Ob-Gyn questions? Ask a gynecologist online.
Hello this is Dr. Salama MD,
If the sperm can make it past the uterus into the fallopian tubes using fertile cervical fluid channels, they can live there, waiting for the release of an egg, for up to five days.
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It's possible but not likely that it was the guy on day 10.
More likely to be the guy on day 16.