Weeks is a reasonable metric; it's what's used in those laws in Europe, too. Note that there's a ~2 week difference in the week metric between the way we talk

Weeks is a reasonable metric; it's what's used in those laws in Europe, too. Note that there's a ~2 week difference in the week metric between the way we talk about pregnancy (weeks since LMP) and the way these laws are generally written (weeks since conception).