Infants born to mothers with GDM are at risk of being both large for gestational age (macrosomic)[70] in unmanaged GDM, and small for gestational age and Intrauterine growth retardation[71] in managed GDM. Macrosomia in turn increases the risk of instrumental deliveries (e.g. forceps, ventouse and caesarean section) or problems during vaginal delivery (such as shoulder dystocia). Macrosomia may affect 12% of normal women compared to 20% of women with GDM.[21] However, the evidence for each of these complications is not equally strong; in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study for example, there was an increased risk for babies to be large but not small for gestational age in women with uncontrolled GDM.[70] Research into complications for GDM is difficult because of the many confounding factors (such as obesity).