The sonography performed on a pregnant patient is called an obstetric ultrasound. Ultrasound is the safest modality for diagnosis in pregnancy as it does not involve any radiations, but utilises ultrasonic sound waves, resulting in least harm to the unborn baby. Serial ultrasound examinations are required during pregnancy, in order to ensure appropriate growth and development of the baby as well as to detect any problems in the pregnancy
The various abnormal conditions which can be diagnosed by ultrasound are enumerated as follows:

• Ectopic pregnancy – Abnormal location of the pregnancy
• Missed abortion , threatened abortion – poor or no growth of the pregnancy
• Placenta previa – abnormal location of the placenta resulting in untimely bleeding during pregnancy
• Anomaly detection – To assess for developmental,structural defects in the body parts of the fetus
• IUGR – restricted growth of the fetus, low weight of the baby

At least three ultrasounds are mandatory during the course of a healthy pregnancy, viz.:

• Early ultrasound – It should be performed earliest after detection of pregnancy to confirm normal position of pregnancy, as well as the age of the pregnancy. It also rules out miscarriages and ectopic gestation
• At 5 months of gestation – A crucial ultrasound is performed which can segregate foetuses with abnormal anatomical development body organs,like kidney maldevelopment, spine problems, brain formation defects, facialfeature dysformation etc. This helps in diagnosis of any chromosomal defective fetus like Down’s Syndrome, Neural tube defects
• Third trimester scan – This sonography is done during the later part of pregnancy, to ensure adequate growth of the fetus. Measurements of various bony structures of the baby are taken, to check for any growth lag.
  Placental problems are detected during this ultrasound

An unhealthy pregnancy may require more frequent sonography to address the concerned issue as well as to modulate the therapeutic approach for the same.