Visuddhimagga XVI-37

 540. Tatridaṃ gabbhokkantimūlakādibhedaṃ dukkhaṃ – ayaṃ hi satto mātukucchimhi nibbattamāno na uppalapadumapuṇḍarīkādīsu nibbattati, atha kho heṭṭhā āmāsayassa upari pakkāsayassa udarapaṭalapiṭṭhikaṇṭakānaṃ vemajjhe paramasambādhe tibbandhakārenānākuṇapagandhaparibhāvitaparamaduggandhapavanavicarite adhimattajegucche kucchipadese pūtimacchapūtikummāsacandanikādīsu kimi viya nibbattati. So tattha nibbatto dasa māse mātukucchisambhavena usmanā puṭapākaṃ viya paccamāno piṭṭhapiṇḍi viya sediyamāno samiñjanapasāraṇādirahito adhimattaṃ dukkhamanubhotīti, idaṃ tāva gabbhokkantimūlakaṃ dukkhaṃ.

此中，（一）由于入胎等类的苦：有情生时，不是生于青莲、红莲、白莲之中，但是生于母胎中，在生脏（胃）之下，熟脏（直肠）之上、粘膜和脊椎的中间、极其狭窄黑暗、充满着种种的臭气、最恶臭而极厌恶的地方，正如生在腐鱼、烂乳、污池等之中的蛆虫相似。他生于那样的地方，十个月中，备尝种种苦，肢体不能自由屈伸，由于母胎发生的热，他好像是被煮的一袋菜及被蒸的一团麦饼。这是说由于入胎之苦。

Ñ(XVI,37): Here the suffering classed as 'rooted in the descent into the womb', and so on, is this: When this being is born in the mother's womb, he is not born inside a blue or red or white lotus, etc., but on the contrary, like a worm in rotting fish, rotting dough, cess-pools, etc., he is born in the belly in a position that is below the receptacle for undigested food (stomach), above the receptacle for digested food (rectum), between the belly-lining and the backbone, which is very cramped, quite dark, pervaded by very fetid draughts redolent of various smells of ordure, and exceptionally loathsome. And on being reborn there, for ten months he undergoes excessive suffering, being cooked like a pudding in a bag by the heat produced in the mother's womb, and steamed like a dumpling of dough, with no bending, stretching, and so on. So this, firstly, is the suffering rooted in the descent into the womb.