A new study suggests the wider use of long-term reversible types of birth may greatly improve family planning by reducing the incidence of quick repeat pregnancies for women.

Investigators from the University of California at San Francisco say women using intrauterine devices (IUDs) and similar types of contraceptives were four times more likely to avoid a repeat pregnancy within 18 months of childbirth. As the world population surges, the World Health Organization recommends an even longer term of two years as the standard waiting period between childbirths.

Lead investigator Heike Thiel de Bocanegra says the time between pregnancies “cannot be explained only by the mother’s preferences,” given so many other factors in play. In the study, she and her colleagues analyzed Medicare and state-based data from more than 117,000 mothers in California who’d borne at least two children. Of that group, nearly two-thirds waited 18 months or longer between pregnancies while one-third gave birth sooner.

In comparing pregnancy data to information about access to birth control, the research team found things to be a bit more complex than previously thought. Anitra Beasley, an expert on family planning at Baylor College of Medicine, commented on the study. "We assumed that access to contraception… would improve birth spacing," she told Reuters Sunday. “This study actually examines this assumption.”

Surprising to some was the revelation that access to birth control alone was insufficient to adequate family planning. Women who used only “barrier” contraceptives, such as condoms or spermicide, were least likely to experience an 18-month break between pregnancies. In the study, more than half of women used long-term contraceptives when resuming a birth control regimen -- and they were twice as likely as others to maintain the recommended spacing between pregnancies.

Moreover, the numbers held firm when investigators looked at possibly confounding factors such as race, education, age, and national origin. However, a mother’s level of income made a big difference in whether she received birth control in any follow-up visits for care after childbirth, according to Thiel. "Low-income women are sometimes seen only once after giving birth,” she said. “Some women receive contraception -- some do not," she said.

The investigators recommend that pediatricians inquire about a mother’s chosen type of birth control.

Source: De Bocanegra, Heike Thiel, Chang, Richard, Howell, Mike, Darney, Philip. Interpregnancy Intervals: Impact Of Postpartum Contraceptive Effectiveness And Coverage. AJOG. 2013.