The development of high venous velocity at the fetal umbilical ring during gestational weeks 11-19.
OBJECTIVE
To determine the occurrence of high venous velocities at the umbilical ring in the normal early second trimester, based on the assumption that a narrow umbilical ring may cause obstruction and increased venous blood velocity at the abdominal wall.


METHODS
Cross-sectional study.


METHODS
Hospital antenatal clinic.


METHODS
One hundred and one low risk singleton pregnancies specifically recruited for the study.


METHODS
Ultrasound was used at 11-19 weeks to determine the diameter and velocity in the umbilical vein at the fetal end of the cord and at the inlet through the abdominal wall. Outcome measures 10th, 50th and 90th centiles were estimated for the time-averaged maximum velocity in the cord and at the abdominal inlet. The increase of velocity as the blood entered the abdominal wall was calculated in percent of the velocity in the cord.


RESULTS
During weeks 11-12 there was hardly any difference between blood velocity in the umbilical vein at the umbilical ring and that in the cord. From week 13 onwards it was increasingly common to find blood acceleration at the umbilical ring of 50-500%. Velocity increment >50% was found in 0/12 fetuses (0%) at 11-12 weeks, 5/20 (25%) at 13-14 weeks, and in 21/28 (75%) at 17-19 weeks.


CONCLUSIONS
Blood velocity is higher in the umbilical vein at the abdominal wall than the cord, particularly after 13 weeks of gestation. If acceleration of blood velocity at the umbilical ring is a sign of a narrow inlet, it seems that a progressive tightening occurs during the second trimester.
Department of Obstetrics and Gynaecology, Bergen University Hospital, Norway.
S M
SM
Skulstad
S
S
Rasmussen
O E
OE
Iversen
T
T
Kiserud
D000009:Abdominal Muscles; D001783:Blood Flow Velocity / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D016216:Ultrasonography, Prenatal; D014470:Umbilical Cord / Q000098:blood supply* / Q000196:embryology; D014471:Umbilical Veins / Q000196:embryology / Q000502:physiology*