Oligohydramnios (Low Amniotic Fluid) & Hypoxic Ischemic Encephalopathy (HIE)
Oligohydramnios is a health condition that occurs when the amount of fluid in the amniotic sac drops, usually because the placenta does not work properly. Amniotic fluid helps the developing fetus mature, receive nutrients, grow and maintain its body temperature, so a decrease in volume is a serious health risk. Oligohydramnios is associated with IUGR, cord compression, HIE, cerebral palsy, PROM, meconium aspiration syndrome, preeclampsia and placental abruption. This health issue can be prevented with early screening (via ultrasound and AFI) and management, including hospital bed rest, fetal monitoring, hydration and delivery at first signs of fetal distress.
What Is Amniotic Fluid?
Amniotic fluid is a clear liquid in the amniotic sac that surrounds and protects the baby during pregnancy. Initially, the fluid consists mainly of water. At approximately 20 weeks, the baby’s urine becomes the primary substance. The baby breathes and swallows amniotic fluid, which aids in nutrition, lung maturation, growth, and maintaining a consistent temperature. The volume of amniotic fluid increases during pregnancy and reaches its peak at about 34 weeks. When the volume of amniotic fluid decreases and becomes inadequate, it is called oligohydramnios. Oligohydramnios is a very serious condition that is associated with
- Fetal growth restriction
- Cord compression
- Hypoxic ischemic encephalopathy (HIE)
- Cerebral palsy
- Uteroplacental insufficiency
- Premature rupture of membranes (PROM)
- Preterm birth
- Meconium aspiration
- Placental abruption
What Is Oligohydramnios? How Does It Cause Hypoxic Ischemic Encephalopathy (HIE)?
Oligohydramnios is typically a sign that the placenta is not functioning properly, and a mother with this condition might have to deliver a premature baby, or she may be induced to deliver the baby before the infant is harmed by placental dysfunction or umbilical cord compression during labor. Oligohydramnios affects 4 – 8 % of pregnancies and needs to be diagnosed and managed early to prevent the baby from having brain damage. If diagnosed early, most cases can be managed or treated with hospital bed rest, fetal monitoring, oral and intravenous hydration, and delivery when the fetal monitor shows abnormal heart rates.
Polyhydramnios is the opposite of hydramnios: it is a condition of excessive amniotic fluid. This condition occurs in about 1% of pregnancies, and can usually be managed well if diagnosed in a timely fashion.
Causes of Oligohydramnios
The volume of amniotic fluid is ultimately determined by the amount of fluid flowing into and out of the amniotic sac. Rupture of the membranes is the most common cause of oligohydramnios. Since amniotic fluid is primarily fetal urine in the latter half of pregnancy, the absence of urine production or a blockage in the fetus’ urinary tract also can cause oligohydramnios. Oligohydramnios can be chronic and occur over a period of time, or it can be acute, and happen very quickly. The acute condition can occur in the presence of fetal hypoxia; severe preeclampsia is one condition that can cause this.
Oligohydramnios is rare in the first trimester, and the causes of it during this period are often unclear. Oligohydramnios usually occurs during the second or third trimester. Causes of oligohydramnios are listed below.
Maternal causes of oligohydramnios are those associated with uteroplacental insufficiency, and they include:
- 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
Placental causes of oligohydramnios include:
- 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 include:
- 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 and a macrosomic (large) baby.
- Ruptured fetal membranes, PROM & PPROM
- Congenital abnormalities, especially those associated with impaired urine production. This occurs when there are problems with the baby’s kidneys, such as a kidney obstruction or one or both of the kidneys fail to develop.
- Chromosomal abnormalities, such as Down’s syndrome or an abnormality that causes problems with swallowing.
Risk Factors for Oligohydramnios
Many women who develop oligohydramnios have no identifiable risk factors. Thus it is crucial for physicians to monitor a woman’s amniotic fluid levels during pregnancy, even in the absence of risk factors. Risk factors for oligohydramnios include:
- Maternal high blood pressure
- Maternal diabetes
- Placental problems
Signs and Symptoms of Oligohydramnios
- Rapid growth of the uterus
- Discomfort in the abdomen
- Leaking amniotic fluid
- Little to no fetal movement inside the womb
- Uterine contractions
Diagnosis of Oligohydramnios
Oligohydramnios typically is diagnosed with physical examination, history, and an ultrasound. In some cases, an ultrasound can detect the cause of oligohydramnnios, such as multiple pregnancies. The condition may first be suspected when the uterine size is less than expected for gestational age.
