Yoga in Pregnancy - First Trimester

The First Trimester of Pregnancy is up to week 13. Take it easy and adjust to changing energy levels and hormones.

Cautions:

Listen to your body. Do what feels right for your body and take rests when you need to. Before pregnancy you may have worked hard with exercise and pushed the body to limits but now is a time to use yoga and exercise to keep the body moving but not to push yourself too hard. Pregnancy is not the time to try challenging new poses.
Use relaxed, Ujjayi breath. Do not use breath that creates a pumping action in the stomach such as Kapalabhati.
No jolting movements such as jumping into asanas
Minimise twisting, particularly around the waist or lower spine. Concentrate twisting to the upper back. Generally minimise any strain on twisting and just do gentle movement.
Avoid backbends
You can lie on the stomach until you start to show in pregnancy as the foetus is small and protected.
Balances are ok providing you feel comfortable and you don't feel there is a risk of falling. Note that as you get bigger during pregnancy you balance will feel different so take more care.
It is advisable to discuss doing a yoga practice with your doctor or midwife so that they can assess your individual circumstance, particularly if you did not have a yoga practice before pregnancy.

Good areas of focus:

Pelvic awareness exercises:
Bridge rolls (Setu Bandhasana)
Reclined Bound Angle Pose (Supta Baddha Konasana)
Thunderbolt pose (Swastikasana, Vajrasana)
Hero Pose (Virasana)
Wide-Angle Forward Fold (Upavista Konasana)
Cow Face (Gomukhasana)
Happy Baby Pose (Ananda Balasana)
One-Leg King Pigeon (Eka Pada Raj Kapotasana Prep)
Garland (Malasana)
Shoulder Strengtheners and Openers
Hip Openers
Extended Triangle (Utthita Trikonansana)
Warrior II (Virabhadrasana II)
Extended Side Angle (Utthita Parsvakonasana)
Relaxation
Legs up the wall pose (Viparita Karani)
You can also explore the asanas and props used in the second and third trimester.