在孕妇上厕所时，丈夫从后面突然呼唤她，如果她本能地回头向左看，则是男孩；如果向右看，则是女孩。这是因为男胎受孕于左侧子宫，女胎受孕于右侧子宫。男胎位于左侧，则左侧身体较重，因此回头时会小心保护较重的一侧而转向左边；女胎位于右侧，则右侧身体较重，因此回头时会小心保护较重的一侧而转向右边。将此原理推演到脉诊上，道理也是一样的。胎气在左侧，则气血护佑胎气而在左侧旺盛，所以脉象也随之变化，左侧脉搏跳动急促为男孩，左侧脉象盛大也为男孩；胎气在右侧，则血气护佑胎气而在右侧旺盛，所以脉象也随之变化，右侧脉搏跳动急促为女孩，右侧脉象盛大也为女孩。《内经》说：“阴部脉搏动有力而与阳部分别开来，称为怀孕。”意思是受孕部位在脐腹之下，则血气护佑胎气而在下部旺盛，所以尺部（阴）的脉搏鼓搏有力，而与寸部（阳）的脉象明显不同。又比如痈疽疖肿发于上部，则血气趋向于上部，寸脉就旺盛；发于下部，则血气趋向于下部，尺脉就旺盛；发于左侧，则血气趋向于左侧，左脉就旺盛；发于右侧，则血气趋向于右侧，右脉就旺盛。
When the pregnant woman is going to the toilet, if her husband calls out to her suddenly from behind and she instinctively turns her head to the left, it indicates a male fetus; if she turns her head to the right, it indicates a female fetus. This is because the male fetus conceives in the left uterus, while the female fetus conceives in the right uterus. When the male fetus is on the left, the left side becomes heavier; thus, when turning her head, she instinctively protects the heavier side by leaning towards the left. When the female fetus is on the right, the right side becomes heavier; thus, when turning her head, she instinctively protects the heavier side by leaning towards the right. Applying this principle to pulse diagnosis (Mai Zhen), the logic remains the same. If the fetus is on the left, Qi and Blood (Qi Xue) protect the fetus and become abundant on the left; consequently, the pulse reflects this, with a rapid pulse on the left indicating a male, and a large pulse on the left also indicating a male. If the fetus is on the right, Qi and Blood protect the fetus and become abundant on the right; consequently, the pulse reflects this, with a rapid pulse on the right indicating a female, and a large pulse on the right also indicating a female. The Classic states: "When the Yin pulse beats vigorously and is distinct from the Yang, it signifies pregnancy." This means that since conception occurs below the navel and abdomen, Qi and Blood protect the fetus and become abundant in the lower part; therefore, the Chi pulse (associated with Yin) beats vigorously and is distinctly different from the Cun pulse (associated with Yang). Similarly, if an abscess or boil appears on the upper body, Qi and Blood flow upwards, causing the Cun pulse to be vigorous; if it appears on the lower body, Qi and Blood flow downwards, causing the Chi pulse to be vigorous; if it appears on the left, Qi and Blood flow to the left, causing the left pulse to be vigorous; if it appears on the right, Qi and Blood flow to the right, causing the right pulse to be vigorous.