For the record, the child’s nervous system begins developing a few scant days after fertilization, the brain begins forming mere days later and by the time Mama’s period is due the child is moving independently, turning his head side-to-side, wriggling little bud arms and forming eyes and ears that may already work to some degree. At three weeks the child has a doll face with big black eyes that have moved to the front, lips, the beginning of eyelids, arms long enough to start forming elbows, little legs, little paddle-like fingerless hands, and the pseudotail, which was the spine of course, is gone, because she has grown along it. The eyes definitely react to light then, and the ears to loud sudden noises. Brain activity is so constant at four weeks that he has recognizably human brainwaves. Two weeks after that, she sleeps, wakes up, swims gracefully and swiftly around in several directions, shows a wide range of facial expressions, feels the cord and her hands and feet with her fingertips, hugs herself, and has every organ she will ever have, most of them up and running the way they will all her life. Only the lining of the lungs, the fatty deposits, the reproductive system, a few of the slower-growing brain lobes (corpus callossum e.g.), parts of the immune system and pancreatic system, myelin sheathes and other last-minute finishing touches still need time. Of course, she won’t use her repoductive system to reproduce (its central purpose) until she is at least adolescent, but preferably later than that. However, it is already working to feminize her body and brain by producing hormones. If the child is male, his reproductive system is producing hormones to masculinize his body and brain. That is at six weeks after conception (eight weeks gestational age, four weeks after Mama had any reason to suspect pregnancy at all.) Abortion is extremely rare that early.
It’s fairly normal to miss a period and then have the next a week or two late without being pregnant, so she might not even suspect pregnancy until the child is seven weeks along – there are no signs or symptoms of pregnancy until much later than that. Also, sometimes the first and even the second “missed” period is actually present but very light, so many women don’t know until even later. Even if she gets the OTC test the day it was expected to start, it’s sometimes falsely negative at that early stage.
The frontier of viability is now moving into the late part of the first half of a normal term. The challenge is the lungs. Other than that, a second-trimester child is identical to a nine-monther only a lot shorter, a whole lot skinnier, and therefore needing to be fed more frequently and kept warmer. There are also slight immune deficiencies, but nothing an incubator doesn’t take care of. The key difference between a baby of nine months and a baby of half that age is the lining of the tiny lungs.