Most women deserve a gold medal for pushing out their spawn. But I'll take a yellow gold Emily & Ashley pendant when I deliver my second, thank you very much.
For a baby-themed gift, I'd pick the 14K Zodiac Disc necklace. The 16" necklace is available at Fragments for $300 (husband are you reading this?). Personalize the gift by selecting the birth sign of the baby and it's a gift mom will treasure forever.
If astrology isn't your thing, how about treating yourself to a monogram necklace with the baby's new initials? Mom gets to wear the necklace for the first few years then the necklace can become an heirloom. What a sweet tradition. Find these at Max & Chloe.