Study	Reason for exclusion
Alhamdan 2007	Participants: couples planning to marry and applying for marriage licence Intervention: premarital screening programme for sickle cell and beta‐thalassemia Comparator: none Outcome: number confirmed sickle cell and beta thalassemia carriers, decision for marriage Design: observational, cross‐sectional study Excluded due to non‐RCT design
Archibald 2017	Participants: woman prior to pregnancy or early in pregnancy (recommended ≤ 12 weeks gestation) Intervention: simultaneous genetic carrier testing for CF, FXS and SMA Comparator: none Outcome: number of carriers for CF, FXS and SMA Design: observational, cross‐sectional Excluded due to non‐RCT study design
Bekker 1993	Participants: adults 18 ‐ 45 years Intervention: genetic carrier testing for cystic fibrosis Comparator: none Outcome: anxiety Design: observational, before and after intervention study Excluded due to non‐RCT study design
Castellani 2011	Participants: infertile couples undergoing cystic fibrosis screening as part of assisted reproduction process Intervention: genetic counselling via computer program Comparator: standard care genetic counselling session Outcome: knowledge Design: RCT Excluded because intervention was method of delivering genetic counselling and not preconception genetic carrier testing or screening compared to standard care
Cheuvront 1998	Participants: relatives of people with CF Intervention: home‐based pretest education from pamphlet with genetic test Comparator: clinic based pretest education via genetic counselling with genetic test Outcome: anxiety, knowledge, satisfaction, reproductive intent Design: RCT Excluded because intervention was method of delivering genetic counselling and not preconception genetic carrier testing or screening compared to standard care
Childs 1976	Participants: carriers of Tay‐Sachs disease identified prospectively or retrospectively during population screening Intervention: genetic carrier population screening Comparator: none Outcomes: knowledge, attitudes, anxiety, concerns, satisfaction Design: observational, cross‐sectional Excluded due to non‐RCT study design
Clayton 1996	Participants: non‐pregnant adults visiting clinical and non‐clinical sites Intervention: genetic carrier testing for CF Comparator: none Outcome: attitudes, beliefs Design: observational, before and after intervention design Excluded due to non‐RCT study design
Fan 2018	Participants: adults > 18 years old with no known carriers status Intervention: educational online module for carrier screening for Tay Sach disease Comparator: in person genetic counselling Outcome: post‐interventional genetics knowledge, perception of genetic risk score and anxiety score Design: RCT Excluded due intervention is not preconception genetic carrier testing or screening and participants are not known carrier status
Fisher 1981	Participants: adults carriers of beta‐thalassaemia 18 ‐ 65 years in a HMO Intervention: genetic counselling through video Comparator: conventional counselling by a trained physician Outcome: knowledge, sexual activity, mood change, behaviour, anxiety Design: RCT Excluded because the intervention is not preconception genetic carrier testing or screening
Hegwer 2006	Participants: adults of Ashkenazi Jewish background in prenatal and preconception settings Intervention: genetic carrier screening and education programme for Tay‐Sachs disease Comparator: none Outcome: knowledge, concern, attitudes, perceptions of genetic risk Design: observational, before and after intervention Excluded due to non‐RCT study design
Henneman 2001	Participants: adults aged 20 ‐ 35 years invited through Municipal Health Service or General Practitioner Intervention: genetic carrier screening for cystic fibrosis Comparator: none Outcome: knowledge, attitudes, understanding, satisfaction, psychological well‐being, uptake, worry, reproductive intentions, sharing of information Design: observational, before and after intervention Excluded due to non‐RCT study design
Honnor 2000	Participants: adults 18 ‐ 50 years in a primary care setting Intervention: genetic carrier testing and counselling for cystic fibrosis Comparator: none Outcome: anxiety, knowledge Design: observational, before and after intervention Excluded due to non‐RCT study design
Moudi 2016	Participants: couples went for pre‐marital counselling center Intervention: motivational interviewing before carrier screening for thalassaemia Comparator: usual care Outcome: screening rate Design: RCT Excluded due intervention is not preconception genetic carrier testing or screening and partcipants are not known carrier status
Payne 1997	Participants: adults 16 ‐ 45 years in a primary care practice in South Wales Intervention: genetic carrier testing for CF Comparator: none Outcome: knowledge, anxiety Design: observational, before and after intervention Excluded due to non‐RCT study design
Punj 2018	Participants: women planning a pregnancy Intervention: genome sequencing of the expanded genetic screening program Comparator: screening for CF Outcome: number of variants reported Design: RCT Excluded due intervention is not preconception genetic carrier testing or screening and participants are not known carrier status
Quigley 2018	Participants: parents of children who were identified as increased risk of CF following newborn screening programme Intervention: information pack on CF Comparator: no information pack on CF Outcome: knowledge and stress score Design: RCT Excluded due intervention is not preconception genetic carrier testing or screening
Rémus 2020	Participants: parents of children who were identified SCD carrier following newborn screening programme Intervention: methods for invitation to come for screening: letter and a follow‐up phone call; letter and 3 follow‐up text messages within 5 days. Comparator: invitation by letter only Outcome: screening rate Design: RCT Excluded due intervention is not preconception genetic carrier testing or screening
Sallevalt 2021	Participants: consanguineous couples Intervention: exome sequencing of preconception carrier testing Comparator: none Outcome: variants from exome‐sequencing and preconception carrier testing gene panel analysis Design: cross‐sectional study Excluded due to non‐RCT study design and intervention is not preconception genetic carrier testing or screening
Tambor 1994	Participants: adults 18 ‐ 44 years in a HMO Intervention: invitation offering CF carrier screening and information giving either by personal education on‐site or by mailed brochure Comparator: none Outcome: attitudes, tolerance, utilization Design: observational, before and after intervention Excluded due to non‐RCT study design
Temme 2015	Participants: parents of infants with positive newborn screening results for CF and one identified CFTR mutation Intervention: genetic counselling plus a 4‐minute video on CF Comparator: genetic counselling only Outcome: knowledge: understanding of carrier status, autosomal recessive inheritance, the newborn screening process, and symptoms of CF Design: RCT Excluded due to intervention being the method of delivering genetic counselling and education and not preconception genetic carrier testing or screening
Watson 1991	Participants: adults 16 ‐ 44 years from primary care practices and family planning clinics Intervention: genetic carrier testing for CF Comparator: none Outcome: anxiety, response to positive results, knowledge, reproductive intentions, behaviour Design: observational, before and after intervention Excluded due to non‐RCT study design
Wilkie 2013	Participants: adults 18 ‐ 35 years with sickle cell disease or sickle cell trait from clinics and community settings Intervention: web‐based multimedia educational intervention Comparator: usual care information e‐book Outcome: knowledge, reproductive intent and behaviour Design: RCT Excluded because the intervention was the delivery of education and not preconception genetic carrier testing or screening

CF: cystic fibrosis
FXS: fragile X syndrome
SCD: sickle cell disease
HMO: health maintenance organisation
RCT: randomised controlled trial
SMZ: spinal muscular atrophy