The forgotten pill--and the paramount importance of the pill-free week.
Omissions in the taking of contraceptive pills appear to be of the greatest concern when they lead to a lengthening of the pill-free interval (PFI). The time of pregnancy risk is at the end of lengthened PFI, but the causaton of the lengthening can either be by delay in restarting a new packet or by omissions at the end of the previous packet if these are nevertheless followed by the usual 7-day break. It is clear that the PFI potentially impairs the efficacy of the pill, and it can also be associated with side effects such as withdrawal headaches. On the other hand, there are proven and probable benefits: regular reassurance of a withdrawal bleed; a lesser total quantity of artificial steroids ingested per year; and a tendency for certain metabolic variables to return to normal by the end of the PFI, implying important benefits to health, and possibly to reversibility, by a monthly rest from the pill's systemic actions. It is preferable to shorten the PFI, usually to 4 days, in women where there is a suspicion of increased risk of breakthrough ovulation.