What is the ruling of the Shari'ah on knowing the sex of the fetus (male or female) during the months of pregnancy using modern medicine?

There is no harm in knowing the gender of the fetus, and this does not contradict His (the Most High) saying: (And He knows what is in the wombs). Allah knows all the details of the fetus, including its happiness and misery, and these are matters that none but He knows. The doctor's statement about the gender of the fetus based on physical signs is based on custom, not on definitive knowledge. Advances in medicine have proven that knowing the gender of the fetus is possible during the "increase" stage of pregnancy. As for the "decrease," it is part of the knowledge of the unseen that Allah has reserved for Himself.