Science News reports:

Like most aspects of biology, early human development involves many complex processes. Despite the rhetoric around these issues, clear lines — between having a heart and not having a heart or being able to survive outside of the uterus — are scarce, or nonexistent.

“There aren’t these set black-and-white points for much of this,” says obstetrician-gynecologist Nisha Verma, a fellow with the American College of Obstetricians and Gynecologists in Washington, D.C.

Here’s what’s known about five key aspects of pregnancy biology that often come up in abortion debates.

1. The early timeline of a pregnancy is easy to misunderstand.
That’s because how dates are determined is supremely confusing. The standard pregnancy clock actually starts ticking before a sperm cell encounters an egg, two weeks before, on average. An ovary releases an egg around day 14 of an average 28-day menstrual cycle. (Day 1 is the first day of menstruation; day 1 is also when a pregnancy officially begins in the month an egg is fertilized.) That means that when a sperm fertilizes an egg, a person is already officially two weeks pregnant. As nonsensical as that sounds, it’s the simplest way medical professionals can date a pregnancy.

That timeline means that abortion bans at six weeks, enacted in Texas, Oklahoma and Idaho, take effect earlier in pregnancy than many people think, Verma says. In 2020, she surveyed people in Georgia, where she was practicing medicine at the time, about their understanding of the timing. “Some people will say the six weeks is after your first missed period,” she says. “Some people think it’s from the date of conception.” Neither is correct.

The ban would start four weeks after fertilization. Counting back, that’s two weeks after a missed period, which is often a person’s first indication that they might be pregnant. Such bans leave a person very little time — two weeks after a missed period — to access an abortion.

What’s more, these dates are based on averages. Many women have irregular menstrual cycles. Birth control isn’t 100 percent effective, and certain types can eliminate menstruation altogether, throwing even more uncertainty into the early timeline of pregnancy.

2. Pregnancy takes more than sperm meeting egg.
That meeting, which usually takes place in one of the two fallopian tubes near the ovaries, is fertilization, a process in which two cells fuse and mingle their genetic contents, creating what’s known as a zygote. But a fertilized egg does not automatically lead to a pregnancy, says obstetrician and gynecologist Jonas Swartz of Duke University School of Medicine. “Equating them doesn’t make sense from a medical standpoint.” Up to 50 percent of fertilized eggs do not implant in the uterus, researchers have estimated.

The genetic material needs to combine in the right way. The growing ball of cells needs to travel to the uterus and implant itself in the right spot. And the right balance of hormones need to be churned out to support the pregnancy. “There are so many things other than the sperm meeting the egg that actually matter for this to become a pregnancy that has a chance to develop further,” says Selina Sandoval, an obstetrician and gynecologist who specializes in complex family planning at the University of California, San Diego.

Lawmakers in some states are considering abortion rules that apply to a fertilized egg; Oklahoma had already passed such a law. That includes fertilized eggs that lodge in the wrong spot, the fallopian tube, for example. Called an ectopic pregnancy, this can lead to life-threatening medical emergencies when the growing tissue ruptures the tube and internal bleeding ensues. “These are pregnancies that under no circumstance can become a healthy pregnancy,” Sandoval says. “In fact, if they aren’t treated and continue to grow, they will kill the patient.” Laws that apply to a fertilized egg could “limit our ability to treat patients for ectopic pregnancies,” she says. [Continue reading…]