1. 1.

    Amniocentesis  – sampling of amniotic fluid

    1. (a)

      Most common indication during second trimester is cytogenetic analysis of fetal cells

      1. (i)

        Occasionally used to determine AFP levels and acetylcholinesterase activity to diagnose fetal neural tube defects

    2. (b)

      Not recommended prior to 15 weeks’ gestation due to a high incidence of procedure-related pregnancy loss

    3. (c)

      Performed later in pregnancy for non-genetic indications:

      1. (i)

        Measures lecithin and sphingomyelin to assess fetal lung maturity

      2. (ii)

        Amnioreduction in pregnancies with severe polyhydramnios

      3. (iii)

        Confirm preterm rupture of membranes (PROM)

      4. (iv)

        Confirm or exclude an intra-amniotic infection

      5. (v)

        For spectrophotometric analysis of amniotic fluid bilirubin to determine fetal Rh type in pregnancies complicated by isoimmunization

  2. 2.

    Oligohydramnios  – decreased amniotic fluid volume

    1. (a)

      In the latter half of pregnancy (and in the absence of ruptured membranes) reflects chronic uteroplacental insufficiency and/or increased renal artery resistance causing diminished urine output

    2. (b)

      Predisposes fetus to umbilical cord compression, which may cause intermittent fetal hypoxemia, meconium passage, or meconium aspiration

  3. 3.

    Polyhydramnios  – increased amniotic fluid volume

    1. (a)

      Typically indicates fetal anatomic abnormalities (e.g., esophageal atresia)