王宇泰曰∶种子之道有四，一曰择地，地者，母血是也；二曰养种，种者，父精是也；三曰乘时，时者，精
血交感之会是也；四曰投虚，虚者，去旧生新之初是也。
袁了凡曰∶天地生物，必有 之时，万物化生，必有乐育之候。猫犬至微，将受娠也，其雌必狂呼而奔
跳，以 乐育之气触之，不能自止耳。此天然之节候，生化之真机也。凡妇人一月经行一度，必有一日
之候，于一时辰间，气蒸而热，昏而闷，有欲交接不可忍之状，此的候也。此时逆而取之，则成丹；顺而施之，
则成胎矣。
慎斋按∶以上四条，序种子之道，有保养聚精乘时之法也。夫保养聚精乘时之法，在男子之调摄。然亦有
男子尽其法，而终身不育者，其咎不在男子之不得其法，而在女子之必有其故也。故以妇人不孕，序之于后。
《圣济总录》曰∶妇人所以无子，由冲任不足，肾气虚寒故也。《内经》谓∶女子二七天癸至，任脉通，
太冲脉盛，阴阳和，故能有子。若冲任不足，肾气虚寒，不能系胞，故令无子。亦有本于夫病妇 者，当原所
因调之。
缪仲淳曰∶女子系胞于肾及心胞络，皆阴脏也。虚则风寒乘袭子宫，则绝孕无子，非得温暖药，则无以去
风寒而资化育之妙。唯用辛温剂，加引经，至下焦，走肾及心胞，散风寒，暖子宫为要也。
王宇泰说：生育的方法有四项，第一是选择土地，所谓土地，指的是母亲的血液；第二是培育种子，所谓种子，指的是父亲的精液；第三是把握时机，所谓时机，指的是精气与血液交感融合的会合时刻；第四是趁虚而入，所谓虚，指的是去旧生新的初始阶段。
袁了凡说：天地化生万物，必定有特定的时节，万物生长繁衍，必定有适宜乐育的候机。猫狗这类微小的动物，在即将受孕时，雌性必然狂呼乱跳，这是因为受到乐育之气的触动，无法自控罢了。这是天然的节律和生化真机的体现。凡是妇女每月月经来潮一次，必定有一天是受孕期，在一个时辰之间，体内气蒸发热，头昏胸闷，有难以忍受的性交欲望，这就是确切的受孕期（的候）。此时若逆其势而取之（指避孕或阻断），则结成丹石（此处指代某种病理产物或比喻为不成胎）；顺应其势而施之（指行房事），则能成胎。
慎斋按语：以上四条，阐述了生育之道，包含了保养聚精、把握时机的方法。保养聚精、把握时机的方法，关键在于男子的调养摄生。然而也有男子完全掌握了这些方法，却终身不育的情况，这过错不在于男子没有掌握方法，而在于女子必定有其病因。因此将妇人不孕的原因放在后面叙述。
《圣济总录》说：妇女之所以不能生育，是因为冲任二脉不足，肾气虚寒所致。《内经》说：女子十四岁天癸至，任脉通畅，太冲脉旺盛，阴阳调和，所以能够生育。如果冲任不足，肾气虚寒，不能维系胞宫，所以导致不孕。也有源于丈夫有病或妻子有病的，应当探究其原因进行调理。
缪仲淳说：女子的胞宫系属于肾及心包络，这些都是阴脏。如果虚弱，风寒就会乘虚侵袭子宫，从而导致绝孕无子，如果不使用温暖性质的药物，就无法去除风寒并发挥化育的奇妙作用。只有使用辛温的方剂，加入引经药，使药力到达下焦，作用于肾及心包络，以散除风寒、温暖子宫，这才是关键所在。
Wang Yutai stated: There are four principles in the art of conception. The first is selecting the soil; "soil" refers to the mother's blood. The second is nurturing the seed; "seed" refers to the father's essence (Jing). The third is seizing the timing; "timing" refers to the convergence when essence and blood interact and sense each other. The fourth is acting upon emptiness; "emptiness" refers to the initial stage of discarding the old and generating the new.
Yuan Liaofan stated: Heaven and Earth, in creating all things, must have specific seasons; for all things to transform and be born, there must be a favorable period for nurturing. Even in humble creatures like cats and dogs, before conception occurs, the female will cry out wildly and jump about because she is touched by the Qi of joyful nurturing and cannot restrain herself. This is the natural rhythm and the true mechanism of biological transformation. For any woman who menstruates once a month, there is certainly one day of fertile opportunity within a single two-hour period (Shichen), where Qi steams and generates heat, accompanied by dizziness, stuffiness, and an unbearable desire for intercourse. This is the precise fertile window (De Hou). If one acts against this trend to prevent conception, it results in [abnormal formation]; if one acts in accordance with this trend to engage in intercourse, pregnancy will be conceived.
Shen Zhai commented: The above four points outline the principles of conception, including methods for preserving and gathering essence and seizing the right time. The method of preserving essence and seizing the time lies in the regulation and care of the man. However, there are cases where a man fully applies these methods yet remains childless throughout his life. The fault does not lie in the man's failure to apply the methods correctly, but rather that the woman necessarily has an underlying cause. Therefore, the causes of female infertility are discussed subsequently.
The *Shengji Zonglu* states: Women fail to conceive due to insufficiency of the Chong and Ren vessels and deficiency-cold of Kidney Qi. The *Neijing* states: When a girl reaches fourteen years of age, Tian Gui arrives, the Ren vessel becomes unblocked, and the Tai Chong vessel becomes abundant. With Yin and Yang harmonized, she can conceive. If the Chong and Ren vessels are insufficient and Kidney Qi is deficient and cold, it cannot sustain the Bao Palace (uterus), thus causing infertility. There are also cases originating from illness in either the husband or wife, which require investigation of the root cause for treatment.
Miu Zhongchun stated: The Bao Palace in women is connected to the Kidneys and the Pericardium Collaterals, both of which are Yin organs. If they are deficient, Wind-Cold will invade the uterus, leading to sterility. Without warm-natured medicines, one cannot dispel Wind-Cold and facilitate the miraculous process of gestation. It is essential to use acrid-warm formulas, adding guiding herbs to direct the medicinal action to the Lower Jiao, targeting the Kidneys and Pericardium, to disperse Wind-Cold and warm the uterus.