Polyhydramnios (hydramnios) means the presence of an excess amount of amniotic fluid in the amniotic sac (or ‘bag of waters’). This is evaluated according to the gestational age of the fetus (meaning how far along the pregnancy is). It is a fairly common condition, affecting about 1-4% of all pregnancies. It occurs during the 2nd and 3rd trimesters of pregnancy and is a condition that is linked with increased perinatal morbidity and mortality.
Usually, its diagnosis is incidental during a routine pregnancy scan. Its causes are numerous and can be any one of the following:
The likelihood of there being an underlying pathologic condition increases according to the severity of the polyhydramnios. That is to say that while mild polyhydramnios is usually idiopathic, when the polyhydramnios is either moderate or severe, an underlying disease will typically be found.
Fetal malformations associated with polyhydramnios are mainly:
Although an ultrasound scan needs subjective assessment by the doctor, it is nevertheless the most important diagnostic test for polyhydramnios. This is because it allows direct evaluation of the volume of amniotic fluid. It also permits measurement of the deepest pocket of amniotic fluid and determination of the amniotic fluid index: in this way, the classification of mild, moderate or severe can be achieved.
In polyhydramnios, during the 2nd trimester the ratio between the amniotic fluid and the baby is greater than 1 to 1, whereas by the 3rd trimester an excessive amount of amniotic fluid is observed between the baby and the uterine walls. Two other important sonographic measurements can be taken for the evaluation of amniotic fluid volume. These are:
If polyhydramnios is identified, then the following examinations need to be performed:
Ultrasound, or sonography, examination can also diagnose multiple gestation (i.e. the presence of two or more embryos in the uterus), the chorionicity of the pregnancy (to find out if the embryos share a placenta or have different placentas) and the number of gestational sacs. Ultrasound can also identify any fetal defects associated with polyhydramnios.
Finally, it can diagnose a possible pregnancy complication sometimes associated with polyhydramnios, namely intrauterine growth restriction (IUGR, when a fetus is very small for the week of pregnancy), as well as fetal macrosomia (when a fetus is very large for the week of pregnancy) which may result from gestational diabetes.
Polyhydramnios can result in:
The goal of treatment is both to prevent fetal complications and to relieve maternal symptoms that are brought about by the excessive amount of amniotic fluid. While mild polyhydramnios is normally managed in a conservative manner (i.e. bed rest and monitoring), more severe cases might require intervention to reduce the excess amniotic fluid. You may be given steroid injections after 24 weeks to protect the baby, if the baby is likely to be born premature.
The most common treatment options are:
Also of great importance is the management of the maternal or fetal causes of polyhydramnios, if the cause is known. One example is the management of blood glucose levels in the case of gestational diabetes. If severe IUGR is identified, and provided that fetal lung maturity is seen to be adequate, labour induction can also be considered.
The prognosis of mild idiopathic polyhydramnios is generally excellent. When a cause of polyhydramnios is identified, the prognosis depends much more on that cause, and the degree of severity of polyhydramnios.
As mentioned above, the ultrasound scan is a subjective diagnostic tool used for the evaluation of amniotic fluid volume and, therefore, its sensitivity may be affected by a number of factors, including body-mass index, the mother’s use of skin solutions, fetal position in the uterus, as well as the examiner’s experience and ability. This means that amniotic fluid volume could possibly be either overestimated or underestimated.
Also, in a few cases, co-existing fetal malformations cannot be identified—which results in a mistaken diagnosis that the existing polyhydramnios does not result from other underlying pathological conditions. This is why routine monitoring is essential, even when polyhydramnios is the only finding. Lastly, ultrasound scan cannot precisely predict the final pregnancy outcome and possible perinatal complications, nor can it determine the clinical outcome of a fetal malformation after the baby’s birth.
As mentioned, the reliability of the diagnosis depends on the examiner’s experience and ability. Therefore, our recommendation is that sonographic exams be carried out in a prenatal center staffed by highly trained and experienced sonographers and physicians to avoid any critical oversights, for example of the presence of underlying fetal malformations.
The following are questions you could ask the sonographer:
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Last updated September 2019