Diseases & Abnormalities of Fetal Membranes

Chapter 29. DISEASES & ABNORMALITIES OF THE FETAL MEMBRANES


Sept. 29, 1997. 1st year Resident J. S. Kim. M.D.




I. DISEASE OF THE CHORIOAMNION



A. Meconium staining



  • Meconium passage is uncommon prior to 38wks and it increases after 40wks.
  • Table 29-1
  • The neonatal mortality rate was 3.3% in the group with meconium-stained membranes compared
    with 1.7% in those without such staining.
  • Severe fetal acidemia was significantly more common with meconium-stained births.
  • Cesarean delivery was doubled in the meconium group.


B. Chorioamnionitis




  • When mononuclear & polymorphonuclear leukocytes infiltrate the chorion, the resulting microscopic finding is designated chorioamnionitis
  • Figure 29-1
  • Management of clinical chorioamnionitis is antimicrobial administration and expedient delivery.


C. Amnionic cysts



  • Small cysts lined by typical amnionic epithelium are occasionally formed.
  • The common variety results from fusion of amnionic folds, with subsequent retention of fluid.


D. Amnion nodosum




  • Squamous metaplasia of the amnion
  • Amnionic caruncles
  • Most commonly seen in the amnion in contact with the chorionic plate.
  • Appear near the insertion of the cord as elevations that are multiple, rounded or oval, and shiny
    grayish-yellow opaque.(<φ1~5mm)
  • Associated with oligohydramnios and are most commonly found in fetuses with renal agenesis or
    prematurely prolonged ruptured membranes or in the placenta of the donor twin with twin -
    transfusion syndrome.


E. Amnionic bands



  • Figure 42-21
  • Disruption of the amnion may lead to formation of bands or strings that adhere to the fetus and impair growth and development of the involved structure.(ex. intrauterine amputations)




II. DISORDERS OF AMNIONIC FLUID VOLUME


  • Amnionic fluid index
  • Table 29-2
  • Hydramnios > 24cm

A. Hydramnios




  • Figure 29-3
  • Causes of Hydramnios


    • In almost half of cases with moderate and severe hydramnios, a fetal anomaly was identified.


    • Significant hydramnios is frequently associated with fetal malformations, especially of the
      central nervous system or gastrointestinal tract.


    • There were 47 singletons with one or more anomalies;

      gastrointestinal (15), nonimmune hydrops (12), central nervous system (12), thoracic (9),
      skeletal (8), chromosomal (7) and cardiacb (4)


    • Moiseb (1991)

      : The normal range for the amnionic fluid index exceeds 24cm between 26 and 39wks.

      The best criterion for hydramnios is an index greater than three standard deviations, or the 97.5 percentile for gestational age.


  • Figure 29-2
  • Figure 29-3
  • Pathogenesis



    • During the first half of pregnancy, transfer of water and other small molecules takes place not only across the amnion but through the fetal skin.


    • During the second trimester, the fetus begins to urinate, swallow, and inspire amnionic fluid.


    • Fetal swallowing is by no means the only mechanism for preventing hydramnios.


    • In cases of anencephaly and spina bifida, increased transudation of fluid from the exposed meninges into the amnionic cavity may be an etiological factors.


    • Another possible explanation in anencephaly, when swallowing is not impaired, is excessive urination caused either by stimulation of cerebrospinal centers deprived of their protective coverings, or lack of antidiuretic effects of impaired arginine vasopressin secretion.


    • In hydramnios associated with monozygotic twin pregnancy, the hypothesis has been advanced that one fetus usurps the greater part of the circulation common to both twins and develops cardiac hypertrophy, which in turn results in increased urine output.


    • Hydramnios that rather commonly develops with maternal diabetes during the third trimester remains unexplained.


  • Symptoms




    • Dyspnea, edema, severe oliguria
    • Acute hydramnios leads to labor before 28wks,or the symptoms become so severe that intervention is mandatory.


