Numbness in the lateral thigh during pregnancy is usually caused by compression of the lateral femoral nerve.
The lateral femoral cutaneous nerve runs through the lateral border of the psoas major muscle to the groin, crossing the inguinal fascia. During pregnancy, the physiological structures such as the pelvis change in angle and tend to compress the lateral femoral cutaneous nerve, resulting in lateral thigh numbness, which often disappears with the end of pregnancy.
There is another reason for lateral thigh numbness during pregnancy, because the pregnant woman had a herniated lumbar disc in the past, with the growth of the fetus, resulting in increased pressure on the intervertebral disc of the pregnant woman, further compressing the nerve, resulting in numbness in the thigh, after the end of pregnancy, the symptoms can be relieved, or may persist, but the degree will be reduced.