I met a lady in hospital who had her 4d scan at 18 weeks, beforethe 5 month scan and she said it ruined all fun of herscheduled 20 week scan. If you do it around 30 weeks baby will be more developed and only 10 weeks left before meeting baby
I'm doing one today I'm and ill be 24 weeks. I asked the people doing it and they told me to wait til after 20 weeks but after 30-34 would be the latest they would wait because you may not get the pictures you want because they are getting bigger and all squished in there.
I have mine scheduled for 27 weeks next week and I'm so excited! Although my doctor said she wouldn't recommend past 30 weeks because baby would be bigger and at any point past 26 weeks features are noticeable.