At approximately the half-way point in pregnancy, most women will undergo a second-trimester obstetrical ultrasound exam. A 20 week scan provides a wealth of information about the pregnancy. This is still a good time to date a pregnancy so measurements are done of the fetal head, abdomen and femur. The placenta location is noted as a placenta positioned over the cervix (placenta previa) is a life threatening condition for both mother and baby. The cervical length is measured. A shortened cervix during the second trimester may indicate pre-term labor.
The ability to visualize fetal anatomy during second-trimester ultrasound exams has improved dramatically thanks to major technological advances. Many aspects of the brain are evaluated in the fetal head. The fetal face, spine, arms, legs, hands, feet, stomach, kidneys, bladder and umbilical cord are imaged for proper development. With the latest high resolution ultrasound equipment, even subtle abnormalities such as cleft-lip or club- foot are apparent. In the early days of ultrasound, only fetal heart motion could be detected. Now virtually all major congenital heart defects are detected. Not only can the heart motion be seen and heard, but all 4 chambers of the heart are documented. It is now also possible to visualize the aorta arising from the left ventricle and the pulmonary artery from the right. The returning veins into the right and left atria are readily visualized as well as the aortic arch and its branches. Last but not least, this is the time when the fetal gender is easily determined for the parents wanting to know the sex of their baby!