Unfortunately, it's true, you can breathe a sigh of relief when your baby is in your arms. My pregnancy was perfectly fine, good heartbeats at every appointment, and at 21 weeks our ultrasound showed that her little heart had stopped. She had turner syndrome and we just had no idea until then.
NORMALLY though, once you get to the 2nd trimester, you can relax a little. I know I worried about everything, and I am sure my next pregnancy will be a million times scarier, but good luck and enjoy your pregnancy.
Mostly is after the first trimester, or when a hertbeat is detected. With my second pregnancy last october we had a hertbeat and i thought i was safe but at 7 1/2 weeks the baby's heart stopped. So i m/c again. Honestly you never relax until you have your baby in your arms. And for those who had a m/c you are always afraid.
to be honest, you can have a miscarriage at any time. However, after the first trimester, your risk for miscarriage goes way down.
I think it the normal time frame is 3 months along...when you can get through your first trimester which is through week 12, you can usually breathe.