Recommendations depend heavily on the MILF's age bracket. 30–40, try something a trifle sceney; something that kicks up the mischievous streak she might have abandoned after the first trimester. I'm thinking Ciano, Shea Gallante's opulent Italian tavern in the Flatiron District. There can be some aggravating seating chart politics at play here, so do plan ahead. The best seats are by the massive roaring fireplace; you'll want to request one of those if you're looking to close.
40–50, something a bit more tranquil may be in order. La Grenouille (3 East 52nd St.) comes to mind, an old warhorse for romantics. The main dining room is where the real swains choose to sit, but ascend the stairwell, as far as they'll allow, to discover the room once used to stable horses. It's now occasionally a private room, occasionally open to diners and always exquisite, with soaring paneled windows and multiple open-format levels. Piano keys tinkling, peonies on the white-clothed tables. Your MILF may recall a time when such fineries were the norm, and in a wistful state may be all the more vulnerable to your advances.