The term alpha thalassemia refers to inherited disorders of hemoglobin caused by reduced or absent synthesis of alpha globin chains. This paper highlights that in the presence of a alfa2-Tal (-α/αα), called the silent, the biochemical diagnosis turns out to be insufficient. In these cases, the molecular study of alpha-globin genes is necessary for identification. In reason of this we present the following case report. A woman of 29 years, pregnant at 12(a) weeks, arrived at our observation to undergo prenatal screening test for Down and Edwards syndromes (bitest). The medical history of the couple revealed that both had doubts haematological indices: Mr. T.G. had a biochemical framework related to alpha1-Tal (MCV 58.8fl, MCH 19.8pg, HbA2: 1.9, HbF:0.4, erythrocytes 6.58x10(6)/ul ed Hb 13g/dl), which was confirmed by molecular analysis (genotype alfa(0-20.5Kb)). Particular difficulties of interpretation presented the C.F. patient who had a biochemical phenotype border line (MCV 79.8fl, MCH 27.2pg, HbA2: 2.9, HbF: 0.6, erythrocytes 5.11x10(6)/ul, Hb 12.8 g/dl). Only molecular analysis has found with certainty that Mrs. C.F. appeared to be phenotypically alpha2-TAL (-α/αα) for the presence of the mutation "alfa2 init.Cd(T>C) NcoI". In the event, as in our case, there is a couple where one spouse is alpha2-TAL (-α/αα) and the other alpha1-TAL (--/αα), must have to inform the couple about the possibility of conceiving a child with hemoglobin H (HbH). Far from the authors refer to the idea of prenatal diagnosis for couples at risk to bear children with HbH, but it is worth highlighting the importance of a careful study of the blood parameters and an extensive and precise information about the clinical implications related to complications of alpha thalassemia.