Module 5 Physiology of the 1st trimester Flashcards
Pregnancy is dated how?
By weeks from first day of the last menstrual period or LMP
How long is gestation in weeks?
40 weeks
How long is gestation in days?
280 days
How many trimesters are there for gestation?
Three trimesters
What is the first trimester?
Week 0-12
6/7 weeks long
What is the second trimester?
Week 13-27
6/7 weeks long
What is the third trimester?
Week 28-40
The conceptus is called what?
Embryo
When can we call the embryo a embryo?
from 10 weeks from LMP
What dates do sonography uses?
LMP
What dates does Embryologists use?
Conception dates
After 10 weeks LMP the embryo is called what?
Fetus
In the first trimester what can we do? 5
- Confirm pregnancy
- Confirm location of pregnancy
- Confirm that the size of the embryo agrees with the LMP dating
- Confirm the number of embryos
- Confirm viability
How do we define location of pregnancy?
Intrauterine pregnancy vs uterine pregnancy
What measurement do we use to size the embryo with LMP dating?
CRL- crown rump length
When does ovulation occur?
Day 14 of the ideal cycel
What must happen for ovulation to occur?
LH must surge
Ovum lives for how long?
12 to 24 hours
During ovulation what happens to the ovum?
It is ejected from the follicle and is propelled towards the fallopian tube
Approximately how many sperm cells are deposited near the cervix?
Around 200-500 million
How many sperm reach the ovum?
300-500 sperm
What is the normal sperm count?
100 million sperm/ml
What amount of sperm is considered as sterile males?
20 million or less
How long does sperm live for?
24 hours (some have been known for living up to 72 hours)
How many autosomes are given from each sperm/egg?
22 autosomes
How many sex chromosomes are given from each sperm/egg?
One
What happens during fertilization of the sperm head?
The sperm head becomes enlarged to become the male pronucleus
During fertilization the ovum completes what? and this does what?
It completes it second meiotic division at this time to become the female pronucleus
Both pronuclei fuse and what happens to the chromosomes?
They intermingle
What does fertilization start with?
The sperm passes through the zona pellucida
What happens during cleavage? What are the daughter cells called?
The chromosomes of the zygote arrange in the preparation for the 1st cleavage division. The two daughter cells are called blastomeres
What is cleavage?
Rapid cell division without a change in the size of the original zygote
12- 16 blastomeres are called what?
Morula
What is a zygote? What is it also called?
- Union of the sperm and ovum
- Also called conceptus
What is the morula? What happens to the morula with each division?
- Cluster of cells
- The morula remains the same size but the cells become smaller and smaller with each division
How is the blastocyst formed?
Secretions cross the zona pellucida and enter the morula forming a fluid cavity
What is the journey of the ovum?
The ovum travels about 24-36 hours to reach the ampullar portion of the fallopian tube where fertilization occurs
What day does the blastocyst enter the uterus?
It enters the uterus 6-7 days after fertilization
What is the dating that Implantation is complete when?
By 11-12 days post ovulation or 9-10 days post fertilizations
Fluid enters the zygote and separates into how many parts? What are they called?
Two parts
1. Trophoblast
2. Embryoblast
What is a trophoblast?
Outer cell to be placenta and chorion
What is a embryoblast? What are the sections?
Inner cell mass forms
1. Embryo
2. Yolk sac
3. amnion
Once the zona pellucida disappears what happens?
The blastocyst implants in the uterus
During implantation, the blastocyst does what?
Attaches to endometrial epithelium
What does the trophoblast do during implantation? (What does it differentiate into?)
Differentiates into two layers
1. syncytiotrophoblast
2. Cytotrophoblast
What does the syncytiotrophoblast produce? What does the Syncytiotrophoblast do?
- Produces hCG
- Invasively erodes the endometrial stroma, which allows the blastocyst to sinks into the endometrium
What are lacunae?
The eroded spaces from the formation of the syncytiotrophoblast
The lacunae becomes what?
The intervillous spaces of the placenta
What does the cytotrophoblast do?
