We get standard ultrasounds at 12 weeks and 20 weeks. Later on if there are concerns over growth they should be offered an additional ultrasound - but even so it is not usual to be offered a c section here due to a large baby. Especially as measurements from ultrasounds are more inaccurate further along the gestation.
That baby looks as if the mother had undetected GDM which is pretty appalling - however antenatal care differs across the country and with the cutbacks on midwives the NHS is facing it can have really bad consequences. Less midwives + a rising birth rate = less time the midwife can spend with each women = things have a higher risk of getting missed.
Very sad but thankfully they are all ok in this particular story, and it goes to show that women can give birth to big babies vaginally, it is not necessarily an indication for csection