Oligohydramnios | |
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Specialty | Obstetrics |
Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (AFI) measures less than 5 cm or when the single deepest pocket (SDP) of amniotic fluid measures less than 2 cm. [1] Amniotic fluid is necessary to allow for normal fetal movement, lung development, and cushioning from uterine compression. [2] Low amniotic fluid can be attributed to a maternal, fetal, placental or idiopathic cause and can result in poor fetal outcomes including death. The prognosis of the fetus is dependent on the etiology, gestational age at diagnosis, and the severity of the oligohydramnios.
The opposite of oligohydramnios is polyhydramnios, or an excess of amniotic fluid.
The amount of amniotic fluid available is based on how much fluid is produced and how much is removed from the amniotic sac. In the first trimester, the main sources of amniotic fluid are fetal lung secretions, transportation of maternal plasma across the fetal membranes, and the surface of the placenta. By the second trimester, the fetal kidneys start to produce urine which becomes the main source of the amniotic fluid for the remainder of the pregnancy. [3]
The development of oligohydramnios may be idiopathic or have a maternal, fetal, or placental cause. [4]
The volume of amniotic fluid typically increases until 36 weeks and starts decreasing after 40 weeks in post-term gestations. [3] For this reason, discrepancies between fundal height measurements and gestational age can be a clinical indication of amniotic fluid abnormality and should be evaluated by ultrasound. Other common clinical presentations include fetal malpresentation, undue prominence of fetal parts, premature rupture of membranes, and reduced amount of amniotic fluid.[ citation needed ]
Diagnosis of oligohydramnios is made by conducting a transabdominal ultrasound of the abdomen. There are two methods that can be used to make the diagnosis. The first is by using an amniotic fluid index (AFI). In this method, the sonographer measures the amniotic fluid in each of the four quadrants of the abdomen (right upper quadrant, left upper quadrant, right lower quadrant, left lower quadrant) and adds the values together. For reference, a normal AFI is 5–25 cm. An AFI <5 cm is considered oligohydramnios and an AFI >25 cm is considered polyhydramnios. Randomized control trials have shown that use of AFI can cause an increased number of false positive diagnosis of oligohydramnios and recommend using the measurement of a single deepest pocket (SDP) of amniotic fluid to diagnose oligohydramnios instead. [1]
To calculate a single deepest pocket, the sonographer scans each of the four quadrants of the abdomen looking for the deepest pocket of amniotic fluid that does not include any fetal body parts or an umbilical cord. It is measured from the 12 o'clock position to the 6 o'clock position. For reference, a normal SDP is 2–8 cm. A SDP <2 cm is considered oligohydramnios and a SDP >8 cm is considered polyhydramnios. The use of a SDP for diagnosis of oligohydramnios is associated with less false positives and thus less unnecessary interventions without an increase in adverse perinatal outcomes. [1]
In a multiple gestation pregnancy, measuring a single deepest pocket is the most accurate determination of adequate amniotic fluid levels. [2]
After initial diagnosis of oligohydramnios has been made, the next step is to perform a thorough history and physical exam, followed by diagnostic testing if indicated. [2]
There is no way to permanently increase the volume of amniotic fluid, but it can be temporarily increased to allow for a complete anatomy scan of the fetus on ultrasound.[ citation needed ]
One way to achieve this is through an amnioinfusion, which is the insertion of 200mL of saline into the amniotic sac. One study showed an improvement in fetal structure visibility by 26% (51% to 77% before and after the infusion respectively). There is also some low quality data that may indicate a potential benefit of amnioinfusion is to facilitate external cephalic version. [2] Amnioinfusion can be used during labor to prevent umbilical cord compression. There is uncertainty about the procedure's safety and efficacy, and it is recommended that it should only be performed in centers specializing in invasive fetal medicine and in the context of a multidisciplinary team. [5]
One to two liters of oral hydration can temporarily increase amniotic fluid in dehydrated patients with isolated oligohydramnios. [6]
Other investigational therapies may also be useful such as desmopressin, tissue sealants, or sildenafil citrate. These methods are less commonly used and are experimental. [4]
In case of congenital lower urinary tract obstruction, fetal surgery seems to improve survival, according to a randomized yet small study. [7]
Patients who are preterm are managed in the outpatient setting with weekly or biweekly testing to monitor for accurate fetal growth and decrease chances of unexpected fetal death. This includes a weekly non-stress test (NST) and single deepest pocket (SDP) assessment which is also referred to as the modified BPP. [1] Sonographic fetal growth exams may also be indicated.[ citation needed ]
Idiopathic, uncomplicated, and persistent oligohydramnios can be delivered at 36 0/7 weeks – 37 6/7 weeks of gestation or at diagnosis if diagnosis is later. [1]
Complications may include cord compression, musculoskeletal abnormalities such as facial distortion and clubfoot, pulmonary hypoplasia and intrauterine growth restriction. Amnion nodosum is frequently also present (nodules on the fetal surface of the amnion). [8]
The use of oligohydramnios as a predictor of gestational complications is controversial. [9] [10]
Potter syndrome is a condition caused by oligohydramnios. Affected fetuses develop pulmonary hypoplasia, limb deformities, and characteristic facies. Bilateral agenesis of the fetal kidneys is the most common cause due to the lack of fetal urine.
