Bg 1.40

adharmabhibhavat Krishna
pradusyanti kula-striyah
strisu dustasu varsneya
jayate varna-sankarah

Word for word: 
adharma — irreligion; abhibhavat — having become predominant; Krishna — O Krishna; pradusyanti — become polluted; kula-striyah — family ladies; strisu — by the womanhood; dustasu — being so polluted; varsneya — O descendant of Vrsni; jayate — comes into being; varna-sankarah — unwanted progeny.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When irreligion is prominent in the family, O Krishna, the women of the family become polluted, and from the degradation of womanhood, O descendant of Vrsni, comes unwanted progeny.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Good population in human society is the basic principle for peace, prosperity and spiritual progress in life. The varnasrama religion’s principles were so designed that the good population would prevail in society for the general spiritual progress of state and community. Such population depends on the chastity and faithfulness of its womanhood. As children are very prone to be misled, women are similarly very prone to degradation. Therefore, both children and women require protection by the elder members of the family. By being engaged in various religious practices, women will not be misled into adultery. According to Canakya Pandita, women are generally not very intelligent and therefore not trustworthy. So the different family traditions of religious activities should always engage them, and thus their chastity and devotion will give birth to a good population eligible for participating in the varnasrama system. On the failure of such varnasrama-dharma, naturally the women become free to act and mix with men, and thus adultery is indulged in at the risk of unwanted population. Irresponsible men also provoke adultery in society, and thus unwanted children flood the human race at the risk of war and pestilence.