2nd/3rd Trimester Placenta and Umbilical Cord (Ch. 56 & 57)

T/F: placenta is a multifunctional organ

True—it acts as baby’s lung (supply oxygen), kidneys (filter waste), and GI and immune systems (deliver nutrients and antibodies)

placenta

• major role in exchanging oxygenated maternal blood with deoxygenated fetal blood

• develops from trophoblastic cells

what are the functional units of the placenta?

chorionic villi

placenta anatomy

divided into 2 parts

1. chorionic plate (fetal surface)

• surface facing amniotic fluid

• continuous with chorion

2. basal plate (maternal surface)

• surface facing uterine wall

• continuous with decidua basalis

placenta plate facing amniotic fluid/fetus is called…

chorionic plate

placenta plate facing uterine wall/mom is called…

basal plate

placenta physiology: 3 functions

• respiration (supply oxygenated blood to baby)

• excretion (remove waste produce and deoxygenated blood)

• nutrition

placenta physiology: hormones

• placenta produces and secretes:

  • HCG

  • estrogen

  • progesterone

placenta fully develops at __ weeks

15

what is a normal placenta size?

2 to 4 cm AP thickness

measuring technique for placenta

• measure in AP dimension

• thickest portion perpendicular to uterine wall

• DO NOT include uterine wall in measurement

• typically measure after 23 weeks

causes for large placenta

• diabetes

• anemia

• hydrops

• torch infections

3 causes for small/thin placenta

• infection

• intrauterine growth restriction (IUGR)

• aneuploidy (chromosomal abnormality)

SONO: placenta

• homogeneous

• pebble-gray—mildly more echogenic compared to uterine wall

  • may be more echogenic in 1st trimester

• smooth borders

• highly vascular structure

• rim of myometrium outside placenta should be noted

• prominent maternal vessels may be seen posterior to placenta (anechoic tubes)

• placental lakes may also be seen in placenta

what to document when evaluating the placenta:

• size/shape/position

• cord location

• abruption

• hematoma

• location (previa)

describing placental location in uterus and in relation to cervical os

1. in uterus

• anterior

• posterior

• fundal (in uterine fundus)

2. in relationship to cervical os

• close to os

• away from os

• covering os

  • if covering internal os, that is called previa

3 ways placenta appearance can be temporarily altered

1. placental migration

2. distended bladder

3. Braxton-Hicks contraction

placental migration

• refers to when placenta changes position in uterine cavity

• primarily explained by 2 theories:

  • LUS growth theory (when expanding uterus pulls placenta upward)

  • trophotropism theory (atrophic placenta in areas of low blood supply)

• location of placenta can be identified in 1st trimester

distended bladder

• changing bladder shape can create appearance of placental movement or a change in placental shape

• full bladder can elongate cervix and give false impression of previa

• emptying bladder allows cervix to be in normal position

** have patient empty bladder and reimage if previa is seen

Braxton-Hicks contraction

• practice/false contractions

• transient myometrial (uterine wall) contraction

• created appearance of a placenta mass (distorts placenta shape)

placental PW doppler and SONO evaluation

uterine artery PW (varies based on trimester):

• high RI flow pattern in 1st trimester

• low RI flow pattern in 2nd trimester

  • lots of blood flow going through uterine artery to get to placenta and supply baby with oxygen

SONO evaluation:

• use optimal gate, gain, scale, placement

• measure waveform and RI

4 permanent placental variations

1. succenturiate lobe

2. circumvallate or circummarginate

3. battledore cord insertion

4. velamentous cord insertion

succenturiate lobe

• aka accessory placental lobe

• one or more accessory placental lobes

circumvallate or circummarginate

• rare (1-2% of pregnancies)

• chorionic plate (fetal side) is smaller than normal —> amnion and chorion membranes fold back around the edges of placenta

  • ”double back”

battledore cord insertion

• aka marginal cord insertion

• cord attaches at edge of placenta

• “battledore” means badminton racket —> placenta is woven racket and cord is the handle

• 7-9% of pregnancies

• MC in twins

battledore cord insertion is usually ok, but could lead to…

• IUGR (intrauterine growth restriction)

• preterm labor

• fetal distress during labor

• risk of placental abruption

velamentous cord insertion

• RARE (0.1-0.8 of pregnancies)

• cord attaches to fetal membranes (amnion and chorion) increase of placental disc

• fetal arteries and vein are UNPROTECTED by Wharton’s Jelly at insertion

• high risk of cord compression, trauma, and rupture—especially during labor

delayed umbilical cord clamping

• babies are born with 2/3 of their blood

• 1/3 of their blood is still in placenta

• umbilical cord clamping/cutting is not done immediately after birth

  • wait 30-60 seconds after birth to allow more blood to transfer from placenta to baby

• benefits:

  • babies have higher hemoglobin

  • higher iron

  • better transition to breathing outside

** now a widely recommended as standard care

umbilical cord

• connecting yolk stalk and allantois ducts become the umbilical cord

  • allantois connect to fetal bladder (abdominal/fetal cord insertion point)—becomes belly button

• allantoic vessels become umbilical vessels

• surrounded by mucoid connective tissue: Wharton’s Jelly

• cord covered by amniotic membranes

• normal diameter: 1-2 cm

umbilical cords have how many vessels

• 2 smaller arteries, 1 large vein

• single umbilical artery (2 vessel cord) is found in 1% of singleton births

  • can be isolated

  • can be associated with congenital malformation

** umbilical arteries and vein functions opposite from typical a. and v.

umbilical arteries

• 2 umbilical arteries carry deoxygenated blood from fetus to placenta

  • umbilical arteries can be noted on either side of bladder at fetal insertion

umbilical vein

1 umbilical vein carries oxygenated blood from placenta to fetus

umbilical cord color Doppler

• color Doppler is used to visualize umbilical arteries and vein

• the bladder, when full, is seen between 2 umbilical arteries

• umbilical cord should be images in cross section and with color Doppler at level of bladder to confirm the number of cord vessels

type of placenta?

succenturiate lobe (accessory placenta)

type of placenta?

circumvallate/circummarginate (chorionic plate is smaller than basal plate —> folded membranes)

type of placenta?

battledore cord insertion (umbilical cord attaches to edge of placenta, rather than center)

type of placenta?

velamentous cord insertion (umbilical cord inserts into fetal membranes rather than placenta)

type of placenta?

battledore cord insertion

chorion frondosum

“portion of chorion that develops into fetal portion of the placenta” (chorionic plate)

chorionic villi

“microscopic vascular projections from chorion that combine with maternal uterine tissue to form placenta”

which part of the decidua surrounds the chorionic sac?

decidua capsularis

which part of the decidua unites with the chorion to form the placenta?

decidua basalis

placenta accreta vs. placenta increta vs. placenta percreta

placenta accreta

• growth of chorionic vlli superficially to myometrium; not does penetrate through myometrium

placenta increta

• growth of chorionic villi deep into myometrium

placenta percreta

• growth of chorionic villi through the myometrium to the uterine serosa

Wharton’s jelly

mucoid connective tissue that surrounds the vessels within umbilical cord