The eggs, which shelter the face-huggers until some hapless victim comes to knock on it, can be seen in the movie as having a cross-like opening. This wasn't always so. Originally, H.R. Giger had designed a vertical slit as its opening, and yes, it was meant to resemble a vulva. A yucko vulva that gives birth to yuckier creatures, which themselves own a vulva and a penis, and which inseminates other beings with the seed of what will become a giant penis-headed female-like killer. The producers of the movie couldn't take the sexual opening, because, as they said, the movie would air in many Catholic countries, and obliged Giger to change it. As the artist himself notes in his book about the alien project, he decided to complement the egg's opening with yet another slit, horizontal this time, to look like the Cross that Catholics liked so much; and that's paraphrasing a quote of Giger's. So, the opening moved from being a vulva to a cross. From the sexual to the religious, the gross to the divine. (And no, I don't mean to say that vulvas are gross, only that our sexes aren't the part of ourselves we expose the most, or that we're proud of having, and etc.)
Our sexes are indeed the parts that we think are most alien to us. It's the most animal part too, and we all come from one, and give life with one.
Back to the pregnancy. Giger based his work, for the movie but not only, on what would usually take place while giving birth. Of course, this won't apply to this day's giving birth, but that of millennia ago. Death was extremely frequent during child-delivery. The other thing, and I know many of you won't like it, and others won't even believe it, is that child-delivery can cause sexual pleasure, and yes, even orgasms. Naturally, if you're on anaesthetics, you may not feel that, but remember that the days I am talking about did not have those things. I also know from an acquaintance who had two children, that she came during both deliveries.
The point here is that in this important moment of birth, both sex and death dance together. And this is perfectly true of the alien creature and its cycle. You may also think of the strange fact that people who are hanged eventually ejaculate before they die. The mandragora, root of the mandrake plant, was said to come from the seed of the hanged people, because this root is shaped like a tiny human being. As an aside, I don't think the hanging in question is the neck-breaking kind, rather the slow choking one.
The other thing about this alien pregnancy is that the being inside the host is utterly alien to it, and that's not a pun, or not quite. Pregnant women vomit during their pregnancy, and lots of other things happen to their bodies, and all, or so it seems, tend to indicate that the body itself doesn't recognise the guest as belonging to the same body. Being no doctor, I could be entirely wrong about this, but I was given to understand that the throwing up came because of something related to that, or to that directly. I claim no authority on the issue, but it is well known that giving birth can be damaging to the host, and in olden times, it was very often lethal.
So, the victim of the alien is first raped by the face-hugger, impregnated by it, then forced to nurture a monster in his innards, the latter of which eventually gives itself childbirth by clawing through the host's body to get out. A most unpleasant way to die, I am sure. And traditional human childbirth is the model for this gruesome delivery. Both are bloody and disgusting (and don't give me that "but childbirth is beautiful! You are heartless!" because I got it before, and I think it's still bullcrap. Child-delivery is yucko from A to Z, even if you want to think that giving life is beautiful; they don't have to be related. I love Tiramisu more than any other dessert, and the day I made some, it was yucko, and yucko ingredients were used; I still love the result, but the process is yucko).
I hope that this chapter made the alien creature more interesting to you.