22/10/2017 Polyhydramnios and Oligohydramnios: Background, Pathophysiology, EtiologyPolyhydramnios and Oligohydramnios Updated: Sep 20, 2017 Author: Brian S Carter, MD, FAAP; Chief Editor: Dharmendra J Nimavat, MD, FAAP more... OVERVIEW Background 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 volume varies. 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. An inadequate volume of amniotic fluid, oligohydramnios , results in poor development of the lung tissue and can lead to fetal death. Polyhydramnios occurs in 1% of pregnancies, [1] whereas oligohydramnios occurs in about 11% of pregnancies. [2] No age variables are recognized. In pregnancies affected by polyhydramnios, approximately 20% of 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 the fetus's urinary tract can also result in oligohydramnios. Fetal swallowing, which occurs physiologically, reduces the amount of fluid, and an absence of swallowing or a blockage of the fetus's gastrointestinal tract can lead to polyhydramnios. A near term fetus produces 500-1200 mL of urine and swallows between 210 and 790 mL of amniotic fluid per day. [3] Etiology Polyhydramnios The underlying cause of the excessive amniotic fluid volume is obvious in some clinical conditions and is not completely understood in others. Causes include the following: Twin gestation with twin-to-twin transfusion syndrome (increased amniotic fluid in the recipient twin and decreased amniotic fluid in the donor) or multiple gestations Fetal anomalies, including esophageal atresia (usually associated with a tracheoesophageal fistula), tracheal agenesis, duodenal atresia, and other intestinal atresias Central nervous system abnormalities and neuromuscular diseases that cause swallowing dysfunction https://reference.medscape.com/article/975821-overview#showall 1/4 Milder forms of renal dysplasia or obstructive uropathy can be associated with a mild to severe degree of pulmonary hypoplasia and long-term renal failure. Fetal akinesia syndrome with absence of swallowing In a study by Kollmann et al of 860 singleton pregnancies complicated by polyhydramnios. varicella-zoster. herpes infection) serology. most commonly trisomy 21. mortality is 100%. the prognosis is usually good. congenital anomalies. respiratory failure in the neonate. resolution was more likely when it was diagnosed early in pregnancy and when the AFI was low. [4] Oligohydramnios Causes of oligohydramnios include the following: Fetal urinary tract anomalies.8% of the polyhydramnios cases were idiopathic. and parvovirus infection Poorly controlled maternal diabetes mellitus (Oligohydramnios may also be seen if severe vascular disease is present.8% of cases. The prognosis in these cases is related to the volume of amniotic fluid and the gestational age at which oligohydramnios develops.5%. the likelihood of determining the etiology increases. in 8. chorioamnionitis is an additional important maternal complication from oligohydramnios due to rupture of the membranes. 68. Placental insufficiency. Studies show that as the severity of polyhydramnios increases. polyhydramnios (amniotic fluid index [AFI] >24 cm) is associated with an increased rate of fetal malformations. https://reference. pulmonary hypoplasia. the greater the fetal risk of bronchopulmonary dysplasia. high-frequency ventilation.22/10/2017 Polyhydramnios and Oligohydramnios: Background. or postmaturity syndrome when the pregnancy extends beyond 42 weeks' gestation Maternal use of prostaglandin synthase inhibitors or angiotensin-converting enzyme Prognosis If polyhydramnios is not associated with any other findings. rubella. According Desmedt et al. or any urinary obstructive lesion (eg. and.9%. maternal diabetes. such as renal agenesis. Yefet et al reported that even with normal detailed prenatal ultrasonographic evaluation. in severe cases. posterior urethral valves [5] ) Premature rupture of membranes and chronic leakage of the amniotic fluid. fetal-to-maternal hemorrhage. in 2. [7] When idiopathic polyhydramnios persisted across the pregnancy. there was an increased risk of macrosomia and preterm delivery. the likelihood of finding a significant problem is only about 16. [1] In a study of 163 women with idiopathic polyhydramnios. which has an incidence of 21-74%. conditions that may only be diagnosed postnatally. followed by trisomy 18 and trisomy 13. neurologic disorders. [6] About 20% of infants with polyhydramnios have some type of an anomaly. and developmental delay. In cases of pulmonary hypoplasia. whereas maternal diabetes was found in 19. there is a 61% perinatal