Screening at 11-13+6 weeks' gestation.

Ultrasound examination of the conceptus and the uterine blood supply between 11 and 13 weeks' gestation provides important information about the state of the pregnancy at that point in time and about its future progress. Nuchal translucency measurement in conjunction with maternal serum markers (free-beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A), has been shown to be a highly effective method for screening for aneuploidy. This is further improved by the addition of other more recently discovered first trimester ultrasound markers resulting in detection rates that exceed 90% with a false positive rate of 2.5%. Many fetal structural anomalies can be detected at this gestational age. Recently described first trimester evaluation of the posterior brain (intracranial translucency (IT)) provides an effective screening tool for the presence of open neural tube defects. Doppler measurement of the pulsatility index in the uterine arteries in conjunction with maternal history and examination as well as maternal serum biochemistries helps to accurately establish the risk of developing preeclampsia.