Note: “6 weeks” counts from last-period-date, so it means as little as two weeks since conception, which is before many women realize they are pregnant
Note: “6 weeks” counts from last-period-date, so it means as little as two weeks since conception, which is before many women realize they are pregnant
Oh that’s interesting. This was years ago but I thought the doctor I used guessed the age based on size/features seen in the scan.
Fetal development is not really that consistent, to guess it down to a week or two based on physical appearance. Anything from 37 to 42 weeks is considered a “normal” pregnancy length. That means someone oversimplifying things could say any milestone might be +/- a couple of weeks. Edge cases might move the length of an otherwise-healthy pregnancy down or up an entire month.
Even implantation isn’t that consistent. I’ve heard that sperm can linger for something like 5 days before implantation occurs. The whole middle-school health class version where the sperm swim up and race to the egg is kind of total nonsense.
Sperm can linger for 5d to fertilize. Implantation of the embryo is a separate process.