Here are some general rules about exercising during pregnancy:

1. Listen to your body. If it hurts then stop! If you experience abdominal pain or pain in your pelvis then you need to stop and rest. Don’t be afraid to take it easy if feeling tired, nauseous or energy deplete. You are growing a human and that is hard work as it is!
2. If you were previously active you can generally do what you were previously with some modifications. For example if you usually perform a couple of HIIT workouts a week these can usually be safely continued with some modifications for the higher intensity parts. High intensity and high impact exercises can put a strain on your lax joints due to pregnancy hormones and pelvic floor. Eg. Instead of jump squats just perform squats, instead of box jumps do step-ups, instead of burpees do these without the jump. You can still get your heart rate up and feel a bit sweaty with these modifications if you did these prior to pregnancy. If you were previously a runner, then jogging can usually be continued under guidance from health professionals (eg. Doctors and Physiotherapists). (There are also a lot of alternatives available to jogging which may be more pelvic floor friendly, especially in the last trimester).
3. Avoid too much ab work after 20 weeks. The growing uterus puts strain on your abdominal muscles. Once you have a small bump I recommend avoiding sit-ups and similar as this can cause the rectus abdominal muscles to be on stretch and cause them to separate (rectus diastasis) this can be uncomfortable and can be hard to reduce post birth and can also lead to reduced ab strength. Any exercise that requires breath holding/grunting/bearing down should be avoided. Instead do some ab squeezes (hugging baby towards your back) and ab activation exercises. I recommend seeing a Women’s Health Physiotherapist if you are unsure how to do these or what is safe.  Other exercises to avoid are any that are prone to abdominal trauma such as contact sports and horse riding.
4. Be mindful of your pelvic floor. Your pelvic floor is an intricate web of muscles at the bottom of your pelvis. These are connected to the bones and organs of your pelvis with connective tissue and ligaments. These are a little like a trampoline and support the bladder, bowel and growing uterus. With each movement up and down the trampoline moves up and down and can cause stretching of the supports of your pelvis.  Sometimes you can experience a heavy feeling when there is too much pressure on your pelvic floor. Other times you may experience discomfort during exercise if there are forces of gravity exerted on your pelvic floor. If you feel any pressure/heaviness or vaginal bulge then you need to stop doing the exercise and see a pelvic floor physio. Don’t forget to activate your pelvic floor whilst exercising particularly if lifting weights etc. Don’t forget to do your pelvic floor exercises daily too to strengthen these important muscles. If your pelvic floor doesn’t feel right then stop what you are doing and you may also like to see a Women’s health physio for an assessment and advice about your exercise program. Avoid unnecessary strain on your pelvic floor – eg. I wouldn’t be running every day whilst pregnant and wouldn’t be jumping especially after 20 weeks as the heavy uterus will be putting pressure on your pelvic floor by this time as it is. Definitely avoid heavy weights that require breath holding/bearing down.
5. Your heart rate IS allowed to go above 140bpm. There are old studies suggesting pregnant women should not increase their heart rate and are not up to date. If you were previously able to get your heart rate up to 160bpm no worries during a HIIT or jog then this should be ok whilst pregnant providing you don’t have any pregnancy complications and providing you feel ok.  You will find it takes a lot less to get your heart rate to this level though as your heart rate is naturally higher in pregnancy.
6. Stay hydrated. We know that over-heating, especially in the first trimester, is not good for the development of the baby.  Staying hydrated is important to maintain your body temperature and also helps supply baby with the necessary fluids and nutrients it needs.
7. You may need some abdominal support during exercise from the second trimester onwards. Certain belly bands can be useful. Again see a Women’s health physio to learn more about these.
8. Don’t forget to check with your doctor prior to starting a new exercise program and check with your doctor if continuing any form of physical activity during your pregnancy.  
9. Pelvic instability can cause pain in your pubic bone area with exercise. If this occurs see a Women’s health physio and avoid doing exercises on one leg.
10. Be prepared to change your exercise program especially as you progress through the pregnancy. Swimming and non-weight bearing exercises can be helpful later on and walking can be great if this is all you can do. Things like yoga that aren’t pregnancy specific can become very difficult as you approach the 3rd trimester as standing for long periods may make you feel faint and lying on your belly becomes uncomfortable. 

Happy Exercising! Bronwyn Hamilton x

https://www.uptodate.com/contents/exercise-during-pregnancy-and-the-postpartum-period?search=exercise%20pregnancy&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H207614221 

https://ranzcog.edu.au/RANZCOG_SITE/media/RANZCOG-MEDIA/Women%27s%20Health/Statement%20and%20guidelines/Clinical-Obstetrics/Exercise-during-pregnancy-(C-Obs-62).pdf?ext=.pdf