1-2 weeks pregnant

I’m confused by the “haven’t had the sex to seal the deal” comment. The urine tests they’re using say “1-2 weeks pregnant” as in they conceived around 1-2 weeks ago. It’s measuring the hCG in the urine. It is not the same as the first two weeks of your pregnancy for dating purposes - this would be 2 weeks from your last LMP. In the case of using LMP, the first 1-2 weeks would be before/at ovulation. But like I said the urine tests aren’t dating that way, they say how many weeks estimated from conception based on hCG levels. 

Blood tests can pick up hCG earlier in a pregnancy than urine tests can. Blood tests can tell if you are pregnant about six to eight days after you ovulate. Meaning if they got a positive urine pregnancy test, they very much should get a positive blood test. 

I get what you mean OP.  *Technically* a woman finds out about her pregnancy around the week of her missed period, so typically 4-5 weeks after her last, or week 4/5 of the pregnancy.  Pregnancy is considered 40 weeks total because it accounts for the first 4 before a missed period.  I get what you mean by "you haven’t had the sex that’s gonna seal the deal" because that *generally* happens around week 2 of the cycle/ovulation time.  

Are these women claiming they're "1-2 weeks" because of the digital tests that say "Pregnant, 1-2/3-4 weeks" ?  I assume those tests' numbers are 1-2 weeks/3-4 weeks after conception, when HCG starts being produced.  

I wouldn't try to explain all the math myself... leave that for the patient's OB.  Simply ask when their last period was, if they've had sex since then, and wait to see if there's a second line on your ER test.  If it's positive, their pregnancy *technically* began on the date of their LMP, regardless of when conception actually took place. 

ETA: this is assuming the woman has typically regular, 28ish day cycles.  It gets a little more interesting when women with reproductive disorders such as PCOS can go 6-12 months without a cycle and it be considered normal for them.