J.
Like a couple of the other mom's, I also was on celexa during my pregnancy(celexa and lexapro are in the same cateogry and are pretty much the same drug with a minor twist). It is a selective serotonin reuptake inhibitor (SSRI) as is prozac, zoloft, paxil, etc. After talking with my doctor (which you should do!) I decided to wean off of the medicine at the end of the second trimester and monitor my symptoms closely. This was based on a couple of studies that found increased risk if the medicine was continued in the third trimester (though there were also many studies that found it was safe to continue for the duration of pregnancy). I resumed the celexa several weeks after our son's birth when I started having symptoms again and continued breastfeeding him while on the meds. He is a happy and healthy 18 month old and *I* am a happy and healthy mom.
So here's the trick about meds and pregnancy...nobody wants to do big organized studies using pregnant women to see happens if some are given a drug and some aren't (not sure if I would sign up for a study while pregnant...) But there have been lots of studies looking at women who did take the meds throughout pregnancy or for part of pregnancy and how the kids turned out afterwards. If you look up the FDA pregnancy category on meds, most will be category C which means we have no clue one way or the other...they haven't been studied well or studies have been inconclusive. Category A is proven safe to take in pregnancy (this would be like folic acid and some B vitamins), Category B has drugs that have been used a lot in pregnancy and are generally found to be safe in the first two trimesters (tylenol, ibuprofen, some antibiotics). Category D is probably causes more harm than good but you could still take if the benefits far outweigh the risks...and Category X means that it is known to cause birth defects and there is no benefit that would outweigh the risk (Accutane is a good example of this...they generally make women be on some form of birth control while on these meds...) My favorite site for looking up drug info is epocrates.com (pregnancy and lactation info is under the "safety monitoring" tab once you look up a drug from the main page).
Your doctor should be up to date on these studies or at least have access to journals that would have the results. If you are feeling adventurous, many of these articles (or their abstracts) can be found by using the google scholar search engine. The most widely studied antidepressant in pregnancy is prozac (fluoxetine) and I know my doc and I discussed maybe switching to that. The big thing is to keep taking your meds until you talk to your doc...going off cold turkey is usually not a good idea and you need to work out how you will taper off if you do decide to stop or switch.
As for conceiving...I know that many of the SSRIs can cause sexual side effects, but as long as you feel like having sex I have not heard of lexapro causing physical problems with conceiving.
Good luck in conceiving! Listen to your body, get a good dialogue going with your doc(s) and make sure to monitor your symptoms...having a bad bout of depression while in the end stages of pregnancy or post partum can also be bad for you and the baby so catching symptoms early is vital. Have fun!