Effects of early aspirin therapy on utero-placental hemodynamics in patients at risk of preeclampsia.

OBJECTIVES

To evaluate the effects of early aspirin therapy on the mean pulsatility index of both uterine arteries (utA PI) at 1st and 2nd trimester in women at risk of preeclampsia (PE).

METHODS

Uterine artery (utA) blood flow characteristics were obtained in 315 women, 73 women at risk for PE and early aspirin treatment (group 1), 124 without specific risk factors and no aspirin treatment (group 2) and 118 women with manifest PE (group 3). Mean utA PI of group 1 and group 2 were compared within and between the groups at the 1st and 2nd trimester time points. Furthermore, values at 2nd trimester were compared with those of group 3. Observed to expected mean utA PI ratio (O/E ratio) were calculated for comparison between the groups.

RESULTS

Mean utA PI of group 1 was significantly higher in the 1st trimester compared to group 2 (1.74 vs. 1.47, p = .0117). In the 2nd trimester mean PI decreased significantly in both groups from 1.74 to 1.16 in group 1 and from 1.47 to 0.90 in group 2 (p < .0001). Nevertheless, the difference between the groups was significantly higher in the 2nd trimester than in the 1st trimester (0.29 vs. 0.27, p < .001). Correction for gestational age by analyzing mean utA O/E ratios showed a comparable pattern with a significantly decrease in both groups (1.40 to 1.10 in group 1 and 1.18 to 0.78 in group 2, p < .0001), but a significant higher decrease in the 2nd trimester in group 2 (0.31 vs.0.22, p < 0001). The prevalence of PE was 15.1% (11/73) in group 1 (4 early/7 late onset PE) and 4.7% (6/124) in group 2 (1 early/5 late onset). Mean utA PI and O/E ratio obtained in the 2nd trimester were higher in all PE cases with no significant difference between early and late onset PE (1.49/1.57 and 1.25/1.36 in group 1 and 0.80/0.97 and 0.77/0.99 in group 2). However, mean utA PI and O/E ratio decreased in all cases without PE in both groups, whereas mean utA PI was 1,37 and O/E-ratio was 1,29 in patients with manifest PE at admission, with significantly higher values in early onset than in late onset PE (1.45/1.31 vs. 1.07/1.02, p < .0001).

CONCLUSIONS

Our results show that early aspirin treatment leads to a decrease of elevated mean utA PI between 1st and 2nd trimester in patients at elevated risk for PE which is inferior to the decrease observed in women at standard risk for PE. While aspirin improves trophoblast invasion during early second trimester, vascular resistance remains well above average levels. Limited vascular remodeling capacity in the utero-placental perfusion area seems to be the explanation why aspirin does not abrogate PE in all women and has little effect on birth weight. Another explanation might be that a dose of 100 mg aspirin was used as compared to the 150 mg which is recommended today. Our findings underscore the need to study the effects of intervention already during the early stages of trophoblast invasion in the first trimester.