SB 6.9.9

śaśvat-kāma-vareṇāṁhas
 turīyaṁ jagṛhuḥ striyaḥ
rajo-rūpeṇa tāsv aṁho
 māsi māsi pradṛśyate
Synonyms: 
śaśvat — perpetual; kāma — of sexual desire; vareṇa — because of the benediction; aṁhaḥ — the sinful reaction for killing a brāhmaṇa; turīyam — one fourth; jagṛhuḥ — accepted; striyaḥ — women; rajaḥ-rūpeṇa — in the form of the menstrual period; tāsu — in them; aṁhaḥ — the sinful reaction; māsi māsi — every month; pradṛśyate — is visible.
Translation: 
In return for Lord Indra’s benediction that they would be able to enjoy lusty desires continuously, even during pregnancy for as long as sex is not injurious to the embryo, women accepted one fourth of the sinful reactions. As a result of those reactions, women manifest the signs of menstruation every month.
Purport: 

Women as a class are very lusty, and apparently their continuous lusty desires are never satisfied. In return for Lord Indra’s benediction that there would be no cessation to their lusty desires, women accepted one fourth of the sinful reactions for killing a brāhmaṇa.