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Evidence library
Every clinical claim in our articles links back to a source on this page. We log the guideline body or paper, the jurisdiction it applies to, and any population caveats that shape how generalisable the evidence is.
Why we surface this: most fertility evidence is built on white European cohorts. UK NICE, India ICMR, US ACOG, Australia RANZCOG and Canada SOGC all give different answers to the same questions, sometimes for good reason and sometimes because different populations were studied. We want you to see the evidence base, not just the conclusion.
What is live right now
68
Articles
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13
Evidence-cited
Linked to reference bank
38
References
Browse at /evidence
6
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UK, IN, US, AU, CA, EU
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Day-one, not afterthought
38 of 38 references
NICE Clinical Guideline CG156: Fertility problems: assessment and treatment.
Core UK NHS framework for fertility assessment and treatment access. Sets thresholds for when to investigate, when to refer, and the funded IVF pathway.
NICE Public Health Guideline PH56: Vitamin D: supplement use in specific population groups.
UK supplementation guidance recommends 10 micrograms (400 IU) daily for adults in autumn/winter, with at-risk groups including those with darker skin advised to supplement year-round.
Population caveat
Standard recommendation (400 IU adults) is bone-health focused, derived largely from lighter-skinned populations. South Asian, African, and Caribbean populations in northern UK frequently remain deficient at this dose due to lower dermal synthesis.
Government of India. The Assisted Reproductive Technology (Regulation) Act 2021.
Indian regulatory framework for ART clinics and donor-gamete use. Sets clinic registration requirements, age limits (women up to 50, men up to 55), donor anonymity rules, and prohibits commercial surrogacy.
ICMR National PCOS Task Force Recommendations.
India-specific PMOS (formerly PCOS) guidance acknowledging higher prevalence and earlier metabolic complications in Indian women compared with white European cohorts.
ASRM Practice Committee. Evaluation and treatment of recurrent pregnancy loss: a committee opinion. Fertil Steril 2020;113(3):533-535.
ACOG Committee Opinion: Vitamin D screening and supplementation during pregnancy.
ASRM Practice Committee. Definitions of infertility and recurrent pregnancy loss.
RANZCOG Statement: Fertility: what is normal and when to investigate.
SOGC Clinical Practice Guideline: Recurrent implantation failure, guidance from the Society of Obstetricians and Gynaecologists of Canada.
ESHRE Working Group on Recurrent Implantation Failure. ESHRE good practice recommendations on recurrent implantation failure. Hum Reprod Open 2023.
ESHRE working group definition and management framework for recurrent implantation failure following IVF/ICSI.
Teede HJ et al. International evidence-based guideline for the assessment and management of polycystic ovary syndrome 2023.
Most current international PCOS guideline. Recognises ethnic-specific risk profiles and recommends adjusted thresholds for South Asian populations.
Population caveat
International guideline acknowledges that South Asian women have higher PMOS prevalence with more severe metabolic features at lower BMI thresholds. Recommends ethnic-specific BMI cut-offs for assessment in South Asian populations.
Darling AL et al. Vitamin D status in UK South Asian populations. Br J Nutr 2013.
Demonstrated that 25(OH)D deficiency is highly prevalent in UK South Asian women even with conventional supplementation; suggests higher dose may be required to achieve replete status.
Chu J et al. Vitamin D and assisted reproductive treatment outcome: a systematic review and meta-analysis. Hum Reprod 2018;33(1):65-80.
Meta-analysis suggesting higher live birth rates in IVF cycles where women had replete vitamin D status compared with deficient status. Causation not established.
Population caveat
Heterogeneous trial populations; subgroup analysis by ethnicity is limited. Findings are observational; randomised evidence remains scarce.
Roque M et al. Fresh versus elective frozen embryo transfer in IVF cycles: a systematic review and meta-analysis. Hum Reprod Update 2019;25(1):2-14.
Comprehensive comparison of fresh vs elective frozen embryo transfer outcomes. Frozen transfer associated with higher live birth in some patient subgroups but not all.
Geng T et al. Routine use of ICSI for non-male factor infertility: a systematic review and meta-analysis. Reprod Biol Endocrinol 2021.
Reviews evidence that ICSI is no better than conventional IVF for non-male-factor infertility despite widespread use. Adds a small additional procedure cost and risk.
Levine H et al. Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries. Hum Reprod Update 2022;29(2):157-176.
Documents global declining trend in sperm count over decades, accelerating in recent years. Drivers debated.
Persad E et al. Surgical or radiological treatment for varicoceles in subfertile men. Cochrane Database Syst Rev 2024.
Cochrane review of varicocele treatment. Modest improvement in pregnancy rates after repair in selected populations; benefit population-dependent.
Plowden TC et al. Subclinical hypothyroidism and thyroid autoimmunity are not associated with fecundity, pregnancy loss, or live birth. J Clin Endocrinol Metab 2016;101(6):2358-2365.
Large prospective study challenging the 'lower TSH for fertility' practice. Subclinical hypothyroidism (TSH 2.5-10) was NOT associated with reduced fecundity or higher pregnancy loss in this cohort.
Boivin J et al. Tackling burden in ART: an integrated approach for medical staff. Hum Reprod 2012;27(4):941-50.
Framework for understanding emotional burden of ART, including the two-week wait period. Foundational paper for psychosocial support in fertility care.
Cimadomo D et al. Recurrent implantation failure: a comprehensive summary from current evidence to future directions. Hum Reprod Update 2023.
Critical synthesis of recurrent implantation failure literature; cautions against unproven add-on treatments commonly offered in private clinics.
