Oligohydramnios occurs during pregnancy when the amount of amniotic fluid, the protective fluid surrounding the unborn baby in the womb, is less than normal. This condition occurs in 1 to 2% of all pregnancies. Oligohydramnios can be a separate disease, meaning that any other medical condition or birth defect does not accompany it. Still, it is also associated with some birth defects and genetic disorders.
Pregnant women typically have about 500 ml to 1000 ml of amniotic fluid. Too much (Polyhydramnios) or too little amniotic fluid can cause problems. Oligohydramnios increases the risk of miscarriage or stillbirth. It can also cause the baby to be born with severe abnormalities, including immature lungs, movement problems, and umbilical cord dysfunction.
Symptoms
The main symptoms of amniotic fluid deficiency are not obvious, so you must ensure you have all the prenatal exams. If you have low amniotic fluid, your obstetrician may make more appointments to check the fetus’s condition. These symptoms include:
- Leaking of the amniotic fluid
- Low amniotic fluid on an ultrasound
- Measurements of size smaller than what is normal for gestational age
- Premature rupture of membranes (PROM)
- Abdominal discomfort
- A sudden drop in fetal heart rate
- The fetus is immobile or has reduced mobility
- Abnormal findings on a fetal monitor, including fetal distress
- Low maternal weight gain
- The uterus is smaller than expected for how far along you are in pregnancy
Is oligohydramnios common?
About 4 in 100 pregnant women suffer from an amniotic fluid deficiency. This can happen at any time of pregnancy, but it most often occurs in the last trimester.
Causes
After the twentieth week of pregnancy, more amniotic fluid is made up of the baby’s urine. Therefore, anything that causes the baby to produce less urine than usual can lead to low amniotic fluid. Oligo hydramnios can occur at any time during pregnancy but are most commonly diagnosed in the third trimester. Several factors can lead to lower-than-normal levels of amniotic fluid.
Placental issues
If the placenta does not provide enough nutrients for the baby to grow, it may reduce or stop fluid excretion, so amniotic fluid is reduced.
Birth defects
Some birth defects cause problems with the fetal urinary tract and kidneys, resulting in inadequate urine production.
Premature rupture of membranes(PROM)
Rupture of the amniotic sac before 37 weeks of gestation is called PROM, which occurs in about 8 to 10% of all pregnancies, resulting in preterm delivery.
Leaking of amniotic fluid
Rupture of the membrane can cause leakage of amniotic fluid.
Post-date pregnancy
A pregnancy that is 42 weeks old is at risk for oligohydramnios because amniotic fluid can be reduced by half after this time.
Maternal problems
Maternal conditions can affect the volume of amniotic fluid. Some of these conditions include diabetes, dehydration, and high blood pressure.
Medication
Some medications, such as those used to treat high blood pressure, can reduce amniotic fluid, so talk to your doctor about medications.
Dr. Arjang Naim, MD checks the amount of amniotic fluid in each examination to ensure adequate.
Diagnose
In addition to a complete medical history and physical examination by an ob-gyn, an ultrasound is used for a more detailed examination. Ultrasound is done to check the level of amniotic fluid, also when the size of the spine is smaller than normal and in cases where a premature rupture of the membrane has occurred.
Ultrasonic diagnosis of oligohydramnios is made by obtaining a measurement called the amniotic fluid index, or AFI. AFI is calculated by measuring the depth of amniotic fluid in four parts of the uterus and squeezing them together. The doctor can take objective measurements using AFI and diagnose oligohydramnios when the amniotic fluid index is less than five, and the deepest part is less than 2 cm.
The doctor should also monitor the downward trend in amniotic fluid. High-risk pregnancies or women with risk factors for oligohydramnios should have an AFI assessment once a week. If the measurement is between 5 and 10 cm at the gestational age of fewer than 41 weeks, an AFI evaluation is performed twice a week.
Complications
Decreased amniotic fluid volume can cause the following complications:
- Increased chance of stillbirth or miscarriage
- Premature birth
- Intrauterine growth restriction
- Cord compression
- Cerebral palsy
- Preterm birth
- Meconium aspiration
- Compression of fetal organs
Managing oligohydramnios throughout pregnancy
There is no long-term treatment for oligohydramnios. However, a few things can temporarily increase amniotic fluid levels:
- Oral intake of fluids: Experts advise women to stay hydrated if they have oligohydramnios. Oral hydration is the easiest, but in some cases, intravenous hydration may be needed.
