Fertility, the natural ability to give birth to offspring, is expressed in Chinese Medicine by the concept of Tian Gui 天癸. Tian 天, meaning ‘heaven’, has two aspects: the pre-heaven and the post-heaven. That which is given at birth is pre-heaven. It includes not only ancestral and hereditary factors, DNA, and genes, but also astrological and karmic influences. That which comes after birth is post-heaven. This is our nourishment: food and water, the air we breathe, and the physical and emotional environments we live in. The pre-heaven and post-heaven are mutually dependent: the pre-heaven offers potentials and sets limits; the post-heaven enables the expression of these potentials. The pre-heaven is the seed; the post-heaven is the soil, the water, and the sun.
Gui 癸 is the last of the Ten Celestial Stems. What is important to know here is that Gui pertains to the Water element and, more specifically, to Yin Water (while the ninth stem Ren 壬 pertains to Yang Water). Yin is the substantial embodiment of Qi. Tian Gui 天癸 can be translated as ‘Heavenly Water’. Indeed, the expression Tian Gui Shui 天癸 水, or ‘Tian Gui Water’, is used to describe seminal and menstrual fluids. The Water element is related to the Kidney organ, so in fertility (or infertility), the energetics of the kidneys are the most important thing to consider. Tian Gui 天癸 is the expression of 腎氣 Kidney Qi in terms of fertility.
In the Su Wen, Huangdi asks of Qi Bo 歧伯:
In old age a person is not able to produce offspring, is it because of the exhaustion of vitality, or is it predestination by the law of nature?
Qi Bo answers by describing the developmental stages of seven- and eight-year cycles in females and males, respectively:
When a girl reaches the age of seven, Kidney Qi is rich so the baby teeth are replaced by adult teeth and the hair grows long.
Hair is the flourish of Kidney Qi, teeth is the excess of bones. Both hair and bones are expressions of Kidney Qi. The condition of the hair and the teeth is a good indication of the condition of Kidney Qi.
At the age of two times seven, or fourteen, Kidney Qi is full, Tian Gui arrives, the Ren Mai courses, and the Chong Mai becomes rich and full. When the menstrual cycle becomes regular, she is fertile.
The Ren Mai connects to the uterus and is the Sea of Yin. The Chong Mai is the Sea of Blood. Both vessels are governed by Kidney Qi; their proper functioning is essential to fertility. So fertility problems can be treated with the Chong and the Ren. Also, the menstrual cycle must be regular; hence, regulating the cycle is the basic method in promoting fertility.
At the age of three times seven, or twenty-one, Kidney Qi is calm and even, the wisdom teeth come in, and the hair grows long and luscious.
At the age of four times seven, or twenty-eight, the sinews and bones are strong, the hair is luscious, and the body is fully developed.
At the age of five times seven, or thirty-five, the Yang Ming Mai weakens, the complexion starts to wither, and the hair starts to fall out.
Women are Yin creatures, and so are naturally deficient in the Yang; therefore, problems show in the Yang channels first. The Yang Ming governs the face, hence the withering complexion and the hair loss.
At the age of six times seven, or forty-two, the three Yang channels weaken in the top part of the body, so the complexion withers and the hair starts to turn white.
Now not only the Yang Ming but also the Tai Yang and Shao Yang channels are deteriorating.
At the age of seven times seven, or forty-nine, the Ren Mai is deficient, the Chong Mai dwindles, Tian Gui stops, the body starts to weaken, and fertility comes to an end.
When a male reaches the age of eight, Kidney Qi is becomes firm, the hair grows long and the infant teeth are replaced by adult teeth.
At the age of two times eight, or sixteen, Kidney Qi and reproductive Essence are full and ready to discharge: Tian Gui has arrived. At this point, if the male and the female unite, they can produce a child.
At the age of three times eight, or twenty-four, Kidney Qi is calm and even, the sinews and bones are strong; therefore, the wisdom teeth come in and the hair grows long.
At the age of four times eight, or thirty-two, muscles, sinews, and bones are fully developed and at their strongest.
At the age of five times eight, or forty, Kidney Qi starts to weaken, the hair starts to fall, and the teeth weaken.
Men are Yang creatures, and so are naturally deficient in the Yin. Decay, therefore, shows in the Yin, i.e., Kidney Qi, first.
At the age of six times eight, or forty-eight, the Yang Qi weakens at the top part of the body so the complexion starts to wither and the hairs turn white.
At the age of seven times eight, or fifty-six, Liver Qi weakens, so the sinews become stiff.
Liver governs sinews and is dependent on the Kidney.
At the age of eight times eight, or sixty-four, reproductive Essence dwindles, the Kidneys and the body as a whole become weak, teeth and hair fall out, and Tian Gui comes to an end. The Kidneys govern Water but they depend on receiving the Essence of the Five Zang and the Six Fu Organs to store Water. So when the Organs are flourishing, Kidney Essence is full and it can discharge. Now that all the Organs are weak, bones and sinews slack and droop, so Tian Gui ends, the hair turns white, the body feels heavy, and even the gait is unsteady; it is no longer possible to produce offspring.
Proper Kidney functioning depends on the nourishment from the other organs. This paragraph reinforces the interdependence between the Kidneys and the other organs, and also between pre-heaven and the post-heaven Qi. The clinical significance is that the ‘tonify the Kidney’ school notwithstanding, it is important to support the healthy functioning of the other organs in order to strengthen the kidneys.
Huangdi then asks:
Then how come sometimes a child can be conceived in spite of old age?
Qi Bo: These are rare cases in which the parent is blessed with exceptionally strong pre-heaven Kidney Qi, so Qi, Blood, and the channels still flow unimpeded in spite of age. Normally a man cannot produce a child past the age of eight times eight and a woman cannot produce a child past the age of seven times seven because both pre-heaven and post-heaven Qi and Essence would be exhausted.
Huangdi: And the ones who are most accomplished in nourishing life in accordance with nature, when they are close to a hundred years of age, can they still produce a child?
Qi Bo: Yes, for these accomplished ones, even as they age they maintain their full form and functioning so they can still produce a child.
Understand this to mean that with proper practice in living and nourishing life in accordance with nature, a person can indeed stay healthy, strong, and vital, and live to an old age.