BACKGROUND:
Previous literature has repeatedly shown disparities in perinatal outcomes by mothers’ socioeconomic status. The Finnish Medical Birth Register used to collect information on maternal occupation and recoded it to socioeconomic status. In the 2010s, however, several maternity hospitals stopped providing the information due to data protection concerns. Our aim to explore if routine linkage to the Education Register can be used to routinely monitor socioeconomic disparities in perinatal health in Finland.

METHODS:
The Finnish Medical Birth Register 2002-2023 was linked to the Education Register with mothers’ encrypted personal identity codes (N=1 186 335 deliveries and 1 203 417 newborns). Perinatal health was measured by five indicators: preterm birth (<37 gestational weeks), low birth weight (<2500 grams), being SGA or LGA (small/large-for gestational age), and perinatal death.

RESULTS:
Substantial differences were observed between different educational groups. Largest differences were found for maternal age, IVF, smoking and pregnancy history. Differences in mode of delivery were modest but increased after adjustments. For perinatal health, perinatal death and SGA had the largest disparities when comparing women with basic education to those with university education (excess age- and period-adjusted risk 70–84%). The risks were moderate for preterm birth and low-birth weight (30-51%), and small for LGA (8%). By time, excess risk increased for preterm birth and low birth weight, remained similar for perinatal death and SGA and diminished for LGA.

CONCLUSIONS:
The record linkage was technically straightforward with a very high success rate and should be routinely applied to official perinatal statistics. A major drawback was related to missing registration of primary and lower secondary education. Also, 40% of those not born in Finland had no registered education, since the Finnish Education Register is less complete for education completed abroad.