Pregnancy is only really considered to begin once the embryo successfully implants.
Tips
mistakes
着 here is read zhuó (second tone) 'to attach', not zháo or zhe. Same zhuó as 着陆 (zhuólù) 'to land' and 着重 (zhuózhòng) 'to emphasize'. Don't read it as zhāochuáng or zháochuáng.
usage
Primarily a medical/biology term - embryo attaching to the uterine wall (also used for oyster larvae attaching to a substrate). Modern figurative use 'take root' is recent and journalistic, e.g. 理念在企业文化中着床 'the idea takes root in corporate culture'.
