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OBGYN BOARD > Normal OB Anatomy (All Trimesters) > Flashcards

Normal OB Anatomy (All Trimesters) Flashcards

1
Q

Fertilization

A

Ovum is released from the grafiaan follicle on day 14 of the menstrual cycle or during ovulation.

Fertilization occurs 24-36 hours after ovulation in the ampulla of the fallopian tube. Cell division then begins, with each cell containing 46 chromosomes (23 pairs)

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2
Q

Early embryonic stages of cell division

A

Gamete: the male and female reproductive cell (ovum and spermatozoa)

Zygote: single celled fertilized ovum prior to mitotic division

Blastomere: dividing fertilized ovum at 2-cell and 4-cell stages, located within ampulla of the fallopian tube

Morula: mass of dividing cells located in isthmus of oviduct and enters uterus 4 days after fertilization

Blastocyst: organized collection of cells which implants into endo 7 days after fertilization.

  • The outer lining consists of trophoblasts, which produce hCG to extend the life of the corpus luteum
  • Inner fluid filled cavity (blastocele) contains the inner cell mass, which will become:
    • yolk sac (primitive)
    • embryonic disk
    • amnion
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3
Q

hCG levels

A

Human chorionic gonadotropin is a glycoprotein produced by trophoblastic cells and then later by the placenta and is believed to support the corpus luteum, thereby assuring a continuous supply of progesterone in the 1st trimester

Can be detected in maternal serum and urine.
-Detectable in bloodstream 7-10 days after ovulation

Doubles every 2-3 days
Plateaus around 8-9 weeks, then declines

Abnormal levels of hCG in maternal blood can indicate a problem with a developing pregnancy.
-Greater than expected levels:
~incorrect dates (farther along than expected)
~gestational trophoblastic disease
~multiple gestations

-Less than expected levels:
~incorrect dates (not as far along as expected)
~ectopic pregnancy
~embryonic demise or abnormal IUP

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4
Q

Primitive germ layers

A

Three germ cell layers that make up the embryonic disk by 5 weeks after LMP:

1) Endoderm: inner layer, becomes the GI & respiratory systems
2) Mesoderm: middle layer, becomes the musculoskeletal & circulatory systems
3) Ectoderm: outer layer, becomes the brain & nervous system and skin

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5
Q

Implantation

A

By the end of the 3rd week, the blastocyst begins to implant into the decidualized endo.

During this process, trophoblastic tissue invades the endo, and vaginal bleeding may occur.

Three distinct layers of the decidualized endo may be seen on US:

1) Decidua basalis: develops where blastocyst implants
- Maternal contribution to placenta
2) Decidua capsularis: closes over and surrounds the blastocyst
3) Decidua parietalis/ decidua vera: results from hormonal influence on the uninvolved endo tissue

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6
Q

Placentation

A

Placenta contains both maternal and fetal tissue

Maternal component derived from decidua basalis

Fetal component derived from trophoblastic tissue

By 5 weeks, trophoblast develops into chorionic villi. Chorionic villi in contact with decidua basalis rapidly proliferate to become the chorion frondosum, the fetal part of the placenta

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7
Q

Chorion

A

At the end of the 3rd week, chorion differentiates

Chorion will become the fetal contribution to the placenta

  • Part of it will proliferate
  • Other part will surround the gestational sac
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8
Q

Amnion

A

Forms the inner cell mass

Amniotic cavity expands to fill the chorionic cavity

Amnion and chorion begin to fuse by the middle of the first trimester (Fusion is complete by 12-16 weeks)

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9
Q

Gestational sac

A

Fluid-filled structure normally found in the uterus, containing the developing embryo

First sonographic evidence that a normal intrauterine pregnancy is present

A GS should be seen with a normal IUP when the following discriminatory levels are reached:

  • Serum BhCG > 1000-2000 mIu/ml (transvaginal)
  • Certain LMP >5 weeks (with a normal 28 day cycle)

Normal sono findings:

  • GS can be round, oval, or teardrop shaped
  • Should be located toward uterine fundus or mid-uterus
  • Double decidual sign
  • Echogenic, intact borders
  • Grows about 1 mm/ day
  • Yolk sac present when MSD is greater than or equal to 8 mm TV
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10
Q