- Installation of a saline solution into the amniotic sac during labor: When the amniotic fluid level decreases, doctors use catheters to add more fluid to the amniotic fluid. This fills the umbilical cord, reducing the risk of umbilical cord compression, which provides better oxygenation to the fetus.
It is important to note that the above techniques are temporary if successful. They do not cure the root cause of oligohydramnios. Early delivery may be needed when the baby’s blood circulation is compromised.
Managing oligohydramnios during the first trimester
Decreased amniotic fluid is rare in the first trimester. Repeated ultrasounds help track the natural history of pregnancy, which helps get complete information about the baby’s condition.
Managing oligohydramnios during the second trimester
Diagnosis in the second trimester can be due to fetal or maternal issues. Some fetal disorders, such as kidney or urinary tract disorders, or maternal problems, such as placental abruption, ruptured membranes, and more, may be present.
Medical professionals usually perform serial ultrasounds to determine if the condition is stable. More severe oligohydramnios in the second trimester may cause fetal complications or miscarriage.
Managing oligohydramnios during the third trimester
In the third trimester, cases of oligohydramnios often occur due to maternal conditions such as preeclampsia or maternal vascular disease. These conditions are often related to premature rupture of membranes or placental insufficiency. Oligohydramnios in the third trimester can cause serious harm to the baby. Due to this risk, pregnant women are evaluated according to the volume of amniotic fluid and the process of reducing its level.
The longer the oligohydramnios lasts, the greater the baby’s risk of death and injury. Doctors can usually control the condition better when they know what is causing the decrease in amniotic fluid. Still, in cases where the cause is not known, preterm delivery (cesarean section) is recommended.
What is the baby’s long-term prognosis?
If fluid volume loss is due to a ruptured membrane or poor placental function, it depends primarily on the baby’s gestational age and weight at birth. However, many babies need care at the NICU because they are small or premature. For infants with oligohydramnios due to a congenital defect in the kidney or bladder, it depends on the kidneys’ function after birth. Some babies need dialysis or a kidney transplant in infancy or early childhood.
If the amount of amniotic fluid is very low during the second trimester of pregnancy, when lung growth peaks, the baby may not have enough lung tissue and may have difficulty breathing during delivery. These babies need respiratory support and sometimes do not survive due to poor lung growth. Babies who lose amniotic fluid after 23 to 24 weeks usually have enough lung tissue, even if fluid levels are very low in late pregnancy.
Prevent
Although there is no way to prevent oligohydramnios, it is important to talk to your doctor about managing your medications and any conditions associated with amniotic fluid deficiency, including diabetes and high blood pressure. Regular checkups will allow you to measure your abdomen and ensure enough amniotic fluid for your baby to grow properly.
Dr. Arjang Naim MD uses advanced equipment to monitor the fetus’s condition in all regular visits to pregnant women to take the necessary measures if there is a decrease in amniotic fluid levels.
Additional questions
- What is the most common problem with umbilical cord abnormalities?
Atresia, aplasia, or agenesis of an artery can lead to single umbilical artery syndrome. Single umbilical artery (SUA) is the most common umbilical cord anomaly.
- What are the four most common birth defects?
- Heart defects
- Cleft lip/palate
- Down syndrome
- Spina bifida
- What is the most common cause of preterm premature rupture of membranes?
In most cases, the cause of PROM is unknown. Some possible causes or risk factors include:
- Infections of the uterus, cervix, or vagina
- Excessive stretching of the amniotic sac
- How many mL of amniotic fluid is normal?
While the baby is in the womb, it floats in the amniotic fluid. The amount of amniotic fluid is the highest around the 34th week of pregnancy, which averages 800 ml. About 600 ml of amniotic fluid surrounds the baby at full term.
- Does bed rest increase amniotic fluid?
Resting the mother in the left lateral decubitus position increases fetal urine output, increasing the estimated amniotic fluid volume in uncomplicated pregnancies.
References
https://www.marchofdimes.org/find-support/topics/planning-baby/oligohydramnios
https://www.sciencedirect.com/topics/medicine-and-dentistry/oligohydramnios
https://www.webmd.com/baby/what-is-oligohydramnios
