A 35 year old female, Gravida 2, Para 1, Gestational Age = 37w 2d, was scheduled for a follow up ultrasound to monitor fluid level and cord Doppler. Previous ultrasound exams revealed a fetus, small for gestational age and declining amniotic fluid level. 1 week prior, the fetus measured 2 weeks behind gestational age with an estimated fetal weight at the 9th percentile. The AFI was 6.5cm. Normal AFI levels should be 5.0 -20 cm. Therefore, the AFI was considered to be low normal.
With all OB exams, fetal position and fetal heart rate should always be performed. Exam revealed fetus was vertex/cephalic presentation. Fetal heart rate was 146 bpm. Visual assessment of fluid level was very low. Only two pockets of fluid were located, right upper quadrant and right lower quadrant, totaling 2.7cm. Due to the decline of amniotic fluid and growth restriction, this patient was scheduled at the hospital for a cesarean delivery at 5:00 pm that evening.
Amniotic fluid is instrumental in the development of fetal growth, muscle tone, and lung development. When fluid level is low, the fetal movement is limited. Lungs are developed by “breathing” actions of the fetus, “breathing” the amniotic fluid. Limited fluid levels, limit the fetal lung development.
When the fluid level is low, obtaining a cord Doppler is challenging. Sometimes, repositioning the patient in a decubitus position or attempting various angles, can assist in locating a section of cord adequate to Doppler. In this case, the Doppler was normal, at 2.0 and displayed diastolic flow. Doppler of the umbilical cord is performed to assess possible compromise of the fetus, especially the intrauterine growth restricted fetus (IUGR). It assists in identifying placental insufficiency and fetal distress.
Assessment is based on the systolic to diastolic ratio. At 30 weeks gestational age or greater, the S/D ratio should be 3 or less and display a low resistance waveform pattern. Low, absent or reversal of diastolic flow is an indication of fetal distress with an increased risk of perinatal morbidity and mortality. It is recommended to always perform a cord Doppler on all IUGR fetuses.