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Mysteries of Birth Control Pills Solved!

birth control pills
August 31, 2009
From the WebMD Archives

While most every birth control pill (BCP) user is familiar with information usually found in BCP package inserts and patient handouts, there are some questions which take a detective to answer. For that purpose I’m putting on my “Nancy Drew, Girl Detective” hat to share with you the answers to the following mysteries of birth control pills:

  • Am I ovulating at mid-cycle when on my BCPs?
  • Am I protected during my week of sugar pills?
  • When will my cycle return?
  • When will I be able to conceive?
  • Which of my lifestyle choices might impact BCP effectiveness?

Midcycle ovulation should not be happening on birth control pills.
One of the most important ways that BCPs protect against unintended pregnancy is by suppressing ovulation. The most commonly used BCPs contain both synthetic estrogen and synthetic progesterone (“progestin”). Both types of hormones work to suppress development of follicles and the dominant follicle which was intended to ovulate. This is why BCPs are sometimes prescribed to help prevent growth of ovarian cysts. In one study (Egarter, 1995) 97% of women on birth control pills did not ovulate at any time in their pill pack. Interestingly, the two women who did have evidence of ovulation did not become pregnant.

By contrast, among women who use the progestin only “mini pill,” only 29% did not ovulate (Tayob, 1986). Remember that the progestin only mini pills have no synthetic estrogen, and their doses of synthetic progesterone are very small. Pregnancy is prevented by other, additional mechanisms such as thicker cervical mucus and thinner lining of the uterus.

You should be protected during the placebo week of sugar or iron containing pills.
The suppression of ovulation described above is based upon the long “half-life” of synthetic estrogen and progestin. The two hormones were designed to last a longer time before being broken down than their “natural” counterparts. This increases contraceptive protection so that missed, or late pills, do not leave an opportunity for accidental pregnancy.

You may have been told, when starting BCPs for the first time, to take the first pill on the first day of your period-rather than waiting until the first Sunday. This is to provide better suppression of ovulation right away. In the “start your new prescription on the first day of your period” regimen, a woman will not need to use a back up method (e.g. condoms). Once the BCPs are started, one simply takes an active or sugar pill every day. They will be protected during the placebo week.

One study of 99 women (Elomaa, 1998) the women were asked to deliberately start their new pill pack three days late. This would create a ten day vacation off the hormones. Ultrasounds of the ovaries and blood hormone levels were taken. While many women showed enlarged follicles in the ovaries, no one actually ovulated. Thus suppression of ovulation may actually extend beyond the recommended seven days of sugar pills. However, as lower doses of synthetic estrogen are used (e.g. 20 micrograms), it becomes more likely that a dominant follicle might actually ovulate (van Huesden, 1999). In summary, to provide the widest protection to the greatest number of women, we still say protection is best when seven days (or less) of placebo pills are used.

Spontaneous periods should resume within 90 days.
Among 187 women using continuous BPCs (Lybrel) for one year, periods resumed most frequently only 32 days after the last BCP was taken. The incidence of spontaneous periods and/or pregnancy was 98.9% within three months of stopping BCPs. In this study (Davis, 2008) the time to return of periods was not related to duration of missed or very light flows while on Lybrel.

Lybrel is a very low dose BCP. If one is using a higher dose BCP the return of periods MIGHT take longer. This is especially true if you had a history of missed or irregular periods before starting to use BCPs – although some women with previously normal periods can have a delay in restarting as well. The incidence of no periods for six months after stopping BCPs (“post Pill amenorrhea“) is probably less than 1%. Also, delay in return of menses does not seem to be linked to length of usage nor brand of BCP (Huggins, 1990)

Generally, if a woman has not resumed natural flows by six months after stopping BCPs it is time to get follow up with a GYN.

Within 12 months of stopping BCPs, conception rates are the same as untreated women.
In women using a very low dose, continuous BCP (Lybrel), the rates of conception were followed after they stopped their Lybrel. It took 57% three months to conceive, 81% twelve months to conceive, and by thirteen months 86% had conceived. (Barnhart, 2009).

This compares favorably to pregnancy rates among the general population where 57% have conceived within three months of trying. By twelve months of unprotected sex 85% of women will have conceived.

Both smoking and drinking can have a theoretical impact on BCPs.
Most women are aware that combining smoking and BCPs can increase the likelihood of blood clots in the arms, legs, lungs, heart (i.e. heart attack) or even the brain (i.e. stroke). But did you know that smoking cigarettes can actually lower blood estrogen levels? Among women smokers using postmenopausal hormone therapy, it may take higher doses of estrogen to get the same effects as seen in non-smokers. (Transavatdi, 2004). Nicotine can decrease blood estrogen levels whether in a BCP user or a condom user. This effect is thought to occur starting at about one pack per day. The concern is, among low dose BCP users, the blood levels of estrogen may not be high enough to suppress ovulation.

Given the known risk of clots in blood vessels, and the theoretical concern about reducing active hormone levels, one should consider quitting smoking if they use BCPs.

In one large study of over 17,000 women, women who consumed the equivalent of 8 oz of wine or 12 oz of beer had higher blood levels of several types of estrogens (Onland-Moret, 2005). None of the women studied were using hormones, but it is presumed that hormone users may show similar effects where alcohol increases estrogen levels.

Another study looked at the effects of using either grapefruit juice or herb tea to take a 50 microgram dose of synthetic estrogen (the type found in BCPs). Grapefruit juice, when used to take the estrogen pill, increased both the levels of estrogen and the duration of its effects. The herb tea did not show this result. It was postulated that the grapefruit juice inhibited the metabolism of the estrogen thus increasing estrogen effects (Weber, 1996).

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