Background:
Many factors influence choice of genetic investigations during preconceptional period : epidemiological data, economic considerations and ethical values interfere to propose appropriate guidelines.

Objectives:
As the weight of ethical arguments can be in opposition to evidence based proposals, we establish guidelines taking into account these three components of decision making.

Methods:
We answer 3 questions: 1. Why to propose screening during the preconception period whereas we cannot act before pregnancy 2. On which basis to choose those diseases to screen ? 3. Which ethical values do interfere with the proposed guidelines?

Results:
(i). The proposal to screen before conception is justified by the whish to offer the parents time to avoid precipitate decision during pregnancy. It appears unethical not to inform the patient that such exams can be performed. (ii). The choice of the diseases to screen is motivated by the prevalence of the abnormal gene, the difficulty to select an at-risk population, the severity of the condition and the legitimacy of abortion in this situation. (iii). The 1st ethical value to be taken into account is the patient's autonomy. The 2nd ethical issue concerns the practitioner's ability to integrate the concept of democratic eugenics in his practice. The 3rd ethical issue concerns his ability to integrate the stochastic dimension of clinical manifestations of inherited diseases. The 4th one is economic because these genetic exams are expensive: a rigorous cost-benefit study can avoid difficulties in a public health point of view. The 5th issue concerns perception and communication of risks linked to the screened pathology. Finally, we propose guidelines regarding the principles of bioethics: autonomy, beneficence, non-maleficience and justice.

Conclusion and implications for practice:
We propose to screen systematically Cystic fibrosis, Fragile X syndrome, Sickle cell anaemia and Thalassemia. 1, guidelines are based on evidence including epidemiological data; 2, we adapt these guidelines to a personal perception of the risks, including the expected quality of life for the child; and 3. we adopt an empathic attitude to each particular case, including the right for the patient to accept or to refuse the proposed guidelines, after exhaustive and pertinent information, including alternative options.