mortality in polyhydramnios associated with a fetal or placental malformation. as seen in pregnancy-induced hypertension. genetic syndromes. neurologic complications. and a positive TORCH (toxoplasmosis. In the setting of oligohydramnios with renal agenesis. the prognosis depends on the severity of the anomaly. polycystic kidneys.com/article/975821-overview#showall 2/4 .) Chromosomal abnormalities. other [such as syphilis. In cases of mild polyhydramnios. the effectiveness of many treatments such as the administration of surfactant. this should be communicated to the parents. Etiology Congenital cardiac-rhythm anomalies associated with hydrops. The earlier chorioamnionitis occurs in pregnancy. and nitric oxide has not been established.medscape. Pathophysiology. parvovirus B19].5%. in these cases. cytomegalovirus. 1-8 cm) does not appear to be a risk factor for adverse perinatal outcomes in uncomplicated. fetal heart conduction abnormalities. In cases of intrauterine growth restriction (IUGR). In a series.22/10/2017 Polyhydramnios and Oligohydramnios: Background.5%. poor tolerance of labor. [11] Studies show an increased risk of associated fetal anomalies in more severe forms of polyhydramnios. and fetal acidosis.5 deaths per 1000 patients with oligohydramnios. increased maternal uterine tone. Other complications include premature rupture of the membranes (PROM). maternal Rh sensitization. cardiovascular system (22%).com/article/975821-overview#showall 3/4 . lower Apgar scores. umbilical cord compression. In addition to chest wall fixation. Etiology Borderline oligohydramnios (AFI 5. or genitourinary system (13%).12 deaths per 1000 patients with polyhydramnios and 56. is frequently reflective of the extent of placental dysfunction. Oligohydramnios is also associated with meconium staining of the amniotic fluid. and the remaining 8. there is an increased risk of primary cesarean delivery with increasing maternal BMI. preterm labor. Other complications are placental abruption.97 deaths per 1000 patients. the degree of oligohydramnios is often proportional to growth restriction. the PMR increased to 4. the PMR of patients with normal fluid volumes was 1. fetal-maternal hemorrhage. 20% of cases of polyhydramnios involved associated fetal anomalies. which limits movement of its diaphragm. and cesarean delivery. multiple gestations occurred in 7. [13] However.5% were due to other causes. The lack of amniotic fluid allows compression of the fetal abdomen. at least 50% of the patients had no associated risk factors. Risks of amniocentesis include fetal loss (1-2%). In twin gestation with twin-to-twin transfusion. Maternal body mass index (BMI) does not appear to be associated with oligohydramnios in late gestation. late preterm pregnancies. Complications Polyhydramnios Risks and complications of amnioinfusion include amniotic fluid embolism. [10] Preterm labor and delivery occurs in approximately 26% of mothers with polyhydramnios. the lack of amniotic fluid flowing in and out of the fetal lung leads to pulmonary hypoplasia. central nervous system (26%). [8] Morbidity/mortality When Chamberlin used ultrasonography to evaluate the perinatal mortality rate (PMR) in 7562 patients with high-risk pregnancies. and postpartum hemorrhage. The risk of fetal infection is slightly increased. [9] However. and is associated with a corresponding increase in the PMR. However. abruptio placenta. Pathophysiology. malpresentation. nonvertex presentation. [12] Among these cases of polyhydramnios. An increase in the risk of maternal or fetal infection is not substantiated. including problems of the gastrointestinal system (40%). polyhydramnios may occur in the recipient twin. This complication is associated with high morbidity and mortality rates. and transient fetal respiratory distress. maternal respiratory distress. 5% were due to maternal diabetes. Polyhydramnios Idiopathic polyhydramnios appears to increase the risk of prolonged first stage of labour. and fetal pneumothorax. https://reference.medscape. Oligohydramnios The mortality rate in oligohydramnios is high. and oligohydramnios may occur in the donor. 22/10/2017 Polyhydramnios and Oligohydramnios: Background. Etiology Oligohydramnios The primary complications of oligohydramnios are those related to fetal distress before or during labor. The risk of fetal infection is increased in the presence of prolonged rupture of the membranes. Clinical Presentation https://reference.com/article/975821-overview#showall 4/4 .medscape. Pathophysiology.
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