I don't think you will find the answer to your question on this page but it may still be interesting.
To answer your question:
It would be important to discuss this with the doctor. He or she can examine your child's fontanelles and measure his or her head circumference to tell you more. If your doctor confirms that there is a premature closure of one or both fontanelles, this will require further testing. The main problem with premature closure is that the skull will not develop properly and the brain may not have enough room to form properly.
When is the next follow-up appointment with your baby's doctor? I suggest you call your clinic to speak to a doctor or nurse who can guide you and reassure you.