When I was pregnant I shopped for the maternity wear essentials at Old Navy. I didn't get a chance to stock up on sweaters since I was large mostly in the summer and early fall when it's warm here in San Francisco. If you are pregnant now in this cold winter, I recommend this Old Navy Maternity Jersey Wrap Cardigan in Purple Broach (on sale for $15). You can't beat the price or the color. You'll probably be able to cozy up with the baby in this cardigan later on as well!
Here are more great Old Navy Maternity Sweaters:
Maternity Metallic Open-Weave Sweaters (on sale for $17.99)
Maternity Pleated-Collar Sweater Coat (on sale for $39.99)
Maternity Belted Boyfriend Cardigan ($29.50)
Maternity Empire V-Neck Sweater (on sale for $12.99)