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Conceptual age aka age considers is first day of pregnancy .
age aka menstrual age considers day of last menstrual period is beginning of gestation .

Gestational age aka menstrual age considers day of last menstrual period is beginning of gestation .

is the conceptus 12 days after conception , during implantation process
is the conceptus from time of implantation until end of 10th week menstrual age
is the conceptus after first 10 week s

During 28 - day menstrual cycle , a mature ovum typically released on day this is called . The follicle that released it forms the and begins secreting .
occurs within the distal fallopian tube ( ) 1 to 2 days after ovulation . Fertilized conceptus is now called a which includes an egg nucleus , sperm nucleus , and a membrane surrounding it called the .
The zygote undergoes rapid cellular division to form 16 - cell this dividing is called .

Further cell proliferation brings morula to stage and it typically enters uterus 4 to 5 days after fertilization containing + cells The cells are not just copies of the originals , they have now into new cells that will form into new human parts .
The " inner cell mass " forms the while the outer cells along the perimeter will become the and secrete
hCG causes uterine endometrium to convert to , a glycogen rich mucosa that nourishes early pregnancy .
Implantation into uterine decidua completed within days after fertilization
During implantation , produced by trophoblasts " eat into " decidual tissue .
This creates spaces for trophoblastic cell .
At end of implantation process , zygote has buried itself within one of uterus .
Implantation bleeding - when this process results in light vaginal bleeding about same time as expected menstrual period .
Within the implanted conceptus , the inner cell mass matures into the embryonic disc ( future embryo ) and primary yolk sac .
At approximately days menstrual age , yolk sac is pinched off by extra
embryonic , forming the secondary yolk sac .
yolk sac is the yolk sac seen sonographically throughout first trimester .

Phase is between weeks 4 and 10
system undergoes rapid development , with initial occurring between 5½ and 6 weeks .
Embryo appearance changes from , disk - like configuration to - shaped structure and develops a recognizable appearance
During this period , crown - rump length ( CRL ) develops rapidly , measuring mm by end of week .

Weeks 11 and 12 constitute the beginning of this period when there is continued growth of and structures formed during embryonic period .
The fetal head is disproportionately than rest of fetus ( the same size as the body ) , constituting one of CRL .

hCG : urine results are positive or negative
Quantitative hCG : provides specific levels of hCG in blood . Provide a specific number
value .
Normal gestational sac is expected to be seen when hCG level is mIU / ml or greater .
With Down ? s Syndrome hCG levels plateau and fall more
Greater than expected hCG levels seen with dates ( further along than expected ) , Gestational disease & gestations
Lower than expected levels of hCG associated with dates ( not as far along as expected ) , pregnancy , demise / abnormal IUP / impending miscarriage .
Gestational Sac aka sac is the first visual evidence of IUP during week .
It appears as 1 - to 2 - mm sac with ring having sonolucent center which represents the cavity .
Circumferential echogenic rim seen surrounding gestational sac represents tissue and associated reaction
Echogenic ring around gestational sac divided into
o Decidua - Portion on or burrowing side of conceptus .
o Decidua - Villi covering developing .
The double decidual sac sign is the interface between decidua and decidua .
Normal gestational sac features
o placed in relation to endometrial cavity , secondary to its implantation
o location noted
o Round or slightly oval in shape
o contours
o Decidual wall thickness mm
? Gestational sac grows at predictable rate of mm / day in early pregnanc y

Sac should be seen when mean sac diameter is mm .
Routinely visualized between and weeks of gestation
o Provide to developing embryo
o : Formation of blood
o Development of embryonic
At approximately weeks gestation , with amniotic cavity expansion , the yolk sac ,
which lies between and membranes , detaches from yolk .
? Visualization of yolk sac predicts viable pregnancy in of cases .
? Failure to visualize yolk sac , with minimum of - mm MSD , using transvaginal
sonography , is suspicious for abnormal pregnancy .
o Transabdominal studies have shown that yolk sac should be seen within mean
sac diameters of to mm and should always be visualized with mean sac
diameter of 20 mm .
? Normal diameter should not exceed mm measured from inner edge to inner edge
? Typically , yolk sac resorbs and is no longer seen sonographically by weeks .