It is common for pregnant women to experience back pain due to the changes happening in their bodies. However, if the pain becomes severe or persistent, it is important to consult with a healthcare provider. As for vanishing twin syndrome, it occurs when a woman initially conceives twins but one of the embryos fails to develop and is absorbed by the mother's body. This can result in symptoms such as bleeding or cramping. While vanishing twin syndrome can be emotionally distressing, most women go on to have healthy pregnancies without any further complications. If you have concerns about your pregnancy or are experiencing any unusual symptoms, it is always best to consult with your healthcare provider for proper guidance and support.