I am sure you will get mixed responses here - including that you should switch to sertraline as that is the 'safest' in pregnancy.
I can only tell you what my psychiatrist advises (big swinging Harley Street one if that makes a difference). She is 100% happy for me to conceive while I take escitalopram, and to stay on it throughout pregnancy. Her views (and other obstetric physicians I have since asked) is that all SSRIs are now believed to be the same, and ok, during pregnancy. She would be far more concerned about me trying to change drugs or stop them while pregnant, and strongly urges me not to.
She is less relaxed about breastfeeding however, where I am told that sertraline is the preferred one. She advises me to mixed feed (some breast / some formula), if I want to BF while on escitalopram.
Based in what I have been told I would not put yourself under any pressure to change anything. Just be aware that, like me, because of your pre-existing depression you will probably have a tendency to antenatal or post-natal depression which may require increased doses.