Obstetric Ultrasound Flashcards
The first trimester covers what period?
From conception to the end of the 13th menstrual week.
This include the entire embryonic period (0 to 10 weeks) and is a tume of dyanamic growth and the differentatiation and development of most organ systems.
The early gestational sac can be seen by transvaginal sonography at how many weeks?
3.5 to 4.5 menstrual weeks
As a tiny cystic structure implanted within the echogenic decidua, the intradecidual sign.
A normal gestational sac is visualized by the transabdominal apprach by how many weeks?
5 menstrual weeks
The normal gestation sac appears on ultrasound as what?
As a smoothly contoured, round, or oval, fluid-containing structure positioned within the endometrium near the funds of the uterus.
The normal gestation sac has an echogenic border greater than how many mm thick?
2 mm thick
Which represents the choriodecidual reaction
This sign is produced by visualization of three layers of decidua early in pregnancy (After 5 weeks).
Double decidual sac sign
It is evidence in about 85% of normal pregnancy.
This term refers to the endometrium of the pregnant uterus.
Decidua
The decidua vera lines the ______.
Endometrial cavity
The decidua capsularis covers the ______.
Gestational sac
The decidua basalis contributes to the formation of the _____ at the site of implatation.
Placenta
This is a 2- to 6 mm diameter, spherical, cystic structure that is connected to the midgut of the embryo by a think, stalk, the vitelline duct.
Yolk sac
It is generally the earliest structure visualized within the gestation sac and serves as a definitive evidence of early pregnancy.
The yolk sac should always be visualized in the normal pregnancy in gestational sacs of how many mm in diameter?
20-mm mean sac diamater (MSD) by transabdominal ultrasound
8 mm MSD by transvaginal ultrasound
Embryo:
MSD greater or equal to 25 mm on transabdominal US
MSD greater or eqaul to 16 mm on TVS
The yolk sac is general seen between how many weeks of gestational age?
5 to 12 weeks of gestational age
The earliest demonstration of the embryo is the ______ sign, produced by the amniotic sac and the yolk sac with the embryonic disc between them.
Double bleb sign
Embryos as small as how many mm can be detected by transvaginal ultrasound?
2 mm
This develops on the ovary at the site of the dominant follicle from which ovulated occurred.
Corpus luteum
The corpus luteum secretes estrogens, progesterone, and other hormones that are essential for establishing and maintaining pregnancy.
This is measured from the top of the head to the bottom of the torso of the visualized embryo or fetus.
This is useful until about 12 weeks GA, when other fetal measurements become more accurate.
Crown-rump length
This is measures on an axial image of the fetal head at the level of the third ventricle and thalamus.
By convention, the measurement is made from the outer table near the cranium to the inner table of the far cranium.
Biparietal diameter
This measurement is affected by head shape and provides an inaccurate estimate of GA if significant dolicehocephaly (elongated skull) or brachycephaly (round skull) us present.
This is the outer perimeter of the fetal cranium measures in the same plane as the BPD.
Head circumference
The HC measurement is relatively independednt of head shape.
This is the outer perimeter of the fetal abdomen measures on an axial plane image at the level of the intrahepatic portion of the umbilical vein.
Abdominal circumference
This is the measurement of the ossified portion of the femoral diaphysis.
Femur length
The entire femur must be imaged, and the femoral shaft must be centered in the beam so that it casts an acoustic shadow.
Normal placenta is first apparent on ultrasound at about how many weeks?
About 8 weeks as a focal thickening at the periphery of the gestational sac.
The disc-like shape of the placenta becomes evident by how many weeks?
12 weeks
By 18 weeks the placenta is finely granular and homogeneous with smooth covering chorionic membrane along its fetal surface.
The _______ of the decidual and myometrial veins forms a prominent sonographic landmark.
Retroplacental complex
The normal placenta has a maximum thickness of how many cm?
4 cm
A minimum thickness of 1 cm
The normal umbilical cord consists of how many artery(ies) and vein(s)?
Two arteries and one vein
Surrounded by Wharton Jelly
As pregnancy advances, ______ becomes the major source of amniotic fluid.
Fetal urine
The composition of amniotic fluid is dynamic, with turnover of the entire volume every how many hours?
3 hours
The fetus swallows amniotic fluid what what rate?
At a rate up to 459 mL per 24 hours
This is a rough ultrasound measurement of amniotic fluid volume obtained by measuring the vertical diameter of the deepest pockets of fluid in the four quadrants of the uters and adding these values together.
Amniotic fluid index
Pockets are selected that do not include fetal parts or umbilical cord.
Normal values of the amniotic fluid index.
5 to 20 cm