The normal first trimester Flashcards
what is gestational age?
used by clinicians and sonographers
aka menstrual age
1st day of pregnancy is 1st day of LMP
adds 2 weeks (14 days) to conceptual age
What is conceptional age?
used by embryologists
aka embryologic age
1st day of pregnancy is conception
what is the ovum?
egg released from ruptured graffian follicle
what is the zygote?
fertilized ovum
for 12 days after conception during implantation process
what is the morula?
16 stage cell and greater
what is a blastocyst?
enters uterus at day 4-5 after fertilization
implants into the endometrial lining lining begins 7-9 days after fertilization
What is the baby call the Embryo?
from implantation until end of 10th week
When is ovulation
day 14 of 28 day cycle
fertilization occurs when?
within 1-2 days after ovulation
in distal Fallopian tube
fertilized ovum becomes ZYGOTE - zona pellucida forms around zygote prevents sperm from penetrating
What happens when the ruptured graffian follicle becomes corpus luteum
secretes progesterone and estrogen
What is the job of the morula?
continues cellular proliferation
becomes blastocyst - fluid filled cavity
What does the blastocyst consist of?
blastocyst
trophoblast
inner cell mass
What happens during the blastocyst stage?
Contains trophoblastic cells (cells that make up the placenta)
secretes hCG (causes endometrium to convert to decidua)
form chorion and placenta
“inner cell mass” become future embryo, yolk sac and amnion
enters uterus 4-5 days after fertilization
When is implantation completed?
6-9 days post fertilization (super complete by day 12)
What do trophoblast produce?
enzymes
create lacunae (blood pools formed by eroded maternal capillaries) which nourish trophoblastic cells
What happens during implantation?
Enzymes produced by trophoblast
blood exchange network formed between mother and blastocyst
mature into placental/maternal circulation
when complete zygote buried in one wall of uterus
may cause light vaginal bleeding (implantation bleeding)
When complete trophoblast forms primary villi which encircle early gestational sac
What produces the hCG?
trophoblastic cells
What is the outer membrane of the gestational sac?
chorion
what is chorion frondosum?
early chorionic villi
attaches to endo becomes fetal side of placenta
is the chorion laeve involved with implantation?
no
what creates the “double bubble?”
the decidua capsularis + decidua vera parietalis = decidua vera (double bubble)
the white reaction around the gestational sac
What does the deciduas basalis turn into?
the placenta
maternal component of placental attachment
Do we ever see the primary yolk sac?
no we only see the secondary
When does the secondary yolk sac form?
approx day 23 (9 days after fertilization) primary yolk sac is “pinched off”
What happens with the secondary yolk sac during early gestation development?
seen sonographically in first trimester
Function: transfer of nutrients, hematopoiesis (forming blood cells), angiogenesis ( forming of blood vessels), formation of digestive tract
amniotic and chorionic cavities develop at the same time period
What happens around 5 weeks?
gastrulation - creating 3 germ cell layers
cardiovascular formation begins - begins to form immediately after gastrulation is complete in 5-8 weeks
(normal FHR 120-160bpm)
neurulation - formation of neural tube - complete closure by 7 weeks
When is the embryonic phase?
week 6-10
What happens in the embryonic phase?
organogenesis - main feature
all major internal and external structures begin to develop
embryo changes from flat dislike appearance to C-shaped structure, then human like appearance
CRL rapid development - 35mm by 10th week
most susceptible to teratogens
nearly all congenital malformation originate before or during
limb buds form
brain growth
midgut herniation
When is the embryo most susceptible to teratogens?
during the embryonic phase
radiation, drugs, viruses, poor nutrition, toxins, alcohol, smoking etc
When is the beginning of the fetal period?
weeks 11 and 12
What happens in the fetal period?
organ and structures continue to grow and develop
fetal head disproportionately large almost 50% of the baby
fetal anatomy fully developed in late 1st trimester
in maternal biochemistry what kind of relationship is there between quantitative bHCG and sonographic findings?
Direct relationship
What is PAPP-A?
a pregnancy marker
associated plasma protein - A
insulin like growth factor in pregnancy
associated with growth processes bone and tissue formation
decreased levels in early pregnancy - marker for trisomy 21
levels may be linked with preterm labor and preeclampsia
What is the TA sonographic technique and evaluation?
overall view of pelvic sturctures/anatomic relationships/pelvic masses
What is the sonographic technique for TV?
more detailed evaluation of pelvic anatomy/pathology
sagittal and coronal/semicoronal planes
more detailed evaluations of gest. sac and contents, fetus
Why would you use the transperineal sonographic techinque?
visualize cervix - sometimes done in first trimester…usually done in second
can be done if patient refuses tv
Why would you use 3D evaluation in first trimester?
clinical value not really established
Pulsed doppler should be used in first trimester?
only if absolutely necessary….use M-Mode.
Who sets the standards for OB sonography?
ACR
AIUM
ACOG
What major components are scanned in the first trimester?
Uterus and adnexa - presence of gestational sac
sonographic measurements of embryo and or gestational sac
presence/absence of fetal cardiac activity
fetal number and chronicity of multiple gestations
uterus, adnexa, cul-de-sac, ovaries
What are the normal sonographic features of the gestational sac?
round or oval
fundal position
eccentrically placed
smooth contours
decidual wall thickness > 3mm
if there is implantation in the LUS what are the placenta issues?
placenta accreta
placenta previa
What is MSD?
mean sac diameter
What is the measurement of the yolk sac between 5 - 5 1/2 weeks gestation?
> 12 mm MSD
embryo - > 18mm MSD
Gest Sac grows 1mm/day in early pregnancy
Where do you find the yolk sac?
within the chorionic sac
what is the earliest intragestational sac that you can see?
yolk sac - normally seen from 5 weeks gestation
how is the yolk sac initially attached to the embryo?
yolk stalk
What is the typical size of the yolk sac?
2-6 mm
over 6mm = abnormal
When is the baby called a fetus?
after the first 10-12 weeks
What is the zygote or conceptus?
undergoes rapid cellular division
forms 16-18 cell morula
What is Decidua?
glycogen rich mucosa - nourishes early pregnancy
What is the decidua capsularis?
layer of endo that heals over the implanted gestational sac
What is decidua vera parientalis?
endo not in direct contact with gestational sac
What is the lab values when the gestational sac is visualized transvaginally?
500-1000 mIU/ml
What is the lab value for visualization of the gestational sac transabdominally?
1800 mIU/ml
What should happen to the hCG levels every 48 hours in the first 6 weeks?
it should double
hCG levels plateau and then decline at 9-10 weeks
What is suspected when hCG levels do not increase normally?
pregnancy is abnormal
possible ectopic or trisomy 21
What two values are used in combination in 1st trimester (9-11 weeks) as a marker for trisomy 21 (downs syndrome)
hCG level and PAPP-A
when can the amniotic cavity and membrane, chorionic cavity, yolk sac and embryo be seen?
5.5 - 6 weeks
What happens to the yolk sac at approximately 8 weeks gestation?
with amniotic cavity expansion, the yolk sac, which lies between amniotic and chorionic membranes detaches from the yolk stalk
When is the yolk sac resorb and no longer seen?
Sonographically by 12 weeks
persistent yolk sac does occur
persistent yolk sac my be visualized at placental umbilical cord insertion where amniotic and chorionic membranes fused
At the beginning of the 5th week bilaminar embryonic disk undergoes gastrulation and converts into what?
trilaminar (three germ layer) embryonic disk
What does visualization of the yolk sac predict?
viable pregnancy in 90% of cases
When the yolk sac typically no longer seen?
by 12 weeks
