Cozen O’Conner’s annual Pennsylvania Society cocktail party at The 21 Club in Manhattan was wall-to-wall packed as always Friday night. But one person there really wanted to get out.

Aren Platt, a political consultant who now works for Todd Carmichael at La Colombe, was attending the party with his wife, Jessica Cosme, when her water suddenly broke — announcing impending arrival of their daughter, Elouise Cosme Platt, one month early.

Platt said the couple left the party quietly and took the subway to Mount Sinai Hospital — faster than an Uber in Midtown by five minutes — where Elouise arrived 18 and a half hours later.

Cosme, a lobbyist at Bellevue Strategies, and Platt had been considering the name Elouise as they walked by The Plaza Hotel this weekend, the setting for the book series “Eloise at The Plaza,” about a precocious six-year-old who lives there.

“She chose her name,” Platt said of his daughter. “When she was born in Manhattan, it was going to be Elouise.”

Mother and baby are doing well and have been heralded on social media as — finally — a story about Pennsylvania Society that does not involve scandal or fisticuffs or the other various misbehaviors that occasionally occur when the state’s political class decamps to Manhattan for oh so many cocktail parties.