WHEN I recently mentioned to a pregnant acquaintance that I was writing a book about egg freezing (and had frozen my own eggs in hopes of preserving my ability to have children well into my 40s), she replied, “You’re so lucky. I wish I had known to freeze my eggs.”

She was 40 years old and wanted two children, so she and her husband were planning to start trying to conceive a second child shortly after the birth of their first. “Now everything is a rush,” she said. Married at 38, she didn’t think to talk to her obstetrician-gynecologist about fertility before then. If her doctor had brought up the subject, she said, she might have put away some eggs when she was younger.

In our fertility-obsessed society, women can’t escape the message that it’s harder to get pregnant after 35. And yet, it’s not a conversation patients are having with the doctors they talk to about their most intimate issues — their OB-GYNs — unless they bring up the topic first. OB-GYNs routinely ask patients during their annual exams about their sexual histories and need for contraception, but often missing from the list is, “Do you plan to have a family?”

OB-GYNs are divided on whether it’s their responsibility to broach the topic with patients. Those who take an “ask me first” approach understandably don’t want to offend women who don’t want children, or frighten those who do. It doesn’t take much for an informational briefing to spiral into a teary heart-to-heart about dating woes. Do you reassure a distraught 38-year-old that she’s still got time; encourage her to seriously consider having a baby on her own; or freak her out so she settles for a lackluster relationship? And considering that fertility figures are averages (while one woman may need fertility treatment at age 36, another can get pregnant naturally at 42), when is the right age to sound the alarm?