The term oligohydramnios literally means “scant amniotic fluid” and is diagnosed when an ultrasound reveals an amniotic fluid index (AFI) of less than 5 cm. For reference, the normal value for AFI is 5-25 cm.
What is amniotic fluid?
Amniotic fluid is a complex fluid that nourishes and cushions the developing fetus while also helping to regulate temperature and aid in pulmonary, digestive and renal maturation. It is initially made up of maternal plasma that has diffused across the placenta, but over time will change to include urine and other secretions from the fetus. Amniotic fluid contains proteins, carbohydrates, lipids, antimicrobial peptides, hormones, electrolytes and other substances necessary for fetal development.
What causes oligohydramnios?
There are many precipitating factors that can lead to oligohydramnios. Some of the key ones are:
- Premature rupture of membranes (most common cause)
- Uteroplacental insufficiency
- Medications such as ACE inhibitors, NSAIDs and lithium
- Post-term pregnancy
- Fetal growth restriction
- Fetal abnormalities including renal conditions such as a blocked urinary tract or absence of one or both kidneys
- Maternal dehydration/hypovolemia
- Maternal and or fetal hypoxia (leads to decreased fetal renal perfusion which decreases urine output)
- Anyone considered high risk – age under 17 or over 35, history of renal disease or diabetes, multiparity, previous high-risk pregnancies, or a family history of genetic conditions that could affect renal development.
What are the complications of oligohydramnios?
Complications vary depending on when the oligohydramnios first started. If the pregnant person had low levels of amniotic fluid during the first or second trimester, the complications can be especially devastating – these include preterm labor, IUGR (intrauterine growth restriction) and even death to the fetus.
If oligohydramnios occurs in the third trimester, it generally has less impact but can still be detrimental, which is why it is absolutely vital that the mother be monitored closely. Complications can include umbilical cord compression, meconium aspiration and placental insufficiency.
Now that you have an overview of oligohydramnios, let’s go through it using the Straight A Nursing LATTE method. Ready?
L: How does the patient LOOK?
Much of the time, the pregnant patient may not have any outward signs of oligohydramnios.
- Fundal height may be small for gestational age.
- The patient may state they are leaking urine, when in reality this is amniotic fluid.
- The patient may complain of painful fetal movement which is due to the lack of cushioning normal amounts of amniotic fluid provide.
- If the cause is dehydration or hypovolemia, the patient could be tachycardic, hypotensive, complain of fatigue or thirst, and produce small amounts of amber-colored urine.
A: How do you ASSESS this patient?
- Full set of vital signs, paying close attention to blood pressure and heart rate since preeclampsia and hypovolemia can be precipitating factors.
- Ask the patient if they are experiencing pain with fetal movement.
- Measure weight – if less than expected, it could indicate oligohydramnios.
- Measure fundal height. If it’s smaller than the gestational age, it could be a sign of oligohydramnios.
- Obtain a thorough medical history making note of any hereditary conditions that increase the risk of developing Potter syndrome (which includes significant renal impairment and even absence of kidneys) or other conditions that lead to low amniotic fluid such as hypertension or diabetes.
- Perform a “kick count” by asking the patient to lie still and count fetal movement (this can also be done at home). A count of less than 10 in one hour could indicate reduced fetal movement and be a sign of oligohydramnios.
T: What TESTS will be ordered?
The gold standard for measuring the amniotic fluid is ultrasound (US), but note that ultrasound alone is not a perfect indicator of amniotic fluid levels as various pressures put on the transducer can affect the accuracy of the measurements. Other tests include:
- Anatomy ultrasound – This is a specific US done at around 20 weeks gestation that also evaluates the fetus’ major organs, namely the kidneys.
- Non-Stress Test (NST) – This test involves the mother wearing a monitor to assess fetal heart rate while at rest for a period or 20 to 30 minutes (longer if the mother has been involved in a trauma, is bleeding, or has experienced decreased fetal movement).
- Biophysical profile (BPP) – This is a type of ultrasound that assesses breathing, amniotic fluid volume, fetal tone (episodes of extension and flexion), and body movement.
- Doppler blood flow analysis to assess for fetal hypoxia.
- Nitrazine paper test – This test of pH assesses fluid from the birth canal to determine if it is amniotic fluid or something else. If the paper is blue it is most likely amniotic fluid.
T: What TREATMENTS will be provided?
The least invasive treatment is to encourage maternal hydration or provide IV fluids to correct dehydration/hypovolemia. If further intervention is needed, treatments include:
- Amnioinfusion may be utilized to relieve cord compression. In this procedure, 0.9% sodium chloride or Lactated Ringer’s solution is infused into the amniotic cavity and can be done transcervically or transabdominally.
- Induction of labor either naturally or by cesarean.
- In cases of Potter syndrome where no kidneys are present, the family may need grief counseling as the child will not survive – consider requesting a spiritual care or social work consult.
E: How do you EDUCATE the patient/family?
A key education point for your patient with oligohydramnios is the importance of adequate hydration. According to the American College of Obstetricians and Gynecologists (ACOG), most pregnant women should take in between 64 to 96 ounces of water a day.
Other key teaching points include:
- If your patient is taking an ACE inhibitor or other culprit medication and plans to become pregnant, instruct them to discuss their medication options with their physician.
- Teach your patient how to perform kick counts to monitor fetal movement.
- Teach the importance of not smoking during pregnancy since smoking can decrease fetal blood flow and lead to hypoxia (which leads to reduced fetal renal blood flow and oligohydramnios).
- Teach the patient they are at higher risk for preterm delivery and when to seek medical care.
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