Lidocaine is the preferred local anesthetic for pregnant women because it has a well-established safety profile and is classified as FDA pregnancy category B. It has minimal placental transfer and low fetal toxicity, making it safer for both mother and fetus during surgical procedures. Additionally, lidocaine provides effective anesthesia with a rapid onset and intermediate duration, which is suitable for most obstetric and minor surgical interventions. Other local anesthetics like bupivacaine carry higher risks of cardiotoxicity and fetal complications. Therefore, lidocaine is the anesthetic of choice due to its proven maternal and fetal safety.

Reference: Miller's Anesthesia, Miller RD, 9th Edition.