More American babies than ever got their start in a fertility clinic in 2014. In its yearly review, the Society for Assisted Reproductive Technology reported a total of 65,175 live births resulting from a variety of procedures — up from 63,286 in 2013.

Amid growing concern about the numbers of twins and triplets born to women who undergo infertility treatments, the assisted reproduction industry also detailed its progress in reducing the number of multiple births, and for the first time reported preterm births among its patients. About 78 percent of babies born to women who underwent such procedures as in-vitro fertilization were singletons, up from 75.5 percent in 2013.

In 2014, between 22 percent and 31 percent of women undergoing infertility treatment were electing to have just a single embryo transferred, with women under 35 choosing that option at higher rates than women over 40. That rate of “elective single-embryo transfers,” however, remains much lower than physician groups have called for.

Infertility treatments generate an estimated 18 percent of all twin deliveries in the United States, according to the American College of Obstetricians and Gynecologists. Mothers carrying more than one baby in a pregnancy are at greater risk of birth complications, as are the babies they bear.

The nation's 375 assisted-reproduction practices performed 190,384 assisted reproduction cycles in 2014 — up from 174,962 the year before. That uptick reflects a major acceleration of growth in infertility clinics' business since 2009, when a flagging economy cut deeply into a medical practice that relies on patients' willingness to bear steep out-of-pocket treatment costs.

A single cycle of in-vitro fertilization treatment, which includes the stimulation of egg growth with medications, a procedure to retrieve those eggs, fertilization and incubation, and eventual transfer of embryos into a woman's uterus, can cost between $15,000 and $18,000. While health insurance might cover some of those expenses, much of the cost is borne by patients.

As a result, the medical practice of assisted reproduction has been largely self-regulated and strongly entrepreneurial. As the leading industry group for infertility clinics and practices, the Society for Assisted Reproductive Technologies has tracked and produced yearly reports on the industry's activities since the mid-1980s.

The number of procedures performed in 2014 represents a 43 percent growth in two years alone, said Jake Anderson-Bialis, co-founder with his wife, Deborah Anderson-Bialis, of FertilityIQ.com, a website that allows patients to review and compare fertility practices. The couple said the increase appears to be driven by the economic recovery, a continuing surge in older women and gay and lesbian couples seeking treatment, and by an increase in the number of procedures individuals are willing to undergo.

In-vitro fertilization was the most commonly performed procedure, and its success remained closely tied to the age of the woman seeking to use her own eggs to produce a child. Among women under 35 using their own eggs to conceive a baby through IVF, 48.6 percent of 40,805 cycles resulted in the live birth of a child. But the percentage of successful outcomes declined to 38.3 percent among women ages 35-37 and to 24.3 percent among women 38-40.

Among women ages 41-42, 12.3 percent of IVF cycles using a woman's own eggs resulted in a live birth, and the success rate fell to 3.8 percent for women older than 42.

Those rates of live births reflect the growing use of embryo-freezing in U.S. fertility clinics. In some cases, multiple attempts to initiate a pregnancy using embryos that resulted from a single IVF cycle were required to achieve those success rates.

The Society for Assisted Reproduction Technology's annual report shows that the number of women looking to conceive babies using eggs that come from someone else continues to increase. In 2014, 9,961 cycles were initiated in which eggs were harvested from one woman, fertilized with sperm, and transferred into the uterus of another woman.

Roughly 70 percent of those procedures used eggs freshly produced by egg donors, which resulted in a live birth in 53.5 percent of cases. The remaining 30 percent of egg donor cycles were performed with frozen eggs, resulting in a live birth 38.5 percent of the time.

The growth of egg donor cycles is substantial, said Jake Anderson-Bialis of FertilityIQ.com. There were close to 700 more such procedures in 2014 than in the previous year.

“This idea is clearly taking hold,” said Anderson-Bialis. “The data suggests it's going to be a trend.”

The Society for Assisted Reproduction Technology has aimed to improve its reporting of outcomes, the Anderson-Bialises said. But they added that the SART website, and efforts by the Centers for Disease Control and Prevention to track the rise of infertility treatments, have done little to help women and couples find the procedure that will best help them build a family. That shortcoming prompted the Anderson-Bialises to launch their site.