He alone knows what is in the wombs (31:34) However, today it is possible to determine a babys gender. So, how should we understand the verse?
Baby in the mothers womb is surrounded by the liquid called amniotic fluid and he grows through umbilical cord. In this stage, it is possible to learn the gender of the baby by some scientific methods.
The most commonly used methods are ultrasound and taking amniotic fluid sample for measurements. Ultrasound vibrations are too high for human perception. These high frequency sound waves are transmitted though uterus to a baby. Gel is used to allow ultrasound waves to pass into the body. And by examining the organs which appear on a computer screen, babys gender is determined. In the second method, the cells, which are taken from the baby, cultured in amniotic fluid; the sample of about (20ml) amniotic fluid is taken and examined under microscope. In this way, a gender of the fetus is determined 80-90% in accuracy. In the verse at issue, what is in the wombs is mentioned, gender is not the matter.
With the expression, his special talents, features, personality, and emotions in the future are meant. Will he be very talented? What will be his state of mind and what will be the conditions of his organs? His face surely will be different than others but how will he look like?
We do not know these and such like features of him, but He alone knows what is in the wombs and everything that we could not know. Many other facts are meant in the verse. Even if we know a babys gender at a certain stage, there are many features of a baby that we cannot know. Besides, even after his coming to this world, we will continue not to know many things. Moreover, gender determination is only possible after four months.
If we say, The things that we know, compare to that we do not know is just like a drop of water from the Ocean it fits perfectly.