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MIDS 187 > Ch 4 Amniotic Fluid, Normal Placenta + Cord > Flashcards

Ch 4 Amniotic Fluid, Normal Placenta + Cord Flashcards

1
Q

What is amniotic fluid?

A

A dialysate of maternal serum

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2
Q

List 3 reasons why amniotic fluid is essential?

A

-Maintains even temperature + homeostasis
-Allows fetal movement + growth
-Develops tracheobronchial tree

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3
Q

S/F of amniotic fluid?

A

Usually anechoic, but can see milky debris typically in 3rd trimester due to vernix caseosa

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4
Q

What is vernix caseosa?

A

-White, creamy, milky biofilm that naturally covers the skin of the fetus during the 3rd trimester
-Baby cheese

(it comes off and goes into amniotic fluid)

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5
Q

At 12 weeks gestation how much fluid volume should there be?

A

60 mL

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6
Q

At 20 weeks gestation how much fluid volume should there be?

A

500 mL

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7
Q

From week 12-16, how much does the fluid volume increase?

A

20-25 mL per week

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8
Q

From week 16-20, how much does the fluid volume increase?

A

50-100 mL per week

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9
Q

How does the fetus contribute to fluid volume?

A

-Transudation through skin surfaces (includes skin, cord, chorion + amnion)
-Fetal urine (begins at 12 wks, not significant until 18-20 wks)

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10
Q

When does fetal urine start entering amniotic fluid + when does it become significant?

A

-Starts week 12 (insignificant)
-Becomes significant b/w week 18-20

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11
Q

How much urine does the fetus produce each day in the 3rd trimester?

A

450 mL urine per day

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12
Q

Do we actually measure the fluid during exams?

A

1st/2nd trimester:
-eye ball it subjectively
-report SDP if abnormal b/w 18w - 26w + 6d

3rd trimester:
-measure it objectively
-SDP + AFI (amniotic fluid index)
-semiquantitative measurements

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13
Q

By week 20 the fetus can’t supply fluid through transudation through skin surfaces anymore, how is fluid volume maintained now?

A

-By swallowing + fetal urination
-Can be maintained with only 1 functioning kidney

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14
Q

What is oligohydramnios + polyhydramnios?

A

Oligo: low amniotic fluid volume (<2cm)
Poly: excessive amniotic fluid volume (>8cm)

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15
Q

List SDP measurements for normal, oligohydramnio + polyhydramnio?

A

Normal: b/w 2-8cm
Poly: over 8cm
Oligo: under 2cm

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16
Q

How do we find + measure the SDP?

A

-Check 4 quadrants in uterus to determine which is deepest pocket free of cord + body parts
-Use CD to ensure we are not measuring “invisible” cord
-Measure perpendicularly (b/c fluid is gravity dependent) from anterior uterine wall down to 1st structure encountered (ex. leg, body, placenta, posterior uterine wall, etc)
-Imagine 1cm wide box + make sure nothing invades that box

(pocket should fit 2x1cm rectangle with long axis at right angle to uterine wall)

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17
Q

What should we do next if we measure an abnormal SDP?

A

Repeat measurement again to ensure we did not accidentally include cord, etc.

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18
Q

How do we measure AFI?

A

Measure fluid in 4 quadrants of uterus + add all measurements together (in cm)

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19
Q

Normal AFI value?

A

5-25 cm

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20
Q

AFI value that indicates oligohydramnios + polyhydramnios?

A

Oligo: under 5cm
Poly: over 25cm

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21
Q

What is the median AFI value?

A

14cm (from week 20-35 b/c fluid volume begins to reduce)

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22
Q

T/F: It is a very common reason to do an u/s if they think the mom is leaking fluid.

A

True

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23
Q

List reasons that cause oligohydramnios?

A

-Uteroplacental insufficiency
-Drugs
-Postterm pregnancy
-IUGR
-Fetal death
-Fetal chromosomal abnormalities
-Rupture of membranes
-Idiopathic
-Fetal malformations (m/c ones that decrease urine production)

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24
Q

List reasons that cause polyhydramnios?

A

-Fetal malformations
-Multiple gestation
-Maternal diabetes
-Fetal anemia (includes Rh incompatibility)
-Idiopathic
-Other fetal disorders/infections or genetic abnormalities

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25
Q

How many vessels make umbilical cord?

A

3 (2 arteries + 1 vein)

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26
Q

In fetuses, the umbilical arteries + vein carry what kind of blood?

A

Arteries: deoxygenated
Vein: oxygenated

(remember opposite from adults)

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27
Q

Where do the umbilical arteries + vein carry blood to?

A

Arteries: to placenta (from fetus)
Vein: to fetus (from placenta)

28
Q

What 4 things should we be assessing when viewing the placenta?

A

-Size
-Shape
-Consistency
-Location

29
Q

What 4 things do we document when evaluating the umbilical cord on u/s?

A

-Confirm # of vessels
-Document length (subjective, never measure)
-Appearance of cord
-Image fetal + placental cord insertion sites!!

30
Q

The umbilical cord originates from fusion of YS stalk + omphalomesenteric duct at what week?

