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) forms the bones; this is the foundation of all things, originating from Qianyuan (Heaven/Yang/Father). Blood provides external protection and constitutes the Bao (Uterus), while Jing internally fills and facilitates transformation and reproduction; this is the foundation of all things, born from Kunyuan (Earth/Yin/Mother). When Yin and Yang interact, the embryo begins to coagulate. The place where the fetus resides is called the Zigong (Uterus); it has a ligament connecting downwards at the base, and two openings upwards, one leading to the left and one to the right. If Jing overcomes Blood, Yang becomes dominant, conception occurs in the left Zigong, and the male form is established. If Jing does not overcome Blood, Yin becomes dominant, conception occurs in the right Zigong, and the female form is established. After pregnancy is formed, it begins to transform into a fetus. (This theory distinguishes sex based on the left and right sides of the Zigong.)
Ma Xuantai stated: The innate Qi of males, at the moment of parental intercourse and essence union, results in a male if Yin cannot overcome Yang. All texts state that if Yin blood arrives first and Yang sperm follows, with Zong Qi arriving to assist, the Blood opens to wrap the Sperm, resulting in Yin outside and Yang inside, thus forming a male. The rationale here is subtle, but generally, if Yin cannot overcome Yang, a male is formed. The innate Qi of females, at the moment of parental intercourse and essence union, results in a female if Yang cannot overcome Yin. All texts state that if Yang sperm enters first and Yin blood follows, with Heng Qi assisting, the Sperm opens to wrap the Blood, resulting in Yin inside and Yang outside, thus forming a female. The rationale here is also subtle, but generally, if Yang cannot overcome Yin, a female is formed. (This theory distinguishes sex based on the mutual overcoming of the innate Yin and Yang of the parents.)
Cheng Mingqian said: If one believes Chu’s words, then why do some conceive a boy by ejaculating first and a girl by ejaculating last? If one believes 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 four or five days prior results in no pregnancy, whereas eight or nine days later…