Mean Sac Diameter (MSD)

A

Can be used to date an early pregnancy

Mean diameter is calculated from three planar sections, measured inner to inner

MSD= length + height + width / 3

MSD (mm) + 30 = gestational age (days)

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11
Q

Yolk sac

A

The first structure seen within the gestational sac (chorionic cavity) and it is attached to the embryo by the viteline duct

  • With TV US, secondary yolk sac is visible at 5.5 weeks and is almost always seen when MSD reaches 8 mm
  • With transabdominal US, should be seen by 7 wee=ks when MSD is 20 mm

Should be measured inner to inner (should not exceed 6 mm)

Sono appearance may be helpful in predicting abnormal outcome:

  • Diameter > 5.6 mm between 5 and 10 weeks is abnormal
  • Calcified yolk sacs are seen with embryonic demise

Provides nutrition to embryo

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12
Q

Crown Rump Length (CRL)

A

Embryo should be seen sonographically when gestational sac reaches 16 mm TV or 25 mm TA

CRL is most accurate method of dating a pregnancy with US and is accurate within 3-5 days if measured properly.

Measured from top of the head to bottom of the rump, excluding legs

Embryo grows at a rate of 1 mm per day

Measured until the 12th week

Rule of thumb:
CRL (mm) + 42 = GA (days)

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13
Q

Embryo

A

Embryonic period extends from 6th-10th week

Initially a local thickening adjacent to yolk sac

Echogenic focus adjacent to yolk sac

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14
Q

Rhombencephalon

A

Anechoic structure seen in posterior portion of embryonic/ fetal brain from 8th-11th week

Is a part of normal development of CNS and should not be confused as an abnormality (such as Dandy-Walker or early ventriculomegaly)

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15
Q

Physiologic omphalocele / midgut herniation

A

Midgut (bowel) herniates into base of the umbilical cord around 9 weeks and returns to abdominal cavity by 12 weeks.

This is necessary to allow for developing of abdominal viscera

Echogenic bulge should not be mistaken for omphalocele or gastroschisis

Usually measures less than 7 mm in size

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16
Q

Diaphragm

A

Superior aspect of abdominopelvic cavity is defined by the diaphragm muscle

Appears sonographically as hypoechoic curved line separating the more echogenic lungs from the liver and stomach

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17
Q

Liver

A

Liver is large and occupies most of the upper abdomen in the fetus

Left lobe is larger than the right in the fetus

The anechoic, fluid-filled gallbladder is seen in the anterior right abdomen, inferior to liver margin

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18
Q

Spleen

A

Seen in the upper left abdomen posterior to the stomach

Echogenic and homogeneous

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19
Q

Stomach

A

On transverse views, it is seen as an ovoid fluid collection in the left upper abdomen

Coronal imaging cab demonstrate the fundus, body and pylorus

Muscular layer is very thin in fetuses

Occasionally echoes may be visualized in stomach representing swallowed cellular debris in amniotic fluid

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20
Q

Esophagus and intestines

A

Difficult to image unless something is wrong

Colon is peripheral and small bowel is centrally located in fetal abdomen

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21
Q

Thorax

A

Axial and coronal sections demonstrate integrity of thorax, fetal breathing movements, and overall size and shape

Fetal heart should occupy approximately 1/3 of thoracic cavity

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22
Q

Lungs

A

Deflated lungs during fetal life appear sonographically as solid, homogeneous and granular

Lung parenchyma is homogeneous and slightly more echogenic than the liver

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23
Q

Fetal heart

A

Four chamber view:

  • Most commonly acquired image of fetal heart
  • Left atrium is chamber closest to spine
  • Apex of heart points 45 degrees to left anterior chest wall
  • Flap of foramen ovale opens into left atrium
  • Prominent moderator bands present in apex of right ventricle
  • Valves separate both atria from ventricles
  • Tricuspid valve inserts inferior (more apical) to mitral valve
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24
Q

LVOT (Left Ventricular outflow tract)

