Pulled muscles in the thighs indicate that the weight the thighs are carrying is too heavy. The weight of the torso plus the weight of the pregnancy all bear down on the thighs and pulled muscles and pain in the thighs definitely indicate that the upper weight is way too heavy.
It is very important to pay special attention to weight gain during pregnancy. The unborn baby is growing too big and this will present difficulty when giving birth. Pre-pregnancy overweight has already been stressing the thigh muscles and the added weight of the pregnancy has definitely surpassed the ability of the thighs to support it. That is why the thighs hurt and the muscles are pulled. Rest the thighs more by sitting more but keep the weight gain under much stricter control.