Normal Pulsatility Index in First Trimester
The provided evidence does not contain specific reference values for pulsatility index measurements in the first trimester of pregnancy, as the guidelines focus primarily on terminology, imaging appropriateness, and general ultrasound practices rather than Doppler parameters.
Key Guideline Recommendations
Pulsed Doppler ultrasound should generally be avoided in the first trimester when evaluating normal or potentially normal intrauterine pregnancies due to potential bioeffects on the developing embryo 1, 2. The American College of Radiology specifically recommends documenting embryonic cardiac activity using M-mode ultrasound or video clips instead of pulsed Doppler methods 2.
When Doppler May Be Appropriate
- Doppler ultrasound may be utilized only after a normal intrauterine pregnancy has been excluded, particularly when evaluating for retained products of conception or arteriovenous malformations 1
- In fetuses at increased risk (such as those with nuchal translucency ≥3 mm at 11-14 weeks), Doppler studies including ductus venosus assessment may be reserved for specific indications 1
Available Research Data (Not First Trimester Specific)
While the guidelines do not provide first trimester PI reference ranges, research studies offer limited data:
- Uterine artery measurements at 11-13 weeks gestation show a mean lower PI of approximately 1.44 and mean PI values that decrease with advancing gestational age 3
- One study reported intrachorionic arterial PI values of approximately 0.47 (mean) during 5-11 weeks gestation, though this represents research data rather than clinical guidelines 4
Critical Safety Consideration
The primary concern is avoiding unnecessary Doppler exposure during early embryonic development when cardiac and other organ systems are forming 1. The as low as reasonably achievable (ALARA) principle mandates minimizing fetal risk from Doppler studies 1.