The safest local anesthetic for use during pregnancy is Lidocaine.

- During pregnancy, the choice of local anesthetic must consider both maternal and fetal safety.
- Lidocaine is classified as a Category B drug by the FDA, meaning that animal studies have not demonstrated a risk to the fetus, and there are no adequate and well-controlled studies in pregnant women but it is widely regarded as safe when used appropriately.

- Bupivacaine has a longer duration and higher potential for cardiotoxicity, making it less desirable during pregnancy. It is usually reserved for procedures where prolonged anesthesia is required, but caution is advised.
- Mepivacaine is category C and has less data regarding safety in pregnancy, so it is generally avoided.
- Prilocaine contains methemoglobin-forming potential, which can pose an additional risk especially to the fetus and neonate.

Therefore, because of its established safety profile, Lidocaine is considered the safest and most commonly used local anesthetic during pregnancy.

Reference: Chestnut's Obstetric Anesthesia: Principles and Practice, 6th Edition, Volume 1, Chapter 15, Page 234