The purpose of this study was to investigate when in pregnancy to stop the administration of low dose aspirin (150 mg/daily) so as to prevent fetal growth restriction (FGR) A randomised, placebo-controlled study was designed. The patients were all screened positive using the Fetal Medicine Foundation (FMF) early pregnancy screening test for preeclampsia (PE) and FGR prediction. One hundred and fifty patients were enrolled and divided equally into three groups: A - the controls who received placebo treatment; B - those who received aspirin till 32 weeks of gestation and C - those who received aspirin till 36 weeks of gestation. The mean gestational age at enrollment was similar for all the groups (12.4 weeks). The growth curves, fetal and maternal Doppler measurements and amniotic fluid index (AFI) were monitored every 4 weeks. Also, the outcome of the pregnancy was noted and all the results were compared between the groups. FGR was defined as a fetal weight below the 10th centile for gestational age. In group C, there were less cases of FGR compared with the other groups: 6% vs. 10% in group B vs. 24% in controls. Also, there was a significant birth weight improvement in this group with a median of 3180 g compared with 2950 g in group B and 2760 g in group A (P=0.01). The gestational age at delivery was similar in all the groups (39 weeks in group C/39.2 weeks in group B/38.6 weeks in group A). In conclusion, low dose aspirin improves the outcome in the selected population and should be offered for prevention of FGR from 12 to 36 weeks.