohydramnios)
o Chromosomal
abnormalities, most commonly trisomy 21, followed by trisomy 18 and trisomy
13.
o Fetal akinesia syndrome with absence of swallowing
•
Oligohydramnios
o Fetal urinary tract anomalies, such as renal agenesis,
polycystic kidneys, or any urinary obstructive lesion (eg, posterior urethral
valves)
o Maternal problems, including placental insufficiency, PROM, and
chronic leakage of the amniotic fluid: The major maternal complication from
oligohydramnios is chorioamnionitis, which has an incidence of 21-74%. The
earlier chorioamnionitis occurs in pregnancy, the greater the fetal risk of
bronchopulmonary dysplasia (BPD); neurologic complications; pulmonary
hypoplasia; and, in severe cases, respiratory failure.
o Maternal use of
prostaglandin synthase inhibitors or angiotensin-converting enzyme (ACE)
inhibitors
o Postmaturity syndrome in infants when a pregnancy extends beyond
42 weeks' gestation (possibly caused by a decline in placental
function)
Lab Studies:
• Lecithin-sphingomyelin (L:S) ratio and
phosphatidylglycerol (PG) levels in the amniotic fluid: If premature delivery is
anticipated with either oligohydramnios or polyhydramnios, the amniotic fluid
L:S ratio and PG concentration are helpful in determining the maturity of the
fetal lungs and, therefore, in assessing the likelihood of respiratory distress
syndrome.
• Polyhydramnios
o Glucose tolerance test for mothers with
suspected type 2 diabetes mellitus
o If associated fetal hydrops is present,
screening for maternal antibodies to D, C, Kell, Duffy, and Kidd antigens to
determine the mother's immunity
o Kleihauer-Betke test to evaluate
fetal-maternal hemorrhage
o Venereal Disease Research Laboratories (VDRL)
test to screen for syphilis
o Immunoglobulin G (IgG) and immunoglobulin M
(IgM) titers to evaluate for exposure to rubella, cytomegalovirus (CMV), and
toxoplasmosis
o Hemoglobin Bart in patients of Asian descent (heterozygous
for alpha-thalassemia)
o Fetal karyotyping for trisomy 21, 13, and 18
o
Test for congenital viruses in the amniotic fluid by using the polymerase chain
reaction
• Oligohydramnios - Test for systemic lupus erythematosus, which
causes immune-mediated infarcts in the placenta and placental
insufficiency
Imaging Studies:
• Prenatal ultrasonography and
polyhydramnios
o Evaluate fetal swallowing. A decrease in fetal deglutition
occurs in anencephaly, trisomy 18, trisomy 21, muscular dystrophy, and skeletal
dysplasia.
o Evaluate the fetal anatomy; assess for diaphragmatic hernia,
lung masses, and the absence of the stomach bubble (which is associated with
esophageal atresia). The double-bubble sign or a dilated duodenum suggests the
possibility of duodenal atresia.
o An abnormally large abdominal
circumference may be observed with ascites and hydrops fetalis or a macrosomic
fetus; these findings are also observed in association with poorly controlled
maternal diabetes.
• Prenatal ultrasonography and oligohydramnios
o
Perform serial measurements of the AFI during the pregnancy. If the mother is in
the third trimester and if the volume is less than 8 cm, suspect
oligohydramnios. Levels less than 5 cm indicate significant
oligohydramnios.
o Visualize the fetal kidneys, collecting system, and
bladder. If these are normal, suspect the chronic leakage of amniotic
fluid.
o Assess fetal growth. If PROM or urinary tract anomalies are absent,
consider placental insufficiency and IUGR. Uterine artery Doppler studies may
aid in diagnosing placental insufficiency.
• Postnatal testing of the
infant: Evaluate those organ systems that are likely to be involved on the basis
of the pregnancy history and results of other prenatal evaluations.
Other
Tests:
Chromosome tests are recommended, depending on the results of
postnatal evaluation of the infant.
Procedures:
• Polyhydramnios
o
Reductive amniocentesis may be performed and has contributed to prolonged
pregnancy in patients who are severely affected by hydramnios.
o This
procedure can reduce the risk of preterm labor, PROM, umbilical cord prolapse,
and placental abruption.
o However, if too much fluid is removed, the risk of
placental abruption due to uterine compression increases.
o Other risks of
the procedure include infection, bleeding, and trauma to the fetus.
•
Oligohydramnios
o The transabdominal instillation of indigo carmine may be
used to evaluate for PROM.
o The transcervical instillation of isotonic
sodium chloride solution (ie, amnioinfusion) at the time of delivery reduces the
risk of cord compression, fetal distress and meconium dilution. It also reduces
the potential need for cesarean delivery.
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