The combined birth control pill uses synthetic hormones akin to the female sex hormones estrogen and progesterone. The chemicals manipulate the ovulation cycle, as well as the uterine lining and the cervical mucus, to ensure that fertilization does not occur. They are 99% effective as a birth control method, when used correctly.
Three Primary Types of Combined Pills
The dosage of the estrogen and progestin in various pills differs. Based on the contents of the pill, they may be classified into three primary types.
- Monophasic: These pills contain the same amount of estrogen and progestin all through the cycle. They are consumed for 21 days followed by a break of 7 days when no pills are taken. This allows the woman to have a monthly period.
- Biphasic: These have the same content of estrogen all through the cycle of 21 days. What varies is the amount of progestin. The first half of the cycle has a lower amount of progestin to allow the endometrium to thicken. This is the innermost layer of the uterus which naturally thickens during menstruation. The second half of the cycle uses a higher level of progestin so that endometrial ripening can take place.
- Triphasic: These pills have either constant or changing estrogen throughout the cycle, while the progestin varies all through the cycle. This means that the dosage must be taken accurately each day for the birth control pills to work effectively as contraceptives.
Of the three different types of combined pills, there is no evidence to prove that any one is more effective than the others. While clinical studies put the efficacy of the combined birth control pills at 99%, in real life studies it has been found to be 91% effective. That means out of 100 women who used birth control pills as a contraceptive measure for a year, 9 became pregnant.
Conventional Combined Pills
The most popular birth control pills pack has 21 active and 7 inactive pills. This means that 21 pills have different amounts of hormones in them depending on the day they are supposed to be taken on, while the remaining 7 are placebos or place holders. The pills are supposed to be consumed each day at the same time. When a pack of 28 pills is consumed, a new pack is begun right away.
The conventional pack of combined birth control pills allows menstruation to occur each month. This typically coincides with the last four to seven inactive pills taken at the end of the cycle. It is possible to use pill packs with just 21 pills where no inactive pills are present. However, to rule out a mistake in restarting the next pack after the 7-day gap, most women prefer the pack with 28 pills.
Extended Cycle Birth Control Pills
These continuous dosing pills come with 84 active pills and 7 inactive ones in the pack. The cycle here only allows four menstruation periods in the year. There is a variant where 365-day pill packs are also available. In this case menstruation stops completely for some women, while it becomes much lighter and more infrequent for others.
This extended cycle for birth control pills is used when a woman suffers from excessive bleeding due to fibroids in the uterus, or as a preventive measure against menstrual migraine, seizures and asthma. It can be used to give pain relief for endometriosis. A doctor must be consulted before the woman begins using extended cycle pills.
Missed a Pill?
No matter how diligent the woman is, there may be occasions where she is unable to consume a birth control pill at the allotted time in the day. This is considered having a late pill. The woman may not have a pill for 24 hours, and this would be considered missing a pill. There may also be a delay in starting the next pack if the woman does not calculate the 7-day gap accurately.
Needless to say, inadequate dosage will result in the possibility of an unwanted pregnancy. The chances of getting pregnant will depend on the time during the ovulation cycle when the pill was missed, as well as the number of pills that were missed. Contraceptive cover is present when only a single pill is missed or the next pack is started only a day or two late.
If the woman has missed more than two consecutive pills or starts the next pack more than 48 hours late, there is a distinct possibility of contraceptive failure. It would be advisable to continue the birth control pills, but add another temporary contraception method such as condoms for the next 7 days, while the ovulation cycle and combined pills reach a steady state.
The general consensus is that you must take the last pill you missed even if it means taking two pills in a day. Leave any earlier missed pills in the pack and continue with the present day’s dosage onwards. Seek medical advice as soon as possible if you have had sexual intercourse in the 7-day period prior to missing the pill.
Reviewed by Liji Thomas, MD