Manhattan publicist Tracey Kahn, 51, is pregnant with her second child, due in February. Her daughter, Scarlett, whom she delivered when she was 49, is 2. The single high flier is among a growing percentage of women undergoing fertility treatment beyond the age of 50 — according to the Centers for Disease Control and Prevention, there’s been a nearly fourfold increase in the number of babies born between 1997 and 2008 to moms age 50 and up. Here, Kahn tells The Post’s Jane Ridley about her decision to embrace later-in-life motherhood.

Sitting in the waiting room at the clinic, I glance at the other moms and would-be moms, anxiously anticipating whichever procedure or test they’re scheduled for that day. Most appear to be in their late 30s or 40s, but several, like me, have clearly reached — or passed — the big 5-0.

“Would you like to come through, Tracey?” asks the nurse, leading me toward the ultrasound room. “Bet Scarlett can’t wait to meet her new playmate!”

My daughter might only be 2, but she loves the idea of a sibling. And my pregnancy is no big deal to the staff at Reproductive Medicine Associates of New York, which regularly treats women over 50. If anyone else thinks it’s strange and unnatural, they’re entitled to their opinion — but I honestly don’t give a s – – t.

I’m confident, attractive, successful in my career and own a $1 million apartment on the Upper East Side. One day, I’ll likely meet Mr. Right, get married, and my kids will have a loving father in their lives. It’s 2014 — who cares about the “traditional” order of things?

When I was in my 20s and 30s, I always knew I’d be a mother. But with a 14-hour-a-day job in advertising and a hectic social life, the timing never seemed right.

It wasn’t as if I lacked suitable boyfriends. When I was 33, I got engaged — but called it off three weeks before the wedding. The decision was mutual because, amid all the frantic planning, we realized we were incompatible.

“This isn’t going to work,” I told my then-fiancé, slipping off the elegant, $15,000, 2-carat, emerald-cut diamond ring. “Neither of us will wind up happy.”

After that, I had a string of long-term relationships with gorgeous, driven men whose Type A personalities matched mine. We’d discuss marriage and kids, but, for one reason or another, it didn’t happen.

Then, in 2008, when I was 45, two years after establishing my own business publicizing high-end jewelry and accessories, I accidentally got pregnant by a guy I’d been dating for less than one month.

I was over the moon and planned to have the baby, whether or not my new boyfriend stuck around. Unfortunately, we never got to figure out a long-term plan because I miscarried at seven weeks. It was sad, but I didn’t go to pieces. I’m not that kind of person. Instead, the loss put me on the next path — seeking fertility treatment.

By now, I was 46 and all I could think about was babies. Our relationship ended, so I determined to go it alone, at least for the time being. I looked into adoption, but desperately wanted to experience pregnancy for myself. I craved the bonding that goes with carrying a child for nine months. I had the money, the energy and the endless reserves of love to raise a child. Nothing was in my way.

I enrolled at Weill Cornell and had five unsuccessful attempts at IUI (intrauterine insemination) using donor sperm, before moving on to IVF using donor eggs because my own mature eggs were clearly not making the grade. It was pretty intense choosing the donors — and it was done with the same dedication I apply to my work.

The egg donor was a fashion major at Parsons — and, like me, Jewish, petite and from a big family. The sperm was donated by a tall, dark, sporty type with long limbs, beautiful eyes and almost a perfect SAT score. He was exactly the kind of guy I’d have dated in my 20s.

I had the embryo transfer on Labor Day 2011. Fortunately, the embryo took the first time and I was pregnant with a girl. Telling my mom, in her 80s and very old-fashioned, was no mean task. “How are you going to manage?” she asked. “Everyone’s doing it, Mom,” I insisted. “It’s a new age. It’s very hip.” I went into the physicality of the anonymous sperm donor because I knew that approach would appeal to her. Next thing, she was calling up her sister, bragging: “Tracey’s pregnant. And the father’s gorgeous. He looks like a prince!”

It wasn’t the easiest nine months, since I was nauseous the entire period. But I’ve always looked after myself — eating well, going to the gym — so, if anything, the exhaustion came from working my usual 14 to 16 hours a day. I look young for my age — friends say I pass for 10 years younger and I’ve had the occasional Botox and collagen injection — so nobody raised eyebrows when they discovered I was pregnant, at least to my face.

Scarlett was born via Caesarean on May 30, 2012, three days after my 49th birthday. She was perfect. Holding her in my arms, I was elated. The fertility treatment had cost about $75K, but I knew I’d do it again in a heartbeat. I’m proof that just because a woman is single, older and career-oriented, she doesn’t have to give up on her dreams of being a mom. You really can have it all.

If anyone asks how I cope as an older mother, I’m honest about my strategy. I’m hands-on, but also an expert delegator. Scarlett had a $350-a-day baby nurse for the first three months, and I now employ an amazing full-time nanny. Yes, it’s expensive, but with a business with an annual $500K turnover, I can more than afford it.

My main motivation for having this second baby is providing Scarlett with a sibling. I’m one of four children and particularly close to my sister, Andrea Fisher, who is 13 months older than me. I want the same for Scarlett.

This time around, I was rejected for a second round of IVF at Weill Cornell because their maternal cutoff age to enroll is 46. But RMA treats women up to the age of about 55. I used the same donors and the embryo was successfully transferred in June. I was thrilled to find out it was another girl. The nausea is back and I’m not feeling my best, but I’ll survive.

As for the future, I know there will be challenges. Getting old is a bummer. The first 25 years with the kids will be great — I’m planning on lots of European vacations, and they’ll go to the best private schools in Manhattan — but, yes, it will get harder after that. God willing, by the time I’m in my 80s and they’re in their 30s, I’ll have raised them properly with the help of a good man whom I’ll meet and eventually marry.

And they won’t be the ones looking after me when I’m elderly. I’ll hire a live-in aide. Odds are that I’ll be a viable, feisty, outgoing 80-year-old. It’s always been important to me to have a very good attitude.

Meanwhile, a friend recently asked what I’d say to someone who mistakes me for the girls’ grandmother. It could happen in a few years, though I’ll probably have some work — probably a face-lift — by then. “No, I’m their mother,” I’ll reply proudly. “And aren’t they lucky?”