How old is too old to become a parent?

For nearly 40 years, fertility treatment has grown ever more advanced and so entrenched that it's not uncommon for couples to begin their families in their late 30s, 40s or even 50s.

But even as questions about the technology to extend fertility have been answered - yes, children born through in vitro fertilization are healthy; yes, freezing embryos appears to be safe; yes, mothers can generally deliver babies safely well beyond the classic childbearing years - another important question is emerging: How old is too old for their offspring?

Offspring like Hayley, the 10-year-old daughter of a 58-year-old, Ann Skye.

"I knew that she was going to really need to build her own support system in life, or potentially would need to," said Skye, who lives in North Carolina and works in public health. "I think that has really impacted the way we parented her. We were strong proponents of letting her cry [herself] to sleep for that same reason: She needs to be able to self-soothe."

In December, two prominent psychologists and two reproductive endocrinologists published an opinion paper in the Journal of Assisted Reproduction and Genetics questioning whether it was time to establish age restrictions in the field. They wrote that research has shown that children often experience social awkwardness if their parents are a half-century older than them and face greater risk of autism and psychopathologies. These children are also more likely to serve in a caregiving role and experience bereavement as adolescents or teens compared with their peers whose parents gave birth in their 20s and 30s, they wrote.

Do those risks constitute the potential for "great harm" to the child and outweigh a person's right to "reproduce without limitation or interference" at any age, the authors asked.

"It is a self-perpetuating issue; the more older patients that seek [fertility] treatment, the more people feel that it is reasonable to seek treatment, especially in an age where sensational births are widely celebrated as positive events in the media," they wrote.

In the United States, the number of live births to mothers ages 45 to 49 increased from 3,045 in 1996 to 8,257 in 2016, and the number to mothers ages 50 to 54 increased from 144 births to 786 births over the same time period, according to the National Center for Health Statistics. The average age of women becoming mothers in the United States is now 26, up from 23 in 1994, according to the Pew Research Center.

My parents weren't planning on having children, but a decade into their marriage, when my mom was 39 and my dad was 52, I arrived.

They were very caring and dedicated, and I had a happy childhood.

I also remember feeling anxious that my dad's age in particular might strike other kids as strange.

Still, our house was always the gathering place for my friends. My dad had a goofy sense of humor - claiming that he had Tom Cruise-level good looks, asking fellow Jews what parish they belong to - which my friends liked.

At some point in my late teens, however, he started not being able to remember my friends' names. I got mad at him for it. Feeling guilty, he took out my high school contact book and asked me for details about them. He wrote them down next to their names to try to remember them.

Then I felt guilty because I realized he couldn't help it.

He declined over the next 10 years because of vascular dementia and was living in the memory care unit of an assisted-living facility when he died in 2016 at age 82; I was 29.

I am now 33, and my mom, is 72, healthy and very active. But when she has rare memory lapses, I get nervous and become like a prosecutor, ready to submit these moments as evidence that she will follow the same trajectory as my dad.

"The experience of parental bereavement has a very substantial impact on a person's life, particularly a young person's life," said Julia Woodward, a clinical psychologist at the Duke Fertility Center in Durham, North Carolina, and one of the authors of the December opinion article. She recently launched a study with women who received fertility treatment to "learn about the longer-term implications for parents and for their children."

There are some clear positives, which were apparent to me.

"Having a more mature parent can benefit a child, in terms of the parent being more patient, having more of an investment in the parenting role because they have already achieved some other life goals," Woodward said.

But the possibility that the parent will die before the child has embarked on life or even reached adulthood is a significant negative. When a parent gives birth at age 50 or above, the probability of death by the time that child turns 20 is 22 percent for a male parent and 14 percent for a female parent, according to a 2015 study from Julianne Zweifel, a psychologist at the University of Wisconsin School of Medicine and Public Health. That is more than double the probabilities for new parents at age 40.

That potential for children losing parents at an early age is what caused fertility doctor Mark Sauer, a pioneer of egg donation technologies, to rethink his earlier unworried attitude about providing fertility treatments for women who want to conceive in their 50s. "I'm a lot less cavalier today than I was 30 years ago," he said.

He once treated single, older women or couples where the mother was in her 50s and the father was in his 70s, with friends and relatives who were also around that same age. Some of the older single mothers later had medical problems and died and "left a child without a mother."

"I would be reluctant to do that today because, I hate to say it, I think I know better," said Sauer, who also co-wrote the December opinion piece.

The American Society for Reproductive Medicine (ASRM) released new guidelines in 2016 stating that fertility "treatment of women over the age of 55 should generally be discouraged," but it remains up to individual doctors and their patients to decide how old is too old.

Zweifel, who also signed on the December article, would like to see the ASRM and fertility clinics come up with guidelines and policies to set an age-50 limit for fertility treatments, such as IVF, because "that allows us more than 20 years, hopefully, of expected life span and a good portion of those years to be healthy. But even so, then we have women [possibly] dying" when their children are 20, she said. She thinks the same age considerations should apply to men, who without medical intervention are typically able to reproduce for longer than women.

For his part, Sauer does not think there should be an age limit for fertility treatments. "There are some 22-year-olds who are going to be pretty terrible parents but can certainly have children, and there are some really good [new] parents who are 60 years old. So I think age as an arbitrator is not necessarily a good demarcation," he said. Sauer said he signed on to the opinion article to support the authors "who were saying, 'Caution here. It's not always a happy ending.' "

Others in the field admit that the long-term implications of births to parents at advanced ages have not received significant consideration. Jacques Moritz, an obstetrician-gynecologist and medical director of the Tia Women's Health Clinic in New York, recently delivered twins to a 57-year-old couple.

"When the child goes to high school graduation, both the father and the mother will be on Medicare, and what does that mean? We haven't given it much thought," he said. "The science has gone faster than the societal issues, and I don't pass judgment on these things."