OB Ch 55-57 Flashcards
What are the fetal membranes comprised off
- Chorion
- Amnion
- Allantos
- Yolk sac
Chorionic plate
The fetal surface of the placenta
Basal plate
The maternal surface of the placenta
Chorion frondosum
Forms the fetal part of the placenta and contains the villi
Chorion laeve
The nonvillious part of the chorion around the gestational sac
Decidua basalis
Decidua reaction that occurs between the blastocyst and the myometrium
Decidua capsularis
Decidua reaction that occurs over the blastocyst closest to the endometrial cavity
Decidua vera (parietalis)
Decidua reaction except for the areas beneath and above the implanted ovum
Functions of the placenta
- Respiration
- Nutrition
- Excretion
- Protection
- Storage
- Hormonal production
What is the major functioning unit of the placenta?
Chorionic villus
Velamentous placenta
Refers to the insertion of the umbilical cord that inserts on the membranes
Battledore placenta
Refers to the insertion of the umbilical cord at the margin of the placenta, within 10 mm of the edge
Labor may cause the cord to prolapse or be compressed during contractions
Weeks that the chorion and amnion fuse together
16th week
How big is the yolk sac
.8 mm
Function of hCG
- Causes the uterine endometrium to convert to decidua, a glycogen rich mucosa that nourishes the early pregnancy
- Keeps the corpus luteum functioning, so that the corpus luteum continues to produce estrogen and progesterone
Primary cause of placentomegaly
Maternal diabetes and Rh incompatibility
Common site of fibrin deposits
Appears as hypo echoic areas beneath the chorionic plate of the placenta
Complications of previa
- Preterm delivery
- Maternal hemorrhage
- Increased risk of placental invasion
- Increased risk of postpartum hemorrhage
- IUGR
Three placental invasions
- Percreta
- Increta
- Accreta
*Penetrates beyond the endometrial lining of the uterus
Placenta percreta
Penetration of the chorionic villi through(per-) the uterus
Placenta increta
Further extension of the chorionic villi into (in-) the myometrium
Placenta accreta
The chorionic villi attach to the myometrium without muscular invasion.
-Occurs in 1 to 2500 deliveries
Circumvallate
Attachment of the placenta membranes to the fetal surface of the placenta rather than to the underlying villous placental margin
-Occurs in 1-2% of pregnancies
Succenturiate
The presence of one or more accessory lobes connected to the body of the placenta-by-placenta vessels.
- Occurs in 3-6% of pregnancies
- Lobes develop infarcts and necrosis
Placental abruption
Refers to the separation of a normally implanted placenta prior to term delivery
- Occurs in 1 in 120 pregnancies
- Bleeding into the decidua basalis
Types of abruption
- Retroplacental abruption
- Marginal abruption
Retroplacental abruption
Results from the rupture of spiral arteries and is a “high pressure” bleed. Associated with hypertension and vascular disease.
-Hematoma is between the placenta and uterus
Marginal abruption
Most common type; also known as subchorionic bleeds.
Results from tears of the marginal veins and represents a “low pressure” bleed.
Hemorrhage arises from the edge of the placenta, dissects beneath the placental membranes
Associated with little placental detachment
Marginal previa
Does not cover the os, but its edge comes to the margin of the os
Complete previa
The cervical internal os is completely covered by placental tissue
-20% of patients
Partial previa
Only partially covers the internal os
Low-lying placenta
Is implanted in the lower uterine segment, its edge does not reach the internal os
Maternal conditions that cause small placenta
- IUGR
- Intrauterine infection
- Aneuploidy
Vasa previa
Potentially life-threatening fetal complication that occurs when large fetal vessels run in the fetal membranes across the cervical os.
-Occurs in 1 of 2500 deliveries
Two common causes of vasa previa
- Velamentous insertion of the umbilical cord into placental membranes
- When a succenturiate lobe is present and the connecting vessels traverse the cervix
Most common benign vascular tumor of the placenta
Chorioangioma
-1% of pregnancies
Umbilical cord knots
- True knots
- False knots
True knots of the umbilical cord
Arise from fetal movements and are more likely to develop during early pregnancy when relatively more amniotic fluid is present.
