Amniotic Fluid Flashcards
What abnormalities are associated with the Amniotic Fluid in pregnancy?
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Oligohydramnios
Polyhydramnios
Oligohydramnios
Prevalence: 1 in 100 pregnancies at <24 weeks’ gestation.
Ultrasound: The vertical measurement of the deepest pocket of amniotic fluid free of fetal parts is <2 cm or the amniotic fluid index (sum of vertical pockets in the four quadrants) is <5 cm.
Assoc Abnorms: There are essentially three major causes of oligohydramnios at <24 weeks’ gestation:
Urinary tract abnormalities: bilateral renal agenesis, multicystic or polycystic kidneys and urethral obstruction.
Preterm prelabor rupture of the membranes: normal fetal growth, anatomy and fetal Doppler, with maternal history of vaginal loss of clear or blood stained amniotic fluid.
Uteroplacental insufficiency: Fetal growth restriction with Doppler evidence of high impedance to flow in the uterine and / or umbilical arteries and redistribution in the fetal circulation.
Follow-Up: Ultrasound scans every 1-3 weeks to monitor fetal condition and assess amniotic fluid volume. In cases of rupture of the membranes assessment of lung growth may be useful in predicting pulmonary hypoplasia.
Therapeutic amnioinfusion is not useful.
In uteroplacental insufficiency assessment of fetal growth and Doppler in the umbilical artery, ductus venosus and middle cerebral artery will help decide the best time for delivery.
Prognosis: Depends on gestational age at diagnosis, cause and gestational age at delivery. In oligohydramnios <24 weeks’ gestation the prognosis is generally poor.
Bilateral renal agenesis, multicystic or polycystic kidneys are lethal abnormalities, usually in the neonatal period due to pulmonary hypoplasia.
Preterm rupture of membranes at ≤20 weeks’ gestation is associated with a poor prognosis; about 40% miscarry within 5 days of membrane rupture due to chorioamnionitis, and, in the remaining 60% of pregnancies, more than 50% of neonates die due to pulmonary hypoplasia.
Uteroplacental insufficiency resulting in oligohydramnios at ≤24 weeks’ gestation is very severe and the most likely outcome is intrauterine death.
Recurrence: Renal abnormalities: agenesis or multicystic 1-3%, infantile polycystic 25%.
Preterm rupture of membranes: 10-25%, but can be reduced by cervical cerclage and progesterone
Uteroplacental insufficiency: 10% but can be reduced by aspirin (150 mg/day) from 12 weeks’ gestation.
Polyhydramnios
Prevalence: 1 in 100 pregnancies.
Ultrasound: The vertical measurement of the deepest pocket of amniotic fluid free of fetal parts is used to classify polyhydramnios into mild (8–11 cm), moderate (12–15 cm) and severe (≥16 cm).
In about 80% of cases the polyhydramnios is mild, in 15% moderate and in 5% severe.
Most cases of mild polyhydramnios are idiopathic, but most cases with moderate or severe polyhydramnios are due to maternal or fetal disorders.
In most cases, polyhydramnios develops late in the second or in the third trimester of pregnancy. Acute polyhydramnios at 16–22 weeks is mainly seen in association with twin-to-twin transfusion syndrome.
Assoc Abnorms: There are essentially two major causes of polyhydramnios:
Reduced fetal swallowing: due to brain abnormalities (e.g anencephaly, Dandy-Walker malformation), facial tumors, gastrointestinal obstruction (e.g. esophageal or duodenal atresia, small bowel obstruction), compressive pulmonary disorders (e.g. pleural effusions, diaphragmatic hernia, CPAM, CHAOS), narrow thoracic cage due to skeletal dysplasias), and fetal akinesia deformation sequence (due to neuromuscular impairment of fetal swallowing).
Increased fetal urination: maternal diabetes mellitus and maternal uremia (increased glucose and urea cause osmotic diuresis), hyperdynamic fetal circulation due to fetal anemia (e.g. red blood cell isoimmunization or congenital infection), fetal and placental tumors (e.g. sacrococcygeal teratoma, placental chorioangioma), or twin-to-twin transfusion syndrome.
Follow-Up: Ultrasound scans every 1-3 weeks to monitor fetal condition, amniotic fluid volume and cervical length.
Prenatal Therapy: Maternal diabetes mellitus: good glycemic control.
Hydrops due to dysrhythmias: antiarrhythmic medication.
Hydrops due to fetal anemia: intrauterine blood transfusion.
Pulmonary cysts or pleural effusions: thoracoamniotic shunting.
Twin-to-twin transfusion syndrome: laser occlusion of placental anastomoses.
Fetal or placental tumors: laser occlusion of feeding vessels.
Defects resulting in reduced fetal swallowing or severe idiopathic polyhydramnios: serial amniodrainages if there is cervical shortening. However, the procedure itself may precipitate premature labor. An alternative and effective method of treatment is maternal administration of indomethacin; however, this drug may cause fetal ductal constriction, and close monitoring by serial fetal echocardiographic studies is necessary.
Prognosis: This depends on the cause of polyhydramnios and the gestational age at delivery.
Recurrence: Idiopathic: no increased risk.
Associated maternal or fetal conditions: depends on the cause.