Amniotic fluid normally increases steadily to about 1 liter by 34 – 36 weeks, and then decreases thereafter; most studies report a decrease of about 25% per week. The rate of decline may be as high as 150 milliliters per week at 38 – 43 weeks. In some cases of oligohydramnios, the volume may be reduced to only a few mL.
Physicians diagnose oligohydramnios with an ultrasound by obtaining a measurement called the amniotic fluid index, or AFI. AFI is calculated by measuring the depth of the amniotic fluid in four sections of the uterus and adding them together. Near term, an AFI between 8 – 18 centimeters is considered normal, although 5 – 25 cm sometimes is considered normal. At gestational ages 20 – 35 weeks, the AFI in a healthy pregnancy is approximately 14 cm. At weeks 34 – 36, the amniotic fluid starts to decrease in preparation for birth.
If the AFI is less than 5 cm between weeks 32 – 36, the woman has oligohydramnios, although some clinicians diagnose oligohydramnios when the AFI is less than 8 cm. Typically, oligohydramnios is diagnosed when AFI is less than 5 cm, and an AFI of 5 – 8 cm is considered borderline / low normal fluid volume. During weeks 36 – 42, a normal AFI is 12.9 +/- 4.6 cm. Since amniotic fluid volume depends on the gestational age, oligohydramnios also can be defined as an AFI less than the 5th percentile of normal AFI for that age.
Other characteristics that assist physicians in diagnosis of oligohydramnios include the following:
- Amniotic fluid volume of less than 500 mL at 32 – 36 weeks’ gestation
- Single deepest pocket (SDP) measurement (the depth of the largest of the four sections used to calculate AFI) of less than 2 cm.
- The absence of a single vertical pocket greater than or equal to 3 cm.
- Doppler blood flow studies, studies in which physicians can view and assess maternal and fetal vessels, often demonstrate problems with flow in the placental circulation and redistribution of flow in the fetal circulation. This indicates uteroplacental insufficiency, which is a risk factor for oligohydramnios.
Amniotic fluid testing throughout pregnancy
Since abnormal amniotic fluid volume is associated with a number of complications, the assessment of amniotic fluid is used in conjunction with the biophysical profile (BPP) and nonstress test (tests that evaluate the baby’s heart rate, breathing, movements and muscle tone) as part of an assessment of fetal well being.
Around week 32 – and sometimes many weeks earlier for women at risk of pregnancy loss – a comprehensive ultrasound evaluation with fetal biometry is performed. In addition, a woman suspected of having oligohydramnios typically is evaluated for fetal abnormalities, such as growth restriction, placental problems and chromosomal disorders that can account for decreased amniotic fluid volume.
A baby with a BPP score of 8 out of 10 possible points, with decreased amniotic fluid as the reason for the loss of the two extra points, is considered at high risk for chronically low oxygen levels and acute decompensation. Thus, the baby should be closely monitored and the low amniotic fluid should be managed.
High risk pregnancies, or women with risk factors for oligohydramnios, should have an AFI assessment once a week if they are less than 41 weeks of gestation and the AFI is 8 cm or higher. If the AFI is 5 – 8 cm at less than 41 weeks, a twice-weekly AFI assessment is justified because these women have a high risk of AFI being 5 cm or lower within 4 days.
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. It should be the case that the more unstable the maternal or fetal condition, the more frequent the testing. Furthermore, when oligohydramnios is present, BPP should be performed more frequently than once per week and may be indicated on a daily basis. 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 (drinking) of fluids, having a saline solution instilled into the amniotic sac (amniofusion), and other intravenous fluid delivery can temporarily increase amniotic fluid.
Oligohydramnios in the first trimester
Reduced amniotic fluid during this period is an ominous finding due to the fact that the pregnancy usually aborts. Serial ultrasounds are helpful for following the natural history of the pregnancy.
Oligohydramnios in the second trimester
During this period, management and prognosis depend on the cause and severity of the oligohydramnios. In boderline / low normal amniotic fluid volume, there typically is a good prognosis. Serial ultrasounds are recommended to determine if the condition is stable, resolved, or has progressed to oligohydramnios and fetal growth restriction.
When oligohydramnios is present in the second trimester, fetal or neonatal death often occur. Preterm delivery, either spontaneous or indicated by maternal or fetal complications, takes place in more than 50 % of cases. Treatment includes giving the mother liquids to drink for hydration, or an amniofusion (thinning the meconium (feces) that has passed into the amniotic fluid) if the baby cannot be adequately visualized. If rupture of membranes is uncertain, amniofusion with dye can facilitate the diagnosis of PROM and visualization of fetal abnormalities. Serial ultrasounds should be obtained to monitor the amniotic fluid volume, fetal growth and fetal well being. Specific pregnancy complications associated with oligohydramnios should be managed as appropriate for the condition. Expectant management (waiting for the baby’s lungs to mature and labor to occur naturally) sometimes is the most appropriate course of action when a preterm baby has oligohydramnios.
