Lara Freidenfelds, Ph.D., is the author of the forthcoming book "Perfect Pregnancies and Mourned Miscarriages: A History of Modern Childbearing" and a regular contributor to Nursing Clio.

In her new book, “Becoming,” Michelle Obama reveals that she miscarried her first pregnancy, and went on to conceive her two daughters by in vitro fertilization. In an interview with ABC’s Robin Roberts, the former first lady described feeling “lost and alone” and like a failure after she miscarried. She didn’t realize that early miscarriages are very common, ending about 20 percent of confirmed pregnancies.

Obama’s revelation underscores a striking irony. Although the past two centuries have witnessed dramatic growth in knowledge and control of reproductive processes, that wealth of knowledge has simultaneously obscured what used to be commonly understood: Many pregnancies simply do not work out.

Contemporary Americans may be book-smart — with sex education classes, high school biology courses and elaborate pregnancy manuals — about the science of conception and embryology. But they are experience-poor. As we prepare ourselves to be parents, we know far more about embryological development and prenatal care than our forebears did, but we are often lacking their practical wisdom.

In Colonial America, married women bore children on average every two to three years. Aside from sometimes deliberately extending breast-feeding for its contraceptive effects, Colonial women did little to try to control the timing of their pregnancies. Reproduction was understood to be in God’s hands, and women were revered for their prolific childbearing. Most families suffered the deaths of infants and young children. Many women experienced at least one stillbirth, and miscarriages were common.

In the Revolutionary War era, women began to envision having more control over their reproductive destiny. The same desire for self-determination that drove Americans to break away from Britain and establish a democracy inspired American women to offer each other support and encouragement for planning and limiting their families. Couples reduced their childbearing using rudimentary forms of birth control, such as withdrawal and douching, as well as abortion. By the turn of the 20th century, American women bore an average of three to four children total.

Control over childbearing accelerated in the 20th century. Margaret Sanger led the movement for birth control and distributed contraceptive diaphragms beginning in 1916. By the 1960s the birth control pill allowed women to prevent pregnancies with previously unimaginable precision. At the same time, public health and medical advancements reduced infant mortality rates and made childbirth much safer for mothers and babies. Sex educators and obstetricians pushed to educate the public about embryological development and healthy pregnancy care.

Our optimistic quest for science-based control over reproduction has had stunning results. Women and babies are exponentially healthier, and women have remarkable control over the number and timing of pregnancies. But though the attitude of faith-filled fatalism has faded, in its place are now unrealistic expectations about pregnancies. With more control over their bodies, women have also started blaming themselves when the promises of modern science and public health do not entirely pan out.

It is time to temper our expectation of perfect control so that we can accept the inevitable limitations of our biology and recognize that early pregnancy loss is a natural part of healthy women’s childbearing.

Miscarriage needs to be integrated into our narrative of the pregnancy process so that sex education, biology and pregnancy education texts and websites give accurate information. Popular models of embryological development — from plaster models of fetal development in the Maternity Center Association’s display at the 1939 World’s Fair, to Lennart Nilsson’s famous 1965 Life magazine photographic portraits of embryos and fetuses, to today’s sex education textbooks — depict development as if a fertilized egg always becomes a baby. Instead, textbooks and websites should offer a more nuanced narrative of embryological development, one that acknowledges the frequency with which pregnancy does not result in live birth.

Advertisers for everything from baby toys to cars to life insurance have been trying to reach pregnant women since at least the 1960s, when they first recognized that couples make large purchases when they are expecting. In recent years they have been targeting pregnant women as early as possible in gestation. Pushing baby products on women who are in their first months of pregnancy and have a substantial chance of miscarrying is unethical, even if it’s good business.

Consider, for example, home pregnancy tests, which came on the American market in 1978. Since that time, they have become increasingly sensitive, able to detect pregnancy ever closer to the moment of implantation of the fertilized egg in a woman’s uterus. Home pregnancy test manufacturers now promise results as early as five days before the test taker’s expected menstrual period. A pregnancy identified that early in gestation has up to a 30 percent chance of miscarrying. Home pregnancy test directions should include this information so that women understand what a positive result actually means.

And of course, as Obama advocates, women need to talk to each other about their miscarriages. Many of us only find out about a friend or relative’s miscarriage when we suffer our own. About a third of women with two or more children have also had a miscarriage. I am one of them, as are many of my friends. When we get pregnant we can be optimistically realistic, hoping for the best, knowing that any given pregnancy is not a sure thing in its first months — and knowing that we are in good company if a particular pregnancy does not work out.

Childbearing is the beginning of a much longer parenting journey, and we start that journey on the right foot if we can recognize that we must balance optimism, realism and an acceptance of what we cannot control.