Lactational amenorrhea (LAM) doesn’t occur with casual breast-feeding. It requires relatively continuous breast-feeding to create the condition with no supplemental feedings, such as formula or table food, for the infant. How it works is simple—the regular suckling of its mother’s breast by an infant suppresses production of hormones necessary to trigger ovulation. No ovulation, no fertility.
Lactational amenorrhea is so effective that it is a recognized form of natural family planning that is even accepted by many religious groups opposed to contraception. Before you try this method at home, keep in mind that it can and does fail, especially the longer it’s been since delivery. A year after birth, that same WHO study found that pregnancy rates climbed to around 7.5 percent. And there are some strict rules you have to follow in order to have reasonable confidence that it will work.
According to Planned Parenthood, using breast-feeding as birth control can be effective for six months after delivery only if a woman:
Does not substitute other foods for a breast-milk meal
Feeds her baby at least every four hours during the day and every six hours at night
Has not had a period since she delivered her baby
If you’re risk-averse and not opposed to contraception, the best way to keep from getting pregnant without hampering your milk supply (estrogen does that) is to combine LAM with the mini-pill, which is progestin only.
The evolutionary benefit of lactational amenorrhea is pretty straightforward. Providing a newborn with all the energy and nutrition it needs places a considerable strain on the body of a woman who is still recovering from the even more significant physiological stress of pregnancy. Adding a new pregnancy to the mix risks not only her ability to carry the new pregnancy to term, but also her ability to secure the success of the new child she has already invested so much in. Not to mention her own health. Since most newborns have possibly not consumed anything but breast milk for most of human history, humans have been using the lactational amenorrhea method for millions of years, however inadvertently.
THERE’S ANOTHER WAY that nature blocks fertility in human women. It happens at the other end of their development—menopause, which takes its name from the Greek words for month and halt. Menopause is a retrospective diagnosis, a year without menstruation in an older women, at which time her reproductive system ends its active period. Typically, menopause occurs in midlife—the average age in western countries is fifty-one. Why does female fertility shut down in midlife while male fertility continues unabated? Well, for most animals, it doesn’t.
A recent study led by Harvard University postdoctoral student Melissa Emery-Thompson followed six populations of chimpanzees and compiled data about their fertility patterns and compared them to similar data from human hunter-gatherer groups. They found that humans and chimps both entered a period of reproductive decline in their forties—but that period of time coincides with normal chimp life expectancy, while humans live on for decades. In fact, female chimps that do live longer had no trouble reproducing well past forty. “Females in the wild and in captivity have given birth in their 50s, and the oldest living captive female, who is about 69, gave birth past the age of 60,” said Emery-Thompson.
In other words, our primate cousins don’t seem to experience menopause. “Human life history is in fact one of the most radical departures from the apes,” Emery-Thompson explained. “We live longer than expected for our size, we have vastly higher reproductive costs, yet manage to reproduce much faster, we mature very slowly, and we have this peculiar post-reproductive period that distinguishes us from most other mammals.”
So why shut down human fertility midstream? There are lots of theories out there. One is simply that the older a woman is, the harder it is for her body to weather the demands of pregnancy and childbirth. And, since newborns need help to survive, there could be evolutionary pressures against late-life pregnancies that put babies at risk of being orphaned at birth or shortly thereafter.
Another theory is the genetic shelf life of eggs. Men make fresh batches of sperm all the time, but it’s thought that for the most part women are born with most of their eggs already in place. The genetic material in those eggs ages along with the rest of a woman’s body, so some researchers believe menopause may prevent the risk of transmitting genetic errors resulting from aged and damaged eggs. Evidence to support this view can be found in the fact that genetic errors in embryos and fetuses climbs rapidly once a woman passes the age of thirty-five. Take Down syndrome, for example, a congenital condition usually caused by an extra copy or part of chromosome 21. At twenty, a woman’s risk of having a child with Down syndrome is one in two thousand; at forty-nine, it is as high as one in twelve. There is some research that also implicates a father’s age in Down syndrome, although it’s still controversial and doesn’t seem to have anywhere near the same strength as the maternal effect.
Still other researchers think there’s no real mystery. For most of history, they say, life expectancy and the age of menopause were about the same.
And then there’s the grandmother theory, a very interesting idea that’s gaining traction. Essentially, according to this notion, by creating nonchildbearing grandmothers, menopause creates a team of unburdened additional caregivers: without children of their own, they can help their children, especially their daughters, raise the next generation.
A study led by Daryl P. Shanley of Newcastle University in the United Kingdom published in 2007, gives more weight to this theory. Shanley and his colleagues studied birth and death records of more than five thousand people in Gambia between 1950 and 1975 to see if they could find any grandmother effect. And they discovered some pretty powerful evidence: children who lost their mothers before they turned two were twice as likely to survive if their maternal grandmother were still alive. “Our results point clearly towards the maternal grandmother having a key role in the evolution of the menopause,” said Shanley. Adding a little more weight to this theory from the perspective of overall cost and benefit to society, Emery-Thompson notes that grandmothers in hunter-gatherer societies bring in more calories than they eat.
