How is the maximum vertical pocket (MVP) of amniotic fluid measured during a routine obstetric ultrasound in a healthy singleton pregnancy?

How to Measure Maximum Vertical Pocket (MVP) in Pregnancy

The maximum vertical pocket (MVP) is measured by identifying the single deepest vertical pocket of amniotic fluid anywhere in the uterus, positioning the ultrasound probe perpendicular to the uterine contour and parallel to the maternal sagittal plane, measuring the maximal vertical depth in centimeters while excluding umbilical cord and fetal parts from the measurement. 1

Technical Measurement Steps

Probe Positioning

• Position the transabdominal convex probe vertical to the uterine contour of the abdomen and parallel to the maternal sagittal plane 2
• Scan all areas of the uterus systematically to identify the deepest pocket 1

Measurement Technique

• Measure the single maximal vertical pocket found anywhere in the uterine cavity 1
• The measurement represents the vertical depth only (not horizontal width) 1
• Exclude umbilical cord and fetal parts from the pocket being measured 3

Handling Umbilical Cord in the Pocket

• If the deepest pocket contains umbilical cord, measure to the cord, not through it 4
• This approach is superior for detecting low amniotic fluid volumes compared to measuring through the cord 4
• The pocket should ideally be free of cord and fetal parts for the most accurate assessment 3

Normal Values and Interpretation

Throughout Gestation

• A single MVP of ≥2 cm is considered normal throughout all of gestation 1, 5
• This threshold remains constant and does not vary with gestational age 5

Pathologic Thresholds

• Oligohydramnios: MVP <2 cm 5, 3
• Polyhydramnios: MVP >8 cm 5, 3

Clinical Advantages of MVP Over AFI

MVP is the preferred method over amniotic fluid index (AFI) because it reduces false-positive oligohydramnios diagnoses by approximately 50% without compromising detection of adverse outcomes. 5, 6

Key Differences

• MVP produces fewer unnecessary interventions compared to AFI 1, 5
• More patients are diagnosed with oligohydramnios using AFI, leading to more obstetric interventions without improving perinatal outcomes 1
• Neither method performs better at preventing intrauterine fetal demise, but MVP avoids overdiagnosis 1, 7

Common Pitfalls to Avoid

• Do not measure through umbilical cord if it is present in the pocket—measure to the cord instead 4
• Do not include fetal parts in the measurement 3
• Do not use AFI as the primary measurement tool as it leads to overdiagnosis 5
• Do not diagnose oligohydramnios based solely on clinical fundal-height measurements when ultrasound shows normal MVP 5