Amniotic Fluid Volume - Significance and Complications

Introduction:

Amniotic fluid is a clear to slightly yellow liquid that cushions a fetus within the amniotic sac. The baby floats in amniotic fluid in the mother's womb during the duration of pregnancy.

What Is Amniotic Fluid?

Amniotic fluid is situated within the amniotic sac, which is a bag formed of two membranes, namely the amnion and the chorion. The fetus grows and develops inside the amniotic sac, surrounded by amniotic fluid.

What Are the Constituents of Amniotic Fluid?

In the early weeks of pregnancy, the amniotic fluid consists of water produced by the mother's body. By around 20 weeks gestation, it is replaced by the fetal's urine, as the fetus swallows and excretes the fluid. Amniotic fluid also contains nutrients, hormones, and antibodies that help the growth and development of the fetus.

What Are the Functions of Amniotic Fluid?

Amniotic fluid is crucial for healthy fetal development. The functions include:

• Protecting the Fetus: It helps the fetus from injury as the amniotic fluid cushions the baby from outside pressures, acting as a shock absorber.

• Temperature Control: The amniotic fluid insulates the baby, helping to regulate the temperature of the fetus.

• Infection Control: The amniotic fluid has antibacterial properties as it contains antibodies.

• Organ Development: Amniotic fluid allows the developing fetus to move around in the womb, the baby practices using the muscles of these systems, which facilitates proper growth and development of the musculoskeletal system, gastrointestinal system, and respiratory system.

• Nutritional Support: The amniotic fluid contains proteins, electrolytes, immunoglobulins, and vitamins that aid in the growth and development of the fetus.

• Umbilical Cord Support: Amniotic fluid flows between the umbilical cord and fetus, and thus, the amniotic fluid in the uterus prevents the umbilical cord from being compressed.

What Is the Normal Volume of Amniotic Fluid?

The volume of amniotic fluid changes with the growth of the fetus:

• From the tenth to the 20th-week gestation, the volume of amniotic fluid increases from 25 ml to 400 ml.

• Approximately in the 10th to 11th week of gestation, the breathing and swallowing of the fetus slightly decrease the amount of fluid.

• At 42 weeks, the amniotic fluid volume is approximately 400 ml.

• At birth, the amniotic fluid volume measures approximately about 500 ml to 1000 ml.

How Is Amniotic Fluid Measured?

The amniotic fluid index is a standardized way to assess the sufficiency of the quantity of amniotic fluid in pregnancy and is an indicator of fetal well-being. The amniotic fluid index is expressed in centimeters and is used to measure the amount of amniotic fluid seen on the ultrasonography of a pregnant uterus. The amniotic fluid is determined by:

1. Four Quadrant Technique: In this technique, the amniotic fluid is measured at the deepest, unobstructed, vertical length of each pocket of fluid in each quadrant and is then summed up to the others.

2. Single Deepest Pocket Technique: The amniotic fluid is measured at the deepest, unobstructed, vertical length of each pocket of fluid.

The Measurements of Amniotic Fluid:

• Normal Amniotic Fluid Index (AFI): The amniotic fluid index is between 8-18.

• Median AFI: The Amniotic fluid level is approximately 14 from week 20 to week 35 of gestation when the amniotic fluid begins to reduce in preparation for birth.

• Oligohydramios: An AFI < 5-6.

• Polyhydramnios: An AFI > 24-25.

What Are the Complications of Amniotic Fluid Volume?

Complications related to the amniotic fluid can occur when there is too much (polyhydramnios) or too little fluid (oligohydramnios).

What Is Oligohydramnios?

Oligohydramnios refers to low levels of amniotic fluid. It usually occurs in four percent of pregnancies and 12 % of post-date pregnancies. Oligohydramnios is determined when the amniotic fluid index (AFI) on ultrasonography measures less than 5 cm and the maximum vertical pocket (MVP) is less than 2 cm.

Causes of Oligohydramnios Include:

• Congenital anomalies most commonly affect the baby's kidney and urinary tract issues.

• Problems with the placenta of the pregnant mother.

• Going more than two weeks past the due date.

• Water breaking before going into labor.

• Hypertension.

• Preeclampsia.

• Diabetes.

• Dehydration.

• A pregnancy that extends past the due date.

• Prelabor rupture of the membranes.

• Poor fetal growth.

• Twin-to-twin transfusion syndrome is a result of identical twins sharing a placenta.

Symptoms of Oligohydramnios Are:

• An inadequate amount of amniotic fluid was seen during an ultrasound exam.

• Low movement of the baby in the womb.

• Smaller uterus than expected for the phase of pregnancy.

• Inadequate weight gain during pregnancy.

• Leaking amniotic fluid.

Management of Oligohydramnios Includes:

• Regular monitoring to assess the amniotic fluid volume.

• Amnioinfusion, where fluid is infused into the amniotic sac. This can be performed during labor if the water has broken.

• Early delivery or preterm labor if oligohydramnios poses complications to the pregnancy and baby.

• Complications of Oligohydramnios Are:

• Deformities in the baby are caused by being compressed in the womb due to insufficient amniotic fluid.

• Preterm birth.

• Miscarriage.

• Stillbirth.

• Infection if water is broken early.

Complications due to oligohydramnios in the last trimester (weeks 28 to 40) of pregnancy include:

• Umbilical cord compression.

• Altered fetal growth and development.

• Pulmonary issues due to underdeveloped lungs.

• Increase risk of caesarian delivery.

• Preterm labor.

What Is Polyhydramnios?

Polyhydramnios is a condition that occurs when there is excess amniotic fluid surrounding the fetus. Polyhydramnios is a rare condition, occurring in one percent of pregnancies.

Causes of Polyhydramnios Include:

• Hyperglycemia or high blood glucose levels.

• Birth anomalies.

• Placental issues.

• Infection in the fetus.

• Identical twins with transfusion syndrome.

• Problems with the fetus' stomach and heart rate.

• Differing Rh factors, most commonly when the mother and baby have different Rh factors.

Symptoms of Polyhydramnios Include:

• Constipation.

• Shortness of breath.

• Heartburn.

• Indigestion.

• A feeling of tightness and cramping in the stomach.

• Enlargement of the vulva.

• Swelling of the legs, hips, thighs, ankles, and feet.

• Frequent urination.

Treatment Options for Polyhydramnios Include:

• Regular monitoring.

• Draining excess amniotic fluid.

• Inducing labor before the full term, usually 37 and 39 weeks of pregnancy, to prevent complications.

Complications of Polyhydramnios Are:

• Preterm labor.

• Premature birth.

• Placental abruption.

• Stillbirth.

• Postpartum hemorrhage.

Conclusion:

Alterations in the levels of amniotic fluid can cause complications in pregnancy as amniotic fluid surrounds the fetus during pregnancy and is an essential factor affecting the fetus's health, growth, and development.