Why maternal grandmothers in particular? Well, there’s the obvious connection: maternal grandmothers were obviously pregnant with their daughters, and their daughters were obviously pregnant with their grandchildren. So they know they’re related to their daughter’s children. Given that men and women can both be unfaithful, and have been so throughout history, before genetic testing the only way to be absolutely certain you were related to somebody was through the maternal line. There’s another way to test paternity-maternity; it’s anything but accurate but in some cases it can work. If both parents don’t have a widow’s peak, a hairline that comes to a point midline and a trait that usually trumps any other hairline, then through a little genetic trick called dominance all their resulting children should not have widow’s peaks. If the children do have widow’s peaks, then most likely their mother cheated. In some cases this is a very visible way to discern fidelity.
But research also shows that the special connection between grandchildren and their maternal grandmothers is a two-way street: the children tend to be closer to their mom’s mom too. I call this curious phenomenon “Darwin’s grandma,” and I think it goes beyond the obvious. Way beyond, in fact—all the way down to a tiny bit of cellular machinery called mitochondria.
Mitochondria have many functions, but their most prominent job is to provide energy for the cells they are part of, which is why they are sometimes called the workhorses of the cell. Mitochondria are fascinating in many ways, but we’re concerned with one way in particular. Mitochondria have their own DNA—and unlike all your other DNA, in almost every cell in your body, mitochondria (except for rare exceptions) come from your mother alone. Which means you share mitochondrial DNA with your mother and with her mother and even her mother’s mother, on up the line, but almost never with your father or anyone on your father’s side. So, in a very real way,
you have a greater biological connection to your maternal grandmother than your paternal one. This may explain, if you’ve ever wondered, where all that extra maternal grandmother attention may have been coming from.
THE HISTORY OF human contraception goes well beyond the natural protection of hormone suppression triggered by breast-feeding or the evolutionary development of menopause. In Contraception and Abortion from the Ancient World to the Renaissance, John Riddle describes thousands of years of human efforts to engage in sex while avoiding pregnancy. Some people used natural methods still practiced today, like coitus interruptus, the dubious practice of halting intercourse before ejaculation.
The rhythm method is the timing of intercourse to avoid the days in and around ovulation when women are most fertile. The rhythm method relies on the detection of a small drop in vaginal or rectal temperature that occurs twenty-four to thirty-six hours before ovulation, which is then followed by an abrupt rise of 0.5 to 0.7°F.
Three days after the temperature spike, a woman is no longer in her most fertile period. By tracking temperature daily, it’s possible to time intercourse around ovulation. Of course, the margin for error is pretty slim.
Other women even track the consistency of their cervical mucus in a natural method called the Billings method. You may remember cervical secretions are usually thick and opaque and somewhat spermicidal, but a few days before ovulation, they become thinner, more watery, and somewhat stretchy. Think mozzarella on a hot pizza, only transparent. This change is thought to allow sperm better access through the cervix, and to the egg, increasing the likelihood of pregnancy. Again, this method can have some success, but it requires a certain degree of skill and dedication.
The first barrier-type contraceptives seem to have involved questionable methods that are hard to imagine anyone ever using—according to some accounts, ancient Egyptians used crocodile feces, and ancient Arabs used elephant dung as vaginal suppositories to prevent pregnancy. Riddle offers his admittedly unscientific (but very understandable) reaction:
A suggestion is made that feces may have actual birth control properties, as an agent that either blocks mechanically the seminal fluid at the os of the cervix or changes pH level. In the absence of more and better evidence, this hypothesis represents too great a modern effort to impose scientific rationality. A simple explanation—probably incorrect—is that inserting feces into a woman’s vagina would be an excellent contraceptive merely by decreasing the libido of a squeamish male.
Primitive versions of artificial methods used today, such as oral contraceptives and condoms, followed. Oral contraceptives were first. According to Riddle, the earliest record of oral contraceptive use is found in an ancient Egyptian medical text now known as the Berlin Medical Papyrus, although we don’t know exactly what was prescribed. The Berlin Medical Papyrus is one of a group of ancient Egyptian papyri that open a window onto the medical thinking and practices of the time. The Berlin Medical Papyrus was found in the vast Egyptian burial ground known as Saqqara, and is believed to have been written around 1300 B.C.E.
Some fourteen hundred years later, the Greek physician, herbalist, and pharmacologist Pedanius Dioscorides wrote De Materia Medica Libri Quinque (“Concerning Medical Matter in Five Volumes”), which was the Physicians’ Desk Reference of its time—and of the next sixteen hundred years, actually. De Materia Medica is one of the few works by Greek and Roman scholars that never fell out of use during the Middle Ages. In it, Dioscorides suggests the use of white willow and juniper root to prevent pregnancy. And there is some modern evidence that both “prescriptions” may have achieved some success. White willow has been shown to contain estriol, a type of estrogen. Estriol is actually produced in extremely high quantities in women who are pregnant. White willow, which contains estriol, might have helped to prevent pregnancies by stopping women’s bodies from ovulating. And juniper root has been shown to prevent embryos from implanting in the uterus of rats. Of course, the possibility exists that some of these herbal remedies worked at least some of the time. As Riddle put it, “Whatever can be written about the hailed placebo effect does not apply to birth control measures.”
