Ultrasound is done in 1st trimester for ALL EXCEPT:

Fetal anomalies scan is done between 18 to 22 weeks. However earliest fetal anomaly that can be detected is anencephaly, which may be detected after 10 weeks. Routine first trimester USG is done for Pregnancy dating Fetal bility Intrauterine or extrauterine Multiple gestation Nuchal transluscency and nasal bone are checked at 11-13 weeks (markers for downs syndrome)