So sorry for your loss I thought they were just LH surge (the test line has to be as dark as or darker than the control line for it to be a positive result). I stopped with them bc they were making me crazy! If your cycle is normally regular I'd say just go a couple with sex every 2/3 days and try not to worry x
OPK tests can detect HCG as it is very similar to LH and it can't differentiate between the two. The general idea is that if a woman gets a very strong positive OPK around the time her period is due then it's very possible she's pregnant.
That's how I found out I was pregnant with my son. I couldn't work out why I was ovulating when AF was due, I came into MN for advice and was told about OPKs detecting HCG so I ran out to buy a HPT and it was positive.