Table 1.

Doppler waveform indices used in this study

Arteries examined	Outcome Indices	Time of measurement	Calculation
Uterine arteries	Mean of Pulsatility Index (PI)	Measured twice at 15–20 and 24–29 weeks’ gestation	PI = (S−D)/A
	Any early diastolic notch in either or both uterine arteries	Measured twice at 15–20 and 24–29 weeks’ gestation	Yes or No
Umbilical artery	Resistance Index (RI)	Measured once at 24–29 weeks’ gestation	RI = (S−D)/S

PI: Pulsatility index, RI: Resistance index, S: Peak systolic velocity, D: End-diastolic velocity, A: Time-averaged maximum velocity