Placental laterality may be a random event and not the result of inherent uterine artery pathology.

OBJECTIVE To determine whether placental laterality and discordant uterine artery impedance during pregnancy is a random event or the result of uterine artery pathology. METHODS We identified 50 patients with unilateral placenta and pathologic uterine artery impedance during their current pregnancy and enrolled them in the study. Thirty-three of these patients met the inclusion criteria and returned during the first 10 days of their third normal menstrual cycle after delivery. We examined the pelvic anatomy to rule out any pelvic pathology and then used color and pulsed wave duplex Doppler to identify the uterine artery in the immediate vicinity of the paracervical area at the level of the isthmus. We obtained the uterine artery resistance index (RI) from each uterine artery. We performed statistical analysis by means of t-test. RESULTS The uterine artery ipsilateral to the placenta exhibited significantly lower impedance than the contralateral in the pregnant state. When the placenta was right, the values (mean +/- SD) were 0.60 +/- 0.11 vs. 0.73 +/- 0.09 for the right and left artery, respectively. When the placenta was left the values were 0.57 +/- 0.08 vs. 0.77 +/- 0.07 for the left and right uterine artery, respectively. In the nonpregnant state, the corresponding values were 0.90 +/- 0.04 vs. 0.90 +/- 0.05 and 0.91 +/- 0.05 vs. 0.90 +/- 0.04, respectively. CONCLUSION In patients with a unilateral placenta and discordant pathological uterine artery impedance during pregnancy, there is no evidence of discordant impedance between the two uterine arteries in the postpartum period. We speculate that the location of placental implantation may not be the result of preexisting uterine artery discordant impedance.