OB 1 Chpt 49 The Early Embryonic Stage of the First Trimester

amniotic cavity

cavity in which fetus exists, forms early in gestation, fills with amniotic fluid to protect the fetus

chorionic cavity

surrounds the amniotic cavity, yolk sac is within

corpus luteum cyst

small, yellow endocrine structure that develops within a ruptured ovarian follicle, secretes estrogen and progesterone

crown rump length

most accurate measurement of the embryo in the first trimester

decidua basalis

the villi on the maternal side of the placenta or embryo, unites with the chorion to form the placenta

decidua capsularis

the villi surrounding the chorionic sac

diamniotic

multiple pregnancy with 2 amniotic sacs

dichorionic

multiple pregnancy with 2 chorionic sacs

monoamniotic

multiple pregnancy with one amniotic sac

monochorionic

type of pregnancy with one chorionic sac

double decidual sac sign

interface between the decidua capsularis and the echogenic, highly vascular endometrium

embryologic age

age calculated from when conception occurs

embryonic period

time between 6 and 10 weeks gestation

endovaginal transducer

high-frequency transducer that is inserted into the vaginal canal to obtain better definition of the first trimester pregnancy

hematopoiesis

production and development of blood cells

hCG

hormone secreted by the trophoblastic cells (developing placenta cells) of the blastocyst, lab test indicates pregnancy when values are elevated

IUP

intrauterine pregnancy

menstrual age/ gestational age

length of time calculated from the first day of the last normal menstrual period to the point at which the pregnancy is being assessed

mean sac diameter

MSD

length + AP + width divided by 3

mean sac diameter formula

primary yolk sac

first site of formation of red blood cells that will nourish the embryo

secondary yolk sac

formed at 23 days when primary yolk sac is pinched off by extra embryonic coelom

yolk stalk

umbilical duct connecting the yolk sac with the embryo

zygote

fertilized ovum resulting from the union of male and female gametes

ovulation

discharge of an ovum or ovule from the ovary

ovum

egg in the ovary of the female, this egg is called the female gamete

zygote

fertilized ovum

distal tube

where does fertilization ocuur

zygote

from conception to implantation, approx 12 days, 2-16 cells

morula

day 4, 16-30 cells, the mass of cells resulting from the cleavage of the zygote before formation of a blastula

blastocyst

enters uterus on days 4 to 5, implantation occurring 7 to 9 days after ovulation, contains trophoblastic cells and the inner cell mass which forms the embryo

2 weeks

how many weeks does gestational age add to conceptual age

embryologist dating pregnancy

conceptual age or embryologic age, conception as the first day of pregnancy

clinicians/ sonographers dating pregnancy

gestational age or menstrual age, first day of the last menstrual period as the beginning of gestation

zygote

fertilized ovum until implantation, 12 days after conception

embryo

from the beginning of implantation until end of 10th week of menstrual age

fetus

after the first 10 menstrual weeks

menstrual

all embryonic dates in this chapter reflect ____ age rather than embryologic age

adding 2 weeks to embryologic age

menstrual age (also known as gestational age) is calculated by ….

menstrual age

aka gestational age, length of time calculated from the first day of the last normal menstrual period as the beginning of gestation or when pregnancy started, during a normal 28 day cycle, a mature ovum is released at day 14

fertilization

ovum is swept into the distal fallopian tube via fimbria, fertilization occurs within this region 1 to 2 days after ovulation, follicle that released the mature ovum hemorrhages and collapses to form corpus luteum

progesterone and estrogen

what does the corpus luteum secrete

cleavage

fertilized ovum, undergoes rapid cellular division through a process called

4-5 days after fertilization

cleavage happens and cell splits but doesn’t grow to form morula, 16-32 cells

morula, blastocyst, blastulation

further cell proliferation brings the ____ to become a _____ - 200-300 cells through a process called ______

embryo

blastocyst contains trophoblastic cells and the “inner cell mass” which forms the _____

eat into, trophoblastic

during implantation, enzymes produced by trophoblasts “____ ____” decidual tissue, creating space for _______ proliferation

lacunae

blood pools, known as _____, form as maternal capillaries erode, nourishing proliferating trophoblastic cells

between days 5 and 12, implantation

primitive blood exchange network between mother and conceptus now formed, lacunae and trophoblastic cells develop into mature placental/maternal circulation complex that will sustain pregnancy, zygote buries itself into one wall of the uterus

around day 12

when is implantation into the uterine decidua completed

days 13-19

cells move towards midline during a process called gastrulation, forming a groove called the primitive streak and developing three germ layers

endoderm

this germ layer gives rise to lining of digestive and respiratory system and organs such as stomach, liver, and pancreas

mesoderm

this germ layer gives rise to bone, muscle, connective tissue, dermis of the skin and urogenital system

ectoderm

this germ layer gives rise to the most outermost skin layer and central nervous system

primary villi

trophoblast goes on to form

primary villi

initially circles the early gestational sac, giving it the sonographic ring appearance

