Abnormal PI, specifically referring to uterine artery Pulsatility Index (PI), indicates unusual blood flow patterns in the uterine arteries, often assessed during pregnancy.
Understanding Uterine Artery Pulsatility Index (PI)
The Pulsatility Index (PI) is a measure used in Doppler ultrasonography to assess the resistance to blood flow in a vessel. In obstetrics, it's commonly used to evaluate the uterine arteries, which supply blood to the uterus and developing fetus.
Defining Abnormal Uterine Artery PI
According to reference [4], abnormal uterine artery Doppler flow velocimetry is defined as:
- A mean PI more than 1.45, or
- The presence of bilateral early diastolic notches.
This means if the average PI value from uterine artery measurements exceeds 1.45, or if both uterine arteries show early diastolic notches (a brief interruption or reduction in blood flow during diastole), it's considered abnormal.
Significance of Abnormal Uterine Artery PI
An abnormal uterine artery PI can be associated with adverse pregnancy outcomes. Reference [5] suggests that second-trimester uterine artery PI can help in predicting pre-eclampsia. Other potential complications include:
- Intrauterine Growth Restriction (IUGR): Reduced blood flow to the fetus can hinder its growth.
- Pre-eclampsia: High blood pressure and organ damage in the mother.
- Placental Abruption: Premature separation of the placenta from the uterine wall.
- Stillbirth: Fetal death in late pregnancy.
Example
If a pregnant woman undergoes a Doppler ultrasound, and the mean PI of her uterine arteries is calculated to be 1.6, this would be considered an abnormal finding as it is greater than 1.45. The presence of bilateral early diastolic notches would also be considered abnormal, even if the PI is less than 1.45.
