Recent studies have suggested that there is no increase in congenital anomalies at birth in the offspring of women undergoing anesthesia during the first trimester of pregnancy, but anesthesia exposure does increase the risk of spontaneous abortion and a lower birth weight in infants. Thus, the choice of sedatives, analgesics and local anesthesia is challenging in terms of the placental transportability of drugs and the risk of spontaneous abortion. We report the case of a 43-year-old patient in her 13th week of pregnancy who underwent a partial glossectomy. A preoperative pathological examination diagnosed the tumor as an oral intraepithelial neoplasia/carcinoma in situ (OIN/CIS) of the tongue. To reduce fetal drug exposure, a partial glossectomy of the left side of the tongue to be performed under intravenous sedation and with a lingual nerve block was scheduled. Oxygen (2 l/min) was delivered through a nasal cannula. The continuous intravenous infusion of 0.3 μg/kg/h of dexmedetomidine (DEX) was initiated, and 0.5 mg of midazolam was administered ; a bilateral lingual nerve block was then performed. After the additional administration of 1.0 mg midazolam, infiltration anesthesia in the area of the tumor was administered. During the operation, the DEX infusion rate was increased to 0.5 μg/kg/h. Throughout the operation, adequate sedation and amnesia were achieved, and sufficient relief of the pain associated with surgical invasion was obtained using the lingual nerve block without any supplemental infiltration or the administration of opiates. If oral malignancy ablative surgery during the first trimester of pregnancy cannot be deferred, anesthesia management using a nerve block together with intravenous sedation can contribute to a reduction in the detrimental effects of anesthesia during early pregnancy.