The Early embryonic stage of the first trimester

Ch 49

Chorionic villi sampling (CVS)

diagnostic genetic testing performed in the first trimester between 11 and 13 weeks.

Gestational Age

menstrual age; used to date the pregnancy with the first day of the last menstrual period (LMP) as the beginning of gestation.

would add 2 weeks onto the conceptual age

Zygote

for 12 days after conception, during the implantation process

buries itself into one wall of the uterus by the end of the implantation process.

Embryo

time of implantation until the end of the 10th week menstrual age

Fetus

embryo after the first 10 weeks

How is the 16 cell morula formed?

rapid cellular division of the zygote. continued cell proliferation creates the blastoma.

Human chorionic gonadotrophin (HCG)

secreted by trophoblastic cells and is absorbed within the tubes; stimulates maternal pregnancy responses.

decidua

a glycogen rich mucosa that nourishes the early pregnancy.

hcg causes the uterine endometrium to convert to this.

when does the blastocyst typically enter the uterus?

4 to 5 days after fertilization

when is implantation into the uterus decidua completed?

within 12 days after fertilization.

Lacunae

blood pools created by enzymes eating into decidual tissues.

maternal capillaries that erode and nourish the proliferative cells

along with the trophoblastic cells- develops into the placenta

Secondary yolk sac

seen sonographically as the first identifiable structure throughout the first trimester

at 5.5 weeks the primitive yolk sac gradually reduces in size and becomes the secondary sac.

Amniotic and chorionic cavities

cavities that develop and evolve during the first trimester.

amniotic cavity

contains the fetus

Gestational sac should be visible by TV ultrasound at weeks, and the yolk sac may be visible at ____ weeks

5; 5.5

what is seen on US at 6 weeks?

the embryo; appears as a 1 to 4 mm echogenic structure within the gestational sac

when is the amnion visualized and what is the embryo measurement?

7 weeks; measures 10 mm in length

Crown rump length (CRL)

measures 35 mm by the end of the 10th week.

embryo changes rapidly from a disk-like configuration to a C-shaped structure

measurement of the mean sac diameter (MSD)

gestational sac size and hCG levels increase until 10 menstrual weeks where it will measure approximately 45 mm

hCG levels where a normal gestational sac is expected to be visible?

greater than 1000mIU/mL to 2000 mIU/mL

hCG indications of a possible ectopic

greater than 2000- 3000 mIU/mL

IUP

intrauterine pregnancy

Normal IUP less than 7 weeks _____

doubles hCG levels every 3.5 days

what happens to hCG levels at 9 to 10 weeks?

they plateau and decline while gestation continues

what happens to the hCG levels in a trisomy 21 pregnancy?

plateau later and decrease much slower.

trisomy 21

down syndrome

image A

yolk sac, decidua basalis, decidua parietalis, chorionic cavity, decidua capsularis, chorion laeve

image B

amniotic cavity, placenta

yolk stalk

connects yolk sac to the embryo

at what week development do the intestines return to the abdominal cavity?

week 10, with a full return by the end of the 11th week.

gestational sac is also known as the

amniotic cavity

sonographic appearance of the gestational sac

anechoic fluid collection containing a yolk sac or an embryo with cardiac activity.

2 to 3 mm sac w/ an echogenic ring having a sonolucent center.

echogenic ring represents the chorion/ decidua capsularis; anechoic center represents the chorionic cavity.

decidua basalis

portion on the myometrial or burrowing side of the conceptus

decidua capsularis

villi covering the developing embryo

double decidual sac sign

interface between decidua capsularis & decidua on opposite endometrial cavity wall

gestational sac should be where?

eccentrically placed in relation to the endometrial

three essential functions in embryonic development are

providing nutrients to the developing embryo, hematopoiesis, development of embryonic endoderm (which forms the primitive gut)

diameter measurements of the yolk sac

2 to 6 mm diameter, and measured from inner border to inner border.

indications of fetal abnormality or pending loss?

yolk sac is abnormal in appearance (normal is a circular structure), too small or too large, calcified, misshapen, or highly echogenic

regarding TV scans, a failure to visualize ____ would be suspicious of abnormal pregnancy

the yolk sac with a minimum of 12 MSD

TA studies, yolk sac should be seen ___

within MSDs of 10 - 15 mm and should always be seen with an MSD of 20 mm

growth rate of the yolk sac

0.1 mm/mL of MSD growth when MSD measures less than 15mm,

and

0.03 mm/ mL of growth of MSD through 1st trimester

normal diameter of yolk sac

should not exceed 6mm

in twin pregnancies -monochorionic, monoamniotic pregnancy means what?

one yolk sac

in twin pregnancies two yolk sacs signifies

diamniotic, monochorionic

or

diamniotic, dichorionic

embryo heart motion is detected when?

about 5.5 to 6 weeks when CRL is about 3 mm

after 5.5 weeks the amniotic membrane can be seen separating what two cavities?

amniotic ca

choriamniotic fusion

fusion of the chorionic and amniotic membranes and occurs at 14 - 15 weeks.

what structure is closed at approximately the 6th week of gestation and how is it seen sonographically?

the spine; appears as parallel echogenic lines