精，精成其骨，此万物之资始于干元也。血则外护而成胞，精则内实而化育，此万物之
资生于坤元也。阴阳交媾，胚胎始凝，胎所居名曰子宫，一系在下，上有两口，一达于
左，一达于右，精胜其血，则阳为之主，受气于左子宫而男形成，精不胜血，则阴为之
主，受气于右子宫，而女形成，孕成而始化胎也。（此成胎以子宫之左右分男女也。）
马玄台曰∶男子先天之气，方父母媾精时，阴气不胜其阳则成男。凡书谓阴血先至
阳精后冲，纵气来乘，血开裹精，阴外阳内则成男，其义亦渺，大约阴气不胜其阳，则
为男也。女子先天之气，方父母媾精时，阳气不胜其阴则为女。凡书所谓，阳精先入，
阴血后参，横气来助，精开裹血，阴内阳外则成女，其义亦渺，大约阳气不胜其阴则为
女也。（此成胎以父母先天之阴阳相胜分男女也。）
程鸣谦曰∶信褚氏之言，则人有精先泄而生男，精后泄而生女者，何与？信东垣之
言，则有经始断，交合生女，经久断，交合生男，亦有四五日以前交合无孕，八九日以
Jing (Essence), which forms the basis of bone, marks the beginning of all things relying on the "Qianyuan" (Primordial Origin of Heaven/Yang). Blood provides external protection and constitutes the Bao Gong (Uterus/Womb), while Jing fills the interior to facilitate transformation and gestation; this is how all things rely on the "Kunyuan" (Primordial Origin of Earth/Yin) for growth. When Yin and Yang interact, the embryo begins to condense. The place where the fetus resides is called the Zi Gong (Uterus); it has a ligament connecting at the bottom and two openings at the top, one leading to the left and one to the right. If Jing overcomes Blood, Yang becomes dominant; conception occurs in the left Zi Gong, resulting in the formation of male characteristics. If Jing does not overcome Blood, Yin becomes dominant; conception occurs in the right Zi Gong, resulting in the formation of female characteristics. Only after pregnancy is established does the differentiation of the fetus begin. (This theory distinguishes sex based on the left or right side of the Zi Gong.)
Ma Xuantai stated: The congenital Qi of males, at the moment of parental intercourse and conception, forms as a boy when Yin Qi fails to overcome Yang Qi. All texts state that if Yin Blood arrives first and Yang Jing rushes in subsequently, accompanied by Zong Qi (Direct Qi), the Blood opens to envelop the Jing, with Yin outside and Yang inside, thus forming a male. This reasoning is also obscure; generally, it is because Yin Qi fails to overcome Yang Qi that a male is formed. The congenital Qi of females, at the moment of parental intercourse and conception, forms as a girl when Yang Qi fails to overcome Yin Qi. All texts state that if Yang Jing enters first and Yin Blood follows, assisted by Heng Qi (Horizontal Qi), the Jing opens to envelop the Blood, with Yin inside and Yang outside, thus forming a female. This reasoning is also obscure; generally, it is because Yang Qi fails to overcome Yin Qi that a female is formed. (This theory distinguishes sex based on the mutual overcoming of the parents' congenital Yin and Yang.)
Cheng Mingqian said: If one believes in Chu Shi's words, then why are there cases where emitting Jing first results in a boy and emitting Jing later results in a girl? If one believes in Dongyuan's (Li Dongyuan) words, then why does intercourse immediately after menstruation ceases result in a girl, while intercourse after menstruation has ceased for a long time results in a boy? There are also cases where intercourse before the fourth or fifth day yields no pregnancy, but from the eighth or ninth day...