Jennifer Aniston said she wished someone had told her to freeze her eggs. A fertility doctor says your 20s are the best time to do it, but it can be helpful even close to 40.

• Jennifer Aniston said she wished someone had told her to freeze her eggs.
• It's best to freeze eggs in your 20s or early 30s, a doctor told Insider.

Jennifer Aniston opened up this week about her fertility struggles, and ultimately accepting that she would not have biological children. While acknowledging "the ship has sailed," Aniston, 53, also said she "would've given anything" if someone had told her to freeze her eggs.

The best time to freeze your eggs is in your 20s or early 30s, said Dr. Jamie Grifo, a program director at the NYU Langone Fertility Center and the chief executive physician at Inception Fertility.

"This is when a woman is at her peak fertility," Grifo said. "Not only is she likely to have a higher ovarian reserve — meaning a strong number of eggs — but also good egg quality, which is important to getting pregnant and having a healthy pregnancy."

Still, there's plenty of hope for women who are older than that and are still interested in freezing their eggs, Grifo says.

Grifo studied egg freezing at age 38 and beyond

Fertility typically starts to decline when a woman is 30. That decline accelerates in the mid-30s, so Grifo recommends that women try to freeze their eggs before the age of 35. In general, younger is better.

While that's ideal, it's not a hard cutoff. Grifo and his colleagues conducted a study of older women who froze their eggs. The study included about 500 women, who, on average, froze their eggs when they were 38.2 years old. Fifty-eight percent of women who had at least 20 eggs frozen had a baby. For women who froze when they were younger than 38, the rate was 70%.

"This study gives women more hope and allows them more time and options when it comes to freezing their eggs," Grifo said.

The number of eggs frozen is important, especially for older women

Age is one important number when it comes to freezing eggs, but the number of eggs that you retrieve also affects your odds of success. Especially for older women, freezing more eggs gives you more chances for a healthy, viable pregnancy, Grifo said.

That can be tricky, though, since older women generally retrieve fewer eggs each cycle. Women who are under 35 freeze about 15 eggs per cycle on average; for women who are over 42, the average is just six eggs.

As more women pursue egg freezing and attempt to get pregnant with those frozen eggs, there will be information available to help guide individual decisions.

"As we continue to thaw more eggs, we will have an even larger data set that will be useful in helping patients with information that can better predict their outcome based on age, number of eggs, and number of cycles," Grifo said.

Ultimately, it's up to you — along with your doctor

Age is the first thing that Grifo considers when a patient asks him about egg freezing. But it's far from the whole picture.

"We can look further into a woman's fertility health, including her ovarian reserve, through blood work and ultrasounds," he said. If you're considering freezing your eggs, talk with your doctor about what testing might inform you about your chances of success.

For many women — even those who are well into their 30s — egg freezing can support reproduction on their own timeline.

"Mother Nature designed a system that hasn't evolved with societal norms, and that isn't a woman's fault," Grifo said. "Luckily, we have the proven science and technology to help women have a baby when they are ready."