Module 5.1 : First Trimester Normal Flashcards
pregnancy dates
- pregnancy dated by weeks from first day of last menstrual period (LMP) or (LMNP)
- 40 weeks completed gestation (41)
- 280 days
- 3 trimesters
1st trimester dates
0 - 13 6/7 weeks
2nd trimester dates
14 - 27 6/7 weeks
3rd trimester dates
28 - 40 weeks
embryo
- the conceptus is called an EMBRYO from conception up to 10 week LMP
- after 10 week called a FETUS
importance of ultrasound - first trimester
- confirm pregnancy
- confirm location ( intrauterine vs. extrauterine)
- confirm size of embryo agrees with LMP dating (CRL)
- confirm number of embryos
- confirm viability ( fetal heart rate with m-mode)
ovulation
- occurs at day 14 in ideal cycle
- LH must surge for ovulation to occur
- ovum ejected from follicle and propelled toward fallopian tube
- lives fro 12 - 24 hours
sperm
- 200 to 500 million sperm deposited near cervix on 300 to 500 reach ovum
- 100 mill / ml is normal
- under 20 million considered sterile
- usually survive for 24 hours
fertilization
- sperm passes through the ZONA PELLUCIDA ( doesnt allow more sperm to fertilize ovum)
- sperm head enlarges to become male pronucleus and tail breaks off
- ovum completes second meiotic divison at this time to become female pronucleus
- both pronuclei fuse and the chromosomes intermingle
zygote
union of sperm and ovum
+ also called conceptus
morula
- cluster of cells 12-16 BLASTOMERES
- morula remains the same size but the cells become smaller and smaller with each divisions
blastocyst
- secretions cross the zone pellucida enter the morula forming a fluid filled cavity
The Journey
- the ovum travels 24 - 36 hours to reach the ampullae portion of the fallopian tube where fertilization occurs
- the blastocyst enters the uterus 6-7 days after fertilization
- implantation is complete by 11-12 days post ovulation or 9-10 days post fertilization
cleavage
- rapid cell division without a change in the size of the original zygote is CLEAVAGE
blastomeres
- chromosomes of the zygote arrange in the preparation for the 1st cleavage division the two daughter cells are called BLASTOMERES
blastocyst
- fluid enters the zygote and separates it into 2 parts
+ TROPHOBLAST
= outer cell to be placenta and chorion
+ EMBRYOBLAST
= inner cell mass ( forms embryo, you sac, amnion) - once the zone pellucida disappears the blastocyst implants in the uterus
implantation
- blastocyst attaches to endometrial epithelium
- trophoblast differentiates in to 2 layers
+ SYNCYTIOTROPHOBLAST
+ CYTOTROPHOBLAST
syncytiotrophoblast
- PRODUCES HCG
- invasively erodes the endometrial stroma and blastocyst sinks into endometrium
lacunae
- the spaces eroded in the endometrium by the syncytiotrophoblast
- become intervillous spaces of the placenta
cytotrophoblast
- produces finger like projections that extend into the forming lacunar network called PRIMARY CHORIONIC VILLI
primary chorionic villi
- finger like projection of cytotrohphoblast
- form
+ chorion frondosum
= villi directly at implantation site
= early placenta
+ smooth chorion or chorion laeve
= all the remaining villi around gestational sac (become chorionic membrane)
decidua (endometrium) reaction in the uterus
- decidua cells of the endometrium increase in size and content for implantation due to progesterone
- the endometrium will undergo a decidua reaction with an ectopic pregnancy as well regulating in pseudo sac
- if pregnancy occur in bicornuate uterus the decidua reaction will occur in the non pregnant horn making it look like twins
- trophoblastic cells of embryo produce hCG regardless of location of implantation supporting the corpus luteum on ovary
decidua layers of uterus
BCP
- decidua BASALIS
- decidua CAPSULARIS
- decidua PARIETALIS ( VERA)
decidua basalis
- part of decidua underlying the conceptus
- eventually becoming the maternal side of the placenta
decidua capsularis
- part that covers over the gestational sac
decidua parietalis ( vera)
- all remaining decidua
double decidual sign
- sonographic descriptor
- opposed layers of decidua parietalis and capsularis can be identified on early ultrasound
- should always try to identify this to rule out pseudo gestational sac before embryo can be seen
gift wrap
- in real pregnancy with gestational sac the layers of decidua will be easily indented and uniform in concentric layers
- in pseudo sac the layers are not uniform and har to see
fusion of decidua
- the decidua vera and capsularis fuse
- prior to this fusion there is potential space between the 2 layers this might cause some light bleeding
amniotic cavity
- small spaces occur between the inner cell mass and the trophoblast
- by day 9 from conception these form the amniotic cavity
- THE BLASTOCYST CAVITY NOW CALLED THE PRIMITIVE YOLK SAC ( not seen on ultrasound)
double bleb sign
- 2 blebs represent the early amnion and the yolk sac
- only seven on EV at 5 1/2 weeks
embryo divison
- while implantation is occurring the inner cell mass also changing
- inner cell mass becomes the BILAMINAR DISC (embryonic disc) at 4 weeks LMP
