- Design
- Nationwide registry cohort, Denmark
- Population
- 1,086,136 live-born children, 37,228 conceived with assisted reproduction
- Primary outcome
- Incident childhood cancer
- Effect
- ART overall HR 1.26 (1.07–1.48); frozen embryo transfer HR 2.18 (1.45–3.29); ICSI HR 1.48; IVF HR 1.01
This Danish national cohort followed 1,086,136 live-born children for a median 20 years, 3.4% of them conceived with assisted reproduction. There were 3,736 cancers.
Against naturally conceived children (18.3 cancers per 100,000 person-years), assisted reproduction overall was associated with a higher rate (23.6; HR 1.26, 95% CI 1.07 to 1.48). The excess sat with frozen embryo transfer (41.1; HR 2.18) and intracytoplasmic sperm injection (27.9; HR 1.48). Conventional IVF showed no difference (HR 1.01). Results held when compared with children of women with infertility, which points towards the procedures rather than infertility itself.
This is observational, and the type-specific estimates rest on small numbers with wide intervals. Absolute risks remain low: even the highest rate is about 4 cancers per 10,000 child-years. It is a reason for honest counselling and further study, not for changing fertility practice on one cohort.
- Absolute risk stays low: about 2 to 4 cancers per 10,000 child-years after assisted reproduction.
- The association was with frozen embryo transfer and ICSI, not with conventional IVF.
- Be ready to discuss this with couples choosing between fertility techniques.
- No change to childhood surveillance is suggested by this finding.
Why it matters
Frozen embryo transfer is increasingly the default, and this raises a question about it worth answering.
Don't overread it
This is an association in one national cohort; it does not show that frozen embryo transfer causes cancer.
The statistics, in plain English
A hazard ratio of 2.18 doubles a small baseline rate, from about 18 to 41 per 100,000 person-years. Subtype results, such as the HR of 7.63 for sarcoma, come from very few cases, which is why their intervals are so wide.
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