The earlier in pregnancy that such measurements are performed, the more accurate and reliable the dating however, the earlier the gestation, the less well fetal anatomic structures are demonstrated. Very early identification of an embryo, at about 5 weeks, can be made with transvaginal imaging if there is a suspicion for ectopic pregnancy. Ultrasound can also be used in conjunction with a knowledge of HCG levels, to in many cases exclude the presence of etopic pregnancy. The relationship of the placenta to the cervix, can change as a pregnancy proceeds. When placenta previa is suspected, follow-up examination can be beneficial in confirming a persistent relationship of the placenta to the cervical canal.
Tables are available that relate measured fluid levels to gestational age.
Major and most common anomalies. Neural tube closure and defects- Meningocele , Myleomeningocele , Chiari II malformations and Anencephaly Meningocele is related to a neural tube closing defect and is also known as spina bifida. A meningocele only contains fluid. The myelomeningocele also contains neural tissue. There is typically a defect of the spine at the level of the meningocele or the Myleomenignocele, especially the lumbosacral region.