In this paper, we present the very rare case of a 21 weeks pregnant woman, examined clinically and by ultrasound. We could observe the present of two heads and a common trunk and therefore we proceeded to the small caesarian of necessity. We examined the fetus from the clinical and pathological point of view and we could observe a rare case of pregnancy with a bicephalous malformed fetus. During the autopsy, we could reveal the common elements and the devised ones, which are described as it follows. The case is a very rare one and that probably explains the fact that until the 21 weeks examination, even if she was clinically and ultrasound examined there was the appreciation that it was a twin pregnancy with a normal evolution. In this case, it is necessary to underline that the difficulties concerning the diagnosis and the medical behavior are also because the patient was a primipara 34-year-old woman without any pathological or specific family history. This case analysis shows the necessity of a preconception genetic advice together with the extension of the analysis of the genetic risk in all mothers under 35-year-old, mandatory and supported by the medical system. At the same time, an ultrasound examination of great performance proves to be necessary in order not to prolong the development of a pathological pregnancy.