First Trimester Development Flashcards
What day of the cycle is an ovum released?
~14
Where does fertilization of the ovum occur? When?
In fallopian tube 1-2 days after ovulation
What happens after zygote cellular division?
forms 16 cell morula
What happens at day 20?
zygote proliferates into blastocyst
What is a blastocyst?
Contains trophoblastic cells and inner cell mass, becomes embryo
What do trophoblastic cells release?
hCG
What is the effect of hCG?
stimulates pregnancy response, begins to convert endometrium to decidua
What is decidualization?
endo is converted to decidua by hCG
When does the blastocyst enter the uterus?
4-5 days after fertilization, begins implanting
When is implantation complete? What occurs?
12 days after fertilization, blastocyst has attached to posterior wall of ut
What are chorionic villi?
formed by trophoblastic cells, encircle blastocyst and provide nutrients for future embryo
What forms the embryo and yolk sac?
Maturation of inner cell mass
When do amniotic and chorionic cavities form?
simultaneously with inner cell mass
What is decidua?
Glycogen mucosa that helps support early pregnancy
What are the 3 layers of decidua?
Capsularis: chorionic villi surrounding blastocyst
Parietalis: hormonal influence on endo tissue
Basalis: where blastocyst attaches, becomes maternal portion of placenta
What is the chorion cavity?
- Embryonic tissue lining exterior of sac, invades decidua
- Highly vascular, surrounds amnion and YS
When do amnion and chorion fuse?
16 weeks
What are the layers of chorion?
Frondosum: located at implantation site
Laeve: faces endo cavity, thin coverage
What is the amnion cavity?
- inside the sac
- encloses embryo and amniotic fluid
- becomes umb cord covering
- nonvascular
When does the GS form? What is the rate of growth?
Forms week 4/5 of menstrual cycle, seen TA week 5
Grows 1mm/day
What is the sono app of GS?
- double sac sign
- round, oval
- smooth, anechoic
How thick is the echogenic ring surrounding the GS?
3 mm or greater
At what GS sizes are the YS and embryo visible?
GS >10 mm= YS vis
GS >18 mm= embryo vis
How do you calculate mean sac diameter?
L+W+H/3
When does the primary YS form?
forms and disappears at week 4 and secondary forms
What happens to the YS at weeks 8 and 12?
YS attaches to embryo via yolk stalk
Wk 8: detaches from yolk stalk
Wk 12: YS reabsorbs
What is the yolk sac responsible for?
Responsible for hematopoiesis, formation of primitive gut, provides nutrients for embryo
What is the sono app of the YS?
- earliest intragestational sac anatomy vis
- not vis after 12 wks
- donut shaped structure w/ echogenic walls & sonolucent center
Visualization of YS predicts a viable pregnancy what percentage of the time?
> 90% of cases
How large is a normal YS? What is considered abnormal?
2-5 mm, >5.6 mm at 5-10 wks = abnormal, thin walls = abnormal
What causes suspicion of threatened ab?
nonvis of YS at MSD of 8 mm
What size is fetal pole seen at? What rate does it grow at?
CRL 1-2 mm, grows 2 mm/day 1st tri
What is the sono app of embryo & fetal pole at different weeks of gestation?
4-5 wks: TV
6-7 wks: TA
Wk 2-8: embryo
Wk 8/10 on: fetus
What indicates lagging growth?
> 1 wk discrepancy b/w meas. & menstrual age
sac sz = MSD-CRL
Normal >/= 5 mm
Abnormal </= 4 mm
What is organogenesis AKA?
embryonic phase
What is organogenesis?
- embryo assumes c-shape
- fetal anatomy fully developed by end of 1st tri
- wk 4-10
What is developed by wk 10 of organogenesis?
- neurocranial axis
- CV system
- GI system
- urogenital system
- primitive skeleton & muscles
What is the first organ to function?
heart
When is the heartbeat visualized TA and TV?
TA: 6-7 wks
TV: 5-6 wks
What is the FHR during embryonic phase, mid 1st tri, and 2nd/3rd tri?
embryonic: 90 bpm
mid 1st: 180 bpm
2nd/3rd: 120-160
What is considered fetal bradycardia?
< 90 bpm, associated with fetal demise
When is skeletal development? At what points in gestation do certain skeletal structures develop?
3-4 weeks post conception
Wk 6: spine, limb buds
Wk 8: skeletal ossification
Wk 9: cranial bones
What causes skeletal anomalies?
environmental, drug and genetic factors
What is nuchal translucency? What is it associated with?
Max thickness of subcutaneous lucency at posterior fetal neck
Used to assess genetic risk, increased NT associated w/ trisomies & abnormalities
What is the criteria to evaluate nuchal translucency?
- 11-14 wks
- CRL: 45-84 mm
- midsag
- embryo away from amniotic membrane
- no hyperextension/flexion
What is a normal hCG level at ~10 wks or 45 mm MSD for a viable pregnancy?
3000mlU/ml or greater
If hCG levels are over 3000 and an embryo is not visualized, what is probable?
Ectopic
What is the normal rate of increase of hCG?
Doubles every 3.5 days or 66% in 48 hours in first 7 wks
What happens to hCG levels at 9-10 wks?
Levels plateau and decline
What is the differences in hCG levels for ectopic and abnormal pregnancies?
Ectopic: lower hCG than IUP, abnormal progression
Abnormal: lower levels for gest age, drastic decline before spont. ab.
What are first trimester complications?
- subchorionic hemorrhage
- ectopic
- heterotopic preg
- anembryonic gest
- abortions
- embryonic oligohydramnios
- gest trophoblastic neoplasia
- hydatidiform mole
- choriocarcinoma
What are indications for 1st tri ultrasound?
- gest age
- confirm IUP/suspected ectopic
- vaginal bleeding
- pelvic pain
- diagnose mult preg
- confirm cardiac activity
- guidance for sampling/device removal
- assess fetal anomalies
- mat pelvic masses/abnormalities
- screen for aneuploidy (NT meas.)
- suspected hydatidiform mole
What is protocol for 1st tri US?
- Eval ut, adns, CDS (fibroids, masses, FF)
- Eval of ovs (CL, ectopic)
- GS location, meas
- Presence of YS/embryo
- Cardiac activity (M mode, cine)
