The forms of birth control that make parents most "comfortable" differ from those that are most effective.

"If your teen's doctor found out your daughter was having sex, is it acceptable or unacceptable to you for the doctor to provide birth control to your teen confidentially?"

The question was posed to a diverse group of parents of girls aged 12 to 17. On a scale from 1 to 4, researchers at UC San Francisco wanted to know, how comfortable were they with their daughters being given birth control pills? Condoms? Emergency contraception? An intrauterine device (IUD)?

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Per the results, published in the Journal of Adolescent Health, 59 percent said they'd be okay with birth control. Only 51 percent approved of condoms. And way down the scale, past injectables (46 percent), emergency contraception (45 percent), the transdermal patch (43 percent), and the implant (32 percent), was the IUD, with only 18 percent approval.

First, the thing that's making them most uncomfortable: Even though the IUD has been recently making a comeback, parents worried about their daughters' health -- and future fertility -- may not have gotten over the Dalkon Shield disaster, where a poorly designed IUD caused miscarriages and even death in the 1970s. 

The American College of Obstetricians and Gynecologists in 2011 endorsed IUDs and implants as "the most effective forms of reversible contraception available" and "safe for use by almost all reproductive-age women." A year later, the group again clarified that both "should be offered as first-line contraceptive options for sexually active adolescents." They also leave a wider margin of error than pills, which need to be taken at the same time every day, and condoms, which need to be on hand every time sex happens. 

We can probably give some of these parents the benefit of the doubt; it's possible they'd be fine with their daughters choosing more invasive forms contraception, as long as it wasn't happening behind their backs. Not surprisingly, the only factor that made parents more accepting of all forms of birth control was passing a seven-item scale meant to measure whether or not they recognized their teen's autonomy.

Even now, many caution that IUDs are best for women in monogamous relationships, because they don't protect against STIs. But birth control pills don't do that, either. Which is why regardless of what other birth control method they may choose, girls need to be using condoms. So why are parents shying away from them?

"The lower than expected acceptability of condoms likely reflects parents' overall low acceptability of contraception in general for their daughters," lead author Lauren Hartman wrote to me in an email. "It also highlights the importance of educating parents about the importance of condoms, both for protection from STIs and pregnancy."

Parents who believed their teenager was likely to have sex in the coming year were more likely to accept their use of emergency contraception and condoms. The authors suspect that they only begrudgingly okay'd those two because "parents may associate these methods with a single episode of sex rather than condoning an ongoing sexual relationship, which would require a more permanent contraceptive method."

Since roughly a third of the girls in question were aged 12 to 13, it would be interesting to see their parents' opinions broken down by age. Hartman also wondered if the results may have been different had the parents been asked about giving condoms to their sons.

But the very first sentence of the study couldn't lay out the stakes more clearly: "The incidence of unintended pregnancies and sexually transmitted infections (STIs) remains high among adolescents." If parents can't get comfortable with their daughters practicing safe sex, they'll be forced to accept the consequences.