Associated with advanced maternal age, multiparity, and long umbilical cord
False knots of the umbilical cord
Seen when the blood vessels are longer than the cord. Folded on themselves and produces nodulations on the surface of the cord
Nuchal cord
Most common cord entanglement in the fetus, seen around the fetal neck
- Single loop 20% of deliveries
- Two loops 2.5%
What might a single umbilical artery by caused from
Atrophy of one of the umbilical arteries in the early development stage
Associated with congenital anomalies in 20-50% of cases
Cord prolapse
Occurs when the cord lies below the presenting part. Exist when presenting part does not fit closely and fails to fill the pelvic inlet
Short cord
<35 cm in length
may predispose the fetus to inadequate descent, cord compression, fetal distress, and oligohydraminos
Long cord
> 80 cm in length
Coiling of the umbilical cord
Normal and related to fetal movement. May coil as many as 40 times, usually to the left and near the fetal insertion site
Thrombosis is more common in which umbilical vessel
Umbilical vein
How is the cord formed
Forms during the first 5 weeks of gestation. Fusion of omphalomesenteric (yolk sac) and allantoic ducts
Length of the umbilical cord in the first trimester
Same length as the CRL
Omphalomesenteric cyst
Cystic lesion in the umbilical cord caused by persistence and dilatation of a segment of the omphalomesenteric duct lined by epithelium of gastrointestinal origin.
Found closer to the fetal cord insertion
More common in females (5:3)
Varix of the umbilical vessels
Focal dilatations of the umbilical vessels affecting the umbilical artery and vein.
Appears as a dilated intra-abdominal, extra hepatic portion of the umbilical vein
Omphalocele
Results in failure of the intestines to return to the abdomen. Hernia may consist of a single loop of bowel or contain most of the intestines.
-1 in 5000 births
Gastroschisis
Right paraumbilical defect involving all layers of the abdominal wall, 2-4 cm. Never covered by membrane; directly exposed.
Amniotic band syndrome
Multiple fibrous strands of amnion that develop in utero that may enable fetal parts to cause amputations malformations of the fetus
Hypoplastic umbilical artery
When one artery is smaller than the other.
Discordant blood flow seen in umbilical artery Doppler.
Resistive index is higher in the smaller artery, and end-diastolic flow may be absent
Associated with placental pathology, polyhydramnios, congenital heart disease, fetal growth restriction, and stillbirth
How is amniotic fluid developed
It is produced by the umbilical cord, the membranes, lungs, skin and kidneys
When does fetal production of urine and swallowing begin
8-11 weeks gestation
*urine production is most significant at 18-20 weeks
What regulates the amount of amniotic fluid
The kidneys; fetus swallowing
How much does amniotic fluid increase each day
10 mL/day
Signs of polyhydramnios
Excessive amount of fluid that causes the uterine size to be larger than expected for gestational dates.
Volume greater than 2000 mL
*Also known as hydramnios
Maternal conditions for polyhydramnios
Diabetes melitus, obesity, Rhesus incompatibility, anemia, congestive cardiac failure, and syphilis
Signs of Oligohydraminos
Reduction in the amount of amniotic fluid resulting in fetal crowding and decrease fetal movement
Amniotic sheets
Identified as echogenic nonfloating bands that cross through the amniotic cavity. Thicker bands associated with amniotic band syndrome.
Doesn’t cause fetal malformations and most likely signify uterine synechiae
Whats the best way a sonographer can assess amniotic fluid
Subjective assessment; “eye-ball”
Do twin pregnancies have a higher or lower AFI
Slightly lower AFI
Function of the amniotic fluid
- Cushion to protect fetus
- Allows embryonic and fetal movements
- Prevents adherence of the amnion to the embryo
- Allows symmetrical growth
- Maintains constant temperature
- Acts as a reservoir to fetal metabolites before their exertion by the maternal system
When may amniotic fluid appear generous
20-30 weeks
What fluid measurement is both valid and reproducible
AFI method
RUQ+RLQ+LUQ+LLQ=AFI
Congenital anomalies associated with polyhydramnios
Central Nervous System and Gastrointestinal system
*Box 57-2 p. 1255
What kind of prognosis does persistent oligohydramnios carry
Poor prognosis regardless of its cause
Synechiae
Scars within the uterus
Particles in the amniotic fluid
- vernix caseosa
- Amniotic sludge-used to describe dense collection of echogenic particles within the fluid at the level of the cervix
Normal AFI
10-20 cm (2 cm pocket)
- Low: 5-10 cm
- High: 20-24 cm
Maximum vertical pocket
Assessment of amniotic fluid is done by identifying the largest pocket of amniotic fluid, should measure greater than 1 cm
Measured at right angles to uterine contour
- Oligo: <2cm
- Normal: 2-8 cm
- Poly: >8cm
Non anomalous reasons for oligohydramnios
- IUGR
- Premature rupture of membranes
- Postdate pregnancy (42 weeks)
- Chorionic villous sampling
