Umbilical artery velocity waveforms: normal reference values for A/B ratio and Pourcelot ratio.

Area of Science:

• Perinatal Medicine
• Fetal Ultrasound
• Doppler Echocardiography

Background:

• Umbilical artery Doppler velocimetry is essential for monitoring fetal health.
• Establishing accurate reference ranges for indices like the Pourcelot ratio and A/B ratio is critical for clinical interpretation.
• Previous studies may lack comprehensive serial data or robust statistical correction.

Purpose of the Study:

• To report normal reference values for the umbilical artery Pourcelot ratio and A/B ratio.
• To provide serial data from 20 weeks of gestation to term.
• To investigate and correct for non-normality in the distribution of A/B ratio centiles.

Main Methods:

• Serial ultrasound examinations were performed on 35 normal pregnant patients.
• Umbilical artery Doppler measurements, including Pourcelot ratio and A/B ratio, were recorded from 20 weeks to term.
• Statistical methods were employed to correct A/B ratio centiles for non-normality using Pourcelot ratio transformations.

Main Results:

• Normal reference values for the umbilical artery Pourcelot ratio and A/B ratio were established.
• Correction for non-normality of the A/B ratio distribution was performed, with greater adjustments needed in the second trimester.
• A trend towards higher waveform indices in nulliparous patients was observed, though not statistically conclusive due to small sample size.

Conclusions:

• This study provides valuable reference data for umbilical artery Doppler indices in normal pregnancies.
• The findings highlight the importance of gestational age-specific reference ranges and statistical correction for accurate interpretation.
• Further research with larger cohorts is needed to confirm the influence of parity on these Doppler indices.