A

7 weeks gest

31
Q

The umbilical arteries + vein are surrounded by what?

A

Wharton jelly (mucoid connective tissue), all enclosed in a layer of the amnion

32
Q

At term, what is the average length of the cord?

A

51.5-61 cm

(circumference = 3.8 cm)

33
Q

Is it easy to scan the entire cord?

A

No, is hard due to length

34
Q

What is a velamentous cord?

A

Cord away from main body of placenta, highest risk b/c can kill baby + mom during birth

35
Q

What 4 things contribute to the placental structure?

A

-Maternal portion (arises from endo)
-Fetal portion (arises from section of chorionic sac)

-Trophoblasts invade decidua + becomes part of placenta

-Villi proliferates into the villous chorion / chorion frondosum (which is fetal side of placenta)

36
Q

What are the metabolic functions of the placenta?

A

Synthesizes sugar, fats + hormones (hCG, estrogen + progesterone)

37
Q

How much does the placenta weigh?

A

480-600 grams at term

38
Q

The fetal side of placenta is a fused layer of what 2 structures?

A

Amnion + chorion, with underlying fetal vessels

39
Q

The maternal side of placenta has how many functioning lobes/cotyledons?

A

20

(composed of maternal sinusoids + chorionic villous structures)

40
Q

Where is the normal cord insertion site into the placenta?

A

Central

41
Q

What is it called when the cord inserts eccentrically near the margins of the placenta?

A

Battledore placenta

(eccentric = away from center, but still on edge)

42
Q

What is it called when the cord inserts below the edge of the placenta?

A

Velamentous insertion

43
Q

Normal placental thickness prior to 24 weeks gestation?

A

Less than 4cm

(not routinely measured)

44
Q

Are the maternal + fetal circulations separate?

A

Yes

45
Q

Explain placental circulation?

A

-Oxygenated maternal blood is pumped through spiral arterioles within decidua basalis + enters intervillous spaces surrounding/bathing the villi

-Deoxygenated fetal blood circulates through capillaries in chorionic villi within the placental lobes

-Resulting oxygenated blood within villous capillaries returns to fetus via umbilical vein

46
Q

Where do gases + nutrients exchange in placental circulation?

A

Across walls of villi

47
Q

The relationship of the placenta + cervix can be best seen with a full or empty bladder?

A

Full, be careful it is not overdistended tho as this can cause a false-positive appearance of placenta previa

(empty bladder may not be able to see cervical os)

48
Q

Bladder is considered adequately full when cervical length is what?

A

B/w 3-5 cm

49
Q

If the cervix is measuring long, what is the m/c cause of it?

A

B/c bladder is too full

(this causes close position of anterior + posterior walls of lower uterus, producing a falsely superior cervical os)

50
Q

How would we measure the placenta?

A

Use thickest part of central placenta, excluding uterine wall

(remember not routinely done)

51
Q

What are placental lakes?

A

-Normal finding
-Hypoechoic structures within anterior placenta

52
Q

How does placental texture change from early pregnancy to end of 1st trimester?

A

Early pregnancy: echogenic focal thickening of wall of gest sac

End of 1st: fine, granular + homogeneous

53
Q

Increased levels of serum alfa fetoprotein is associated with what?

A

Findings of large vascular spaces in placenta

54
Q

In late 3rd trimester, the placenta may have nonvascular cystic areas centrally within delineated lobes, what do these areas represent?

A

Necrosis

55
Q

Is it common for placentas to have some degree of macroscopic calcifications after 33 weeks?

A

Yes, over 50% do

(as the placenta ages they often get hypoechoic areas + calcifications)

56
Q

What is the retroplacental complex composed of?

A

-Decidua basalis
-Portions of myometrium (includes maternal veins draining placenta)

57
Q

At what week is the retroplacental complex visible?

A

Week 14

58
Q

SF of retroplacental complex (RPC)?

A

Hypoechoic area 10-20mm deep to placenta

59
Q

What can an anterior RPC lead to?

A

Excessive bleeding during invasive procedures

(ex C section or amniocentesis)

60
Q

Large venous channels can be seen in the RPC, m/c seen in what location?

A

Posterior placenta

(pressure from gravity can overdistend the veins)

61
Q

What is placental grading?

A

Grades degree of placental calcifications

62
Q

Are placental calcifications still considered a marker for lung maturity?

A

No

63
Q

What factors affect degree of placental calcifications?

A

-Smoking
-Low maternal age
-Parity
-The season

64
Q

Premature placental calcifications can occur in maternal hypertensive states + are associated with what?

A

IUGR

65
Q

What conditions can delay the rate of placental calcifications?

A

-Gest diabetes
-Fetal cardiopulmonary disorders

66
Q

Do we use placental grading on the island?

A

No

67
Q

List the 3 gradings on placental calcifiactions?

A

Grade 0: none
Grade 1: scattered calcifications
Grade 2: basal calcifications with increase in lobulations
Grade 3: basal + interlobar septal calcifications

(basal = base closest to uterus)

MIDS 187 (19 decks)

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