I use a Nikon Nikkkor Z 35mm f/1.8 for my newborn work as it gives me a wider field of view, yet I can keep my hands in the frame for safety, which is absolutely paramount.
Aside from newborn sessions, I use my Nikon Z 50mm f/1.2 and Nikon Z 70-200 f/2.8 lenses, they are the perfect combination for my maternity and boudoir portraits. I am very excited to be the very proud owner of Nikon's newly announced Nikkor 85mm f/1.2 lens, which I have to say is absolutely incredible.