Polyhydramnios
means too much amniotic fluid.
Amniotic fluid volume increases with the duration of pregnancy, with about
200 cc at 16 weeks to about a liter between 28 and 36 weeks. Then it falls
slightly with approaching term, to about 800 cc at 40 weeks. After 40 weeks, the
volume drops further. AFV of more than 2 L is considered polyhydramnios.
Amniotic fluid is removed by the fetal membranes, swallowed by the fetus, and
in the presence of ruptured membranes, may leak out through the vagina. It is
deposited in the amniotic sac by the fetal membranes and by fetal urination. Any
disturbance in the normal equilibrium of fetal swallowing, urinating, or
amniotic membrane fluid transport can result in polyhydramnios (sometimes called
hydramnios)..
Polyhydramnios is both a symptom and a threat. As a symptom, it can reflect
decreased (or absent) fetal swallowing, congenital anomaly, or abnormal membrane
fluid transport. When seen early in pregnancy and in the absence of diabetes, it
carries a risk of about 50% of a major congenital anomaly. It is commonly seen
in pregnancies among diabetic women, particularly if not well controlled.
Regardless of it's cause, polyhydramnios presents a threat to the fetus and to
the mother. Polyhydramnios can lead to premature rupture of the membranes,
premature labor and premature delivery. During labor with polyhydramnios, the
risk of prolapsed fetal small parts and prolapsed umbilical cord is increased.
For the mother, polyhydramnios may contribute to her discomfort during pregnancy
and if severe enough may interfere with breathing. In the most severe of cases,
therapeutic amniocentesis can be performed to relieve (temporarily) the maternal
respiratory distress associated with polyhydramnios.
Several means of identifying polyhydramnios are used, and they are not in
complete agreement. As with oligohydramnios, although the concept of
polyhydramnios is universally accepted, the specific definition of
polyhydramnios is not. Definitions have included:
- Visibly increased AFV on ultrasound. (Both fetal shoulders normally touch
the inside of the uterus. If there is so much fluid present that the anterior
shoulder no longer touches the anterior uterine wall, then polyhydramnios is
said to exist.
- Vertical pockets of AF >8 cm (or 11 cm)
- Amniotic fluid index (AFI) of >25. AFI is the sum of the single deepest
pocket of amniotic fluid in each of the 4 quadrants, in cm.
- Clinical palpation of a free-floating fetus.
When present in a woman not in labor, consideration is given to inducing
labor early, depending on the clinical situation. Therapeutic amniocentesis is
used to treat maternal respiratory distress, although the AF tends to
reaccumulate within a few days.
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