Birth control comes with a weight limit

The average American woman weighs 166 pounds. New data suggests that the Plan B morning-after pill is less effective if you weigh more that 165 pounds, and won't work at all for women who weigh more than 175. What's more, writes Kate Clancy (an anthropologist who studies women's reproductive issues), the dosages for regular old daily birth control are set for average-to-low-weight women. If your BMI is over 25, the pill won't work as well for you.

Popular Science answers your TMI questions

Fun fact you might not be aware of if you are not the owner of a uterus: Periods go hand-in-hand with pooping. Not every person who gets a period will end up with diarrhea, but it's not uncommon because the same hormone that makes a uterus contract (a necessary step in the whole period process) can also end up making your intestines contract. Francie Diep explains this effect — as well as the other hormone-related reason why periods and poops can be linked.

Boob-enhanced armor would have been deadly

Here's a nice analysis of why, were you actually a female warrior of olden times, you would not have wanted to wear a breastplate that showed off your breasts. Shorter version: Room for boobs is good. But outlining each boob in steel could get you killed.

When your heart was just a tube

I've been linking Double X Science a lot lately. That's because they're great. It's rare to get such smart, fascinating, science-centered discussion about female anatomy and reproductive issues that goes beyond the surface dressing we all already kind of know. Case in point: This piece by Emily Willingham about the development of the human heart in utero. You've probably heard at one point or another that a fetus' heart starts beating around 6 weeks (an age which is, by the way, calculated from the date of the mother's last period, NOT from the date of actual conception; so the fetus itself is really only about 4 weeks old at this point, and its mother only missed her period two weeks ago). But what's the heart actually like at that point? Turns out, absolutely nothing like what you imagine. Very cool stuff.

Birth control recall

Failing to prevent pregnancy is a pretty big failure for a birth control pill. Pfizer is trying to avoid that outcome by recalling 1 million packets of potentially defective pills. What's the problem? Every packet contains 3 week's worth of birth control pills and a week's worth of sugar pills—basically to keep you in the habit of taking a pill every day even during your period week. Some of the defective packs don't contain enough sugar pills. That's not really a problem. In others, however, the actual birth control pills have been swapped for extra sugar pills. That's what Pfizer is worried about. The recall includes Pfizer Lo/Ovral-28 tablets and Akrimax Pharmaceuticals brand Norgestrel and Ethinyl Estradiol tablets.

How does biology explain the low numbers of women in computer science?

View more presentations from Terri Oda

A great look at math, and real vs. imaginary Bell curve distributions. Thanks to Gideon for bringing this to my attention!

The case against synchronized periods

Myths about menstrual cycles are a great example of why carefully collected data is important. Without that, it's extremely easy to see a pattern where none exists. For instance, there's no good evidence that menstrual cycles have anything to do with cycles of the Moon.

The evidence is also against there being such a thing as ladies synchronizing their menstrual cycles. I know. I know. It totally happened to you in college. I thought it happened to me, too. And there are few scientists who think the phenomenon is real. But the preponderance of evidence seems to be against them. Again (and this cannot be said enough) humans are really good at spotting patterns—even when patterns don't exist.

Kate Clancy, an anthropologist who studies the evolutionary medicine of women’s reproductive physiology, has a post on Scientific American blogs looking at the research that's poked holes in the synchronized periods hypothesis. A couple of the studies she talks about came out this year.

Maybe we should look to our primate relatives for evidence, then: in fact two papers have come out this year testing this hypothesis in primates! Setchell et al (2011) observed semi free-living mandrills, which is a kind of Old World monkey, a group to which the Great Apes belong. Out of ten observation-years of data, they found a single year that had significant synchrony… only to have that one year fail to be significant once they corrected for multiple testing. Multiple testing corrections are important because of the chance that if you test a hypothesis enough times you will get a spurious significant result (and for a brilliant take on this, see this xkcd comic).

The other equally interesting paper to come out this year on this topic is by Fürtbauer et al (2011), entitled “You Mate, I Mate: Macaque Females Synchronize Sex Not Cycles.” Their study population was wild Assamese macaques, also Old World monkeys. Fürtbauer et al (2011) observed behavioral receptivity and measured fecal ovarian hormones (yes, that means they measured hormones in poop) in order to assess behavioral and hormonal synchrony. They found long periods of behavioral receptivity that synchronized well across individuals, but that actual estrus cycles were randomly distributed within the receptive period. I thought this paper did a great job at providing an evolutionary framework for why mating might evolve to be synchronized, but not cycles, and because the paper was published in PLoS ONE, you can read it yourself for free.

