Third Trimester through Ultrasound

Vasa previa is a rare condition (in 1300 to 1 in 2500 deliveries) that can result in perinatal mortality at rupture of fetal membranes.

Placenta previa is diagnosed when the placenta overlies or is close to the internal cervical os, obstructing delivery. The incidence is of 5 in 1000 deliveries and it has recently increased due to the rise in cesarean deliveries. PP is associated with a higher risk of adverse maternal outcomes.

The placenta accreta spectrum disorders include both abnormally adherent and invasive placenta. Targeted screening is essential for these disorders due to the association between low-lying or previa placenta and previous cesarean delivery. Prenatal diagnosis is possible by ultrasound.

Velamentous cord insertion occurs when the placental end of the umbilical cord contains divergent vessels that are surrounded by membranes and are not supported by Whartons Jelly.

Abnormalities of the umbilical vessels discussed in this chapter include aberrations in numbers of vessels and select structural variations such as umbilical vein varices.

Angiomyxoma of the umbilical cord is a rare tumor that can be detected by Ultrasound prenatally as a complex solid-cystic mass.

Placental lakes or placental lacunae are well-demarcated, mainly sonolucent avillous spaces of diverse size and shape, surrounded by placental tissue with normal echogenicity /subchorionic location. Their etiology is varied, so the contents of the lacunae can vary, with many containing venous maternal blood.

Placental cysts are non-vascular lesions that may occur within the body, or on the surface of the placenta.

The purpose of this chapter is to be able to address three placental pathologies that cause controversy among both imaging specialists and obstetricians: 1) placental hematomas, 2) massive perivillous fibrin deposition (MPFD), and 3) placental infarcts.

Evaluation of cerebral circulation in the fetus has long been used for clinical guidance in growth restriction and those at risk for fetal anemia.

Doppler assessment of the placental circulation plays an important role in screening for impaired placentation and its complications of pre-eclampsia, fetal growth restriction (FGR), and perinatal death.

The ductus venosus is an important regulator of fetal circulation as it shunts oxygenated blood from the umbilical vein directly into the inferior vena cava.

The aortic isthmus (AoI) is an aortic segment located between the origin of the left subclavian artery and the junction of the ductus arteriosus to the descending aorta.

A fetus is considered to be small for gestational age (SGA) when its size falls below a predefined threshold for its gestational age. The most common definition of SGA is estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile of given reference ranges.