needs an advice on pregnancy

I am 39 years old and already has one son. We tried for two years and then gave up. We were happy with one child, but suddenly i realised that i have conceived. Now i am in dilemma as i am not prepared for it mentally. Also, i have learnt the problems of late age pregnancies. The fear entails the down syndrome in the child, more so because my son was an Inter Uterine Growth Retardation(IUGR) baby. I am confused whether to keep the child or go for abortion. My husband has left the decision on me. Please advice/ guide me.