Early embryonic stage of first trimester

Ch. 49 HA; Ch.21 CP

amniotic cavity

enlarges with fluid between the embryo and the amniotic membrane and chorionic cavity

chorionic cavity

Surrounds the amniotic cavity and contains the yolk sac

chorionic villi sampling (CVS)

a prenatal diagnostic test that involves taking a small sample of tissue from the placenta to analyze for genetic abnormalities or other health condition; between 11 and 13 weeks

crown-rump length (CRL)

direct measurement of the embryo that determines gestational dates of first trimester

decidua basalis

the portion on the myometrial or burrowing side of the conceptus 

decidua capsularis

the villi covering the developing embryo

double decidual sac sign

reported to be a reliable sign of an early intrauterine gestation; interface between the decidua capsularis and the echogenic , highly vascularized decidua on the opposite wall of the endometrial cavity forms

embryonic period

time between 4 and 10 weeks of gestation

gestational age

known as the menstrual age, to date the pregnancy, with the first day of the last menstrual period (LMP) as the beginning of gestation. thus adding 2 weeks onto the conceptual age

hematopoiesis

the continuous process of blood cell production that occurs mainly in the adult bone marrow, though it can also happen in other organs like the liver and spleen

human chorionic gonadotropin (hCG)

causes the uterine endometrium to convert to decidua, a glycogen-rich mucosa that nourishes the early pregnancy. 

intrauterine pregnancy (IUP)

a pregnancy in which the fertilized egg implants and develops in the uterus

mean sac diameter

the average measurement of the gestational sac, calculated by adding its length, width, and height and dividing by three

primary yolk sac

a temporary, extra-embryonic structure that forms early in human development from hypoblast cells after implantation

secondary yolk sac

a temporary structure that develops in the early stages of human pregnancy

yolk stalk

zygote

what the conceptus is called for 12 days after conception

amnion

innermost membrane of the developing embryo, eventually fuses with the chorion

amniotic fluid

fluid within the amnion that surrounds and bathes the embryo/fetus. permits symmetric growth of the embryo/ fetus; prevents adhesions from forming in the fetal membranes; cushion the embryo maintain proper temperature of the developing embryo; allows normal development of the respiratory, gastrointestinal, and musculoskeletal systems; helps to prevent infection; and may be a source of nutrients for the embryo

amniotic fluid volume (AFV)

amount of amniotic fluid in the amniotic cavity and can be determined by variety of methods reflects the state of gestational well-being. many abnormalities are associated with marked increases (polyhydramnios) or decreases (oligohydramnios). 

aneuploidy

abnormal chromosomes number

chorion

outermost tissues of the developing embryo. eventually fuses with the amnion

chorionic cavity

part of early development that surrounds the amnionic cavity and contains the yolk sac. eventually obliterated by the amniotic cavity that increases in size to accommodate the developing embryo

chorionic villi

fetal portions of the placenta that are finger-like projections of the blastocyst that extend into the deciduate endometrium. They are surrounded by lacunae, pools of maternal blood. contact of the villi of the embryonic circulatory system with the maternal lacunae facilitates the transfer of oxygen and metabolites and the transfer of carbon dioxide and waste products

corpus luteum/corpus luteal cyst

remnant of the ovarian follicle following ovulation. produces progesterone and a small amount of estrogen to prepare the uterus for pregnancy. may become enlarged and fluid filled during pregnancy and thereafter, gradually diminishing with out complications

decidua

term applied to the gravid endometrium. functional reaction of the endometrium lining to pregnancy. the endometrium becomes thick and edematous from vascular and structural changes to accommodate embryo implantation and development

decidua parietalis

remaining endometrium, or peripheral portion, that is unoccupied by the implanted ovum

double bleb sign

description of the distinctive sonographic appearance of the embryonic disk situated between the newly yolk sac within the chorionic cavity at 4 to 5 weeks gestational period

estrogen

hormone produced by the ovarian corpus luteum to help prepare the uterus for pregnancy. regularly produced by the ovaries as a “feminizing” hormone

fetal vernix

flakes of fetal skin that are sonographically distinguishable in amniotic fluid

follicle-stimulating hormone

hormone produced by the anterior pituitary gland in the brain to promote ovarian follicular growth

gestational age

synonyms with menstrual age; used to date the age of a pregnancy

gestational sac

term used by sonologist to describe the fluid-filled cavity of an intrauterine pregnancy during the first trimester. first fundamental sonographic finding in early pregnancy

gravid

pregnant

human chorionic gonadotropin (hCG)

hormone secreted by the developing placenta to communicate to the rest of the body that a gestation is present withing the uterus

intradecidual sign

description of the sonographic appearance of the normal location of a very early intrauterine pregnancy when the gestational sac is visualized right next to the centrally located endometrial cavity at the level of the fundus or body of the uterus

lacunae

small pools of maternal blood that surround the chorionic villi in the placenta

luteinizing hormone

hormone that, when increased, causes ovulation to occur

mean sac diameter

age-determining measurement of the mean diameter of the gestational sac during the early first trimester of pregnancy.

nuchal translucency (NT) measurement

measurement of the fluid that normally collects at the back of the fetus’ neck between 11.3 and 13.6 weeks of gestation to determine the fetal risk estimate for aneuploidy (abnormal number of chromosomes; example is down syndrome. an increase in the amount of fluid is indication of possible abnormality

ovulation

release of the ovum (egg cell) into the genital tract from a mature ovarian follicle

progesterone

hormone produced by the corpus luteum that helps prepare the uterus for pregnancy

pseudo sac

associated with pregnancies outside the uterus (ectopic pregnancy)

rhonencaphalon

normal cystic hindbrain that is sonographically distinguishable in the developing embryo during the eighth week of gestation

umbilical cord

connection between the embryo/fetus and placenta. consists of two arteries and one vein through which embryonic/fetal blood passes to and from the placenta

vitelline (omphalomesenteric duct)

connection between the yolk sac and early developing embryo. it eventually becomes part of the umbilical cord. also known as the “yolk stalk”

yolk sac

nutrient-filled sac formed by and adjacent to the outer layer of the early developing embryo

zygote

product of fertilization when the egg and sperm fuse together