Purpose To evaluate the use of opioids in pregnant primiparous women and study the effect of opioid use on maternal and offspring delivery outcomes. Methods The study cohort (N = 6231) consists of all primiparous women with a Finnish background who delivered a singleton between 2009 and 2015 in the city of Vantaa, Finland. Data on births, maternal characteristics, pregnancy outcomes, and purchases of prescription drugs were obtained from National Health Registers. Results Of the primiparous women, 5.1% used opioids during pregnancy. Of these, 95.9% used codeine. No differences were observed in purchases of opioids between the different trimesters but more women purchased opioids as pregnancy progressed (.002). Users of opioids more often also purchased other prescription drugs compared with non‐users of opioids, 89% versus 58% (P < .001); age, smoking, education, and body mass index adjusted odds ratio 5.66 (95% confidence interval 3.96 to 8.09). Caesarean sections were more common in users of opioids than in non‐users, 28.3% versus 21.9% (.007). Before the age of 7 days, the offspring of users of opioids more often needed respirator treatment compared with the offspring of non‐users, 3.1% versus 1.6% (.044). Conclusions One out of 20 pregnant women used opioids. Use of opioids during pregnancy was associated with the risk for deliveries by caesarean sections and need for respiratory treatment among the offspring during the first week of life. Further safety evaluations are needed.