This paper resolves a question I’ve had for a long time about menstrual synchrony, which is how in the world it could actually be beneficial to females, particularly those with covert ovulation. Why would you want all the females, or even a subset of them, to be fecund and receptive at the same time? And the answer is, you probably wouldn’t. Humans, other primates, even some cetaceans like dolphins have mating that is largely decoupled from reproductive cycling. That is, we don’t only mate at the time in our cycle when our chances are highest to conceive, though we might find ourselves slightly more proceptive or receptive at that time. Sex is not just about making babies, but is an affiliative behavior, promoting bonding but also plain old enjoyment. Instead, it may in some circumstances make sense to have extended periods of synchronous receptivity, as within a promiscuous species like the Assamese macaques (Fürtbauer et al. 2011). But this isn’t necessarily an adaptive feature of the entire primate lineage.

Image: A group of women from ILGWU Local 62 indicate their choice for president by pointing to a picture of Franklin Delano Roosevelt., a Creative Commons Attribution (2.0) image from kheelcenter's photostream

How To: Use vinegar to diagnose cervical cancer

In developing countries, a new, inexpensive treatment allows nurses to spot pre-cancerous lesions on a woman's cervix and remove them—without needing a medical lab, and without surgery. It has huge implications for women's health, because cervical cancer kills 250,000 women every year.

In fact, before pap smears became commonplace, cervical cancer killed more American women than any other sort of cancer. But in places where the pap smear isn't practical, this new technique can help. From the New York Times:

Nurses using the new procedure, developed by experts at the Johns Hopkins medical school in the 1990s and endorsed last year by the World Health Organization, brush vinegar on a woman’s cervix. It makes precancerous spots turn white. They can then be immediately frozen off with a metal probe cooled by a tank of carbon dioxide, available from any Coca-Cola bottling plant.

... Dr. Bandit Chumworathayi, a gynecologist at Khon Kaen University who helped run the first Thai study of VIA/cryo, explains that vinegar highlights the tumors because they have more DNA, and thus more protein and less water, than other tissue.

It reveals pre-tumors with more accuracy than a typical Pap smear. But it also has more false positives — spots that turn pale but are not malignant. As a result, some women get unnecessary cryotherapy. But freezing is about 90 percent effective, and the main side effect is a burning sensation that fades in a day or two. By contrast, biopsies, the old method, can cause bleeding.

Via Robyn Lloyd

10 under-appreciated women in science

Over at Smithsonian.com, Sarah Zielinski has a great piece about important female scientists whose names aren't as publicly well-known as they ought to be. She lists 10 smart, sciencey ladies. Here's my favorite:

Barbara McClintock (1902 – 1992)

While studying botany at Cornell University in the 1920s, Barbara McClintock got her first taste of genetics and was hooked. As she earned her undergraduate and graduate degrees and moved into postdoctoral work, she pioneered the study of genetics of maize (corn) cells. She pursued her research at universities in California, Missouri and Germany before finding a permanent home at Cold Spring Harbor in New York. It was there that, after observing the patterns of coloration of maize kernels over generations of plants, she determined that genes could move within and between chromosomes. The finding didn’t fit in with conventional thinking on genetics, however, and was largely ignored; McClintock began studying the origins of maize in South America. But after improved molecular techniques that became available in the 1970s and early 1980s confirmed her theory and these “jumping genes” were found in microorganisms, insects and even humans, McClintock was awarded a Lasker Prize in 1981 and Nobel Prize in 1983.

IUDs may offer cancer protection

Really interesting new study of 20,000 women suggests that the use of IUDs might reduce the risk of both major types of cervical cancer, even in women who contracted cancer-causing HPV. The researchers speculate that the IUD's presence—it is, after all, a foreign object in your lady bits—may serve to stimulate immune responses that fight off HPV infection early and prevent it from progressing to cancer. This needs follow up. But it's intriguing. (Via Colleen McCaffery)