More and more American women are waiting until they are older to have children. Why? Because they are building their careers and waiting for Mr. Right. But what if Mr. Right fails to come along before they turn 35? 

As the biological clock ticks along, the chances of having biologically related children diminish steeply, especially as women pass their mid-30s. So some women are now taking out “fertility insurance” by having clinics retrieve and freeze their youthful eggs. 

In May The New York Times devoted some front-page real estate to a new twist on this practice: would-be grandparents subsidizing the freezing of their daughters’ eggs. Fertility specialist Daniel Shapiro, medical director of Reproductive Biology Associates in Atlanta, told the Times his egg-freezing patients often say, “My parents want me to have this as a gift.”

While many women put off childbearing as their careers develop, others are stuck waiting for their relationships to reach the next level, thanks to the fecklessness of modern men. Many women in their late 20s and early 30s are in long-term relationships with men whom they think will eventually father their children. Occasionally, the relationships don’t work out, and the women find themselves in their mid-30s or later without a promising partner. 

Things have been trending this way for a while. The average age of mothers at first birth has increased from 21.4 in 1970 to 25.2 in 2009, according to the most recent vital statistics from the Centers for Disease Control and Prevention. In 2009, the CDC reports, the “rate of 39.1 births per 1,000 women aged 15–19 was the lowest ever reported in the nearly seven decades for which a consistent series of rates is available.” By contrast, the rate for women aged 35–39 was 46.5 births per 1,000 women. In fact, more children are now being born to women over age 35 than to women under 20.

Every advance in assisted reproduction comes with ethical questions, and this one is no different. First, should eggs be set aside at all? In her 2009 Bioethics article, “Egg Freezing: A Breakthrough for Reproductive Autonomy,” North Carolina State University philosopher Karey Harwood notes that infertility occurs when a normal biological process is impeded by disease or defect. Thus assisted reproduction techniques are used to treat the illness of infertility.

But women who decide to have their eggs frozen are not infertile. They are making an “elective” or “social” choice to take advantage of a new technology. Does this make any ethical difference? No, argues Harwood. She points out that contraception and nontherapeutic abortion are both “elective” and do not treat an illness. “The analogy to a contraceptive pill is apt because both egg freezing and the pill can effectuate delayed reproduction,” writes Harwood. “Because egg freezing may be reasonably interpreted as another form of family planning, it can be considered a legitimate exercise in reproductive autonomy.”

One ethical upside to freezing eggs is that it gets around moral concerns about whether frozen embryos are persons, since uninseminated eggs do not have two sets of genes derived from parents. That issue is apt to come up eventually, however, if the frozen eggs are later used to create embryos via in vitro fertilization (IVF) techniques for implantation into a woman’s womb. Standard IVF techniques often involve producing extra embryos that are frozen as backups to be used if those initially introduced into a woman’s womb fail to implant or if patients later want additional children. Consequently, there are often frozen embryos left over once IVF treatments have been completed. Clinics could avoid the issue of what to do with spare embryos by freezing eggs and sperm separately.

The biological clock is relentless. A woman’s fertility, defined as her probability of getting pregnant during a year, falls from 86 percent at age 20 to 52 percent at age 35. Thereafter it drops ever more steeply to 36 percent by age 40 and 5 percent by age 45.

Ethicists fret that egg freezing as “fertility insurance” engenders false hopes, in part because women may overestimate the real chances of having a baby using this technique. If the relevant standard is the success rate of other IVF techniques, recent data from several clinics indicate that the rate of live births using frozen eggs is comparable, with about one in three cycles resulting in a live birth.

Another concern is that women who hear of the technique will wait too long before taking advantage of it. Clinical evidence strongly suggests that the chances of having a baby are greater for women who choose to freeze their eggs before age 35. Eggs frozen after that age do not grow and implant as readily. Older eggs are far more likely to have flaws that prevent them from developing into babies than younger eggs do. 

Another ethical concern is that children born from frozen eggs might be disproportionately at risk of various physical and mental harms. Already some 2,000 children may have been born using frozen eggs. Preliminary evidence indicates that the rate of birth defects among such children is comparable to that among children born by means of conventional IVF techniques. For example, a 2009 study looked at 936 live births from frozen eggs and reported, “Compared with congenital anomalies occurring in naturally conceived infants, no difference was noted.” 

Some ethicists argue that egg freezing amounts to an illegitimate technological fix for persistent problems of sexual inequality. They argue that the ethical thing to do is to change workplaces so there is less conflict between bearing children and having a career. They also say public policy should encourage women to avoid the problem of age-related infertility by having children at younger ages. 

The case of France suggests that attempts to shift public policy in directions friendly to childbearing and rearing may have limits. In pronatalist France, the average age for first childbirth is 29.9 years (vs. 25.2 in the U.S.), and despite all sorts of social programs aimed at easing the burdens of child rearing, French women have a lower labor force participation rate than American women.

Furthermore, egg freezing actually promotes equality between the sexes. In a 2009 paper for the journal Bioethics, Oxford University philosophers Imogen Goold and Julian Savulsecu note: “Men already enjoy the choice of when they have children. Women should have the opportunity to enjoy the same choices as men, if we can provide them, unless there are good reasons not to.” Instead of dismissing egg freezing as a mere biomedical work-around, we should celebrate it as another way in which technological progress is reducing and ameliorating inequalities between men and women. 

Science Correspondent Ronald Bailey is the author of Liberation Biology (Prometheus).