Oligohydramnios (Low Amniotic Fluid)
Oligohydramnios is a health condition that occurs when the volume of fluid in the amniotic sac is lower than average. This condition usually occurs because the placenta is not functioning properly. The fluid located in the amniotic sac – the amniotic fluid – provides nutrients to the developing fetus that help it mature, grow, and maintain a consistent body temperature. Amniotic fluid also provides a cushion around the baby and umbilical cord to prevent the cord compression and decreasing oxygen to the baby. Therefore, a decrease in amniotic fluid volume is a serious health risk. Oligohydramnios is associated with intrauterine growth restriction (IUGR), cord compression, hypoxic-ischemic encephalopathy (HIE), cerebral palsy (CP), premature rupture of membranes (PROM), and several other serious health conditions. Oligohydramnios can be diagnosed with early screening (via ultrasound and amniotic fluid index measurements) and managed with hospital bed rest, fetal monitoring, hydration, and delivery at the first signs of fetal distress.
What Is Amniotic Fluid?
Amniotic fluid is a clear liquid located in the amniotic sac. It surrounds and protects the baby during pregnancy. At the earliest stage of development, amniotic fluid consists mainly of water. At approximately 20 weeks, the baby’s urine becomes the primary substance. The baby breathes in and swallows amniotic fluid; this fluid aids in nutrition, growth, lung maturation, and temperature maintenance. The volume of amniotic fluid increases as the pregnancy progresses and reaches its peak at about 34 weeks.
What Is Oligohydramnios?
Oligohydramnios occurs when the volume of amniotic fluid is decreased and inadequate for support of the growing fetus. Oligohydramnios is typically a sign that the placenta is not functioning properly. Due to this, a mother with oligohydramnios might be required to deliver a premature baby, or she may be induced to deliver before placental dysfunction or umbilical cord compression can harm the infant during labor at term. Oligohydramnios affects 4 to 8 percent of pregnancies and must to be diagnosed and managed early to prevent the possibility of future brain damage in the baby. Oligohydramnios is often associated with the following injuries and complications:
- Fetal growth restriction
- Cord compression
- Hypoxic-ischemic encephalopathy (HIE)
- Cerebral palsy
- Uteroplacental insufficiency
- Premature rupture of membranes (PROM)
- Preterm birth
- Meconium aspiration
- Placental abruption
If diagnosed early, most cases of oligohydramnios can be managed or treated with hospital bed rest, fetal monitoring, oral or intravenous hydration, and in certain cases, early delivery.
Causes of Oligohydramnios
Rupture of the amniotic sac is the most common cause of oligohydramnios, since membrane rupture can cause fluid leakage. Because amniotic fluid is primarily fetal urine in the latter half of pregnancy, the absence or decrease of urine production or a blockage in the fetal urinary tract also can lead to oligohydramnios. Oligohydramnios can be chronic and occur over a period of time, or it can be acute, and happen very quickly. Both forms of the condition can occur in the presence of fetal hypoxia. Frequent causes of oligohydramnios are detailed below:
Maternal causes of oligohydramnios are associated with uteroplacental insufficiency:
- Diabetes / nephropathy (damage or disease of the kidneys)
- Use of certain high blood pressure and heart medications, such as ACE inhibitors
- Chronic hypertension (high blood pressure)
- Collagen vascular disease
- Maternal obesity
Placental causes of oligohydramnios:
- Placental abruption
- Placental thrombosis or infarction (clots or obstructed blood flow in the placenta)
- Uteroplacental insufficiency (placenta not functioning adequately)
- Twin-to-twin transfusion (twin polyhydramnnios – oligohydramnios sequence)
Fetal causes of oligohydramnios:
- Growth restriction: A growth restricted fetus may redistribute blood flow away from the kidneys, which decreases fetal urine production and causes oligohydramnios.
- Gastrointestinal abnormalities that block the passage of fluid
- Fetal demise
- Postterm pregnancy: Numerous complications can occur when a baby is postterm, such as placental insufficiency or a macrosomic (large) baby.
- Ruptured fetal membranes (PROM and PPROM)
- Congenital abnormalities, especially those associated with impaired urine production. This occurs when there are problems with the development or function of one or both of the baby’s kidneys.
- Chromosomal abnormalities, such as Down’s syndrome, that cause problems with swallowing.
Risk Factors for Oligohydramnios
In some cases, women who develop oligohydramnios have no identifiable risk factors. Because of this, it is crucial for physicians to monitor amniotic fluid levels throughout pregnancy. However, other women do have known risk factors for oligohydramnios, including:
Signs and Symptoms of Oligohydramnios
The signs and symptoms of oligohydramnios vary from person to person but some of the most common signs and symptoms are:
- Rapid growth of uterus
- Abdominal discomfort
- Leaking of the amniotic fluid
- Little to no or decreasing fetal movement
- Uterine contractions
- Abnormal findings on a fetal monitor including fetal distress
Diagnosis of Oligohydramnios
Oligohydramnios typically is diagnosed through physical examination, assessment of personal history, and/or an ultrasound.