Amniocentesis is a medical procedure used primarily in the prenatal diagnosis of genetic conditions. It has other uses such as in the assessment of infection and fetal lung maturity. Prenatal diagnostic testing, which includes amniocentesis, is necessary to conclusively diagnose the majority of genetic disorders, with amniocentesis being the gold-standard procedure after 15 weeks' gestation.
The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo until shortly before birth. The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta. On the outer side, the amniotic sac is connected to the yolk sac, the allantois, and via the umbilical cord, the placenta.
The amnion is a membrane that closely covers the human and various other embryos when first formed. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo. The amnion, along with the chorion, the yolk sac and the allantois protect the embryo. In birds, reptiles and monotremes, the protective sac is enclosed in a shell. In marsupials and placental mammals, it is enclosed in a uterus.
Fetal distress, also known as non-reassuring fetal status, is a condition during pregnancy or labor in which the fetus shows signs of inadequate oxygenation. Due to its imprecision, the term "fetal distress" has fallen out of use in American obstetrics. The term "non-reassuring fetal status" has largely replaced it. It is characterized by changes in fetal movement, growth, heart rate, and presence of meconium stained fluid.
Chorionic villus sampling (CVS), sometimes called "chorionic villous sampling", is a form of prenatal diagnosis done to determine chromosomal or genetic disorders in the fetus. It entails sampling of the chorionic villus and testing it for chromosomal abnormalities, usually with FISH or PCR. CVS usually takes place at 10–12 weeks' gestation, earlier than amniocentesis or percutaneous umbilical cord blood sampling. It is the preferred technique before 15 weeks.
Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in about 1% of pregnancies. It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. There are two clinical varieties of polyhydramnios: chronic polyhydramnios where excess amniotic fluid accumulates gradually, and acute polyhydramnios where excess amniotic fluid collects rapidly.
The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus.
Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies in which there is disproportionate blood supply between the fetuses. This leads to unequal levels of amniotic fluid between each fetus and usually leads to death of the undersupplied twin and, without treatment, usually death or a range of birth defects or disabilities for a surviving twin, such as underdeveloped, damaged or missing limbs, digits or organs, especially cerebral palsy.
Rupture of membranes (ROM) or amniorrhexis is a term used during pregnancy to describe a rupture of the amniotic sac. Normally, it occurs spontaneously at full term either during or at the beginning of labor. Rupture of the membranes is known colloquially as "breaking the water" or as one's "water breaking". A premature rupture of membranes (PROM) is a rupture of the amnion that occurs at full term and prior to the onset of labor. In cases of PROM, options include expectant management without intervention, or interventions such as oxytocin or other methods of labor induction, and both are usually accompanied by close monitoring of maternal and fetal health. Preterm premature rupture of membranes (PPROM) is when water breaks both before the onset of labor and before the pregnancy's 37 week gestation. In the United States, more than 120,000 pregnancies per year are affected by a premature rupture of membranes, which is the cause of about one third of preterm deliveries.
Potter sequence is the atypical physical appearance of a baby due to oligohydramnios experienced when in the uterus. It includes clubbed feet, pulmonary hypoplasia and cranial anomalies related to the oligohydramnios. Oligohydramnios is the decrease in amniotic fluid volume sufficient to cause deformations in morphogenesis of the baby.
Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dangerously low blood pressure. Complications for the mother can include disseminated intravascular coagulopathy and kidney failure. Complications for the baby can include fetal distress, low birthweight, preterm delivery, and stillbirth.
Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, is breakage of the amniotic sac before the onset of labor. Women usually experience a painless gush or a steady leakage of fluid from the vagina. Complications in the baby may include premature birth, cord compression, and infection. Complications in the mother may include placental abruption and postpartum endometritis.
Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes used to designate late decelerations of fetal heart rate as measured by cardiotocography or an NST, even if there is no other evidence of reduced blood flow to the placenta, normal uterine blood flow rate being 600mL/min.
Triploid syndrome, also called triploidy, is a chromosomal disorder in which a fetus has three copies of every chromosome instead of the normal two. If this occurs in only some cells, it is called mosaic triploidy and is less severe.
Amniotic fluid index (AFI) is a quantitative estimate of amniotic fluid and an indicator of fetal well-being. It is a separate measurement from the biophysical profile.
Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.
The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals. They are the amnion, chorion, allantois, and yolk sac. The amnion and the chorion are the chorioamniotic membranes that make up the amniotic sac which surrounds and protects the embryo. The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord.
Circumvallate placenta is a rare condition affecting about 1-2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. Circumvallate placenta is a placental morphological abnormality associated with increased fetal morbidity and mortality due to the restricted availability of nutrients and oxygen to the developing fetus.
Amnioinfusion is a method in which isotonic fluid is instilled into the uterine cavity.