It's a good idea to schedule newborn photography sessions while you are still pregnant. This will ensure that you have a spot reserved with the photographer of your choice, and you can plan the session for a time that is convenient for you and your partner. Many photographers recommend scheduling the session for when you are between 28-32 weeks pregnant, as this allows for some flexibility in case the baby arrives earlier or later than expected.
Also, the best time to take newborn photos is when the baby is between 7-10 days old. This is because at this age, babies are still very sleepy and are able to be easily positioned into the cute and curly poses that are typical of newborn photography. Additionally, they tend to have that characteristic "newborn" look, with their tiny features and smooth, unblemished skin. After the first two weeks, babies tend to become more alert and less willing to be posed, so it can be more difficult to get the photos you want. Additionally, newborns can sometimes develop baby acne or other skin conditions after the first two weeks, which can affect the appearance of the photos.