What's the reason behind this healthy young woman's miscarriages?

Prudence, 28, attends the surgery with her husband Geoffrey. She has just been discharged from hospital following a miscarriage at 10 weeks' pregnant.

Eight months ago, she lost a pregnancy at 30 weeks as a result of undefined placental insufficiency.

Prudence is otherwise quite fit, works as a primary school teacher, does not smoke, drinks only occasionally and has a BMI of 27, and a normal regular cycle. There is no family history of note.

Blood tests were done and Prudence attends to discuss the results. She and Geoffrey are very