4.精血先后分男女, 或以奇偶少多分, 或以子宫左右定, 是皆不晓
个中因, 欲识此中真消息, 干道阳男坤女阴.
【注】分男女之说, 先贤有以血先至, 裹精则成男; 精先至, 裹血则
成女. 精血散分并裹则为骈胎, 品胎之原者, 有以月水尽后一, 三,
五日成男, 二, 四, 六日成女. 与夫经水断后一, 二日成男, 四, 五
日成女者; 有以受气于左子宫成男, 受气于右子宫成女者, 皆各执一
见,殊为不晓此中因也. 盖独男独女之胎, 可以日数论. 骈胎, 品胎
,或男, 或女, 亦可以日数论乎? 稽之史载, 一产三子, 四子, 有半
男半女, 或男多女少, 男少女多者, 则一, 三, 五日为男, 二, 四,
六日为女之说, 不可凭矣! 抑岂有一日受男, 而二日复受女之理乎?
丹田, 命门也, 在男子曰精室, 在女子曰子宫, 形如合钵, 并无两岐
可分, 曰左右, 则是有两子宫矣. 此说尤属不经. 然则何以定之? 亦
惟以会合天人, 阳盛干道成男, 阴盛坤道成女, 斯足为确论耳.
5.古以双胎精气盛, 不成男女或兼形, 阴阳变常驳气盛, 事之所有
理难明.
【注】古以双胎, 乃精气有余, 岐而分之, 血因分而摄之故也. 若男
同孕者, 刚日阳时也; 女同孕者, 柔日阴时也; 男女同孕者, 刚日阴
时,或柔日阳时也. 其他或有不成男女, 男不可为父, 女不可为母,
与男女之兼形者, 又皆阴阳变常, 驳气所感, 事之所有, 理之所无,
莫可稽考者也.
4. 关于胎儿性别的决定，有人认为是由精与血到达的先后顺序决定的，也有人通过奇数偶数或天数多少来区分，还有人依据受精卵着床于子宫左侧还是右侧来判断。这些观点都不了解其中的真正原因。想要认识其中的真理，关键在于：阳气主导（干道）则生男，阴气主导（坤道）则生女。
【注】关于胎儿性别形成的说法，先贤中有认为血液先到达，包裹精子则形成男性；精子先到达，包裹血液则形成女性。精气和血液分散并同时被包裹则形成双胞胎或多胞胎。关于多胞胎的起源，有人认为在月经结束后第一天、第三天、第五天受孕生男孩，第二天、第四天、第六天受孕生女孩。还有人说月经结束后第一天、第二天受孕生男孩，第四天、第五天受孕生女孩。也有人说在左子宫受孕生男孩，在右子宫受孕生女孩。这些都各执己见，非常不了解其中的机理。大概单胎妊娠，可以根据天数来论述。但双胎或多胎，或者是男孩，或者是女孩，难道也能用天数来论述吗？查阅历史记载，一次分娩有三个孩子、四个孩子的，有半男半女，或者男多女少、男少女多的情况，那么“一、三、五日为男，二、四、六日为女”的说法就不可靠了！况且，哪有第一天受胎生男，第二天又受胎生女的道理呢？丹田就是命门，在男子称为精室，在女子称为子宫，形状像合起来的钵，并没有分成两半，如果说左右，那就意味着有两个子宫了。这种说法更是荒谬不经。那么究竟如何确定呢？也只在于顺应天人合一的道理，阳气旺盛遵循天道则生男，阴气旺盛遵循地道则生女，这才足以作为确切的结论。
5. 古人认为双胎是因为精气旺盛，分裂而成，不一定分男女，或者兼有畸形。这是阴阳变化失常、驳杂之气旺盛所致，是事情中确实存在的，但其道理难以阐明。
【注】古人认为双胎，是由于精气有余，分歧而分开，血液随之分别摄取滋养的缘故。如果是两个男孩同时孕育，是在刚日阳时受孕；两个女孩同时孕育，是在柔日阴时受孕；一男一女同时孕育，是在刚日阴时或柔日阳时受孕。其他有的不能成为正常的男女，男的不能作为父亲，女的不能作为母亲，以及男女生殖器兼有的情况，又都是阴阳变化失常，受到驳杂之气感应所致，虽然是实际存在的事情，但在常理中找不到依据，无法考证。
4. Regarding the determination of fetal sex, some argue it is based on the sequence of arrival between essence (Jing) and blood; others distinguish by odd or even numbers or the quantity of days; still others determine it by whether conception occurs in the left or right uterus. All these views fail to understand the underlying cause. To truly grasp this mechanism, one must recognize that when the Yang pathway (Gan Dao) prevails, a male is born; when the Yin pathway (Kun Dao) prevails, a female is born.
[Note] Regarding theories of fetal sex determination, ancient sages held that if blood arrives first and envelops the essence, a male is formed; if essence arrives first and envelops the blood, a female is formed. If essence and blood disperse and are simultaneously enveloped, twins or multiple fetuses result. Concerning the origin of multiple pregnancies, some claim that conception on the 1st, 3rd, or 5th day after menstruation ends yields a male, while the 2nd, 4th, or 6th day yields a female. Others suggest conception on the 1st or 2nd day yields a male, and on the 4th or 5th day yields a female. Still others assert that conception in the left uterus produces a male, and in the right uterus produces a female. These views are all subjective and demonstrate a profound ignorance of the true causes. Generally, single pregnancies can be analyzed by days. However, for twins or multiples, which may be male, female, or mixed, can they really be determined by days? Historical records show cases of triplets, quadruplets, half-male/half-female, or varying ratios of males and females. Thus, the theory that "odd days yield males, even days yield females" cannot be relied upon. Moreover, how could there be a logic where a male is conceived on the first day and a female on the second? The Dantian is the Mingmen (Gate of Life). In men, it is called the Jing Shi (Essence Chamber); in women, it is the Zi Gong (Uterus). Its shape is like a joined bowl, with no division into two parts. To speak of "left and right" implies the existence of two uteri, which is an absurd notion. So, how then is it determined? It lies solely in harmonizing Heaven and Humanity: when Yang Qi is abundant and follows the Heavenly Way, a male is born; when Yin Qi is abundant and follows the Earthly Way, a female is born. This suffices as a definitive conclusion.
5. Ancient texts state that twins arise from abundant essence and Qi, splitting apart, potentially resulting in undefined sexes or combined forms. This is due to abnormal changes in Yin and Yang and the prevalence of mixed/impure Qi. Such events occur in reality, but their principles are difficult to elucidate.
[Note] Ancients believed that twins result from excess essence and Qi, which divide, with blood subsequently nourishing both. If two males are conceived together, it occurs during "Gang Ri" (Yang days/times); if two females are conceived together, it occurs during "Rou Ri" (Yin days/times); if a male and female are conceived together, it occurs during a Yang time on a Yin day or a Yin time on a Yang day. Other cases may involve individuals who cannot function as fathers or mothers, or those with combined sexual characteristics. These are caused by abnormalities in Yin and Yang and influences from mixed Qi. While such phenomena exist in practice, they lack basis in standard theory and cannot be verified through conventional examination.