Let's look at what is required for reproduction. The combination of genetic matter is only the first and in some cases less important stage. What really gets interesting us the number of ways that are used to protect and nourish the offspring until they are old enough to fend for themselves.
Most animals use a variation of the egg. A protective coating which contains the nourishment which the young consume until they outgrow their egg. Mammals are the only creatures which don't use a variation on eggs; they use their own bodies to protect and to nourish.
So ask yourself this; what environmental dangers would a young alien face and what would evolve as protection? And at the same time, what would it consume.
Let's create a species which is made up of psychic energy. It lives in a plane of psychic energy, hunted by psychic predators. Infant creatures might be attached to another creature which would mask its tiny psychic signature, and which could absorb energy waste from that species. Or infants might have multiple stages, the first being a psychic dead stage that consumed physical nutrients.
Now, this doesn't fit what you were looking for but the idea is to think about 1. what are the threats to the young and what would most effectively protect them and 2. what do they consume?
Creatures that give birth only once in their lives are doomed to become extinct rather quickly, unless you meant that the birth event happens only once but produces multiple offspring.
What if the creatures died and at that time if their flesh was not too badly damaged, the dormant eggs inside their bodies would be triggered to start developing. They would consume the flesh of their progenitor and eventually eat their way out.
Dying adults would instinctively seek a place where their flesh would be protected (maybe seeking caves or digging their own graves or burrows and sealing themselves in). There might be some sort of ceremony involved as the creatures' society got more sophisticated and the tribe developed ways to protect the lives of their future members.
Or did you want the adults to survive their single birth event? If there would never be more than one chance to reproduce, the instinct to protect their offspring would be even greater than it would in another species who expects to reproduce many times. Maybe as each egg is produced it is attached to the adult's body, where it grows a proboscis which is inserted into the adult's body. Then an armor plating of mud is applied over the top and turns into something as tough as cement. When the young are old enough they must be chiseled out, or perhaps they have their own tools (a beak which is discarded after "birth") to break out.
In any case, from an evolutionary point of view once the single use species has reproduced there's no reason for it to live any longer. The only exception I can think of would be if it was a sentient species, whose education is so complex that simple instinct does not suffice, and if there are no other methods for that learning available (community which can educate the young, extremely strong racial memory, young consume the memories of their progenitor telepathically or by consuming its flesh, etc)
