In cases of rare monoamniotic-monochronic geminie pregnancies there is a high risk of complications by real umbilical cord knots, including the cords of both gemini. In these cases fetal mortality is very high. Modern examination techniques (Colour doppler sonography) are able to detect such cord knots in monoamniotic twins. Therefore it is necessary in all twin pregnancies, especially following fertility treatment, to examine precisely by a routine examinator the question of mono - or diamniotic pregnancy. In monoamniotic pregnancy there should be a look for real knots of umbilical cord in regular intervals. In such a case, if a knot is present, the pregnant woman had to be supervised by CTG, to react immediately at first signs of hypoxia.