the pattern

Barbie Maternity Dress

needle size: 2
yarn: sport or baby sport weight
gauge: about 7-8 sts/inch

CO 36 sts, divide across 3 dpns, join and knit in rd.
Begin with stockinette st for a rolled hem, or if you prefer, a few rows on 3 X 3 rib for a ribbed hem.
Knit in stockinette till 2", or desired length of skirt (measured from inseam, not ridiculous teensy waist).

Designate needles 1, 2 & 3, with needle 1 as the front.

Begin increases for baby bump as follows:

needle 1: k3, m1 (right slanting*), k6, m1 (left slanting*), k3; needles 2 & 3, k to end.
k 1 row
needle 1: k3, m1*, k8, m1**, k3; needles 2 & 3, k to end
k 1 row
needle 1: k3, m1*, k10, m1**, k3; needles 2 & 3, k to end
needle 1: k3, m1*, k12, m1**, k3; needles 2 & 3, k to end
needle 1: k3, m1*, k14, m1**, k3; needles 2 & 3, k to end
(if you're going for Octomom proportions, you can keep going, but this is enough for a decent size baby bump, for a six-month-ish-along Barbie)
k 3 rows

Begin decrease rows:

needle 1: k3, ssk, k to 5 rem sts, k2tog, k3; needles 2 & 3, k to end
repeat until 12 sts remain on needle 1.

knit in rd a few rows until you are ready to divide for armholes (I didn't count rows here, so give your Barbie a fitting or two to determine this.

needle 1 (front): 18 sts; needle 2 (back): 9 sts; needle 3 (back): 9 sts. If needles 2 & 3 are in your way, place those sts on a holder temporarily.

needle 1: knit 10 rows stockinette
row 11: k4, BO 10, k4
rows 12-14 (knit each strap separately): stockinette st, then place sts on holder for 3-needle BO later.

needles 2 & 3: knit 14 rows stockinette, then 3-needle BO with the front strap sts. leave a long tail after BO to use as a string tie closure. Or if you're fussy, sew on a snap. I can't be bothered with that myself.

Finally, pick up some sts on the inside of the dress where the bottom of the baby bump begins, and knit a square flap. Anchor the top and side of the flap on the inside, stuff with some extra yarn or whatever you've got on hand, then stitch closed.

Congratulations, you've knocked up Barbie!

m1* : right slanting increase. Insert left needle into horizontal strand btw sts from back to front. Knit this through the front loop to twist the st and avoid a hole.
m1**: left slanting increase. Insert left needle into horizontal strand btw sts from front to back. Knit through the back loop. (from Vogue Knitting Quick Reference)