6. Patient has had at least one detailed 2nd-trimester ultrasound examination documenting placentation, chorionicity, fetal number, fetal size, amniotic fluid volumes, and fetal anatomy. (This examination must comply with minimum standards such as those published by the American Institute of Ultrasound in Medicine, American College of Radiology, or American College of Obstetricians & Gynecologists It is NOT mandatory that this examination be performed at the research-study center.)