A

Identify origin of aorta arising from left ventricle

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25
Q

RVOT

A

Identify origin of pulmonary trunk arising from right ventricle

Correct orientation of pulmonary artery is “draping” anterior to aorta when seen in cross section (outflow tracts cross)

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26
Q

Aortic arch

A

Oblique sagittal plane

“Candy Cane” appearance

Head and neck vessels seen arising from this

  • Innominate artery
  • Left carotid artery
  • Left subclavian artery
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27
Q

Ductal arch

A

Ductus arteriosus

“Hockey stick” appearance

Arises more anterior in heart

No head/ neck vessels

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28
Q

Tracheal/ 3 vessel view

A

Obtained above the level of the 4 chamber view

Ensures orientation of outflow tracts

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29
Q

Embryology of the CNS

A

Neurulation begins with the formation of the neural plate and then the neural folds and ultimate fusion and closure of the neural tube

The neural tube closes from the center, temporarily leaving both ends open

The neural tube should be closed by 6 weeks

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30
Q

Spine

A

Should be performed in two planes

Transverse:
-Best plane to detect spina bifida
-Evaluation in this plane should include…
~location and configuration of ossification centers
~integrity of musculature of the back
~Integrity of skin line

Longitudinal:
-Used to assess cervical and lumbosacral curvatures, sacral caudal tapering, and configuration of vetebral ossification centers

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31
Q

Cavum Septum Pellucidum (CSP)

A
  • Small anechoic box located in midline portion of anterior brain
  • If seen, almost every subtle midline brain malformation is excluded
  • Filled with cerebrospinal fluid
32
Q

Thalami

A

-Hypoechoic ovoid structures in midportion of brain located in each hemisphere

33
Q

Lateral Ventricles

A
  • Junction of anterior, occipital, and temporal horns
  • Located slightly inferior to level of BPD
  • Evaluated for enlargement
  • Hyperechoic thin ventricle wall and choroid plexus
34
Q

Choroid Plexus

A
  • Hyperechoic structures located within each lateral ventricle
  • Lie along artium of lateral ventricle
  • Cysts may be displayed within this
  • Echogenic cluster of cells
  • Important in production of cerebrospinal fluid
35
Q

Falx Cerebri

A
  • Intrahemisphere fissure
  • Separates cerebral hemispheres
  • Echogenic midline linear structure
36
Q

Cerebellum

A
  • Dumbbell-shaped echogenic structure located in the midline of the posterior fossa
  • Consists of a vermis and two lateral horns
  • Assists in balance
37
Q

Cisterna magna

A

-Fluid filled space located between the undersurface of the cerebellum and medulla oblongata

38
Q

Facial anatomy

A
  • Nose/lips
  • Orbits
  • Nasal bone
  • Profile
39
Q

Kidneys

A

Originate in embryologic pelvis and migrate superiorly during gestation

Can be visualized as soon as 12-14 weeks
-hypoechoic structures adjacent to spine in transverse

Anechoic renal pyramids are distributed evenly throughout parenchyma

Renal sinus fat is more echogenic and can be seen in hilum of each kidney

Occasionally renal pelvis may contain small amount of fluid (normal finding in 18% of fetuses over 24 weeks)

  • 13-20 weeks = 5 mm
  • 20-30 weeks = 8 mm
  • 30 to term = 10 mm
  • > or = 10 mm: 85% have anatomic anomaly
40
Q

Bladder

A

Can be seen as early as 10 weeks and should be routinely seen by 16 weeks

Its presence is important indicator of active renal function

Fetus normally fills and empties bladder every 20-30 minutes

41
Q

Adrenal glands

A

Can mimic kidneys in cases of renal agenesis or ectopia

Seen superior to kidneys

Hyperechoic medulla surrounded by hypoechoic cortex and should always be smaller than the kidneys

42
Q

Genitalia

A

Determination of gender may assist in differential diagnosis of genitourinary anomalies and/or chromosomal syndromes

