Normal 1st Trimester Flashcards
1
Q
Prenatal definition
A
from conception to birth
2
Q
menstrual age
A
aka gestational age
length of pregnancy determined by first day of last menstrual period
3
Q
embryonic age
A
aka conceptual age
age at conception
gestational age adds two week to conceptual age
4
Q
embryo
A
implantation until 8 (10 gestation) weeks
5
Q
fetus
A
after 8 (10) weeks
6
Q
infant
A
between birth and one year of age
7
Q
previable
A
infant delivered prior to 24 weeks
8
Q
preterm
A
infant delivered between 24-37 weeks
9
Q
term
A
infant delivered between 37-42 weeks
10
Q
posterm
A
infant delivered after 42 weeks
11
Q
Pregnancy is divided into…
A
trimesters:
1st until 12 weeks (14 gestational)
2nd from 12(14) to 24(26)
3rd from 24 to delivery
12
Q
What is the difference between menstrual age and embryonic age?
A
Menstrual age is the length of pregnancy determined by the first day of the last menstrual period. Embryonic age is the age of the fetus at conception; it is two weeks less than the menstrual age.
13
Q
Describe the early progression of pregnancy.
A
Day 1: zygote divides into two cells Day 2: zygotes divides into four cells Day 3?: zygote becomes a 16 cell morula Day 4-5: blastocyst enters uterus Day ~7: implantation begins Day 12: implantation is completed
14
Q
What is a morula?
A
ball of cells
15
Q
What is a blastocyst made up of?
A
made up of trophoblast (secretes hCG) and inner cell mass(ICM)
16
Q
What does the trophoblast develop into?
A
the placenta
17
Q
What does the ICM develop into?
A
the embryo and portion of placenta
18
Q
What causes the endometrium to have a decidua reaction?
A
the trophoblastic cells secrete hCG that is absorbed within the tubes and stimulates maternal pregnancy responses;
hCG causes the uterine endometrium to convert to decidua
19
Q
What two layers make up the trophoblast?
A
the outer layer is syncytiotrophoblast and the inner layer is the cytotrophoblast
20
Q
What does the syncytiotrophoblast do?
A
invades endometrium and breaks down glands and blood vessels. The nutrients from the glands will provide nourishment for the embryo.
21
Q
Fertilization…
A
formation of zygote (46 chromosomes)
22
Q
Following implantation, what happens to the ICM?
A
it matures into the embryonic disk, future embryo, and the primary yolk sac
23
Q
What is a decidua?
A
a glycogen-rich mucosa that nourishes the early pregnancy
24
Q
What are the locations of each decidua?
A
decidua basalis: under blastocyst (occurs between blastocyst and myometrium)
decidua capsularis: above blastocyst (occuring over blastocyst closest to endometrial cavity)
decidua parietalis: reaction except for areas beneath and above implanted
25
What does the decidua reaction look like sonographically?
echogenic
| can see double decidual sac sign
26
What is the decidual sac sign?
echogenic decidua capsularis, hypoechoic uterine cavity, and echogenic decidua parietalis
Sign of intrauterine pregnancy , typically fundal location noted
27
When is the secondary yolk sac formed and how?
23 gestational days; primary yolk sac is pinched off by extraembryonic coelm and forms secondary yolk sac, which is between the amniotic and chorionic cavities
28
Which yoke sac is seen sonographically?
secondary yolk sac
29
zygote
first 12 days after conception
30
What is gastrulation?
development of germ layers
31
What are the germ layers?
ectoderm, mesoderm, and endoderm
| all give rise to future human tissues
32
When does organogenesis take place?
between day 14 and 60 (2/3 - 8 weeks)
33
When does gastrulation take place?
during the 5th gestational week
34
What happens during gastrulation?
single layered blastula is reorganized into a trilaminar gastrula (three germ layers)
35
By the endo of the 10th week, what does the CRL of the fetus measure?
35mm; embryo develops C-shaped structure and human-like appearance
36
When is the fetal anatomy fully developed?
in late first trimester
37
When can an intrauterine pregnancy be visualized sonographically and what can be seen?
during the 5th gestational week;
| 1-2mm gestational sac with echogenic ring having sonolucent center (chorionic cavity)
38
Sonographically describe the gestational sac.
round/oval, fundal/middle portion of uterus/eccentrically placed position in middle portion of uterus, smooth, echogenic, 3mm or more in wall thickness;
secondary yolk sac present when MSD >10mm, embryo present when MSD >18mm;
grows 1mm per day
39
When should the amniotic cavity/membrane, chorionic cavity, yolk sac, and embryo be visualized?
between 5.5 and 6th gestational week
40
What does the number of yolk sacs indicate?
the number of amnions
41
When is the yolk sac routinely visualized?
between 5 and 5.5 gestational week
42
What are the functions of the secondary yolk sac?
to provide nutrients to developing embryo, hematopoiesis, development of embryonic endoderm (forms primitive gut)
43
When does the secondary yolk sac detach from the yolk stalk?
~8 weeks gestation, due to amniotic cavity expansion
44
What predicts a viable pregnancy?
visualization of the yolk sac;
| >90% of cases
45
The yolk sac diameter should not exceed...
