The Danish National Birth Cohort from 1996 to 2002 asked 900 Danish pregnant women with gestational diabetes about food they ate during the 25th week of pregnancy.  Approximately 9% reported consuming at least one diet beverage a day, and their children were 60% more likely to have an elevated birth weight compared to women who didn’t drink diet beverages during pregnancy.

They also discovered that women who drank at least one artificially sweetened beverage per day were twice as likely to have a child who was overweight or obese at age 7, as compared to women with gestational diabetes who drank water during pregnancy.

Furthermore, women who substituted water for sweetened or diet beverages reduced their child’s obesity risk by age 7 by 17%.

Reference:

https://academic.oup.com/ije/article/doi/10.1093/ije/dyx095/3861466/Maternal-consumption-of-artificially-sweetened