We aimed to evaluate the adverse birth outcomes of anticancer drug prescription during pregnancy using a Japanese claims database from 2005 to 2019. We applied validated claims-based algorithms to identify pregnant women with birth outcomes, and evaluated drug prescription during pregnancy. The causal relationship between anticancer drugs and adverse birth outcomes was evaluated using the Council for International Organizations of Medical Sciences Working Group VI criteria. Thirteen women with anticancer drugs prescription during pregnancy were identified (mean age: 34.6 years). Atrial/ventricular septal defect was observed in one infant after exposure to cyclophosphamide and doxorubicin for breast cancer in the second and third trimesters. One woman on several anticancer drugs (cyclophosphamide, cytarabine, daunorubicin, l-asparaginase, methotrexate, nelarabine, and vincristine) for acute lymphoblastic leukemia, one on imatinib for chronic myeloid leukemia, and one on cisplatin and fluorouracil for cervical cancer had miscarriages after exposure in the first trimester. A relationship between those anticancer drugs and miscarriage could not be ruled out, while no relationship was identified regarding the atrial/ventricular septal defect considering the period of exposure and organogenesis. Our results suggest increased risk of miscarriage with the use of several anticancer drugs such as methotrexate, imatinib, cisplatin, and fluorouracil in the first trimester.