I am a currently pregnant rising 3L who received offers from both of the firms I worked at this past summer (I did a full summer program at one firm and also returned to my 1L firm). No one even blinked an eye at my pregnancy. I started at 4.5 months pregnant, and while almost no one would have been able to tell, I announced it to my summer class - I had told the firm a few weeks prior - because it was just easier not to have to hide it. None of the attorneys I worked with had anything negative to say about it, and many of the women I worked with said that if they had it to do again, they would have started their families while in law school.
To the OP - the things that were said early on about timing it to your second trimester are great. If it is your first baby, you likely won't 'pop' until after 20-24 weeks or so. It was only in my last 2-3 weeks at my firm that I started to really look pregnant. Also, your second trimester is likely the one where you will be feeling the best. Though not true universally, for most women the extreme exhaustion and possible nausea of the first trimester is gone, and the potential third trimester discomfort has not yet kicked in. I would also consider your schedule for your 3L year in making the choice as to whether to try and get pregnant. My husband and I planned on having a baby during 3L (I am in my early 30s and did not want to take maternity leave as a young associate or wait till I was in my late 30s for a baby) and I structured my classes accordingly during my 2L year. As a result, I am in a relatively good position as I start this academic year. I also chose a law school (NU) that I knew had a good support structure in place for student moms.
OP (or anyone else) please PM me if you have other questions about my experience - giving people the option to respond is why I did not post anonymously. Obviously I cannot tell you exactly what your experience will be, but I am happy to share more about my own.