C5.0: 1st Trimester Normal Flashcards
When is the conceptus called an embryo vs fetus?
Embryo: from conception to week 10 LMP
Fetus: After week 10
By which time are all structures formed and only need to develop?
After week 10
Reasons to do an US in the 1st trim.?
Confirm preg. Confirm location of preg Confirm that the size of the embryo matches with the LMP dating Confirm # of preg. Confirm viability of preg
what is the only way to confirm the viability of the preg?
Demonstrate the fetal heart beat with M mode (not doppler)
How do we confirm that the size of the embryo agree with the dating of LMP?
CRL measurement
A preg under how many weeks should have an EV?
Under 7 weeks
how long does the ovum live for?
12-24 hours
What is a normal sperm count and what is considered sterile? Approx. how long do sperm live?
100 million per ml is normal
20 million or less per ml is sterile
Live for approx. 24 hrs and up to 72 hrs
By what process are sperm and eggs produces?
Meiosis
How many sperm are produced by meiosis, and how many eggs?
4 sperm
1 egg
When does the 2nd meiotic division of the ovum occur?
After fertilization
How many autosomes are contributed by each parent?
And how many sex chromosome?
22 auto from each
1 sex chromo from each
Which sex chromosome does the mom always give?
X
when specifically does the Corona Radiata nourish the egg?
Before implantation
What happens to the sperm during fertilization?
It penetrates the zone pellucida and it drops its tail and the head enlarges to become the male pronucleus
What happens to the egg immediately after fertilization?
It undergoes its second meiotic division to become the female pronucleus
What occurs after the 2 pronuclei are formed?
They fuse and the chromosomes mix
What is a zygote? And whats another term for it?
The union of sperm and egg
Also called conceptus
What is a Morula?
A cluster of cells that undergo cell division but the morula doesnt get any larger…. the cells just become smaller with each division
When does a morula become a blastocyst? and when does the blastocyst enter the uterus?
When fluid penetrates the zone pellucida and enters the morula forming a fluid filled cavity
5-7 days after fertilization
When is implantation complete?
~day 11-12 post ovulation
~day 9-10 post fertilization
Where does the blastocyst usually implant?
On the posterior fundal wall
What is cleavage?
Rapid cell division without a change in size of the zygote
After the first cleavage division, what are the two daughter cells called?
Blastomeres
At what number of cells is the zygote called a morula?
12-16 blastomeres
What are the 2 types of cells in the blastocyst?
1) Trophoblast (outer layer)
2) Embryoblast (inner layer)
What does the trophoblast form and what is its function?
Placenta and chorion
Function is to gain access to maternal circulation
What does the embryoblast form?
The embryo, yolk sac and amnion
What must happen to the zone pellucida before implantation?
It must disappear
The trophoblast separates into which 2 layers?
1) Syncytiotrophoblast
2) Cytotrophoblast
Function of the Syncytiotrophoblast
Produces hCG
Erodes the endometrial stroma so the blastocyst can sink in and forms lacunae in the stroma
What do the lacunae eventually become?
The intervillous spaces of the placenta
What does the cytotrophoblast produce?
Primary chorionic villi which project into the lacunae
what are the 2 types of primary chorionic villi?
Chorion Frondosum
Smooth chorion/Chorion Laeve
Chorion Frondosum
the villi directly at the implantation site… form the early placenta
Smooth chorion/Chorion Laeve
all remaining villi around the gestational sac
Which two samples can be analyzed for chromosomal abnormalities?
Amniotic fluid
Chorionic villi
What is the decidua reaction?
When the decidua cells of the endometrium increase in size to prepare for implantation (caused by hCG and progesterone)
What causes a pseudo-sac to form in the uterus?
An ectopic pregnancy because it triggers the same decidua reaction of the endometrium as an intrauterine preg.
With a pregnancy in a bicornuate uterus, what happens to the non pregnancy horn?
The decidua reaction will occur in the non preg horn (pseudo-sac formed) and it will make it look like a twin preg
What is the acronym to remember the decidua layers of the uterus? And what are the layers?
BCP (birth control didnt work in this instance)
1) Decidua basalis
2) decidua capsularis
3) decidua parietalis (or vera)
what is the location of each of the decidua layers?
Basalis: the area underlying the conceptus (will becomes the maternal side of the placenta)
Capsularis: part that covers the gestational sac
parietalis: all remaning decidua
What is the double decidual sign?
When you can see the layers of the perietalis and the capsularis on US….. rules out a pseudogestational sac before the embryo can be seen
Which layers of a decidua fuse?
The vera/parietalis and the capsularis
what can occur when these layers fuse?
Blood can accumulate in the potential space between these two layers and mimic a twin preg.
Which yolk sac do we see on US?
2ndary yolk sac
What is the amnionic cavity and when does it form?
a small space between the inner cell mass and the trophoblast
forms by day 9
Once the amniotic cavity is formed, what is the blastocyst cavity called?
The primitive yolk sac
whats the double bleb sign and when is it seen?
Represents the early amnion and yolk sac
Seen around 5.5 weeks on EV ONLY
When do the amnion and chorion fuse?
week 16
When does the embryoblast/inner cell mass become the bilaminar disk?
