On the generation ship in one of my stories and possibly more, there exists a positive relationship between the egg laying humanoid aliens who have an egg pouch on their chest and the humans they are transporting to a planet 400 light years away at half the speed of light(so over a period of 800 years).
1 part of that relationship is the complex system they have for human baby defects starting in pregnancy.
Early on in pregnancy the aliens are able to use an endoscope to very gently look at the baby in the embryonic stage. If it isn't developing right, they keep going with the pregnancy and by the fetal stage, they can tell exactly what is wrong externally and/or internally.
External defects, they don't fix, not because they don't have the technology but because of the extreme risks of for example taking a stem cell, making a working arm or leg and then surgically attaching it. Cleft lip and cleft palate are 2 exceptions to this rule that external defects are not fixed.
Internal defects on the other hand are always fixed no matter the risk. This is where it gets really complex.
There is a branch off of the medical bay of the ship where all internally defected babies are taken to be operated on. Depending on the defect, different tubes are put in to stabilize the baby while in surgery.
The baby is on a heart lung machine while the heart is taken out of the baby and repaired. Once the heart is repaired, it is transplanted back into the baby.
With this kind of defect, oxygen is put straight into the blood before the defected lung/lungs are taken out. Once the lung/lungs are repaired, just like with a heart defect, it is transplanted back into the baby and the oxygen supply stopped.
Nutrient IV while defect is repaired.
Dialysis while defect is repaired.
Anyway, this complex system is used to repair all internal defects. External defects are usually left as is and the humans grow and adapt to the defect. For example, without external support a 1 legged, 2 armed person can walk on 3 limbs, walk in a handstand, or hop on 1 foot. A person with no arms can adapt by using their legs and feet for everything from walking to writing to picking things up.
If the cause of the defect or disease happens to be genetic, a permanent reproductive sterilization process begins. At first it is at really low levels to make sure they still develop as male or female but once puberty ends this process quickly goes to completion so that females don't ovulate and thus don't menstruate and males don't produce sperm. This is to prevent bad genes that cause disease or defects from spreading through generations. They still have the male and female hormones, it just isn't affecting their reproductive chances. This way, theoretically, a woman who has a genetic disease can still take care of a baby via induced lactation, she just can't become pregnant.
Is this a good way to prevent genetic defects from spreading while still allowing them to live full lives?
Later on, in the 3rd generation, CRISPR will be allowed for all pregnancies, not just test subjects. This will allow people to have babies with everything from the inability to become obese to the ability to see heat to making IgG antibodies against all kinds of venom and surviving any venomous sting or bite and more.
But before then, defects are not allowed to pass on if they are in fact genetic. If it isn't genetic and it is just a defect then nothing changes from normal except the fact that the person was born with a defect.
So is permanent reproductive sterilization a good way to prevent the spread of genetic disease and defects?
The risk I am talking about when taking a stem cell and forming a working limb is huge. For 1 thing, the aliens working on this would need to know the exact proportions of things like nerves, muscles, blood vessels, etc. Second, even with exact proportions the nerves are likely to be damaged in surgery, much more so than even capillaries. And even if that didn't happen, there is a chance that the nerves in the new limb won't cooperate with the already existing nerves.