When does implantation actually occur in IVF or normal cycles? (We're not focusing on the "window" anymore, but on when real implantation does occur)
A very good study of implantation was published in 1992 by Bergh & Navot.
They studied 33 pregnancies from ovum donation or frozen-thawed cycles with serial HCG levels on the mothers to find the time of "first embryonic signal". The HCG assay used can detect very low levels.
Average first detection was at an embryonic age of 7.1 +/- 0.28 days (range 6.6-7.4 days).
This correlates with the studies of Hertig and Rock in the 1950's (hysterectomy studies) that showed the day of implantation to be day 6.
They did not find any evidence to support the concept of an embryonic diapause in humans.
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