Normal Maximum Vertical Pocket Size on Ultrasound
The Maximum Vertical Pocket (MVP), also called the Single Deepest Pocket (SDP), is the largest vertical measurement of a free amniotic fluid pocket identified on obstetric ultrasound, free of fetal parts and umbilical cord. It serves as a key index of amniotic fluid volume throughout pregnancy. Accurate MVP assessment is essential for diagnosing oligohydramnios and polyhydramnios, both of which are associated with significant perinatal morbidity.
Normal Reference Values
| Measurement |
|---|
| >8 cm |
Clinical Significance
Normal amniotic fluid is generally reflected by an MVP between 2 cm and 8 cm. An MVP greater than 8 cm defines polyhydramnios and warrants further clinical evaluation. Polyhydramnios can be associated with impaired fetal swallowing, excess fetal urination, or maternal conditions, and carries risks including preterm labor, cord prolapse, placental abruption, and perinatal mortality. The degree of elevation correlates with prognosis — severe polyhydramnios (MVP >15 cm) carries a substantially higher risk of adverse outcomes than mild forms.
Clinicians should be aware that MVP assessment may underestimate fluid in cases of diffuse excess, and that serial measurements provide greater prognostic value than a single data point. Fetal anomaly survey and maternal glucose screening are indicated when polyhydramnios is confirmed.
- Fetal gastrointestinal obstruction (e.g., duodenal atresia, esophageal atresia)
- Fetal neuromuscular disorder impairing swallowing
- Gestational or pre-existing diabetes mellitus
- Fetal anemia (e.g., Rh alloimmunization, parvovirus B19)
- Idiopathic polyhydramnios (up to 50–60% of cases)
Reference: Pri-paz S, Khalek N, Fuchs KM et al. Maximal amniotic fluid index as a prognostic factor in pregnancies complicated by polyhydramnios. Ultrasound Obstet Gynecol. 2012;39(6):648-53.
Imaging Notes
MVP is measured on standard 2D grayscale ultrasound by identifying the largest vertical pocket of amniotic fluid free of fetal limbs and umbilical cord loops. The transducer is held perpendicular to the maternal abdomen, and the measurement is taken in the vertical plane only — horizontal dimensions are not included. Color Doppler may be used to confirm the absence of cord within the selected pocket before recording the measurement.
MVP is generally preferred over the Amniotic Fluid Index (AFI) in twin pregnancies and in cases where a single largest pocket assessment is clinically more practical. Standardized technique and consistent operator approach are important, as MVP can vary with fetal and maternal position.