Background: The short- and long-term consequences of restricted fetal growth cause considerable concern, and how prenatal exposure to different antiseizure medications (ASMs) affects fetal growth remains uncertain., Methods: This was a population-based cohort study of liveborn singleton children born in Denmark, Finland, Iceland, Norway, and Sweden from 1996 to 2017. Prenatal exposure was defined as maternal filling of prescriptions for ASM during pregnancy registered in national prescription registries and primary outcomes were adjusted odds ratios (aORs) of microcephaly or being born small for gestational age., Findings: We identified 4,494,918 children (males: 51.3%, 2,306,991/4,494,918), including 38,714 (0.9%) children of mothers with epilepsy. In the overall population, prenatal monotherapy exposure with carbamazepine (aOR: 1.25 (95% CI: 1.12-1.40)), pregabalin (aOR: 1.16 (95% CI: 1.02-1.31)), oxcarbazepine (aOR: 1.48 (95% CI: 1.28-1.71)), clonazepam (aOR: 1.27 (95% CI: 1.10-1.48)), and topiramate (aOR: 1.48 (95% CI: 1.18-1.85)) was associated with risk of being born small for gestational age, and carbamazepine was associated with microcephaly (aOR: 1.43 (95% CI: 1.17-1.75)). In children of mothers with epilepsy, prenatal exposure to carbamazepine (aOR: 1.27 (95% CI: 1.11-1.47)), oxcarbazepine (aOR: 1.42 (95% CI: 1.18-1.70)), clonazepam (aOR: 1.40 (95% CI: 1.03-1.89)), and topiramate (aOR: 1.86 (95% CI: 1.36-2.54)) was associated with being born small for gestational age; carbamazepine, with microcephaly (aOR: 1.51 (95% CI: 1.17-1.95)). No associations with small for gestational age and microcephaly were identified after prenatal exposure to lamotrigine, valproate, gabapentin, levetiracetam, phenobarbital, acetazolamide, phenytoin, clobazam, primidone, zonisamide, vigabatrin, ethosuximide and lacosamide, but except for lamotrigine, valproate, gabapentin, and levetiracetam, numbers of exposed children were small., Interpretation: Prenatal exposure to carbamazepine, oxcarbazepine, clonazepam, and topiramate was associated with increased risk of being born small for gestational age in both the overall population and in children of women with epilepsy suggesting that prenatal exposure to these drugs is associated with fetal growth restriction., Funding: The NordForsk Nordic Program on Health and Welfare (83539), the Independent Research Fund Denmark (1133-00026B), the Danish Epilepsy Association, the Central Denmark Region, the Novo Nordisk Foundation (NNF16OC0019126 and NNF22OC0075033), and the Lundbeck Foundation (R400-2022-1205)., Competing Interests: Jakob Christensen reports funding from the Danish Epilepsy Association, the Central Denmark Region, the Lundbeck Foundation (R400-2022-1205), and the Novo Nordisk Foundation (NNF16OC0019126 and NNF22OC0075033); Speaker honoraria from Eisai AB and UCB Nordic; Scientific advisory board honoraria from Eisai AB and UCB Nordic. Marte-Helene Bjørk reports funding from the NordForsk Nordic Program on Health and Welfare (project no. 83796) and the Norwegian Research Counsil; consulting fees from Novartis Norway, Eisai (advisory board), Jazz Pharmaceuticals, Lundbeck and Angelini Pharma; Speaker honoraria from Eisai, AbbVie, Teva and Lilly. Silje Alvestad reports funding from the NordForsk Nordic Program on Health and Welfare (project no. 83796) and speaker honoraria from Eisai AB. Mika Gissler reports funding from the Research Council of Norway (International Pregnancy Drug Safety Studies project no. 273366), and the European Union: the Innovative Medicines Initiative (project no: 821520). Jannicke Igland reports support from Sanofi and Novartis to conduct post-marketing drug safety research not related to the submitted work. Maarit K. Leinonen reports funding from the Innovative Medicines Initiative (project no: 821520), the Finnish Medicines Agency (Fimea) and the Research Council of Norway (International Pregnancy Drug Safety Studies project no. 273366). Nils Erik Gilhus reports honoraria from UCB, Janssen, Argenx, Merck, Alexion, Immunovant, Denka, Roche, Dianthus, and participation on an advisory board from UCB, Janssen, Argenx, Merck, Alexion, Immunovant, and Dianthus; all unrelated to the present study. Yuelian Sun reports funding from the Independent Research Fund Denmark (9039-00296B). Helga Zoega was supported by a UNSW Scientia Program Award (no number attached). Torbjörn Tomson reports funding from Accord, Glenmark, GSK, UCB, Eisai, Ecu Pharma, Bial, Teva, Sanofi, SF Group, GW Pharma, Zentiva, and Angelini as donations to the EURAP pregnancy registry; Speaker honoraria from Eisai, Angelini, GSK and UCB. Julie Werenberg Dreier reports funding from the NordForsk Nordic Program on Health and Welfare (project no. 83796) and the Independent Research Fund Denmark (1133-00026B and 316-00134A)., (© 2024 The Author(s).)