What: Ms. Magazine reminds everyone that pregnancy dating (i.e. weeks pregnant) starts from the day of the last menstrual period, meaning there is a “four week window where a person might not be pregnant yet—but according to how we measure weeks of pregnancy they already are.”
Why it matters: As author Jennifer Weiss-Wolf explains: “From your period through ovulation you are walking around potentially pregnant every single time. And can potentially be held liable for something you did during that time before you even conceived. Whether it was because you had too much wine, or you smoked a cigarette or you rode a rollercoaster.”
Source: Ms. Magazine