Maturity-Onset Diabetes of the young’ (MODY) or monogenic diabetes accounts for approximately 1–2% of diabetes and is frequently misdiagnosed as type 1 or type 2 diabetes. Here we report a case of a 19-year-old pregnant woman with a MODY3 diabetes expecting a child to a father with MODY 2 diabetes and discuss the implications of the parent’s mutations on the course of the pregnancy in detail. The pregnancy was complicated by drastically falling insulin requirements in the mother in the 3rd trimester as well as preterm labour and delivery at 33+4 weeks gestation.