Firstly the only way you can properly stop the anxiety from returning is to sort out the causes. If you can afford to pay for counselling then private is usually quickest - if not try going through your gp, though there is usually a wait.
Secondly you need to devise some kind of support system for if the anxiety does happen again.
I have anxiety issues from a crappy childhood that got extremely bad during my recent 2nd pregnancy. I treated it with medication (I was in the second trimester by this point so although restricted there was stuff I could have) and I also am still having CBT which works on the behaviour patterns and the way you think (IYSWIM) - that has been fantastic for me but might not work for you at the moment if you are not anxious now.
I also had a lot of support from my midwife and gp (I was under gp-led care for the anxiety). The hospital were made aware of my issues for when I gave birth (there were potential complications because of the medication I was taking) and were very good - e.g. I was placed in a 2 bed room rather than on the 6 bed open ward when I had to stay in. I was assessed by the mother and baby psychiatric team who put me in touch with a charity who would phone me to check on me and let me talk on a regular basis (this really made a big difference).
I had a lot of support from my work (I was off work from about 5 months on sick leave until I went on maternity leave) and then again when I went back to work inJanuary (returning from maternity leave) e.g. my maternity cover stayed on to provide one to one support for 6 months.
I have support from dh's family and our friends (I have no contact with my own family). Luckily in a way for me dh was unemployed so at home full time to look after me (he is now a SAHD) - although I'm much better now I'm nowhere near 'cured' and still need a high level of support from him.
My mind reacted to the severe anxiety by having hallucinations and paranoid delusions. I was on anti-psychotics for this as well as the prozac for the anxiety. I also shook, twitched and stuttered badly (none of which I have ever done before in my life) so came accross as a real headcase.
When the midwife passed me over to the HV after dd was born she to was given my history so could support me. I developed (luckily only mild) PND.
Dh was careful not to let me get sleep deprived (as I said we were lucky he was not working) - we used to do 6 hour shifts at the start. He also kept a very close eye on me e.g. I refused to sleep at all in the hospital so he sent me to bed for about 18 hours when we got home and promised to write down everything she did (times and size of feeds, nappy changes etc) and made sure he stayed awake to watch her.
Sorry this has been an epic but I wanted to show you it can be managed and treated in pregnancy with the right support. Any questions please ask.