bilaminar/embryonic disc
2 layers
- epiblast
- hypoblast
epiblast
- gives rise to nearly all the cells of the embryo
+ also forms amniotic membrane which houses the amniotic fluid
hypoblast
- contributes to the formation of primitive ectoderm
trilaminar disc
- at 5 weeks
- gastrulation occurs = formation of three layers
+ endoderm
+ ectoderm
+ mesoderm
endoderm
- first layer to differentiate (inner)
- linings of the GI and respiratory tracts
ectoderm
- 2nd layer to differentiate (outer)
- forms CNS
- surface ectoderm such as hair, skin and teeth, nails
mesoderm
- 3rd layer to differentiate (middle)
- generally forms muscle and bone
embryonic stages
- zygote = fertilized ovum
- morula = same size but cell splitting
- blastocyst = when fluid enters the zygote at morula stage
- embryo = inner cell mass differentiates
- fetus = after 10 weeks LMP when embryogenesis is complete
neurulation
- begins at 3 weeks conception or 5 weeks LMP
- formation of neural plate, neural folds, and neural tubes
- neural tube closes around day 40 LMP
+ starts to close in middle thats progresses to the caudal and cephalic ends
neural tube abnormalities
- if caudal end doesnt close = spina bifida
- if cephalic end doesnt close = acephaly
visualizing embryo on ultrasound
- the decidua basalis and chorion frondosum appear as thickened area along gestational sac
- embryonic pole develops in close proximity to chorion frondosum
yolk sac formation
- head and tail of embryo fold in, incorporating part of the primitive yolk sac
- the remaining yolk sac called SECONDARY YOLK SAC
+ seen on ultrasound from 5 to 10-12 weeks LMP
yolk sac function
- provides nutrients prior to circulation
- hematopoiesis starts in yolk sac
- forms vessels
- formation of digestive tract
- development of sex glands
allantois
- diverticulum ( pouch) of the yolk sac
- forms umbilical vessels and also involved in formation of the urinary bladder
growth - gestational sac
- grows 1.1mm/day
growth - embryo
1-2mm/day up to 8 weeks
growth - yolk sac
- 6mm is upper limit of normal before 10 weeks
measurements
TAKEN INNER TO INNER
gestational sac sizes
Mean Gestational Age Mean Sac Diameter
6 weeks 0 days 1.5cm = L+W+H/3
7 weeks 0 days 2cm
8 weeks 0 days 3cm
EV scan at 4 weeks
gest sac 2-3mm
EV scan at 5 weeks
gest sac 5-6mm
yolk sac 2-3mm
EV scan at 6 weeks
CRL = 3-4mm
FH seen
EV scan at 7 weeks
CRL= 12-14mm
pregnancy tests
2 types
- qualitative
- quantitative
qualitative pregnancy test
- by urine
- takes short time
- can detect at even earlier than 4 weeks LMP
- must meet certain threshold to be positive
- negative does not exclude pregnancy
- not numbers
quantitative pregnancy test
- by blood
- tests beta sub unit of human chorionic gonadotropin (b hCG)
- takes 8 hours and very sensitive
- having negative test by this method excludes pregnancy
- will show positive 23 days from LMP
- b hCG plateau at 8 weeks
mean sad diameter in relation to beta hCG
- 30mm MSD equal 8 weeks
units for beta hCG
- 1st international reference preparation (FIRP)
- 2nd international standard (SIS) - values 1/2 of FIRP
+ OLDEST - 3rd international standard (TIS) - values same as FIRP
discriminatory zone
- with a beta hCG test of 1000mIU/ ml SIS, you should see small gestational sac = 4 weeks LMP by EV
- 1800 mIU/ml = 5 mm sac = 5 weeks trans abdominal
ectopic pregnancy
- should be considered if no IUP is visualized when the hCG is at or greater than the discriminatory zone
+ 500-1000mIU/ ml (SIS) = endovaginally
+ 1000-2000mIU/ml (FIRP) = endovaginally - mIU = milli international units
fetal heart motion
- should be detected if CRL of embryo is 5mm or greater by EV
levels of beta hCG
- should double every two days in normal intrauterine pregnancy until 8 weeks gestation
example - if patient hCG is 1000 mIU / ml on Monday what would it be on Wednesday?
1000 x 2 = 2000 mIU / ml
ectopic pregnancy effect on hCG levels
- because decidua not great access to maternal circulation so hCG may be less than doubling or the saw
high. beta hCG
- indicates
+ twins ( multiples)
+ hydatitiform moles (more genetic material)
+ choriocarcinoma
+ teratomas (overgrown ecto,endo,meso tumor)
+ gonadotropin producing tumor
low beta hCG
- indicates
+ ectopic
+ missed abortion (fetal demise)
+ inaccurate dates
pseudocyesis
- condition where a women feels pregnant
+ nausea, full feeling in pelvis, bloating - pregnancy test is negative and uterus will be normal non gravid
- no IUP detected within endometrium
- can psychologically create these symptoms
early OB protocol
- sag midline uterus
- trans vag, cx, funds
- MSD if no embryo identified
+ mean sac diameter = L + W + H / 3 - if embryo seen measure CRL 3 times
+ to be accurate
+ may be magnified - document yolk sac if seen
+ measure - m-mode heart rate if motion seen
- document maternal ovaries
- document menatoma near gestational sac if identified
- document free fluid if seen ( 2 planes)
- if 12-14 weeks size do CRL and BPD
- endovaginal always if under 7 weeks gestation
- endovaginal when necessary
+ no embryo
+ no embryonic heart beat seen
