Apple and Facebook are adding a new perk for female employees: Free egg freezing that would let them delay parenting for a few years.

Facebook started offering the service on Jan. 1. Apple plans to begin in January 2015, according to NBC News.

As women age, their likelihood of successful pregnancies begins to dip, though most women will remain fertile well into their thirties. Oocyte cryopreservation, a.k.a. egg freezing, is seen as a method of maintaining fertility over a longer period since younger eggs tend to be healthier.

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Robin McCarthy, vice president of marketing at Eggbanxx, says such employer-based coverage is "not common at all." One main reason for this is that the American Society for Reproductive Medicine stopped calling egg freezing "experimental" just two years ago; McCarthy says previously, egg freezing was mostly intended for cancer patients, who wanted to preserve their eggs in the case of future infertility.

Like IVF, egg freezing is typically not covered by an employer's health insurance. Egg freezing currently costs about $10,000 plus up to $1,000 a year for maintenance. (Facebook and Apple are both covering costs of egg freezing up to $20,000.) McCarthy says the success rates from a frozen egg match those of a fresh egg.

In other words, if you freeze your eggs at age 27 and then wait until age 35 to try in vitro fertilization, the egg will behave like a 27-year-old's. However, the results of an analysis published in August 2013 in the journal Fertility and Sterility indicate that the chances of a live birth after egg freezing for women 30 and older are less than 25%.

Reps from Facebook and Apple could not be reached for comment.

This story was updated on Oct. 14, 2014 at 1:08 p.m. ET.