The authors report three cases of percutaneous fetal blood sampling at 38 weeks of pregnancies complicated by immunologic thrombocytopenia. In each case, the purity was perfect which is essential for using the examination with a view to the obstetrical management. The birth is programmed 24 or 48 hours later. In two cases, the neonatal control is in agree with the fetal blood sampling. In the third observation, the fetal platelet count in 142,000/mm3 and the newborn control 55,000/mm3: the only explanation is a very active process as usually state with newborns. There was no accident, and these samplings led to natural births. This approach seems to be the more effective for the evaluation of fetal platelet count and allow the choice of birth management. A cesarean section is decided in case of fetal thrombopenia lower than 50,000/mm3.