διέσχον “Three days had not separated the child's birth from us”: three days had not passed since its birth. Plut. Tib. Gracch. 18 κελεύσαντος ἐκείνου διασχεῖν τὸ πλῆθος, to keep the crowd off.

βλάστας cannot be acc. of respect （“as to the birth”）, because διέσχον could not mean “had elapsed”: when διέχειν is intrans. it means (a) to be distant, Thuc. 8.79 διέχει δὲ ὀλίγον ταύτῃ ἡ Σάμος τῆς ἠπείρου: or (b) to extend, Hdt. 4.42 διώρυχαδιέχουσαν ἐς τὸν Ἀράβιον κόλπον.