Effect of low-dose aspirin treatment on vascular resistance in the uterine, uteroplacental, renal and umbilical arteries — A prospective longitudinal study on a high risk population with persistent notch in the uterine arteries

Abstract

Objective: The study focuses on the changes of Doppler flow velocity waveforms in the uterine, uteroplacental, maternal intrarenal and umbilical artery in a selected population at high risk for pre-eclampsia or IUGR with original abnormal Doppler of the uterine arteries, defined as persistent bilateral notches at 22–24 weeks of gestation, who were randomised treated with low-dose aspirin compared to no treatment and low risk controls, longitudinally during pregnancy and 6 months postpartum. Methods: High risk and control patients were collected from a population attending routine ultrasound for confirmation of gestational age. One-hundred-and-seventy-eight high risk patients and 29 normal controls had duplex pulsed wave Doppler ultrasound at 22–24 weeks of gestation. Twenty-eight high risk patients showed bilateral notches in the main uterine arteries. Of those 26 were randomised treated with 50 mg aspirin or had no treatment. Additional Doppler ultrasound examinations were performed twice during pregnancy at 28–32 and 33–40 weeks and once 6 months postpartum. Main outcome criteria were incidence of pregnancy induced hypertension (PIH) and intrauterine growth retardation (IUGR). Results: The notches in the uterine arteries in the high risk group were constant throughout pregnancy in both the aspirin and untreated group in 88.5% (23/26) of the cases. The majority of resistance indices (RI) in the main uterine and uteroplacental arteries of the high risk population ranged above the mean line registered in low risk pregnancies, whereas no differences could be seen in the renal and umbilical artery. Aspirin had no effect on the Doppler waveform in any of the examined vessels except the uteroplacental arteries. At 22–24 weeks of gestation the highest RI were found in high risk patients who developed PIH or IUGR later during pregnancy compared to high risk patients without disease or normal controls. Six months postpartum no differences in vascular resistance were seen any more between the different groups and the RI was still lower than reported for non pregnant women. Aspirin treatment could not prevent PIH or IUGR, but was safe for the foetus. However, in the aspirin group there was one uterine haemorrhage at 36 weeks of gestation and one placental abruption at emergency caesarean section for threatening asphyxia at 38 weeks. Persistent bilateral notches in high risk patients selected a group with 35% incidence of PIH and 12% incidence of IUGR. Conclusions: Low-dose aspirin treatment does not affect the resistance index in the uterine, umbilical or renal circulation. Significant notches in the uterine arteries at 22 24 weeks gestation persist usually throughout pregnancy. The phenomenon is related to higher resistance indices but does not prevent ‘physiological’ adaptation of vascular resistance in the uterine artery during pregnancy or postpartum. Combining high risk selection and uterine Doppler at 22–24 weeks of gestation may be useful to find a group with high incidences of PIH or IUGR. However, starting low-dose aspirin treatment based on the pathological Doppler, is possibly too late for prevention of the disease.