A woman’s BMI before she becomes pregnant is likely more important than her gestational weight gain when it comes to avoiding adverse pregnancy outcomes, a study suggests.

The surprise finding, which is stronger among those with overweight and obesity, came as an unintended result of a large meta-analysis of data for nearly 197,000 women enrolled in 25 pregnancy studies across North America and Europe.

The authors wanted to determine the ranges of gestational weight gains that were safest for women embarking on pregnancy, taking into account their pre-pregnancy BMI.

But they found that gestational weight gain was only weakly linked with the adverse pregnancy outcomes: pre-eclampsia, gestational hypertension, gestational diabetes, caesarian delivery, preterm birth, and small or large size-for-gestational-age at birth.