Dear friend, Welcome to Healthcare magic. I have gone through your query and i can understand your concern. You have no reasons to worry. The chances of getting Cystic hygroma in the second baby are very rare. It happens in random in most cases. So you may not worry. I would suggest you to take up an ultrasound again in another month, every months, till second trimester for monitoring. Just because it happened once cannot be taken as a risk factor. But there is nothing wrong in having it checked frequently. Try to relax yourself and keep worries away. I hope i have answered your query. You can feel free to express your concerns with Healthcare magic. Happy to help and wishing you and baby good health.