••• Chapter 18^ Amniotic Fluid^187
❍ Approximately what volume of amniotic fluid is swallowed daily by the fetus near term?
200 to 500 mL/day.
❍ How many milliliters of fluid does the fetal lung secrete per day in the third trimester?
300 to 400 mL/day.
❍ Over the course of 1 day, what is the net turnover volume of the amniotic fluid?
95% of the total amniotic fluid volume is turned over daily.
❍ What is the source of meconium in the amniotic fluid?
Fetal bowel movements associated with fetal stress and/or postmaturity (thought to be associated with maturation
of nerves innervating the GI tract).
❍ What is the incidence of passage of meconium at?
a. <32 weeks?
Rare.
b. Term?
10% to 15%.
c. 42 weeks?
25% to 35%.
❍ Why is the passage of meconium occurring with oligohydramnios of particular concern?
It is thought that there may be an increase in the viscosity of the meconium, and therefore there may be an
increased risk of aspiration pneumonia.
❍ How is amniotic fluid volume most commonly measured?
Ultrasound.
❍ What are the two most commonly used objective methods to measure amniotic fluid volume via ultrasound?
Measurement of the maximum vertical pocket (MVP) and calculation of the amniotic fluid index (AFI).
❍ How is the MVP obtained?
Measurement of the vertical depth of the largest cord- and limb-free pocket of amniotic fluid.
❍ How is the AFI calculated?
Summation of the depths of the largest vertical pocket in each of the four quadrants.
❍ When calculating the AFI, what anatomical landmarks are used to divide the uterus into quadrants?
Linea nigra and umbilicus.
❍ How is the AFI calculated before 20 weeks’ gestation?
Summation of the two MVPs on each side of the linea nigra.