MSRA-0848

A 35-year-old pregnant woman and her husband are informed at the 20-week antenatal scan of the presence of echogenic bowel in the male fetus. They had been trying to conceive unsuccessfully for three years until investigations revealed oligospermia and this pregnancy was a result of intrauterine insemination. Both parents are aged 35 years old. The father has had several episodes of upper respiratory tract infections that have required antibiotics and he has been admitted to hospital in the past with acute gastritis. The mother is fit and well without any significant past medical history.
Which of the following would be the most appropriate next investigation?