Role of aspirin therapy in modulating uterine artery resistance and placental growth between first and second trimesters of pregnancy

Abstract

Objective: To evaluate the impact of low-dose aspirin (LDA) on placental size and uterine artery pulsatility index (UtA-PI) by analyzing longitudinal changes between the first and second trimesters in pregnancies at high risk for early-onset pre-eclampsia (PE).

Methods: This was a prospective observational cohort study of 631 singleton pregnancies. Women at high risk of early-onset PE (delivery ≤ 33 + 6 weeks) were identified using maternal factors or a multivariate screening protocol and were prescribed LDA. Placental size was assessed using two- and three-dimensional ultrasonography, and UtA-PI was measured using transabdominal Doppler, with measurements obtained in the first and second trimesters. Differences in placental measurements and UtA-PI between high-risk women receiving LDA and low-risk untreated women were analyzed.

Results: Among the 631 participants, 53 (8.4%) women were prescribed LDA for the prevention of early-onset PE. Placental size in the first trimester was significantly smaller in the LDA group compared with the untreated group, as exemplified by placental volume (mean ± SD, 68.46 ± 25.19 cm³ vs 76.31 ± 23.63 cm³; P = 0.022), and this trend persisted into the second trimester. However, no significant differences in placental growth from the first to the second trimester were observed between the groups. UtA-PI was significantly higher in the LDA group in both trimesters, but a greater decrease in UtA-PI multiples of the median values between trimesters was noted in these women (mean ± SD, -14.0 ± 0.28% vs -4.5 ± 0.31%; P = 0.021). Perinatal outcomes were similar between the groups, with the exception of a higher rate of Cesarean delivery in the LDA group (38.5% vs 21.1%; P = 0.008).

Conclusions: Women at high risk for early-onset PE have a smaller placenta and higher UtA-PI in the first and second trimesters. Treatment of high-risk women with LDA did not affect placental growth but was associated with a greater reduction in UtA-PI, suggesting a positive effect of LDA on placental perfusion. These findings provide insight into the mechanism of action of LDA in the prevention of PE. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Keywords: first trimester; low‐dose aspirin; placental biometry; placental volume; pre‐eclampsia; three‐dimensional ultrasound; two‐dimensional ultrasound; uterine artery Doppler.

Figure 1

Measurement of placental size using two‐dimensional ultrasound. All variables were measured in two orthogonal planes showing largest view of placenta. BP, basal plate diameter (curvilinear); CP, chorionic plate diameter (curvilinear); PT, placental thickness (linear).

Figure 2

Measurement of placental volume using three‐dimensional ultrasound and QLAB GI3DQ software version 10.5 using 15 placental sections. Each frame depicts placental section with manually traced outer contour.