Better Health: Smart Health Commentary Better Health (TM): smart health commentary

Article Comments

Hormonal Contraception And An Under-Appreciated Effect

Ask any third-year medical student how hormonal contraception prevents pregnancy, and they’ll probably tell you it prevents ovulation. What they won’t tell you is that this effect is variable and dose-dependent, and if we depended on it alone, hormonal contraception would be much less effective.

That’s because of the very important, and in my opinion, much under-appreciated effect of hormonal contraception on cervical mucus.

A Cervical Mucus Primer

Fertile cervical mucus – which forms under the influence of rising estrogen levels in the first half of the menstrual cycle and is maximal around ovulation –- is thin, watery, clear and easy for sperm to traverse.

Non-fertile mucus which forms after ovulation and also in pregnancy under the influence of progesterone –- is the exact opposite: Thick,tacky, non-distensible and impossible for sperm to penetrate. (It’s not called the mucus plug for nothing.)

A Progestin Effect

Cervical mucus during hormonal contraceptive use mimics that of the second half of the menstrual cycle –- scant, thick and impenetrable.

The responsible party here is progestin –- molecules with names like levonorgestrel, medroxyprogesterone, norethindrone, norgestimate and desogestrel –- which mimic the natural effect of progesterone on cervical mucus. Even in birth control pills that contain estrogen, this progestin effect dominates at the cervix.

This effect on cervical mucus explains why the progestin-only pill, Norplant and Implanon work so well to prevent pregnancy, even though ovulation can still occur during use of these methods.

Mirena IUD Thickens Cervical Mucus

Now, a new study shows that the Mirena IUD also thickens cervical mucus and prevents sperm penetration.

This is not surprising, since Mirena contains the progestin levonorgestrel. But it is important information about how this method works to prevent pregnancy –- in addition to impairing ovulation and fertilization, Mirena also prevents sperm from getting into the fallopian tube in the first place. One could argue that in fact, if sperm and egg never meet, the other contraceptive mechanisms of this IUD become unimportant, making the Mirena really mostly a local delivery system for progestin.

This effect on cervical mucus also may explain why users of the Mirena IUD have low rates of pelvic infection, a side effect that doomed the Dalkon Shield. (Of course, the Dalkon Shield also had a multifilament string that allowed bacteria to enter the uterus. Modern IUDs have monofilament strings.)

Could We Thicken Mucus Without Hormones?

I think a lot about this contraceptive effect of progestins, wondering if we could find a way to thicken cervical mucus locally without systemic hormonal exposure. The Mirena comes as close to a local effect as we have to date, although its progestin is still systemically absorbed and has body-wide effects.

But if we could develop a locally applied non-hormonal product that does the same thing, wouldn’t that be a great contraceptive option?

*This blog post was originally published at tbtam*


You may also like these posts

Read comments »


Comments are closed.

Return to article »

Latest Interviews

IDEA Labs: Medical Students Take The Lead In Healthcare Innovation

It’s no secret that doctors are disappointed with the way that the U.S. healthcare system is evolving. Most feel helpless about improving their work conditions or solving technical problems in patient care. Fortunately one young medical student was undeterred by the mountain of disappointment carried by his senior clinician mentors…

Read more »

How To Be A Successful Patient: Young Doctors Offer Some Advice

I am proud to be a part of the American Resident Project an initiative that promotes the writing of medical students residents and new physicians as they explore ideas for transforming American health care delivery. I recently had the opportunity to interview three of the writing fellows about how to…

Read more »

See all interviews »

Latest Cartoon

See all cartoons »

Latest Book Reviews

Book Review: Is Empathy Learned By Faking It Till It’s Real?

I m often asked to do book reviews on my blog and I rarely agree to them. This is because it takes me a long time to read a book and then if I don t enjoy it I figure the author would rather me remain silent than publish my…

Read more »

The Spirit Of The Place: Samuel Shem’s New Book May Depress You

When I was in medical school I read Samuel Shem s House Of God as a right of passage. At the time I found it to be a cynical yet eerily accurate portrayal of the underbelly of academic medicine. I gained comfort from its gallows humor and it made me…

Read more »

Eat To Save Your Life: Another Half-True Diet Book

I am hesitant to review diet books because they are so often a tangled mess of fact and fiction. Teasing out their truth from falsehood is about as exhausting as delousing a long-haired elementary school student. However after being approached by the authors’ PR agency with the promise of a…

Read more »

See all book reviews »