Oligohydramnios is the medical term for low amniotic fluid during pregnancy. The amniotic fluid, which exists in a sac made up of the chorion and amnion membranes, is a large part of the growing baby's life support system. The normal volume of amniotic fluid is between 500 and 1000 milliliters. Physicians associate low amniotic fluid with pregnancy complications and problems with fetal development. Alternatively, abnormal development or health issues of the expectant mother can cause low amniotic fluid.
The amniotic fluid provides a cushion and protects a developing baby from injury during pregnancy. Furthermore, the fluid ensures there is enough room for the baby to grow and move, and maintains a consistent temperature. Amniotic fluid also keeps the umbilical cord from being compressed against the wall of the uterus during pregnancy and delivery. The baby begins breathing and swallowing amniotic fluid during the second trimester.
An ultrasound or amniotic fluid index (AFI) can measure the volume of amniotic fluid in the womb. Doctors confirm a diagnosis of oligohydramnios when the AFI shows fluid levels under five centimeters. Other factors that indicate oligohydramnios are the absence of a fluid pocket two or three centimeters deep, or less than 500 milliliters of total fluid volume between 32 to 36 weeks of pregnancy. Medical professionals measure fluid pockets where the amniotic fluid has maximum depth in a clear area not occupied by the umbilical cord or any part of the baby.
Low amniotic fluid is most common in the third trimester or pregnancies carried past the due date. Amniotic fluid levels naturally decline after 41 weeks. Inducing labor may be the safest course of action if amniotic fluid is declining at or after 36 weeks. A medical professional will monitor the pregnancy and discuss the risks and benefits of this step.
Low levels of amniotic fluid in the earlier stages of pregnancy is a complication medical professionals monitor closely. The first step after discovering the condition is checking the amniotic membrane or waterbag to see if it is intact or ruptured. A broken membrane will release amniotic fluid in a gush or slow trickle, leading to increasingly lower levels.
The amniotic fluid protects an unborn baby and assists in the development of muscles, lungs, limbs, and the digestive system. Low amniotic fluid may interfere with proper development of fetal organs, especially the lungs. If the condition occurs in the second or third trimesters, this can lead to incomplete development of the lungs or pulmonary hypoplasia.
Amniotic fluid begins forming approximately 12 days after conception. The first component is water provided by the mother. Fetal urine is the main component of the fluid by the twentieth week of pregnancy. Doctors can track or assess the urine to help measure the baby's overall health. Some congenital disorders, often those that interfere with the development of the kidneys or urinary tract, can cause low amniotic fluid.
Low amniotic fluid can cause complications during delivery, such as raising the risk of umbilical cord compression. It also contributes to aspiration of meconium, the baby's first bowel movement, in the womb. Amnioinfusion is a technique that adds sterile saltwater to the amniotic fluid during labor. The saline water is infused into the amniotic sac through the cervix, using a catheter. Doctors usually use this method when they detect an abnormal fetal heart rate. The mother may require a cesarean section if the baby is in distress.
Intrauterine Growth Restriction or IUGR refers to babies that are smaller than expected in relation to gestational age. Low amniotic fluid in the second half of pregnancy is a risk factor for IUGR because the baby does not have enough room to grow. Newborns with IUGR are often thin and pale with loose skin. The umbilical cord is dull and thin instead of plump and shiny.
An expectant mother with chronic high blood pressure is at risk for low amniotic fluid. Risk increases if the mother takes certain blood pressure medications. Other conditions that may cause low amniotic fluid are diabetes, hypoxia, dehydration, and preeclampsia. Early in pregnancy, severe morning sickness may cause the condition. Sometimes morning sickness extends into the second trimester and further into the day. An OG-Gyn may recommend bed rest with IV fluids to treat low amniotic fluid due to excessive nausea and vomiting.
Placental abruption -- when the placenta tears either partially or completely away from the uterine wall before delivery -- lowers the volume of amniotic fluid, among other complications. Most doctors recommend bed rest in a hospital and IV fluids after a placental abruption. In serious cases, the placenta is too damaged to supply nutrients to the baby. It is also possible that too much amniotic fluid was lost for the baby to stay in the womb and doctors may induce labor immediately.
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