Gene Roddenberry interviews Sarek. I don't know the year this was made but the content seems pretty risqué.
[yt]https://m.youtube.com/watch?v=IzYxKidfyBI[/yt]
Here's some content (from an earlier a TrekBBS post) from the "Inside Star Trek"phonograph album--now available on CD:
Roddenberry asks Ambassador Sarek about Spock--the first Human-Vulcan hybrid. Sarek replies:
"No, not the first. But the first to survive. As you must know, an Earth-Vulcan conception will abort during the end of the first month. The fetus is unable to continue life once it begins to develop its primary organs. The fetus Spock was removed from Amanda's body at this time--the first such experiment ever attempted. His tiny form resided in a test tube for the following two Earth months, while our physicians performed delicate chemical engineering, introducing over a hundred subtle changes that we hoped would sustain life. At the end of this time, the fetus was returned to Amanda's womb. At the ninth Earth month, the tiny form was again removed from Amanda, prematurely by Vulcan standards, and spent the following four months of a Vulcan term pregnancy in a specially designed incubator. The infant Spock proved surprisingly resilient--there seems to be something about the Earth-Vulcan mixture, which created in that tiny body a fierce determination to survive."
"And, as Spock grew into childhood, Ambassador--"
"Yes, yes. There must have been times when his inner mind wondered, if the fight to survive had been worthwhile. You see, while all Vulcans, including our children, live by the code of IDIC, and believe that diversity is to be admired, and treasured, it must be understood that the display of emotion is considered on our planet to be grossly offensive. No--more than that: shockingly indecent. I can only explain that our attitude is rooted in Vulcan history, involving events of such bloody violence that it's left our race forever scarred, and sensitive to displays of emotion. Whether or not this Vulcan attitude can be defended, the fact is, it exists."
Of course, this is from--what? 1974?--long before we saw a flashback of Amanda in a cave giving birth to Spock.
Also, I'm sure that there are all kinds of technological advances in the 23rd century--perhaps including semi-permeable fields. I remember that Clarke's Third Law is "Any sufficiently advanced technology is indistinguishable from magic." So the source of our incredulity that a human woman could give birth to a half human-half Vulcan child--and in a cave no less--might be due more to our limitations to imagine, than it is due to the actual impossibility of the technology.