This paper uses the confidential files of the Canadian Census 1991–2006 to examine the fertility of married immigrant women (the presence of infants and preschool children in the household) around the time of migration. Then it estimates a proportional hazards model of first‐birth risks of migrants relative to natives from two years before to five years after arrival to Canada. While immigrants have relatively fewer births during the two years preceding migration, these rise after one year in Canada, consistent with both catchup and with concurrent events such as marriage happening during migration. Consistent with the socialization hypothesis, fertility levels vary across origins.