Judy takes a pregnancy test after realizing her period is one day late. When the test comes back positive, she immediately calls her OBGYN to set up an appointment. On the phone, she tells them the date of her last menstrual period and is confused when the doctor refers to her as already being 4 weeks pregnant. If you were the doctor, how would you explain this to Judy? So let's run through these choices and see which one is the best explanation for that.
Choice A reads, conception typically takes place within 1 to 2 days of the menstrual period ending, so using the date of the last period is a pretty accurate marker. And that's definitely incorrect. Right? We know that for conception to take place, ovulation has to occur and ovulation will take place about 2 weeks after the period, not 1 to 2 days after it ends for most women. So, A is definitely not a very good explanation.
Choice B reads that important prenatal events like placenta development actually take place in the time between the menstrual period and conception, and that's also incorrect. We know that there is actually no development taking place during that time at all. We need conception for any development to actually begin. So B is not a good explanation either.
Choice C reads, we often measure pregnancy starting with the date of a woman's last period rather than the date of conception because reporting tends to be more accurate, which means that for 2 of those 4 weeks you weren't even pregnant yet. And that is a fantastic explanation. So we really do, we use that date of the last period because women are just much better at reporting it. Women typically don't know the day of ovulation, they usually know the day of their first, of their period beginning. So C is definitely a great answer.
Then Choice D reads it's impossible to accurately predict the day of conception so it's best to ballpark it and that's not true either. We have a pretty good way to estimate that date using the day of the last menstrual period. Alright, so our answer here is going to be C.