Produces fingerlike projections that extend into the forming lacunar network
What are the fingerlike projections of the cytotrophoblasts called?
Primary chorionic villi
What is the chorion frondosum? 2
- the villi directly at the implantation site
- Early placenta
What is the smooth chorion or chorion laeve?
All the remaining villi around the gestational sac
The decidua cells of the endometrium does what during implantation?
It increases in size and content
When the endometrium undergoes a decidual reaction what happens? what does this result in?
It results in a ectopic pregnancy as well as resulting in what we call a pseudo sac within the uterus
If a pregnancy occurs in a bicornuate uterus this decidua reaction will occur where?
In the non pregnant horn making it look like a twin pregnancy
The trophoblastic cells of the embryo produce what? What is the result of this?
hCG regardless of location of implantation of the pregnancy thus supporting the corpus luteum on the ovary
What is the decidua basalis? What does it eventually become?
- The part of the decidua underlying the conceptus
- Eventually becoming the maternal side of the placenta
What is the decidua capsularis?
The part that covers over the gestational sac
What is the decidua parietalis (vera)?
All remaining decidua
What are the decidual layers?
- Decidua basalis
- Decidua parietalis (vera)
- Decidua capsularis
- Gestational sac
- Myometrium
- Uterine cavity
What is a double decidual sign?
A sonography descriptor
The opposed layers of the decidua parietalis and capsularis can be identified when?
Early Ultrasound.
Why should we always try to identify the decidua parietalis and capsularies early on?
To rule out pseudogestational sac (before the embryo can be seen)
What does the decidua Vera fuse with?
Capsularis
Prior to the fusion of the decidua Vera and capsularis, there is what between them?
Potential space between the two layers
During implantation what may occur and collect in the space?
Blood may occur and blood may collect in the space
What is the amniotic cavity?
Small spaces that occur between the inner cell mass and the trophoblast.
By day 9 of conception the small spaces between inner cell masses and trophoblast form what?
Amniotic cavity
The blastocyst cavity formed fromed from day 9 of conception is called what?
Primitive yolk sac
What is the double bleb sign?
The two blebs represent the early amnion and the yolk sac
When is the Double bleb seen?
Only seen on EV at around 5.5 weeks
For the embryo when implantation is occurring the inter cell mass does what?
Also changes
What are the two layers of the embryo?
- Epiblast
- Hypoblast
What does the epiblast give rise to?
Gives rise to nearly all the cells of the embryo
What does the epiblast also form?
The amniotic membrane which houses the amniotic fluid
What does the hypoblast do?
Contributes to the formation of primitive ectoderm
What is gatrulation?
Formation of the 3 layers
How long does the trilaminar disc take to form?
5 weeks
When does neurulation begin?
Three weeks from conception and 5 LMP
What is neurulation?
Formation of neural plate, neural fold and neural tube
Nureal tube closes around which day?
Around 40 LMP
Neural tube starts to close where and then does what?
Starts to close in the middle then progress to the caudal and cephalic ends
On ultrasound the decidua s basalis and chorion frondosum appear how?
Appear as the thickened area along the gestational sac
The embronic pole develops in close proximity to what?
Chorion frondosum
The head and tail of the embryo fold in, incorporating what?
Incorporating part of the primitive yolk sac
What is the remaining yolk sac called?
Secondary yolk sac
When can you see the remaining yolk sac?
From 5 to about 10-12 weeks LMP
What does the yolk sac do?
Provides nutrients prior to circulation
Hematopoiesis starts where?
In the yolk sac
What does the yolk sac form? 2
- Vessels
- Digestive tract
What does the yolk sac develop into?
Sex glands
What part of the yolk sac does the Allantois form?
Diverticulum (pouch) of the yolk sac
What does the Allantois form?
Forms umbilical vessels and also involved in formation of the urinary bladder
The Gestational sac grows how much?
1.1 mm/day
The embryo grows how much during the first 8 weeks?
1 to 2 mm/day up to 8 weeks
How much does a yolk sac grow in 10 weeks?
6mm is the upper limit of normal before 10 weeks
With EV scanning what can we see during 4 weeks?
