Enjoy the extra energy, mindfully
Welcome to my favorite trimester. Hopefully by now many of the difficult first trimester symptoms have subsided and you feel a surge of energy. In my experience it was more of a return to feeling like my usual self, which did mean more energy compared to first trimester. If you toned down intensity during first trimester because of fatigue, you may feel like you can turn things back up now, but don't go too hard. Listening to your body is still very important.
Continue to work on connection to your core, but you will want to start modifying to avoid any movements where you cannot control the pressure within your abdominal cavity (also known as intra-abdominal pressure, or IAP). Pay attention for any soreness in the pelvic region or low back which can be indicators that you are pushing the intensity too hard and over-stressing your pelvic floor and core. Overhead movements, like pull-ups or shoulder press, can overload the ever-stretching abdominals at this point so keep an eye on your belly if performing these movements. Jumping and high intensity cardio can have negative effects on joints and the pelvic floor so it's a good idea to start modifying these types of movements as well. Crunches and sit-ups are also not advised, but that doesn't mean you can't work on core connection while lying on your back. Supine breathwork is a great way to connect to your pelvic floor and core without over-stressing the abdominals. It's also a great way to train your focus for labor. Again, check out my blog post on this type of breathing.
Mind the growing bump
As your baby grows, so does your belly and you'll start to show at some point this trimester depending on your body and whether you've had a baby before. Especially on the yoga mat you will need to start modifying movements to accommodate the bump. Any position where you are lying on your belly may start to become uncomfortable, like cobra and locust. At this point, move to all fours and practice a similar movement like cat-cow or bird-dogs.
Blocks are going to be your best friend. Use them to modify plank, down dog, and forward folds. They are also great for creating space around the belly in any sort of pose where you are bent over and have one or both hands on the floor - like fingertip lunge or side lunge. You can also widen your stance in any pose to create more space for the belly. Play around with the height of the blocks to find a position that is comfortable for you. This is also the time to be mindful of twisting. Gentle twists in the thoracic spine are ok, but do not force the twist - something I don't recommend to even my non-pregnant students. Placing a hand on the belly for abdominal support and to monitor any unmanaged IAP is also helpful. And of course, if they just don't feel good, don't do them!
I realize much of this post is focused on what you can't do or may have to limit as a pregnant person, but know that there is still so much that your body can do during this time! Personally I felt myself being amazed and appreciative that my body was still able to move on my mat and lift weights all while growing a human inside of me. Sure, some poses looked a little different, I wasn't doing any of my beloved handstands, and I had lowered my weights a bit but I was still moving and breathing and taking time to focus on myself and my body. Pregnancy is temporary. It may not feel that way by the time 36 weeks rolls around (me currently: have I been pregnant for 9 months or 9 years?!), but you will have your baby and with proper post-natal care you will be able to return to your regular movement practice.