You’ve all heard by now that Ohio passed the “detectable heartbeat” anti-choice bill . Women are not to control their own bodies or make their own choices, ever. Not even when they’re the victims of crimes arguably worse than murder. You get to live with the aftermath of torture using sex.
There’s another class of people who don’t get to control their own bodies. Slaves. It’s the definition of slavery. You don’t own yourself.
But, yes, we know all that. What I actually wanted to write about was the biological angle here.
Do you know one of the weird things about live heart cells in a petri dish? They beat.
(Which, speaking as one of those unpoetic scientists who take all the fun out of things, does not mean that heart cells in a petri dish can feel warm fuzzies or celebrate Valentine’s Day or know hope. The beat is a consequence of the chemical and electrical properties of that kind of cell. It’s not actually evidence of a soul. Note also that we’re talking about cells. A functional heart develops by about the 20th week .)
Heart cells in a human embryo are differentiated enough to start beating at about 18 or 19 days following fertilization.
By convention, doctors calculate the duration of pregnancy from the first day of the last menstrual period (not from actual fertilization). That means a heartbeat is detectable at 32 days or four and a half weeks. (The Ohio backers of the bill, at least one of whom doesn’t know why  women get abortions, stipulated 6 weeks because that’s the limit of detection for equipment currently available in doctors’ offices.)
A woman doesn’t even know she’s pregnant at that point.
Fertilization happens in the middle of the ovulation cycle. The exact day varies a bit. Menstruation starts 14 days later. Periods are often 3-5 days later than expected because of common variations in the cycle. A missed period is the way a woman suspects she’s pregnant. She only knows she’s missed a period some 19 days after fertilization at the earliest.
At that point there’s already a heart beat.
No, home pregnancy tests won’t help. They only start working about 14 days after fertilization, and they tend to give false negatives, i.e. unreliable results, up to about 20 days after. For those doing the math, that means they become reliable at about 5 weeks of pregnancy, calculated according to the medical convention.
No, advances in technology won’t change the test timing much. A woman is only pregnant once implantation occurs near the 3 week mark (ten plus or minus a few days after actual fertilization). About half  of fertilized eggs implant, so earlier testing for fertilized eggs, once that is possible, would only mean a lot of false positives that never actually result in pregnancy.
So once research-grade heart beat detection is available everywhere, there will never, even theoretically, be so much as a day when a woman can control her own life.
That’s always been the point and goal of treating women as reproductive organs.