(Image above is a sparkling)

A sparkling develops within the spark of the carrier (or mother). Cybortronian reproduction is much more complicated then the human reproduction system, but is a little similar to it.

First thing you should know is there is a difference between 'sparking' and sparkbonding.

Sparkbonding ONLY happens when the mech and femme have been, what humans call, "married". If sparking is done outside of sparkbonding, then it will be extremely painful. To sparkbond, the mech and femme must reach out and gently touch each others sparks and keep them there until sparkbonding is complete. Sparkbonding is completed when both spark glow extremely bright.

Sparking is similar to what humans call 'sex', but sparking happens in the chest area of the Cybortronian. The inner chest plates protecting the spark open and light energy that looks like tendrils is released from the sparks of the carrier and the sire. These light tendrils intertwine with one another, getting longer and thicker until a strong glow emanates from between the sparks. That glow is the start of a sparkling. The carrier then uses her spark energy to hold the sparkling and the sire uses his energy to protect the sparkling from floating away and from any threat. The carrier then cradles the sparkling in her chest for about 3-4 earth weeks. Is this time period uncomfortable? No it's not.

The sparkling stays relatively the same size until "birth". During these 3-4 weeks in the carrier's spark, the sparkling develops a gender, a color scheme, a personality, and a vehicle type depending on wether one of the parents is a flyer and is one is a grounder. However if both parents are flyers, then the sparkling will be a flyer. Same thing goes for grounders .

Most Cybortronian families will have one sparkling at a time, very rarely will they ever have twins. 1 out of every 1000 Cybortronian families will have twins. Regular twins are difficult to have because it requires both sire and carrier to cradle them in their sparks. Split spark twins are an incredibly dangerous to have. 98% of the time both twins will explode within 2 seconds after being sparked and carrier and sire will die if the carrier isn't quick enough to cradle the twins in her spark.

And that concludes this lesson. If you have any questions, then please speak to me in medbay or write them down here.

(Here)

~Ratchet

(Update) P.S.  Also There has been no record of triplets, quadruplets, or any other ever in Cybertronian History.