Fig. 4.

The relationship between ultrasonographic measurements of length and jet mouth velocity at 11 + 0 to 13 + 6 weeks of pregnancy. Trends are similar at later stages of pregnancy. There is no significant relationship between the two parameters. This lack of relationship, and the predictions that flow velocity at the SA mouth must be much higher than ultrasound measured values to predict accurate jet length, suggest that the density of villous tissue distal to the SA mouth must be a primary determinant of jet penetration.