Background: Globally, about 6% of children are born with a serious birth defect of genetic or partially genetic origin. Carrier screening or testing is one way to identify couples at increased risk of having a child with an autosomal recessive condition. The most common autosomal recessive conditions are thalassaemia, sickle cell disease, cystic fibrosis and Tay-Sachs disease, with higher carrier rates in high-risk populations of specific ancestral backgrounds. Identifying and counselling couples at genetic risk of the conditions before pregnancy enables them to make fully informed reproductive decisions, with some of these choices not being available if testing is only offered in an antenatal setting. This is an update of a previously published review. Objectives: To assess the effectiveness of systematic preconception genetic risk assessment to enable autonomous reproductive choice and to improve reproductive outcomes in women and their partners who are both identified as carriers of thalassaemia, sickle cell disease, cystic fibrosis and Tay-Sachs disease in healthcare settings when compared to usual care. Search methods: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Registers. Date of latest search of the registers: 04 August 2021. In addition, we searched for all relevant trials from 1970 (or the date at which the database was first available if after 1970) to date using electronic databases (MEDLINE, Embase, CINAHL, PsycINFO), clinical trial databases (National Institutes of Health, Clinical Trials Search portal of the World Health Organization, metaRegister of controlled clinical trials), and hand searching of key journals and conference abstract books from 1998 to date (European Journal of Human Genetics, Genetics in Medicine, Journal of Community Genetics). We also searched the reference lists of relevant articles, reviews and guidelines and also contacted subject experts in the field to request any unpublished or other published trials. Date of latest search of all these sources: 25 June 2021. Selection criteria: Any randomised controlled trials (RCTs) or quasi-RCTs (published or unpublished) comparing reproductive outcomes of systematic preconception genetic risk assessment for thalassaemia, sickle cell disease, cystic fibrosis and Tay-Sachs disease when compared to usual care. Data collection and analysis: We identified 37 papers, describing 22 unique trials which were potentially eligible for inclusion in the review. However, after assessment, we found no RCTs of preconception genetic risk assessment for thalassaemia, sickle cell disease, cystic fibrosis and Tay-Sachs disease. Main results: No RCTs of preconception genetic risk assessment for thalassaemia, sickle cell disease, cystic fibrosis and Tay-Sachs disease are included. A trial identified earlier has published its results and has subsequently been listed as excluded in this review. Authors' conclusions: As there are no RCTs of preconception genetic risk assessment for thalassaemia, sickle cell disease, cystic fibrosis, or Tay-Sachs disease included in either the earlier or current versions of this review, we recommend considering potential non-RCTs studies (for example prospective cohorts or before-and-after studies) for future reviews. While RCTs are desirable to inform evidence-based practice and robust recommendations, the ethical, legal and social implications associated with using this trial design to evaluate the implementation of preconception genetic risk assessment involving carrier testing and reproductive autonomy must also be considered. In addition, rather than focusing on single gene-by-gene carrier testing for specific autosomal-recessive conditions as the intervention being evaluated, preconception expanded genetic screening should also be included in future searches as this has received much attention in recent years as a more pragmatic strategy. The research evidence for current international policy recommendations is limited to non-randomised studies.