Oligohydramnios
by Ian Yeoh
Oligohydramnios, or the lack of amniotic fluid, is a paramount issue that concerns the overwhelming majority of ARPKD babies. Oligohydramnios adversely affects fetal lung development, resulting in pulmonary hypoplasia or severe respiratory insufficiency. Amniotic fluid also cushions a fetus from physical trauma, and provides a barrier against sepsis and other forms of infection. Early in a pregnancy, amniotic fluid is generated from maternal plasma and passes fetal membrane through osmosis and hydrostatic equilibrium. Fetal kidneys begin functioning about week 16 in utero, and renal insufficiency from cystic kidneys prevent regular amniotic fluid volumes, which increase with fetal gestational age, peaking at 800 to 1000 mL at 36 to 37 weeks.
Oligohydramnios is defined as having amniotic fluid of less than 500 mL at 32 to 36 weeks of gestation, a maximum vertical pocket (MVP) of less than 2cm, or an amniotic fluid index (AF1) of less than 5cm. Generally, the earlier the onset of oligohydramnios during pregnancy, the poorer the prognosis. Infant mortality in ARPKD babies from oligohydramnios diagnosed in the second trimester is very high, estimated between 80% and 90%.
My son, Mitchell, is presently 20 years old and underwent antepartum amnioinfusion in order to raise his AFI and prolong my wife’s pregnancy, significantly enhancing his perinatal outcome given preterm oligohydramnios. Amnioinfusion refers to the replacement of fluid into the amniotic cavity, and in Mitchell’s case, transabdominal amnioinfusion was conducted a total of 28 times. Mitchell presented an AFI of less than 3 cm at 17 weeks in utero. A standard amniocentesis at 16-1/2 weeks affirmed the ARPKD diagnosis through genetic studies from umbilical cord tissue obtained from Mitchell’s older sister. Under close sonography control and with strict aseptic precautions, a 20-gauge needle was introduced transabdominally into the amniotic cavity. Between 150 to 400 mL of warmed isotonic saline was infused at a rate of 25 to 30 mL/min. Due to the severity of Mitchell’s oligohydramnios, this was conducted initially weekly, and repeated twice a week after 20 weeks in utero, until Mitchell’s pre-term delivery at 34 weeks. The objective for each infusion was to maintain an AFI between 7 to 10 cm.
Terbutaline was given to prevent preterm labor. Betamethasone, a steroid, was also given subcutaneously to aid fetal lung development. Premature lungs lack surfactant, which is a lipoprotein that helps alveoli (lung airways) from collapsing at the end of an exhalation cycle. To the extent possible, this reduced Mitchell’s respiratory distress at birth and minimized intubation and mechanical ventilation. The consequence of non-treatment would have, at minimum, been apnea, hypoxia and permanent brain damage; death would have been inevitable.
By any measure, transabdominal amnioinfusion is a delicate procedure. My wife did not receive anesthesia to reduce the number of needle sticks and to alleviate risks of further complication, and besides, local anesthetics are generally not effective for such procedures. Two decades after Mitchell’s birth, medical teams are still actively deliberating perinatal survivability from transabdominal amnioinfusion. Nevertheless, from the perspective of the family, the only downside is the risk to the medical teams’ reputation. Only upside is present for an infant having no amniotic fluid. Having lost Mitchell’s sister shortly after birth a year earlier from pulmonary hypoplasia, indecisiveness and inaction would have certainly led to a highly adverse outcome.