Andrea Tone, the author of Devices and Desires: A History of Contraception in America, cites Gabriel Fallopius as the first to describe a condom. If his name sounds familiar, it’s because Fallopius, a sixteenth-century Italian physician and anatomist, gets credit for the discovery of the Fallopian tubes. In a paper on syphilis published in 1564, Fallopius urged the use of “a linen sheath” that had been soaked in an herbal bath to prevent transmission of the disease. The leap to pregnancy prevention was not far behind. As Tone writes:
It was not long before people recognized that what prevented sexually transmitted disease probably prevented pregnancy, too. In the early eighteenth century, condoms made from oiled silk, fish bladders, and the intestines of goats, lambs, sheep, and calves were bought and used as contraceptives, making condoms the first modern birth control to acquire commercial validity.
As STIs spread across Europe, condom use became more and more widespread. Even Giacomo Casanova used condoms, supposedly calling them “English riding coats.”
Casanova wore the finest condoms money could buy, but he was hardly enthusiastic about them. It was emasculating and dispiriting, he complained to have to “shut myself up in a piece of dead skin in order to prove I am perfectly alive.” Casanova’s complaint, a familiar refrain among condom-wearing men then and now, did not prevent him from promoting condoms or wearing them during frequent visits to French brothels. The condom, he announced, was a “wonderful preventive” for “shelter[ing] the fair sex from all fear.”
Not everyone credits Casanova with such pure motives. British biographer and actor Ian Kelly thinks that Casanova wore condoms made from “rendered sheep gut” and “he used them mainly with nuns, who were particularly worried about getting pregnant.”
The first rubber condom was made in 1855, and the first latex condoms—thinner, more pliant, and stronger than their rubber cousins—were produced in the 1930s.
Latex condoms weren’t the only contraceptive developments of the nineteenth and twentieth centuries, of course—not by a long shot. A German gynecologist named Friedrich Wilde made custom-molded rubber cervical caps for some of his patients. By covering the cervix and blocking the entrance to the uterus, these caps prevent sperm from reaching an egg. The diaphragm also works by blocking the cervix, but, instead of sitting atop it like a cap, it is a soft dome that has a spring around the rim that creates a seal with the vaginal wall. The first diaphragm is credited to another German gynecologist, C. Haase, who described it in papers published under the pseudonym Wilhelm P. J. Mensinga in the 1880s. One of the benefits of using a diaphragm is that it can be inserted up to six hours ahead of time, which leaves room for spontaneity. And it is reusable. Like a cervical cap, diaphragms need to be fitted by a health-care professional to account for normal anatomical size differences between women. It’s generally recommended that diaphragms be used in conjunction with a spermicide to increase their effectiveness.
The next leap in condom technology happened in the 1990s, when the first polyurethane condom was introduced. Many users found polyurethane condoms better than traditional latex because they conduct heat better, which makes wearing them more pleasurable. On the other hand, polyurethane is not as pliable and is more prone to breaking, which can defeat the purpose. Then there’s the female condom, also made of polyurethane, but with two flexible rings at either end. It’s inserted into the vagina before sex. But many people don’t like them because they’re somewhat bulky. Think baggy as opposed to fitted jeans.
The most popular insertional device of all is the intrauterine device, or IUD. In fact, IUDs are the most popular method of birth control in the world besides sterilization. They are used by more than 150 million women, a great percentage of whom are in China. Unlike other reversible contraceptives, IUDs must be inserted—and removed—by a health-care professional, but
require no other action by the user until they need to be replaced, which is generally between five and ten years from insertion.
The first IUD sold to the public was made by G-spot namesake Dr. Ernst Gräfenberg in 1929. Early IUDs had significant rates of infection and expulsion. Today, there are two types of IUDs available in the United States. The first type contains copper (its technical name is T380A), and the second type releases hormones. Both use one or more small threads leading from the bottom of the IUD, where they protrude slightly from the cervix into the vagina, allowing a woman to check periodically and make sure it’s in place. No one really knows how the copper IUD works. It’s thought that it may prevent fertilization by its simple presence—the body reacts to it more or less as an invader, which creates an unfavorable environment for conception and implantation. As long as the IUD is present in the uterus, the possibility of fertilization is exceptionally small, less than 1 percent. One of the major benefits of using this type of IUD is lifespan and low maintenance. Once inserted properly, it can be left in place for up to ten years. Overall, the IUD is widely regarded as safe today, but that hasn’t always been the case. For a long time, IUDs were thought to increase the risk of ectopic pregnancies. Because IUDs make uterine pregnancies so unlikely, it was thought that IUDs were actually causing the ectopic pregnancies, which doesn’t appear to be the case. The IUD stops pregnancies from progressing once a fertilized egg reaches the uterus, by preventing implantation. But, if a fertilized egg implants before it gets to the uterus, as in the case of ectopic pregnancies, the IUD has no effect on it.
How Sex Works Page 18