6mm; enlarged yolk sac is not a good sign
46
In twin pregnancies, one yolk sac signifies...
monochorionic, monoamniotic pregnancy
47
In twin pregnancies, two yolk sacs signify...
diamniotic, monochorionic or
| diamniotic, dichorionic pregnancy
48
When is the secondary yolk sac no longer visualized?
by 12th week
49
When is heart motion detected in the embryo?
at 5.5 weeks
| when CRL is 3mm
50
When must the embryonic heartbeat be seen?
when the CRL is greater than 4mm
51
When is the amniotic membrane visualized?
after 5.5 weeks
52
Describe the chorionic cavity.
fluid is more dense than amniotic cavity. Waste products are disposed here and can have echogenic materials
53
What can a sonographer do to appreciate the difference in the chorionic and amniotic cavity?
increase the gain
54
When does chorioamniotic fusion take place?
12 weeks
55
How is the yolk stalk created?
when constriction/narrowing between the embryo and yolk sac takes place (due to formation of embryonic head, caudal portions, and lateral folds)
56
When is the embryonic period?
time between 4 and 10 weeks of gestation
57
When can the developing spine be visualized?
at 6 weeks of gestation; parallel echogenic lines with a sonolucent center
58
When does the neural tube close?
around the 6th gestational week (4th embryologic week)
59
By 8 weeks gestation, what primary vesicles are seen within the fetal brain?
prosencephalon (telencephalon and diencephalon), mesencephalon, and the rhombencephalon
they appear as three anechoic portions in the embryo head
60
What does each vesicle give rise to?
telencephalon: cerebrum and retina of eyes
diencephalon: thalamus, hypothalamus, epithalamus
mesencephalon: midbrain
rhombencephalon: brain stem (medulla oblongata, pons), cerebellum
61
What two segments does the rhombencephalon divide into?
metencephalon (cephalic) and myelencephalon (caudal)
62
What can be seen in the embryonic cranium at 8-10 weeks gestation?
cystic rhomboid fossa, posterior aspect of embryonic cranium
63
What can be seen at 9 weeks gestation in the embryonic cranium?
cerebral hemispheres, midline falx, echogenic choroid plexus tissue in lateral ventricles
64
What can be seen at 10 weeks gestation in the embryonic cranium?
choroid plexus (echogenic in anechoic ventricles) and lateral ventricles occupy entire cranial vault, fourth ventricle
65
If the yolk sac is seen, what age should the embryo be?
less than 12 weeks gestation
66
When are limb buds recognizable via sonography?
during 7th gestational week, but not identified until calcification of long bones at 10 weeks
upper limbs form first, followed by lower limbs
develop proximal to distal
67
When are the hands and feet completely formed?
by end of 10 gestational week
| fingers form earlier than toes
68
What begins calcification at 8 weeks gestation?
clavicle; followed by mandible, palate, vertebral column, neural arches
69
When do frontal cranial bones begin calcify?
at 9 weeks, followed by long bones
70
By what week does the maxilla and mandible appear as brightly echogenic structures?
week 9
71
When is the anterior abdominal wall developed?
by 6th gestational week
72
Describe the herniation of bowel.
as amniotic expansion occurs, midgut elongates faster than embryo growing, causing midgut to herniate into base of umbilical cord
73
When does the midgut descend into the fetal abdomen?
at 11th week
74
After __ week of gestation, echogenic umbilical cord mass no longer visualized and echogenic bowel seen within fetal abdomen.
12
75
What is the first organ to function within the embryo?
the heart
76
When does the heart start beating?
at 35 days (5-5.5 weeks)
77
When has the heart obtained adult configuration?
end of 8th week gestation
78
When should (ALWAYS) embryonic heart be seen by?
by 46 menstrual days or when CRL >4mm
79
What are the normal fetal heart rates?
6 weeks: 90-115 bpm
9 weeks: 140-160 bpm
remainder of 1st and 2nd tri: 140 bpm
80
What is the most accurate measurement for sonographic gestational dating?
CRL (until fetus starts to curl at 12 weeks)
81
How do you calculated the mean sac diameter?
length x width x height /3
82
How do you calculate the menstrual age in days with the MSD?
MSD+30
83
How do you calculate the menstrual age in weeks with the menstrual age in days?
menstrual age (days) / 7
84
How early can the CRL be obtained?
5.5 weeks using transvaginal US
85
What is used to assess 1st trimester risk?
amniocentesis, triple screen, chorionic villi sampling, nuchal translucency measurement
86
Overall, twin gestations have __ to __ times greater mortality rate than do singletons
7 to 10
| risk increasing when twins are monozygotic (sharing placenta)
87
Multiple gestation is a ___ risk pregnancy; highest and lowest in what populations?
high
lowest in asian population
highest in African population
88
When the cell splits between days 1 and 3, what develops?
identical twins; dichorionic/diamniotic
| with two different placentas
89
When the cell splits between days 4 and 8, what develops?
monochorionic/diamniotic
90
When the cell splits between days 8 and 13, what develops?
```
monochorionic/monoamniotic
momo twins (sharing placenta)
```
91
There are twins of different genders, how many chorion and amnions?
dichorionic
| dizygotic - different placentas
92
What does the twin peak sign indicate?
dichorionic/diamniotic; two placentas
93
How does the twin peak sign look sonographically?
echogenic placental villi; four layers between embryos (amnion, chorion, chorion, amnion)
94
What does the t sign indicate?
monochorionic; single placenta
95
How does the t sign look sonographically?
one chorion and two amnion
| echogenic amnionic membrane between fetus
96
For monochorionic/diamniotic twins, when does the cell split?
between days 4 and 8
97
For dichorionic/diamniotic twins, when does the cell split?
between days 1 and 3
98
For momo twins, when does the cell split?
between days 8 and 13
99
The number of chorions indicates the number of what?
placentas
