Yoga does wonders even in pregnancy only when it is done under supervision of instructor and only if recommended by physician or doctor. However, there are some yoga poses which are not recommended by any physician or yoga instructor during pregnancy. Below are the list of such yoga poses posted by many yoga experts:

Overstretch

The body produces a hormone throughout pregnancy called relaxin, which is intended to soften your inflexible parts (like bones and ligaments) to make room for the baby and prepare for birth.

This softening of the ligaments can make them vulnerable to over-stretching. Try to avoid going further into poses than you are accustomed because a pulled ligament is a serious injury that takes a long time to heal. Be especially aware of your knees.

Twists and Backbending

During pregnancy, you can twist gently and moderately. What you should avoid are deep twisting positions, compressing or straining your spine and abdomen. Stay away from all yoga positions that stretch your abdominal muscles excessively, such as Back bends, Camel pose, Cobra, Fish pose, Bow pose, Jumps etc..

Fast Breathing

Any pranayama requiring breath retention or rapid inhales and exhales (such as Kapalabhati) should be avoided. Begin to practice birthing breath instead. This technique has a direct application to the birthing process. Learning to focus on the breath and use it to keep you anchored in the present moment may be the most useful thing you learn from prenatal yoga.

Inversions

During your pregnancy always avoid any type of head, shoulder, or handstand positions that require you to be completely inverted or upside down. Due to added pregnancy weight, you may not have the strength or balance needed to accomplish these positions. In addition, it can place unnecessary strain on your reproductive system.

Abdominal work

Poses that are abdominal strengtheners, such as boat pose, should be avoided. Softening the abs a bit allows them to stretch more readily, which may help you avoid conditions like diastasis recti.

Lying on the Belly

Avoid lying on your belly after the first trimester. Examples of face down, belly positions are Cobra, Crocodile, Locust, Bow pose etc..

Bikram/Hot Yoga

While you are pregnant do not practice hot yoga. This type of practice can make you feel very nauseous if done while you are pregnant. Hot yoga in which the yoga positions are done in a well-heated room, should be avoided during your entire pregnancy as it may raise your blood pressure, cause dehydration and raise your body’s core temperature, all of which may compromise the health of your baby.

Vinyasa Yoga

If you practice a very vigorous form of vinyasa yoga, like Ashtanga or Power Yoga, be flexible and willing to try gentler styles as your pregnancy progresses.

Lying on the Back

As your baby gets heavier, avoid lying on your back during pregnancy for long periods of time to prevent Vena Cava Syndrome. Vena Cava occurs when the baby presses on your vena cava artery while you are lying on your back, reducing blood flow and causing you to feel dizzy. Everyone is different and some women do not experience this problem, however it is wise to only lay on your back for short periods of time during your yoga session and periodically shift to your left side to avoid Vena Cava Syndrome.

Please note that there are many other poses which need to be avoid prenatally. Also, make sure any of the yoga poses being practiced prenatally should be done under strict guidance of physician.