23 days

at approx how many menstrual days age does the primary yolk sac pinch off by the extra embryonic coelom forming the secondary yolk sac

secondary yolk sac

which yolk sac is seen sonographically throughout the first trimester

amniotic and chorionic cavities

as secondary yolk sac is forming what else develops

embryonic phase (4-10 weeks)

in this phase all major internal and external structures begin to develop, CRL develops rapidly

heart

what is the first thing to develop

5 to 5 ½ weeks

when is HB seen on TV

1-13

what weeks is the first trimester

fetal period

last 2 weeks of the first trimester mark beginning of the

first trimester

head disproportionately larger than body, head is ½ of CRL, body growth accelerates and catches up, fetal anatomy fully develops by the end and goal of sono is anomaly detection

hCG

what hormone is secreted by the trophoblastic cells of the blastocyst, and indicates pregnancy when elevated

10

gestational sac size and hCG levels increase proportionately until how many menstrual weeks

45 mm MSD

what is the gestational size sac at 10 weeks

plateau, grow

after 10 weeks hCG levels ____ and subsequently decline, gestational sac continues to _____

3000 mIU/ml or greater

TA normal gestational sac can be consistently demonstrated when hCG level is:

500 mIU/ml

TV normal GS can be demonstrated when the hCG level is as low as:

abnormal pregnancies

low hCG level relative to gestational sac development

ectopic pregnancy

suspected when lower hCG level than normal IUP and the gestational sac is not seen within the uterus

doubling, 3.5, 66, 48

normal IUP <7 weeks demonstrates _____ of quantitative maternal serum hCG levels every ____ days, or increase or ___% in hCG levels within ____ hours

down syndrome

increased hCG levels can be used as screening marker for what during first and second trimesters

increased hCG

not a strong marker and does not have sufficient sensitivity to be used by itself for screening for down syndrome, combined with other independent markers to increase detection

35-50

hCG level at 3 menstrual weeks

45-426

hCG level at 4 menstrual weeks

518-7340

hCG level at 5 menstrual weeks

56,500-61,080

hCG level at 6 menstrual weeks

7,650-229,000

hCG level at 7-8 menstrual weeks

25,700-288,000

hCG level at 10-12 menstrual weeks

plasma protein-A

also known as pappalysin-1 or PAPP-A

PAPP-A

insulin-like growth factor produced by trophoblastic (placental) cells during pregnancy, involved in proliferative growth processes such as bone and tissue formation, increases with advancing gestation

PAPP-A

in trisomy 21, lower _____ than normal pregnancies and decreases with gestational ag

PAPP-A

may be useful marker for down syndrome in first semester only

PAPP-A

from 9-11 weeks this is the strongest biochemical marker for down syndrome

PAPP-A

not sensitive enough to use alone but is combined with hCG levels or with hCG and sonographic markers

PAPP-A

recent studies show association between _____ in early pregnancy and preterm labor and preeclampsia

cell-free DNA

fragments of fetal DNA that originate primarily from the placenta found in maternal serum and analyzed from 9 weeks gestation

cell-free DNA

high detection rates for trisomy 21 but false positive and negative results reported

endovaginal

5-7.5 MHz, closer to anatomic structures, usually, better detail than transabdominal, most protocols require TA first and then this

first trimester goals

visualization and localization of the gestational sac, intrauterine or ectopic, identification of embryo and yolk sac, viability, is there HR or is it to early, correlate with hCG levels

first trimester goals

determination of the number of embryos and the chorion and amnion in multifetal pregnancies, estimation of duration or menstrual age of the pregnancy, early diagnosis of fetal anomalies, including identification of embryos that are more likely to be abnormal based on secondary criteria, abnormal yolk sac

not be a successful pregnancy

if there is no corpus luteum cyst that is a sign that it might

4

first __ weeks not clearly visible with TV ultrasound, references vary on when embryonic stage begins

weeks 1-4

development of primary yolk sac, primative streak, intraembryonic coelom, primitive cardiovascular system, chorionic villi

week 4

development of embryotic body, primordium of the brain, oropharyngeal membrane, foregut, liver, heart begins to contract, diaphragm, maxilla and mandible, limb bunds

diaphragm

formed by the intraembryonic coleum being divided by the septim transversum (divides body into pericardial and peritoneal cavities)

week 5

accelerated growth with head growth more than rest, development of face, mesonephric ridges (future kidneys), heart becomes 4 chambered structure, primitve yolk sac is pinched off by the extraembryonic coelom, forming the secondary yolk sac