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A 20-year study of a million children found that kids conceived by IVF frozen embryo transfer had double the cancer rate. 84% of US IVF transfers now use frozen embryos. Danish researchers followed every child born in Denmark from 1996 to 2012 for up to 20 years. The study was published in JAMA last week. Children conceived without assisted reproduction developed cancer at 18.3 per 100,000 per year. After frozen embryo transfer, the rate was 41.1. After ICSI, where a single sperm is injected directly into the egg, it was 27.9. After frozen transfer, leukemia ran more than twice as high. The only method that showed no increase was a fresh embryo, never frozen, created by placing eggs and sperm together in a dish. That version is now the exception. In 2021, 84% of US IVF transfers used frozen embryos and 78% used ICSI, according to the CDC. Compared with children of women with a history of infertility who conceived without treatment, the frozen embryo risk stayed at more than double. In the authors' words, the results suggest "procedure-related, rather than infertility-related, factors." This is not the first time the pattern has shown up. A 2019 JAMA study of the same Danish children at 11 years found it too. A 2022 study of 2.3 million children in Taiwan found those conceived through assisted reproduction had 58% higher cancer risk, "mainly owing to leukemia and hepatic tumor." The absolute risk is small, and most of these children will never get cancer. The Danish children were conceived with older freezing methods, and the authors warn the results "may differ for contemporary protocols." Nobody yet has long-term data on IVF as it is done today. Children conceived with today's methods won't have 20 years of data until the 2040s, so today's IVF children are, in effect, the trial. Parents deserve to hear these numbers before they sign the consent form, because their child is the one who will carry the risk. doi.org/10.1001/jama.2026.18…