Physicians diagnose oligohydramnios with an ultrasound by obtaining a measurement called the amniotic fluid index, or the AFI. AFI is calculated by measuring the depth of the amniotic fluid in four sections of the uterus and adding them together. The assessment of amniotic fluid is used in conjunction with the biophysical profile (BPP) and non-stress test (tests that evaluate the baby’s heart rate, breathing, movements and muscle tone) as part of an assessment of fetal well being.
Near term, an AFI between 10 and 18 centimeters is considered normal, with a mean of 14 centimeters. At this point, an AFI less than 10 centimeters is considered abnormal and less than 5 centimeters indicates oligohydramnios.
High risk pregnancies, or women with risk factors for oligohydramnios, should have an AFI assessment once a week. Further if AFI measurements are between 5 and 9 centimeters at a gestational age of less than 41 weeks, a twice-weekly AFI assessment is justified.
All women at 41 weeks of gestation or higher should have twice-weekly AFI assessments with a modified BPP. However, the frequency of testing should be based on the clinical circumstances of each woman; the more unstable the maternal or fetal condition, the more frequent the testing.
Research indicates that all pregnant women diagnosed with oligohydramnios should undergo a nonstress test (NST) and AFI or BPP once or twice weekly until delivery (especially in cases in which the cause of the condition is unknown), depending on the maternal and fetal condition.
Managing Oligohydramnios Throughout Pregnancy
There is no long-term treatment for oligohydramnios. However, oral intake of fluids, instillation of a saline solution into the amniotic sac (amnio-fusion), and other intravenous fluid delivery methods, can temporarily increase amniotic fluid.
Oligohydramnios during the first trimester
Reduced amniotic fluid during this period is a rare finding, and information regarding the causes of this diagnosis are equally as rare. Serial ultrasounds are helpful for following the natural history of the pregnancy, and help to generate a plan for care of oligohydramnios following the diagnosis.
Oligohydramnios in the second trimester
During this period, management and prognosis depend on the cause and severity of the oligohydramnios. In amniotic fluid levels that border on normal, there typically is a good prognosis. Serial ultrasounds are recommended to determine if the condition is stable, resolved, or has progressed into more severe oligohydramnios or fetal growth restriction. When more severe oligohydramnios is present in the second trimester, fetal or neonatal death may occur.
Oligohydramnios in the third trimester
Due to the risk of adverse outcome, cases of oligohydramnios during the third trimester should undergo assessment of acute and long term fetal conditions at each prenatal visit. Again, the frequency of the testing is dependent on the amniotic fluid volume and the trend of decreasing fluid levels
The longer the duration of oligohydramnios, the higher the risk of death and injury to the infant. When the cause of oligohydramnios is known, outcomes generally are good if there is close monitoring. When the cause of the oligohydramnios is unknown, fetal testing and monitoring might lead to the recommendation of delivery, including the need for C-section delivery. In this case, it is essential for physicians to discuss the risks and benefits of various management plans with mothers.
Oligohydramnios in postterm pregnancies is associated with higher incidence of meconium stained fluid and an increased need for C-section delivery. During labor, continuous fetal heart rate recording should be utilized. If the fetal heart rate is abnormal, delivery should occur right away to prevent birth injuries and hypoxic-ischemic encephalopathy (HIE) . Afterwards, appropriate surveillance of a post-term baby is crucial.
Oligohydramnios and Medical Malpractice
Oligohydramnios, when not treated properly, can have devastating consequences. Therefore, it is essential that physicians follow standards of care and carefully monitor the mother and baby during pregnancy – especially if any of the risk factors for oligohydramnios are present. Some areas that may constitute negligence include the following:
- Failure to obtain a thorough history of the mother, thereby missing risk factors for oligohydramnios
- Failure to properly monitor the mother and baby during pregnancy and recognize low amniotic fluid, decreasing amniotic fluid, placental insufficiency, fetal distress, or risk factors for oligohydramnios
- Failure to prevent conditions that can cause oligohydramnios, such as gestational diabetes, dehydration, chronically high blood pressure, and use of ACE inhibitors
- Failure to follow standards of care regarding timely delivery of the baby, including failure to order and/or perform a required C-section
- Failure to obtain adequate informed consent from the mother regarding the risks, benefits, and alternatives of various methods of treatment pertaining to oligohydramnios and associated delivery
It is crucial for physicians to closely monitor and test the mother and baby to prevent or minimize complications associated with oligohydramnios. In a case where oligohydramnios is not properly managed, or underlying conditions are not correctly diagnosed and treated, it could be considered medical negligence.
Call the Oligohydramnios Attorneys at Reiter & Walsh P.C.
Michigan Birth Trauma Attorneys with a National Presence
If you feel your oligohydramnios was managed improperly and this caused your baby to sustain an injury, please contact the birth injury attorneys at Reiter & Walsh ABC Law Centers. Our attorneys focus solely on birth injury cases, and we have handled cases involving oligohydramnios, intrauterine growth restriction (IUGR), cerebral palsy, hypoxic-ischemic encephalopathy (HIE), and intellectual and developmental disabilities (I/DD).
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