Cobo A et al. Elective and onco-fertility preservation: factors related to IVF outcomes. Hum Reprod 2018;33(12):2222-2231.
Large series quantifying live birth rates per oocyte frozen by age at freezing. Foundational data for counselling on elective egg freezing.
Human Fertilisation and Embryology Authority (HFEA): Fertility treatment 2024, preliminary trends and figures.
UK national IVF outcome data. Stratified by age, treatment type, ethnicity (where data complete), and clinic.
Tjon-Kon-Fat RI et al. IVF or IUI as first-line treatment in unexplained subfertility: the conundrum of treatment selection criteria. Hum Reprod 2017;32(5):1028-1032.
Critical examination of when IUI vs IVF is the right first-line approach for unexplained subfertility. Concludes selection criteria are weaker than commonly claimed.
Esteves SC et al. Diagnosis and management of azoospermia: a systematic review. Asian J Androl 2020;22(3):220-225.
Workup framework for azoospermia (no sperm in ejaculate) including obstructive vs non-obstructive distinction, hormonal testing, and surgical sperm retrieval (TESE/micro-TESE) success rates.
Balen AH et al. The management of anovulatory infertility in women with polycystic ovary syndrome: an analysis of the evidence to support the development of global WHO guidance. Hum Reprod Update 2016;22(6):687-708.
Foundational review of letrozole vs clomiphene vs metformin vs gonadotrophins in PMOS-related anovulation. Letrozole has displaced clomiphene as first line in most international guidelines.
Population caveat
Most underlying trials enrolled predominantly white European cohorts. Letrozole and metformin response in South Asian PMOS may differ.
Legro RS et al. Letrozole versus clomiphene for infertility in the polycystic ovary syndrome. N Engl J Med 2014;371(2):119-129.
Landmark RCT. Letrozole produced higher live birth rates than clomiphene in women with PMOS-related anovulation. Changed first-line ovulation induction practice globally.
Dhillon-Smith RK et al. Subclinical hypothyroidism and hypothyroxinaemia in women of South Asian, Black African-Caribbean and mixed ethnicity in the UK. Clin Endocrinol (Oxf). 2021;94(6):1015-1026.
UK-based cohort study of 899 South Asian, Black, and mixed-ethnicity women. Found substantially higher rates of subclinical hypothyroidism in Bangladeshi (47%) and Pakistani (32%) women than in white British comparators. Supports ethnicity-aware thyroid screening before fertility treatment.
Population caveat
Study population was UK South Asian, Black African-Caribbean, and mixed ethnicity women. 47% of Bangladeshi and 32% of Pakistani women had subclinical hypothyroidism, substantially higher than white British comparators.
Lim AJ et al. Sleep duration, sleep quality and menstrual cycle characteristics among young women. PLOS ONE. 2016.
Women sleeping fewer than 6 hours per night had significantly higher odds of abnormal cycle length (OR 2.1, 95% CI 1.2-3.7) compared to those sleeping 7-9 hours.
Verma A et al. Effects of Yoga on Reproductive Outcomes in Women With Polycystic Ovary Syndrome: A Meta-Analysis. American Journal of Lifestyle Medicine. 2021.
Meta-analysis of 11 RCTs (515 participants). Yoga significantly improved menstrual irregularity (MD -0.41) and reduced serum testosterone vs control.
HFEA. Ethnic diversity in fertility treatment 2023. Human Fertilisation and Embryology Authority.
UK Bangladeshi women have IVF live-birth odds ratio 0.53 vs White British. Pakistani women 0.68. Significant ethnic disparities persist after adjustment.
NICE. Fertility problems: assessment and treatment (NG257). National Institute for Health and Care Excellence. 2024.
Current NICE guideline for fertility assessment and treatment in the UK. Supersedes CG156 (2013). NG257 is the correct citation for post-2024 references.
Mani H et al. Diabetes and cardiovascular events in women with polycystic ovary syndrome: a 20-year retrospective cohort study. Clinical Endocrinology. 2015.
PMOS prevalence in South Asian populations 14-20% vs global pooled 8-13%. South Asian women with PMOS have elevated cardiovascular risk profiles.
Gromski PS et al. Anti-Mullerian hormone levels in South Asian and white European women: a population study. Reproductive BioMedicine Online. 2022.
AMH levels in South Asian women approximately 20% lower than age-matched European controls. Relevant to fertility assessment and IVF stimulation protocols.
Endometriosis UK. Endometriosis in the UK: time for change. 2023 Diagnosis Survey.
Average UK endometriosis diagnostic delay is 8 years and 10 months from first symptom presentation.
Samaritans. Suicide Statistics Report 2023. Samaritans, London.
Men account for approximately 75% of all suicide deaths registered in the UK. Men aged 45-49 have the highest suicide rate.
NHS England. Psychological Therapies Annual Report on the Use of IAPT Services 2022-23. NHS England.
Ethnic minority groups access NHS Talking Therapies (IAPT) at rates significantly below white British populations.
Mind. Mental Health Statistics: Ethnic Minority Groups. Mind, London. 2024.
Ethnic minority communities in the UK face compounded barriers to mental health support including cultural stigma, lower referral rates, and lack of culturally competent services.
National Institute for Health and Care Excellence. Depression in adults: recognition and management. Clinical guideline CG90. NICE, London. 2009 (updated 2022).
NICE recommends psychological therapies (CBT, counselling) as first-line treatment for mild to moderate depression. No formal diagnosis required to self-refer to NHS Talking Therapies.