To study the differences in neonatal outcome and treatment measures in Finnish obstetric units.

A registry study with Medical Birth Register data.

All births (n = 2 94 726) in Finland from 2006 to 2010 with a focus on term, singleton non-university deliveries.

All 34 delivery units were grouped into small (below 1000), mid-sized (1000–2999) and large (3000 or more) units, and the adverse outcome rates in neonates were compared using logistic regression.

Early neonatal deaths, stillbirths, Apgar scores, arterial cord pH, Erb's paralysis, respirator treatment, the proportion of post-term deliveries (gestational age beyond 42 weeks) and the proportion of newborns still hospitalised 7 days after delivery.

From an analysis of term, singleton non-university deliveries, the early neonatal mortality was significantly higher in the small relative to the mid-sized delivery units [odds ratio (OR), 2.07; 95% confidence interval (CI), 1.19–3.60]. The rate of Erb's paralysis was lowest in the large units (OR, 0.65; 95% CI, 0.50–0.84). The use of a respirator was more than two-fold more common in large relative to mid-sized units (OR, 2.38; 95% CI, 2.00–2.83). The proportion of post-term deliveries was highest in the large units (OR, 1.36; 95% CI, 1.31–1.42), where a significantly higher percentage of post-term newborns were still hospitalised after 7 days (OR, 1.50; 95% CI, 1.19–1.89).

There are significant differences in several neonatal indicators dependent on the hospital size. An international consensus is needed on which indicators should be used.