Ch 49 - The Early Embryonic Stage of the First Trimester

what do clinicians and sonographers use to date a pregnancy?

gestational age

conceptual age is also known as…

embryologic age

zygote

fertilized ovum; days after conception

embryo

up to 10 weeks

what does menstrual age refer to?

length of time calculated from the first day of the LMP to the point of pregnancy

a mature ovum is typically released at day …

14

fertilization occurs ____ days after the ovum is swept into the distal fallopian tube during ovulation

1-2

the follicle that released the mature ovum hemorrhages and collapses to form ______

corpus luteum

what does the corpus luteum secrete?

progesterone and estrogen

the fertilized ovum then become a _____ at 12 days after conception

zygote

the zygote undergoes rapid cellular division to form the _____

16 cell morula

after the morula the cell proliferation continues into the _______ stage

blastocyst

the blastocyst contains ______ and ______ that form the ______

trophoblastic cells, inner cell mass, embryo

the trophoblastic cells secrete…

human chorionic gonadotrophin (hCG)

hCG secretes by trophoblastic cells is absorbed within the tubes and ….

stimulates maternal pregnancy responses

the hCG causes the endometrium into to …

decidua

how many days after fertilization does the blastocyst enter the uterus

4 to 5

what happens during implantation?

proselytizing enzymes eat into decidual tissue creating spaces for trophoblastic cell proliferation, lacunae form to nourish these cells

lacunae

blood pools that form to nourish proliferating trophoblastic cells during implantation

what appears after implantation at approximately 23 days menstrual age?

secondary yolk sac

Secondary yolk sac

Yolk sac seen sonographically during the first trimester

At how many weeks should the gestational sac be visible by transvaginal ultrasound

5

the yolk sac may be visible from ____ weeks throughout the first trimester

5.5

at how many weeks is the embryo seen?

6

at how many weeks is the amnion visualized?

7

the embryonic phase occurs between ___ and ___ weeks

4, 9

initial heartbeat occurs at approximately ____ weeks

5-6

rapid development of the cardiovascular system occurs during what phase?

embryonic

the embryos appearance changes from flat disk like to…

C shaped structure

during embryogenesis the CRL develops rapidly measuring ______ by the end of the 10th week

35mm

the last 3 weeks of the 1st trimester (weeks 10-12) constitutes the beginning of the…

fetal period

during what stage is the fetal head disproportionately larger than the rest of the fetus

fetal period

when is fetal anatomy fully developed?

late 1st trimester

a normal gestational sac should be visible when hCG is greater than

1000