A practical approach to maternal phenylketonuria management

More women with phenylketonuria are becoming pregnant and need appropriate management to avoid the effects of raised phenylalanine on the fetus: facial dysmorphism, microcephaly, growth retardation, developmental delay and congenital heart disease. Here we describe our experiences from a single centre gained over almost three decades. A series of six cases is presented to illustrate key points in management. Ideally, phenylalanine-restricted diet is started before conception in a planned fashion, but some women present pregnant and blood phenylalanine must be lowered rapidly. The aims of management are to maintain blood phenylalanine concentration in the target range (100-250 micromol/L) before and throughout the pregnancy, and to ensure adequate maternal nutrition and appropriate weight gain. Blood phenylalanine is monitored twice, three times a week, before and after conception respectively. Weight is monitored on a weekly basis and key micronutrients are monitored every 6-8 weeks in clinic. From the second trimester onwards, dietary phenylalanine intake has to be promptly increased, as phenylalanine tolerance increases rapidly. Postnatal management includes a neurological assessment of the infant at 4-8 weeks and an echocardiogram for infants conceived off diet. Subsequently, offspring are seen at 1 year, 4 years, 8 years and 14 years for neuropsychometric evaluations. Regular follow-up of the mother remains important whether on or off a phenylalanine-restricted diet.