Females
-three echogenic lines for labia

Males
-Turtle sign for scrotum and penis

43
Q

Bones

A

By 15-16 weeks, most bones can be imaged

-ossification center is visualized

44
Q

Anatomy of the placenta

A

Formed by the chorion frondosum and the maternal decidua basalis

Each functional unit of placenta is known as a cotyledon (12-20 per placenta)

Weighs 500-600 gm at at delivery

Usually 2-4 cm in AP dimension

45
Q

Functions of the placenta

A
  • Conversion of fetal steroids to estrogen
  • Secretion of progesterone
  • Secretion of hCG
  • Exchange of oxygen, waste products and nutrients between fetus and mother
46
Q

Placental grading

A

Grade 0:

  • No calcifications
  • Smooth basal and chorionic plates
  • 1st and early 2nd trimester

Grade 1:

  • Scattered calcifications throughout placenta
  • Most common up until 34 weeks (31-36 weeks in ESP)

Grade 2:

  • Calcifications along basal plate
  • Chorionic plate becomes lobular
  • 36-38 weeks

Grade 3:

  • Marked calcifications
  • Distinct hyperechoic lobulations extending from chorionic to basal plate
  • “cotyledon” formation
  • Infarcts/ “fallout” areas
  • 38 weeks +
47
Q

Umbilical cord anatomy

A
  • Formed by fusion of yolk stalk and body stalk (allantoic ducts)
  • Contains two arteries and one vein, which is surrounded by Wharton’s jelly and enclosed in a layer of amnion
  • Arteries are longer than the vein and are twisted around the vein creating “braided” appearance
  • Normally inserts into center of placenta and midline portion of anterior abdominal wall of fetus (umbilicus)
48
Q

Umbilical vein

A

Enters umbilicus and joins left portal vein of fetal liver

Carries oxygenated blood to fetus

49
Q

Umbilical arteries

A

Contiguous with hypogastric arteries on each side of fetal bladder

Exit at umbilicus

Return venous blood from fetus back to placenta

50
Q

Functions of the umbilical cord

A
  • Essential link to the placenta

- Allows for transport of blood between fetus and fetal portion of placenta

51
Q

Size of umbilical cord

A
  • Length is equal to the CRL during 1st trimester and continues to have same length as fetus throughout pregnancy
  • 40-60 cm in length during 2nd and 3rd trimesters
52
Q

Fetal lie

A

Relationship of the fetal long axis to the longitudinal axis of the mother

  • Longitudinal
  • Transverse
  • Other
53
Q

Fetal presentation

A

Refers to the fetal part closest to the internal cervical os

Cephalic (head presenting):

  • Most common
  • Vertex (95% of cephalic presentations at term): parietal bones presenting
  • Sinciput: deflected vertex
  • Brow: cannot deliver vaginally if fetus is term
  • Face: face presenting

Breech (fetal head in fundus of uterus):

  • Footling: hips extended, feet presenting
  • Frank: hips flexed, knees extended
  • Complete: hips flexed, knees flexed

Shoulder:
-Shoulder presenting

54
Q

Amniotic fluid production

A

Produced by fetal kidneys, tissues, skin and fetal membranes

Removed from fetus by GI tract, lungs, membranes and cord

55
Q

Functions of amniotic fluid

A
  • Protective cushion
  • Equalization of pressure/temperature
  • Prevents adherence to membranes
  • Reservoir for fetal metabolites
  • Essential for development of fetal lungs
56
Q

Amniotic fluid index (AFI)

A

Determined by dividing uterus into four quadrants and obtaining a verticle (AP) measurement of deepest unobstructed pocket in each quadrant

Progressive increase in AFI noted until approx. 28 weeks, then after that AFI slowly decreases

Normal AFI range = 5-22 cm

57
Q

Dizygotic Twins

A

“Fraternal” twins

  • Occur when two ova are fertilized by two sperm
  • May be same or different genders
  • Comprises 2/3 of all twins
  • Always have two chorions, two amnions, and two placentas (placentas may appear fused)
  • Lowest risk of all multiple gestations

Sono findings:

  • Only confirmed with fetuses of different genders
  • “Thick” membrane suggestive of dizygotic pregnancy
58
Q

