Time between sonograms

How many weeks did you go between ultrasounds? I'm feeling a little anxious as it will be 5 weeks between our sonos....we have di/di twins and have always measured good with great heart rates so maybe that I why....I had a sono at 13 weeks and the next one isn't until next week which will be at 18 weeks for gender check and anatomy scan.  Just feel nervous because I don't know what's going on in there as I can't fee them yet....just keeping it in the Lord's hands that they are doing good and growing!