Continuous wave Doppler flow velocity waveforms from the umbilical artery in normal pregnancy.
The objective was to establish a normal reference range of the indices of umbilical artery waveforms using continuous wave doppler ultrasound. A prospective longitudinal study was made of 85 uncomplicated singleton pregnancies between 16 and 40 weeks gestation (783 recordings). Pulsatility Index (P.I.), Resistance Index (R.I.) and A/B ratio were measured at each visit. The mothers all delivered normal healthy infants weighing more than the 10th centile for gestational age. All three indices have a positively skewed frequency distribution, a factor not generally appreciated until recently and the ranges are therefore described using non-parametric statistics. Placental resistance decreases as term approaches, the 50% PI at 16 weeks was 2.06, at 32 weeks was 1.08 and at 40 weeks was 0.85. The results show a comprehensive reference of normal values and provides a sound basis for the further study of abnormal pregnancy. It represents the largest published study of its type using continuous wave Doppler.
Fogarty
P
P
Department of Obstetrics and Gynaecology, Royal Maternity Hospital, Belfast, N. Ireland.
Beattie
B
B
Harper
A
A
Dornan
J
J
D000293:Adolescent; D000328:Adult; D001783:Blood Flow Velocity; D005260:Female; D005312:Fetal Blood; D005865:Gestational Age; D006801:Humans; D008137:Longitudinal Studies; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D014465:Ultrasonics; D014469:Umbilical Arteries / Q000502:physiology*