Why do some of my hairs grow out to be really curly and rough surface?

Hair growth: It depends on where the hair is growing as well as your genetic background. Also, during pregnancy, hormonal fluctuations can cause abnormal hair growth and texture. Is there any change in the texture of your skin or only the hair? I would advise against any intervention with this matter while you are pregnant. If its new, it may resolve spontaneously after pregnancy.

Curly hair: The curliness and coarse/rough texture of hair is determined by genetics (inherited from your parents). Hair tends to get even more curly in humid weather, so you may notice it is more difficult to straighten your hair on humid and rainy days. Many people who have straight hair wish they had curls, so you can be proud of your thick curly hair.