It struck me as odd that Sarah had what appeared to be a routine scan so late in her pregnancy. Normal ultrasound scans are done at about 12 and 20 weeks, and it's at the latter one that the baby's sex is usually identified.
Of course, Sarah didn't realise she was pregnant until about 20 weeks, but from the experience of someone I know, the routine scans are still done as close to the usual time as possible in those circumstances and not left until many months later.