The Light and the Dark Side of Maternal PKU: Single-Centre Experience of Dietary Management and Emergency Treatment Protocol of Unplanned Pregnancies

<b>Background/Objectives</b>. Maternal phenylketonuria syndrome (MPKUS) is the most serious pregnancy complication of women with phenylketonuria (PKU). High phenylalanine (Phe) levels are indeed embryotoxic for the fetus. A low-Phe diet started before conception and maintained throughout pregnancy ensures optimal blood Phe concentrations (120-360 μmol/L) and pregnancy outcome. Women with unplanned pregnancies are at higher risk of MPKUS and require a rapid and sustained reduction of blood Phe. In this retrospective study, we evaluated the effects of dietary intervention on Phe levels and on the clinical parameters of offspring at birth in a group of patients with PKU. We also describe the fetal outcome of unplanned and untreated mothers with PKU. <b>Methods</b>. The cohort consisted of 13 patients for a total of 22 pregnancies: 16 successful pregnancies and 6 abortions. Pregnancies were divided into three groups: "Planned Pregnancies, PP (<i>n</i> = 5)", "Unplanned Pregnancies, UP (<i>n</i> = 6)", and "Unplanned and untreated Pregnancies UT (<i>n</i> = 5)". <b>Results</b>. Women in the UP group showed higher levels of Phe than women in the PP group, especially during the first trimester. The offspring of the UP group showed no congenital malformations but lower median auxologic parameters at birth compared to those from the PP group, although these were not significantly different. The women in the UT group received the diagnosis of PKU after the birth of offspring with MPKUS. <b>Conclusions</b>. A low-Phe diet is critical to prevent MPKUS, especially when started before conception or no later than the 10th week of gestation. Intensive effort is necessary to avoid unplanned pregnancies and to identify undiagnosed women with PKU at risk of MPKUS.