Normal Maximum Vertical Pocket Size on Ultrasound >24 Weeks
The maximum vertical pocket (MVP), also called the single deepest pocket, is an ultrasound measurement used to assess amniotic fluid volume during pregnancy. It represents the depth of the largest cord-free, fetal-part-free pocket of amniotic fluid identified in the uterine cavity. Accurate MVP assessment is critical because abnormal amniotic fluid volume is associated with significant fetal and perinatal morbidity.
Normal Reference Values
| Measurement |
|---|
| <2 cm |
Clinical Significance
An MVP of less than 2 cm after 24 weeks of gestation defines oligohydramnios. Oligohydramnios can reflect uteroplacental insufficiency, fetal renal anomalies, rupture of membranes, or post-term pregnancy complications. It is associated with increased risks of fetal distress, cord compression, meconium aspiration, and perinatal mortality.
MVP is often preferred over the amniotic fluid index (AFI) in certain clinical contexts, particularly in post-term pregnancies, due to its lower false-positive rate for diagnosing oligohydramnios and a reduced rate of unnecessary intervention. Clinicians should be aware that borderline values (2–5 cm) require careful clinical correlation and serial monitoring.
- Uteroplacental insufficiency — most common cause in the third trimester
- Premature rupture of membranes (PROM) — acute reduction in MVP
- Fetal renal agenesis or obstructive uropathy — absent or severely reduced fluid
- Post-term pregnancy — progressive placental insufficiency reducing fluid
- Medication effect — NSAIDs and ACE inhibitors can reduce fetal urine output
Reference: Verrotti C, Bedocchi L, Piantelli G et al. Amniotic fluid index versus largest vertical pocket in the prediction of perinatal outcome in post-term pregnancies. Acta Biomed. 2004;75 Suppl 1:67-70.
Imaging Notes
MVP is measured using 2D grayscale ultrasound with the transducer held perpendicular to the uterine floor. The largest pocket of amniotic fluid is identified, and a vertical measurement is taken ensuring the pocket is free of umbilical cord loops and fetal parts. The measurement should be performed in the true vertical (craniocaudal) plane; tilting the transducer can artificially increase or decrease the apparent depth.
Color Doppler is a useful adjunct to confirm the absence of umbilical cord within the selected pocket before recording the measurement. In oligohydramnios, image quality is often reduced due to limited acoustic windows; increasing gain settings or repositioning the patient may improve visualization. Serial measurements are recommended when MVP is borderline, as a single value may not reflect the overall clinical trajectory.