  • Diagnosis.




    • Uterine enlargement in association with difficulty in palpating fetal small parts & in hearing fetal heart tones.


    • The differentiation among hydramnios, ascites, and a large ovarian cyst can usually be made without difficulty by ultrasonic evaluation.



  • Figure 29-4
  • Prognosis


    • In general, the more severe the degree of hydramnios, the higher the perinatal mortality rate.
    • Perinatal mortality is increased further by preterm delivery even with a normal fetus.
    • Preterm delivery was more common with an anomalous fetus
    • The most frequent maternal complications associated with hydramnios are placental abruption, uterine dysfunction, and postpartum hemorrhage.
    • Abnormal presentations and operative intervention are also more common.



  • Management



    • If there is dyspnea or abdominal pain or if ambulation is difficult, hospitalization becomes necessary.
    • Bed rest rarely has any effect, and diuretics and water and salt restriction are likewise ineffective.


  1. Amniocentesis




    • The principal purpose of amniocentesis is to relieve maternal distress, and to that end it is transiently successful.


  2. 2. Amniotomy




    • The disadvantages inherent in rupture of the membranes through the cervix is the possibility of cord prolapse and especially of placental abruption.



  3. Indomethacin therapy




    • Indomethacin impairs lung liquid production or enhances absorption, decreases fetal urine production, and increases fluid movement across fetal membranes.

    • Dose : 1.5 ~ 3 mg/kg/day

    • A major concern for the use of indomethacin is the potential for closure of the fetal ductus arteriosus.
    • Moise (1988) : 50% of 14 fetuses whose mothers received indomethacin had ductal constriction detected by doppler ultrasound.


B. Oligohydramnios



  • In general, oligohydramnios developing earl in pregnancy is less common and frequently has a bad prognosis.


  • Marks & Divon (1992) : Oligohydramnios-defined as an amnionic fluid index of 5cm or less- in 12% of 511 pregnancies 41wks or greater.


  • The risk of cord compression, and in turn fetal distress, is increased as the consequence of diminished fluid in all labors, but especially in postterm pregnancy.


  • Table 29-5
  • Table 29-6
  • Newbould (1994) : described autopsy findings in 89 infants with the oligohydramnios sequence.


    3 % : normal renal tract

    34% : bilateral renal agenesis

    34% : bilateral cystic dysplasia

    9 % : unilateral agenesis with dysplasia

    10% : minor urinary abnormalities


C. Pulmonary Hypoplasia




  • When amnionic fluid is scant, pulmonary hypoplasia is common.
  • Three possibilities that account for pulmonary hypoplasia

    • 1st : thoracic compression may prevent chest wall excursion and lung expansion
    • 2nd : lack of fetal breathing movements decrease lung inflow
    • 3rd : failure to retain amnionic fluid or increased outflow with impaired lung growth and development.



  • Oligohydramnios in late pregnancy



    • Oligohydramnios and decreased fetal urine production prior to labor may also be a markers for infants who may not tolerate labor well.
    • Sarno (1990) : An index of 5cm or less was associated with a fivefold increased cesarean delivery rate.
    • Bush (1996) : a 500ml saline bolus given intravenously to the mother increased amnionic fluid index in most cases of oligohydramnios



  • Amnioinfusion




    • TV amnioinfusion : 600ml or 800ml saline bolus followed by 3ml/min continuous infusion
    • Infusion of crystalloid to replace pathologically diminished amnionic fluid has most often been used during labor to prevent umbilical cord compression.
    • Transvaginal amnioinfusion has been extended into three clinical areas.



      1. Treatment of variable or prolonged decelerations
      2. Prophylactically in cases of known oligohydramnios as with prolonged rupture of membranes.
      3. In an attempt to dilute or wash out thick meconium

        cf) It was not found effective to decrease the incidence of meconium aspiration syndrome (Usta,1995)