The effects of screening for gestational diabetes

I estimate the effects of screening “low-risk” women for gestational diabetes using a regression discontinuity design and exploiting exogenous variation in testing at the overweight threshold of the body mass index in Finland. I find that screening low-risk mothers just above the overweight threshold increases the number of mothers diagnosed with gestational diabetes. There is a 1.5 percentage point, or 27%, increase in the probability of being diagnosed with gestational diabetes at the threshold, which translates into a 10.7 percentage point local average treatment effect given the 14.0 percentage point jump in the screening rates. The estimates on the effect on insulin treatment are, however, small and imprecise, suggesting that screening low-risk mothers did not result in diagnoses needing insulin treatment. The cost estimates in the existing literature suggest that the policy is cost-effective. The results also suggest that universal screening could decrease health disparities between mothers with low and high levels of education, given that gestational diabetes is treated if diagnosed. The effect on the probability of having an abnormal test result is over twice as great for the less educated mothers compared to the more educated mothers. Large effects of around 10–20% on adverse birth outcomes (low birth weight, macrosomia, metabolic testing, and C-section) can be ruled out.