One theory for this has to do with the Y or male sex chromosome being so much smaller than the X or female one. As a result, it can reveal the sex of your baby. Blood tests called cell-free DNA tests have cropped up over the last several years. During fertilization, the sperm cells race toward the mother-to-be's egg cell. Though many women swear heart rate clued them in, the overall results are mixed at best. Yes, men and women are psychologically different and yes, neuroscientists are uncovering many differences in brain anatomy and physiology which seem to explain our behavioral differences. And yet, we all know families that are all boys or all girls.
What you eat during pregnancy is important for your health, as well as the health of your baby.
Girl Brain, Boy Brain?
Buffalo in Africa have mostly sons when it rains and more daughters when the climate is dry. If the sex difference in the SG is present early in life, this strengthens the idea that it is innately programmed. Blood tests called cell-free DNA tests have cropped up over the last several years. Some birds can influence whether they hatch a male or female chick. You can get one as early as around week 9 in your pregnancy.