This is a great pose for opening up the hips and releasing physical and emotional tension that is stored in the hips. It also releases tension in the lower back and is great for sciatica. To be practiced after you have warmed up the body.

From an all fours position, with hands under your shoulders and knees under your hips, bring your right foot behind your left hand where it feels comfortable and straighten left leg behind you, keeping the hips level as you sink downwards. Keeping the arms straight and opening the chest. Stay here if you are in your second or third trimester or until you feel comfortable to take it further. 
Gently lean forwards onto the forearms and make a cushion with your hands resting your forehead on your hands.
If you are in your second trimester and want to take it further you could use a bolster in front of you to rest your head on.

Practice modified versions using props like a  folded blanket under the hips- in second and third trimesters
Always listen to your changing body!
Be cautious not to over do it!