I'm guessing it's a small breasts joke.

I have no idea how they got a baby other then mad science but breast feeding is not an option for Konata.

Well yeah, she's not just flat, she is completely lacking a chest.

Maybe its small doses, like snacks in between Kagami meal time feeding

Serious;y, dudes, you're disappointing me. A healthy mother of any cup size can properly feed her newborn. Kona-chan would just have to feed more often.
Also, unless Kagami was the one who gave birth, she'd have to artificially induce lactation.

Small breasts joke > Science.

Huh. After translation the comic reflects the comments pretty accurately.

Mauvais said:
A healthy mother of any cup size can properly feed her newborn.

Both true and not.
While milk production does increase in response to demand, I think the bigger (heh) issue here is the breast structure. A chest as flat as Konata's makes it exceedingly difficult for an infant to form a proper seal around the nipple with its mouth, making it impossible for the infant to breastfeed directly. This would necessitate that the mother forgo breastfeeding in favor of pumping and bottle-feeding.

Also,

Lalaca said:
Small breasts joke > Science.

Last I checked, a girl's boobs grow when they get pregnant. I'm assuming that Konata's the mother, in the having given birth to her sense. So wouldn't that make her a b cup at least, therefore being sufficient enough?

Not from the looks of things.

Besides, one cup size up from "nearly as flat as an ironing board" is still less than a Western B-cup. (I say Western, because the Japanese use a different cup-size system.)