Honestly, from what I've heard, regular calcium supplements like calcium carbonate or citrate are well-studied for pregnancy and can work just as well, the key is hitting around 1000mg daily, which your doctor is clearly trying to help you reach, and getting enough calcium during pregnancy is genuinely important as it can lower your risk of preeclampsia and support your baby's bone development. My friend was also prescribed coral calcium and her pharmacist mentioned there isn't as much clinical research specifically on coral calcium during pregnancy compared to regular calcium, so she actually switched to a standard calcium with Vitamin D3 (which helps with absorption) and found it much more affordable without her doctor objecting. That said, some mums swear by coral calcium and feel it sits better on the stomach, while a few others felt regular calcium was just as effective at a fraction of the price, so it really can go either way. I would be upfront with your OB about the cost concern and ask if a standard calcium carbonate or citrate supplement would meet your needs just as well, because at the end of the day your doctor knows your specific blood levels and situation best.