Posterior refers to the location of the fetal spine in relation to the body of the mother. This means that at the time of the ultrasound examination the back of the baby was aligned with the back of the mother. This is one of the thousands of normal positions the baby can take in the uterus. As a general rule all patients are advised not to try to interpret their own medical reports, as this, more frequently than not, results in anxiety and anguish for no justifiable reason as in your particular case.