Oligohydramnios in the third trimester
Adverse outcomes during this trimester usually are related to umbilical cord compression, uteroplacental insufficiency and meconium aspiration. Uteroplacental insufficiency and cord compression are associated with fetal heart rate abnormalities that result in C-section delivery and low Apgar scores. The longer the duration of oligohydramnios, the higher the risk of death and injury to the infant, especially if the cause of the oligohydramnios is unknown. Due to the potentially high risk of adverse outcome, these pregnancies should undergo assessment of acute and long term fetal condition at each prenatal visit, and it is crucial for fetal heart rate to be monitored continuously. As mentioned above, NST and AFI or BPP should be performed once or twice weekly.
Where there is a decrease in amniotic fluid over a short period of time or amniotic fluid is borderline, more frequent testing and admission with continuous fetal monitoring should be considered. Informed consent should always be given.
When the cause of oligohydramnios is known, outcomes generally are good if there is close monitoring. When the cause of the oligohydramnios is unknown, indications for delivery include, nonreassuring fetal testing and monitoring. Beyond 36 weeks, lung maturity does not need to be confirmed. Some research suggests delivery at 36 or 37 6/7th weeks. Induction of labor increases the risk of C-section delivery and its potential complications. Alternatively, the woman can be followed with serial NST and BPP testing until term gestation is reached. In this case, it is essential for the physician to discuss the risks and benefits of various management plans with the woman.
In general, the longer a pregnancy continues after 40 weeks, the more risks there are to the baby. If oligohydramnios is present in a postterm pregnancy, delivery is indicated, regardless of the BPP score. In addition, constant surveillance of a postterm baby is crucial. Oligohydramnios in postterm pregnancies is associated with higher incidence of meconium stained fluid and an increased risk of 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).
Oligohydramnios and Medical Malpractice
Oligohydramnios can have devastating consequences. It therefore 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 and risk factors for oligohydramnios
- Failure to prevent conditions that can cause oligohydramnios, such as gestational diabetes, dehydration, chronically high blood pressure and ingestion of ACE inhibitors
- Improper use of forceps and vacuum extractors
- Failure to follow standards of care and timely deliver the baby, including failure to order and / or timely perform a C-section
- Failure to obtain adequate informed consent from the mother regarding the risks, benefits and alternatives of various management plans pertaining to oligohydramnios and delivery
It is crucial for physicians to closely monitor and test the mother and baby to prevent or minimize complications associated with oligohydramnios. The physicians should be prepared to admit the mother to the hospital for continuous fetal monitoring and for a potential C-section delivery, as well as a possible early delivery. It is essential for physicians to properly treat underlying conditions that can cause or lead to oligohydramnios, and properly diagnose and closely monitor decreasing and borderline amniotic fluid levels. When oligohydramnios is not properly managed and / or underlying conditions are not properly diagnosed and treated, it is negligence. When the mother and baby are not properly monitored and tested, or standards of care are not followed and injuries occur, it also constitutes negligence. If this negligence causes oligohydramnios, it is medical malpractice.
Legal Help for Oligohydramnios, HIE and Birth Injury
Michigan Birth Trauma Attorneys with a National Presence
At Reiter & Walsh ABC Law Centers, we are dedicated exclusively to birth injury cases. We understand the complex legal issues involved with oligohydramnios and HIE cases, and we will help you to obtain the compensation to which you are entitled. Our attorneys and in-house medical staff determine the causes of our clients’ injuries, the prognoses of birth injured children and areas of medical negligence. We consult closely with leading medical experts, forensic specialists and life care-planning professionals to secure our clients’ future care and their parents’ peace of mind, knowing their child will be cared for, no matter what. Our specific focus on birth injury allows our attorneys to provide unparalleled legal service to our clients.
The Reiter & Walsh, P.C. birth trauma attorneys handle cases all over the United States, in places including Michigan, Pennsylvania, Wisconsin, Tennessee, Mississippi, Texas, Ohio, Washington D.C., Arkansas, and more. Additionally, our team handles cases involving military hospitals and federally funded clinics. To begin your free case review, please contact Reiter & Walsh ABC Law Centers in any of the following ways:
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Video: Birth Asphyxia and Hypoxic Ischemic Encephalopathy (HIE)
Watch hypoxic ischemic encephalopathy attorneys Jesse Reiter and Rebecca Walsh discuss the causes of birth asphyxia and hypoxic ischemic encephalopathy (HIE).
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