I mostly lurk but had to post about the scans since this is my field!
So Knob has booked a private gender scan, these cost as little as fifty quid these days so not really splashing out big time. The earliest they are done is 16 weeks so he's clearly done his research and got her booked in as early as possible of course. I daresay he looked into harmony tests as well but given they more advertised as genetic screening then I reckon he would of dismissed it knowing it would look far too OTT and make Helen think about his motives.
In theory they could get the sex wrong at the gender scan and find out at their 20 week they were told the wrong gender, but since the whole point of the scan is to spend plenty of time looking with a high quality scanner, I would find that twist pretty poor writing!
I think back when the midwife pointedly told Helen that she could always talk to her about anything will be significant as this pans out. The midwife will start picking up on things if she is any good and start asking the right questions.
Surely Rob won't attend every appointment....although how will she get there now she "can't" drive?
Also, has Helen even said anything about whether she wants to know the gender? Maybe she would like a suprise. Wouldn't that piss him off if she told no to the scan! Not that she would dare, she is far too afraid of him now