By the 4th month is when the baby is able to suck its thumb, yawn, stretch, and make faces.
By the 4th month, or the second trimester of a pregnancy, is when unborns call yawn, stretch, and do all of the listed things above. This is usually the month where you can also identify if the unborn is a male or female, since by month four, they develop their genitals and also organs.