Monozygotic Twins

A

“Identical” Twins

  • Arise from single fertilized ovum
  • Comprise 1/3 of all twins
  • Always the same gender
  • Number of chorions, amnions, and placentas depend on when zygote divides
59
Q

Dichorionic/ Diamniotic Twins

A

Morula divides during first 4 days of gestation (3-5 days-ESP book)

  • 2 sacs
  • 1 or 2 placentas (can be fused)
  • Thick membrane (identical to dizygotic on US)
60
Q

Monochorionic/ diamniotic

A

Zygote splits 5-10 days after fertilization

  • 2 sacs
  • 1 placenta
  • thin membrane

**Most common type of monozygotic twinning

61
Q

Monochorionic/ monoamniotic

A

Zygote splits 10-14 days after fertilization

  • 1 sac
  • 1 placenta
  • 1 yolk sac

**Least common type

62
Q

Conjoined twins

A

If zygote splits after 13 days

63
Q

Biophysical Profile (BPP)

A

Fetal breathing movements:
-Continuous episode lasting at least 30 seconds within a 30 minute period

Gross body movements:
-At least three discrete episodes of fetal body and/or limb movement over 30 minute period

Fetal tone:
-One episode of limb extension/flexion within 30 minute period

Amniotic Fluid:
-At least one pocket of amniotic fluid measuring 2 cm in vertical axis

Non-stress test (NST):
-Demonstration of reactive fetal heart rate, consisting of 2 episodes of acceleration >15 bpm for 15 seconds over 30 minute time frame

64
Q

Biparietal Diameter (BPD)

A

Axial measurement performed at level of thalami, CSP and broken falx

Calipers are placed outer to inner and 90 degree angle to thalamus

First measurable between 10-12 weeks

65
Q

Cephalic index (CI)

A

Defines head shape
Determined by dividing BPD by OFD (occipital-frontal diameter)
-Normal range: 0.70-0.86

Dolichocephaly (<0.70)
Brachycephaly (>0.86)

66
Q

Head Circumference (HC)

A

Measured at same level as BPD

Should not include scalp echoes

67
Q

Abdominal Circumference (AC)

A

Performed at the level of stomach and portal sinus of umbilical vein

Taken along skin line to include soft tissue and subcutaneous fat

Least reliable measurement in establishing GA due to significant variations after 25 weeks

68
Q

Femur Length (FL)

A

Includes only ossified diaphysis and excludes epiphyseal cartilage

Measure anterior femur for more accurate measurement

69
Q

Binocular distance

A

Measure from lateral orbital rim to lateral orbital rim

70
Q

Transcerebellar distance

A

Measured from lateral aspects of cerebellum in axial plane

71
Q

Lateral ventricle

A

Measures < 10 mm throughout gestation, regardless of GA

Measure posterior ventricle

72
Q

Cisterna magna

A

Measured in AP diameter

> 3 mm and < 10 mm

73
Q

Nuchal Translucency

A

Fetus should be spine down and is measured between the skin and soft tissue overlying cervical spine

Calipers are placed on hyperechoic lines (not in nuchal fluid) from inner to inner borders perpendicular to fetus

Should not exceed 3 mm

74
Q

Nuchal fold

A

Posterior aspect of the neck that is measured at same level as cerebellum and cisterna magna

Should not exceed 6 mm between 15-21 weeks

75
Q

Amniotic Fluid Index (AFI)

A
  • Uterus is divided into four quadrants
  • Vertical (AP) measurement of fluid is obtained in each quadrant
  • Normal AFI range 5-22 cm
  • Peaks between 24-28 weeks
76
Q

Single Deepest Pocket for Amniotic fluid

A

Maximum vertical depth of any amniotic fluid pocket

Largest pocket > 2cm and < 8 cm

77
Q

Middle Cerebral Artery (MCA) Doppler

A

Can help determine likelihood of fetal anemia

  • Examined close to its origin from the internal carotid artery
  • Angle of ultrasound beam and direction of blood flow should be 0 degrees
  • Risk of anemia is highest in fetuses with pre-transfusion peak systolic velocity of 1.5 times the median or higher

OBGYN BOARD (4 decks)

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