4 weeks LMP
2 layers of the bilaminar disc
1) epiblast
2) hypoblast
What does the epiblast form?
gives rises to almost all cells in the embryo and forms the amniotic membrane
What does the hypoblast form?
helps form the primitive ectoderm
What is gastrulation and when does it occur?
The formation of the three layers of the trilaminar disk
5 weeks LMP
What are the layers of the trilaminar disk and in what order do they differentiate?
Endoderm (inner): 1st
Mesoderm (middle): 3rd
Ectoderm (outer): 2nd
What do each of the layers of the trilaminar disk form?
endoderm: Lining of the GI and respiratory tract
mesoderm: forms muscles, bone, urogenital tract
Ectoderm: hair, skin, teeth, nails and CNS
What is neurulation and when does neurulation occur?
The formation of the neural plate, neural folds and neural tube
begins at week 3 after conception or 5 weeks LMP
When and how does the neural tube close?
~40 days LMP, it starts to close in the middle and then progresses outwards
Ancephaly and spinal bifida occur when which areas of the neural tube dont close?
Ancephaly: Cephalic end doesnt close
Spinal Bifida: Caudal end doesnt close
what parts of the fetus make up the yolk sac?
the head and tail which fold in to make up part of the sac
when is the yolk sac seen on US?
from 5 weeks until week 10 or 12
Function of the yolk sac
Provide nutrients before circulation
Begins the development of hematopoiesis
Forms the digestive tract
Forms the sex glands
What is the allantois and what does it form?
a pouch of the yolk sac
forms the umbilical vessels and the bladder
how much does the gestational sac and the embryo grow each day?
~1.1mm for gest. sac
~1-2 mm up until 8 weeks
whats the upper limit of normal for the yolk sac before 10 weeks?
6mm (measured inner to inner well)
what is the mean sac diameter of the gest. sac for 6, 7 and 8 weeks?
6: 15 mm
7: 20 mm
8: 30 mm
(L+ W+D/3)
when do you measure the gestation sac?
when you dont see an embryo
What are the gest. sac measurements with EV scanning for weeks 4 and 5? and the yolk sac meas. for 5. weeks?
4: 2-3 mm
5: Gest: 5-6mm
Yolk: 2-3 mm
What is the CRL at 6 and 7 weeks with EV scanning?
6: 3-4 mm
7: 12-14 mm
what are the two types of pregnancy tests and which is qualitative/quantitative?
Urine (qualitative)
Blood (quantitative)
When can a urine test detect pregnancy and what are some draw backs of this test?
at 4 weeks LMP
problems:
must meet threshold to be positive
negative result doesnt exclude pregnancy
how does a blood test detect preg.?
tests the beta sub unit of hCG
at what date LMP will a blood test detect a pregnancy?
23 days
when does hCG plateau?
8 weeks
what are the different units for Beta hCG?
1st international reference preparation (FIRP)
2nd international standard (OLDEST) (SIS)
3rd international standard (TIS same values as FIRP)
when should an ectopic pregnancy be considered (with reference to hCG)?
if theres no IUP and hCG is at or greater than the discriminatory zone
whats the discriminatory zone?
500-1000 mlU/ml 2nd IS
or
1000-2000 mlU/ml IRP
FOR EV SACNNING ONLY
when should fetal heart motion be detected?
if CRL of embryo is >5 mm by EV
day 23
B hCG levels double how often?
every 2 days until 8 weeks gestation
how does ectopic preg. effect B hCG level?
the B hCG levels may not quite double every 2 days…. it could be slightly less, or the same as a normal preg.
what do high levels of B hCG indicate?
twins hydatitiform moles (more genetic material that norm) tumor of the chorion, ovary, or the fetus
what do low levels of B hCG indicate?
ectopic preg
fetal death
inaccurate dating (can also cause high levels of hCG)
what is pseudocyesis?
when a women thinks and feels like she’s pregnant
whats the 1sr trim. OB protocal
- ‘female pelvis’
- MSD if no embryo… if embryo, measure CRL 3 times (look in trans to find longest length)
- measure and document yolk sac
- m mode heart rate
what is the vitelline vessel?
it connects the yolk sac to the embryo
when do you do both an CRL and a BPD measurement?
if the fetus is 12-14 weeks
Is the yolk sac located in the amniotic cavity?
No
Can the amnion be visualized on US if there’s no embryo seen?
Yes
What is rhombencephalon?
the hindbrain of the embryo…. seen only in the 1st trimester.
A cystic structure in the posterior fossa
In week 8 the midgut herniated into the umbilical cord causing a protrusion of the fetal abdomen, what is this called?
Physiological midgut herniation
How long does it take the egg to reach the ampulla portion of the Fallopian tube?
24-36 hrs
What forms the fetal part of the placenta?
Chorion
What’s another name for the bilaminar disk
Embryonic disk
The CRL measurement is very accurate for dating of the preganancy up to how many weeks?
12
Crown rump measurements are accruate to +/- how many days?
3
The yolk sac can often be seen on an EV ultrasound when the MSD is how many mm?
8
The yolk sac is often seen by a transabdominal ultrasound when the MSD measures how many mm?
20
The embryo can often be seen on an EV ultrasound when the MSD measures how many MM?
16
Does the embryonic pole develop in close proximity to the chorion frondosum?
Yes
The embryo is readily visualized on a transabdominal ultrasound when the MSD measures how many mm?
25
after how many wks can a fetal heart beat definitely be detected on EV
after 6
