if it was taken from the womb, fed and taken care of by doctors? Could it be taught to talk, walk and do stuff early? What age would it be if it was “out” for a year but not as developed as a full term baby? Huh? Can you tell that I’m bored?
I can’t be bothered to look, but there must be tons of stuff out there on pre-term babies.
The page also has a chart showing mortality rates for premature births by week, starting at 23 weeks.
Premature Birth and Viability: At What Point in Pregnancy Can a Baby Survive Premature Birth?
Missed this: generally, development like walking and talking will be delayed rather than early: if a full term baby is expected to sit up between 4 and 7 months, a baby born two months early can be expected to sit up between 6 and 9 months. Not only that, but the more prematurely a baby is born the more likely they are to suffer from neurological deficits and long term health problems that could delay development even further.
As far as age, you can figure it either way: chronological from the date of birth or adjusted for how premature they are. The State will figure it chronologically for the birth certificate.
We’re coming up on 9 years with our 23 weeker. Hopefully, she’ll give you an update in another 90, after I’m dead and gone. 
For the first two years, we talk a lot about “adjusted age”, that is, what the age and expected development would be if we calculated from the due date, rather than the day of birth. But their actual age, when filling out forms and stuff, is the day they left the womb - adjusted age comes up when the doctor and therapists are evaluating for disabilites or delays.
So my daughter, born in February but due in June, was on her first Thanksgiving, 9 months old, but “5 months adjusted age”. She had nothing wrong with her that was considered a developmental delay, and her actual abilities were somewhere between a 5 month old and a 9 month old. She wasn’t quite sitting up unassisted, but she slept through the night. She wasn’t interested in solid food, but she was able to wave “bye-bye” when prompted and mimicked speech sounds.
After age 2, the doctors aren’t so concerned with “adjusted age,” but as her mom, it’s something that I still do keep in mind when I become aware that she’s just a wee bit behind other kids her age in some areas. When the other kids were able to hand-over-hand on the monkey bars by the middle of first grade, she wasn’t quite ready for the task until near the end - when her adjusted age matched their chronological age for the same task. Is this due to her prematurity, or just the normal variation in children’s development? I’m not sure, but it keeps me calm to give her an extra 4-5 months before I become concerned. Meanwhile, she’s reading at an 8th grade level (in 3rd grade) and in the highest math group her grade allows, so I’m not at all concerned with her overall intellectual development. Her “slowness” is more in the physical realm, and not even slow enough to be considered a delay. Emotionally/psychologically, she seems right on target with her peers, and spiritually she asks some more “advanced” probing questions that make me feel she’s a little ahead of the pack, but I don’t know that area of development all that well.
Gestational age is most commonly measured from the mom’s last menstrual period before delivery - little Amelia Taylor is often named as the youngest micropreemie to survive, but they counted her from conception; she spent exactly as much time in the womb as my daughter, to the day. Before 23 weeks, with our current technology, they can only rarely be saved. The earliest micropreemie to make it is still, I believe, James Elgin Gill, now 26 years old. He was born at 21 weeks, 5 days from his mom’s last menstrual period, 2 weeks and a day earlier than Amelia or my Caileigh. His story is simply amazing - to the point where some people doubt the accuracy of the dating. No maligning meant to his parents, but it’s possible that some bleeding a couple of weeks into the pregnancy was misinterpreted as a menstrual period.
Most micropreemies (80%) suffer some sort of long term health problems or disabilities, some mild, some quite severe. While she may not be on wikipedia, my daughter is the earliest micropreemie I know of with no - ZERO - long term health problems or disabilities related to her prematurity. We were incredibly lucky. No brain bleeds, no infections, no heart surgeries. The only thing she needed was laser eye surgery on her due date to correct something called Retinopathy of Prematurity, caused by needing extra oxygen for a few weeks after birth (they think.)
When a fetus before 23 weeks is removed from the womb, they usually have a few minutes to a few hours of life - if they’re removed by c-section. If they’re delivered vaginally, they often emerge dead, as they can’t handle the stress of being pushed through the cervix and vagina.
So, does this imply that, assuming the baby survives, development outside the womb proceeds at approximately the same pace as development inside the womb? I find that surprising-- I would have expected that, good though our medical technology may be, it would still be inferior to the environment evolved for allowing fetal development.
Yes, about the same, surprisingly enough. It was actually pretty cool to watch the lanugo come in, and fall out, and watch her little ears unfold from little curled seashells into real human ears, and the eyes, sealed shut like a little kitten’s, slowly split and open. When born, she had no subcutaneous fat, so you could see all the capillaries under her skin, and, right on schedule, the fat started to build in the weeks before her due date. Brain development, likewise… she had apnea, a habit of “forgetting” to breathe, that wasn’t because of a lung problem, but because the respiratory centers of her brain were simply still developing. When she hit what would have been 37 weeks gestation, the apnea just stopped, her brain was ripe. As she got close to her due date, the physical therapist started coming to see her, to check on her movements, which organized themselves right on schedule with in utero development. I was completely fascinated watching her “prenatal” development. Is it any wonder I became a nurse after that?
That’s fascinating, WhyNot. Thank goodness it all worked out! Did she have to be kept on a breathing machine until the apnea disappeared, or what?
Also, it looks like you joined the SDMB around the same time this was happening. Were you posting about your experiences at the time?
I did! Y’all kept me sane. 
Emergency C-section and a 23 week old infant. Ugh.
I’d have to go through that thread to recall the details, but she pulled her own breathing tube twice. The first time, they then went to a CPAP, I believe, and she was on that for a couple of days but then needed to be re-intubated. Then a short time later she pulled it out again and then she progressed from a CPAP to a nasal canula and then nothing at all. (I feel like there may be a machine somewhere in that progression that I’m forgetting about, but it’s time for dinner, so I’ll read through the thread later.)
Every so often while she was on the CPAP or nasal canula, she’d stop breathing and the apnea monitor would go PING! and we’d flick the bottoms of her feet or rub her chest to remind her to breathe. To this day, she’s not fond of having her feet touched. I do remember I was terrified of bringing her home without an apnea monitor. But the nurse assured me we didn’t need one, that now that her brain was ready, she’d be fine. She was right.
Ah, yes, there was one more - a Vapotherm. Sort of like the nasal canula, but with more pressure.
(It’s really funny seeing my pre-nursing school level of knowledge in that thread. I was already a biology nerd, and I learned a whole lot from those NICU nurses, but didn’t know things like “CPAP” )
And Chronos, I should probably amend my earlier statement. Yes, developing outside the womb is inferior, in that there are far more things that tend to go wrong, including bleeding and infections. Even after you account for the many health problems that can cause a baby to be born prematurely, preemies have higher rates of complications and disabilities both early in life and as they grow. It’s not “no difference” to the point where we’d want to pluck babies out prematurely for convenience. But if you get a very lucky case like ours and nothing all that terrible happens, the general pace and process of development is about the same in utero or in isolette.