Why is a 6-week abortion ban nearly a total ban? It's about how we date a pregnancy

Selena Simmons-Duffin

May 01, 2024 / 6:47 am

caption: The medical community dates pregnancy to the first day of a woman's last period, even though fertilization generally happens two weeks after that. It's a long-standing practice but a confusing one.

Florida's abortion ban after six-weeks gestation is in effect as of May 1. That means the time a person has to decide whether or not to have an abortion in Florida is – at most – two weeks.

What?

It has to do with how the medical community dates a pregnancy. Here's the deal:

A pregnancy is measured from the first day of a woman's last menstrual period, or LMP.

For the first two of those six weeks – before ovulation – there is no pregnancy.

Ovulation, sexual intercourse and conception have to happen, generally, about two weeks after the first day of the LMP.

There's about a week between when an egg is fertilized and when it implants in the uterus.

It takes another week before there's enough of a specialized pregnancy hormone in someone's urine for a home pregnancy test to turn positive. That's also about the time that a missed period might clue a woman in that she might be pregnant.

All of the above is true for people with regular menstrual cycles. For the many women with irregular cycles, it can take longer to diagnose a pregnancy.

So, a six-week limit on abortion is really a limit of four weeks after conception, and one or two weeks after a person learns they are pregnant. There are lots of variations in these biological norms from person-to-person and even from month-to-month.

Florida's six-week ban has exceptions if the pregnant patient's life or a "major bodily function" is in jeopardy, in cases of rape, or if the fetus has a "fatal fetal abnormality."

The six-week limit on abortion is not common – it is in effect in South Carolina and Georgia, at the moment. Many more states have full abortion bans.

The first six-week ban went into effect before Roe v. Wade was overturned in September 2021 in Texas. That was a ban on abortion after a "heartbeat" could be detected. Physicians have pointed out that there is no fetal heart at six-weeks gestation, but cardiac activity begins at that stage of development. [Copyright 2024 NPR]