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data’s thin, but the few pre-1950 neonatal bleed series (pre-universal house-call circ) show hdnb rates <2 in 100k. once routine circumcision hit U.S.-obstetrics in the 50s-60s and early vitamin K uptake lagged, bleeding reports in the first 7–10 days jumped to ~4–7 in 100k males—the classic “post-circ scalp/penile hematoma” cases. so the iatrogenic cut gave vit k’s risk-benefit math a big, bloody boost.