SB 3.31.5

mātur jagdhānna-pānādyair
 edhad-dhātur asammate
śete viṇ-mūtrayor garte
 sa jantur jantu-sambhave
Synonyms: 
mātuḥ — of the mother; jagdha — taken; anna-pāna — by the food and drink; ādyaiḥ — and so on; edhat — increasing; dhātuḥ — the ingredients of his body; asammate — abominable; śete — remains; viṭ-mūtrayoḥ — of stools and urine; garte — in a hollow; saḥ — that; jantuḥ — fetus; jantu — of worms; sambhave — the breeding place.
Translation: 
Deriving its nutrition from the food and drink taken by the mother, the fetus grows and remains in that abominable residence of stools and urine, which is the breeding place of all kinds of worms.
Purport: 

In the Mārkaṇḍeya Purāṇa it is said that in the intestine of the mother the umbilical cord, which is known as āpyāyanī, joins the mother to the abdomen of the child, and through this passage the child within the womb accepts the mother’s assimilated foodstuff. In this way the child is fed by the mother’s intestine within the womb and grows from day to day. The statement of the Mārkaṇḍeya Purāṇa about the child’s situation within the womb is exactly corroborated by modern medical science, and thus the authority of the Purāṇas cannot be disproved, as is sometimes attempted by the Māyāvādī philosophers.

Since the child depends completely on the assimilated foodstuff of the mother, during pregnancy there are restrictions on the food taken by the mother. Too much salt, chili, onion and similar food is forbidden for the pregnant mother because the child’s body is too delicate and new for him to tolerate such pungent food. Restrictions and precautions to be taken by the pregnant mother, as enunciated in the smṛti scriptures of Vedic literature, are very useful. We can understand from the Vedic literature how much care is taken to beget a nice child in society. The garbhādhāna ceremony before sexual intercourse was compulsory for persons in the higher grades of society, and it is very scientific. Other processes recommended in the Vedic literature during pregnancy are also very important. To take care of the child is the primary duty of the parents because if such care is taken, society will be filled with good population to maintain the peace and prosperity of the society, country and human race.