Gets sac 2-3 mm
What do we see during EV scanning during week 5
Gest sac 5-6
Yolk sac 2-3
What is the range of CRL during week 6 with EV? What else is seen during this time?
CRL=3-4 mm
FH seen
What is the range for CRL seen during EV scanning around 7 weeks?
CRL = 12-14 mm
What are the two type of pregnancy tests?
- Qualititative
- Quantitative
What is a qualitative pregnancy test done by?
By urine
What is a qualitative pregnancy test?
Must reach the threshold to meet pregnancy.
When can a qualitative test detect pregnancy?
Can detect at 4 weeks LMP
What does a negative qualitative scan does not exclude?
Pregnancy
Why would a qualitative pregnancy be negative?
- To early to meet threshold
- A diluted urine sample result is negative
What is a quantitative test?
Tests the beta sub unit of human chorionic gonadotropin
How long does it take for a quantitative test take?
Eight hours and is very sensitive
Having a negative quantitative test determines what?
It determines that there is no pregnancy
When would a quantitative scan show?
23 days from LMP
What are the three different units for beta hCG?
- 1st international reference position (FIRP)
- 2nd international standard (SIS) values are 1/2 of FIRP.
- Third International standard (TIS) values the same as FIRP
What is the discriminatory zone?
Range of serum beta-HCG concentration above which a gestational sac which can be visualized consistently on ultrasound
An ectopic pregnancy can be suspected if what?
If on trans vagina sonography an intrauterine gestational sac is not demonstrated
With a beta hCG test of 1000 miU/ml, what happens?
You should see a small gestational sac by EV
At 1800 mlU/ml SIS. You should see what?
5- 10 mm sac transabdominally dating approx 5 weeks
An ectopic pregnancy should be considered if what?
No intrauterine pregnancy is visualized when the hCG is at or greater then discriminary zone
Fetal heart motion should be detected when the CRL is what size?
If the CRL of the embryo is 5mm or greater
Beta hCG levels double how many days?
Every two days
What does a higher beta hCG level indicated? 5
- Twins
- Hydratitform moles
- Choriocarcinoma
- Teratomas
- Gonadotropin
What does low beta hCG levels indicates? 3
- Ectopic
- Missed abortion
- Inaccurate dates
What is pseudocyesis?
A condition where a women feels pregnant
Psychologically what can cause pregnancy symptoms?
Psuedocyosis
What is the early Ob protocol ? 5
- Sag midline uterus
- Trans, vag, fundus, cervix
- MSD if no embryo is identified
- If an embryo is seen measure CRL three times and document yolk sac if seen.
- M mode heart rate is seen
What else can we do on a early on protocol? 4
- Document maternal ovaries
- Document a hematoma near the gestational sac If identified
- Document free fluid if see
- If 12 to 14 week size to do CRL and BPD
When do we do an endovaginal scan on all pregnancies?
All pregnancies under 7- 8 weeks gestation
Endovaginal sac is scanned when what? 2
- No embryo seen
- No embryonic heart beat seen
Why is dating important?
Certain tests are performed at specific times in the pregnancy. Inaccurate times may lead to false positives or false negatives
When is is nuchal translucency done? Why is it done?
Completed in the first trimester and assess for
- Chromosomal abnormalities
- Heart abnormalities
- Lung abnormalities
- Skeletal abnormalities
- Congenital infections
- Blood disorders
- Metabolic disorders
- Limited anatomy scan done at this time as well
When is the 2nd trimester routine detailed scan taken?
Approx 18-22 weeks
What do we do during the 2nd trimester detailed scan?
Assess all fetal anatomy measure all structures
What do we scan for during the third trimester?
Monitor for growth and fetal well being, (how well the placenta is working and is the fetus is safe in uterus)
What time do we do blood work during gestation?
- First trimester
- At 16 weeks
- At 24-28 weeks
What kind of blood work is done during the first trimester?
- hCG test
- Pregnancy associated plasma protein test
What kind of tests are done at 16 weeks?
- Triple screen
- Quad screen
What kind of tests are done at 24-28 weeks?
Glucose tolerance tests
