OB Exam 1 Flashcards
How can a sonographer determine what position the baby is in?
Find the head and spine
When is determining a due date the most important?
In the first trimester
Why should color not be used on a 1st trimester ultrasound?
color adds more energy to rapidly changing tissue, creating an added risk
ALARA
As Low As Reasonably Achievable
What do you use to estimate gestational age?
LMP and Naegele’s Rule
Naegele’s Rule
LMP - 3 months + 7 days
Sonographic establishment of gestational age
40 weeks, 3 trimesters
What is the 1st trimester?
- embryological development
- first 13 weeks
What is the 2nd trimester?
- fetal anatomy development
- 13-26 weeks
What is the 3rd trimester?
- fetal growth
- 27-40 weeks
Most babies are about the same size until when?
20-24 weeks
Following fetal growth (no longer gestational age)
- subsequent exam: age should be based on 1st ultrasound EDC/EDD
- look at symmetry of anatomical growth
What to look for in the 1st trimester?
- dating
- pain
- bleeding
- aneuploidy screening
- pelvic mass
What could pain in the 1st trimester be associated with?
ectopic
What could bleeding in the 1st trimester be associated with?
- spontaneous abortion
- check FHT (fetal heart tone)
What is an aneuploidy screening?
- test for abnormal # of chromosomes
- nuchal translucency (space in back of neck)
- maternal biochemical (mom’s blood lab values)
- possible chorionic villus sampling (early placenta biopsy) or amniocentesis (sampling amniotic fluid)
What to look for in the second trimester?
- fetal anatomy survey
- aneuploidy screening
- fetal growth
- pain/bleeding
Genetic markers in an aneuploidy screening
- multiple genetic markers
- hard markers = strong association
- soft markers = some association
What could pain/bleeding be associated with in the second trimester?
extrafetal structures and maternal adnexae
What to look for in the third trimester?
- fetal growth
- fetal well-being
- cervical stability
- presentation
- pain/bleeding
Fetal well-being assessment in the third trimester
- look for fetal abnormalities; anatomy/growth
- maternal conditions
- fetal environment
What could pain/bleeding be associated with in the third trimester?
placenta abruption
Basic protocol of a first trimester exam
- a pelvic exam w/ crown-rump length & heart rate
- evaluate uterus, endo, ovaries, cervix, & adnexae
Basic protocol of a second/third trimester exam
- fetal anatomical survey & gestational age/growth (systematic, organized)
- extrafetal structures: placenta, fluid, cord, cervix, uterus/adnexae
- presentation
- growth
- repeat anatomical development: brain, heart/chest, stomach/kidneys/bladder, genitalia, spine
- cervical integrity
- fetal activity (BPP)
- placento-fetal circulation: cord doppler
Choriodecidua defintion
- chorio = pregnancy/baby
- decidua = endometrial
Cycle phases
Follicular/Proliferative –> Ovulation –> Luteal/Secretory
What can happen after ovulation?
fertilization –> hCG –> implantation
What forms throughout fertilization?
- zygote
- blastomeres
- morula
- blastocyst
What secretes hCG?
trophoblasts (wall of the pregnancy)
What structure is the ‘pregnancy’ and what structure is the ‘baby’?
- trophoblasts are the pregnancy
- inner cell mass is the baby
What occurs during implantation and what does it require?
- blastocyst burrows into endo (w/ aid of chorionic villi)
- needs progesterone to support pregnancy
What are chorionic villi (gray area in drawing)?
- finger like structures that pull blastocyst into endo
- determines where the placenta forms
What is the decidualized endometrium (pink area in drawing)?
thick, heterogeneous
What eventually becomes the umbilical chord?
chorionic stalk
What is the chorionic cavity?
- grows around fetus
- contains yolk sac
What is in the amniotic cavity?
fetus is the only thing in the amniotic cavity
Are the chorionic cavity and amniotic cavity the same thing?
No, 2 separate things
What covers the umbilical chord?
amnion
Is bleeding during pregnancy normal?
Not normal but common
What does fluid touch?
- only touches chorion (gestational sac border is chorion)
- does NOT touch endometrium in pregnancy
What anchors and covers the gestational sac?
- anchored at d. basalis
- covered w/ d. capsularis
- small window of time in pregnancy for it to be visible on ultrasound
What is d. capsularis?
layer around chorion
What is the remainder of the endometrium?
d. parietalis w/ mucus filled cavity between
What is sonoembryology?
- LMP to 14 weeks
- when we can measure things and verify how far along the pregnancy is
What occurs at 3 weeks post LMP?
- implantation to blastocyst
- decidual reaction (thickened endometrium)
What occurs 4-5 weeks post LMP?
first evidence of IUP:
- tiny eccentric anechoic sac
- echogenic borders (trophoblastic rim)
- growth: 1mm/day
What occurs 5-6 weeks post LMP?
- gestational sac is visible (only measure fluid space, not chorion)
In a GS >10 mm . . .
- secondary yolk sac visible
- echogenic ring
- 2-6 mm (inner to inner)
- embryo & faint flicker may be seen
Primary sac and secondary sac
- blastocyst cavity was the primary sac
- blastocyst cavity left behind secondary sac in chorionic cavity
What size should the Gestation Sac not exceed?
- no more than 20 mm
When should we see baby?
want to see at 20 mm but can wait until 25 mm, maybe even 30 mm in some cases
What occurs 6-7 weeks post LMP?
- embryo visible, adjacent to tolk sac
- cardiac flicker recognized
- neurotube closed, too late for folic acid
- flicker seen = need bpm for proof
- spinal chord is first structure we can see
Ideal bpm 6-7 weeks post LMP
- ideal 120-170 bpm
- > 100 bpm
- if btwn. 100 & 120, F/U in a few days
What do we use to measure heart rate in early pregnancy?
M-mode (motion-mode) b/c less aggressive
What occurs 7-8 weeks post LMP?
- choriodecidua: double sac sign
- chorion ; decidua ; endometrial cavity (look at image)
What occurs at 7 weeks?
- embryo begins to take on a ‘peanut’ or ‘C’ shape
- amniotic and chorionic cavities are distinguishable
Difference btwn. chorionic and amniotic cavity on ultrasound?
- chorionic cavity has low level echoes & fluid is thicker than amniotic cavity fluid
- ex. syrup vs. water
What occurs at 8 weeks?
- rhombencephalon is evident
- limb buds begin to develop (gummy bear appearance)
- neurotube visualized
Rhombencephalon
- hindbrain
- intracranial cystic space
Neurotube
hypoechoic line posteriorly
What occurs at 10-12 weeks?
- embryo looks more like a fetus
- system development: cardiac chambers, bony ossification, facial features, GI tract, GU tract (bladder), brain is cystic
What are the earliest bony structures to develop to visibilty?
- skull and femur
- at 10-12 weeks
What part of the GI tract develops at 10-12 weeks?
- physiologic midgut herniation
- should resolve by 15 weeks
First trimester measurements
- uterus and ovaries (ALWAYS)
- heart rate
- crown-rump length (CRL)
- yolk sac
- gestational sac
What is the most accurate measurement for dating pregnancy?
- crown-rump length (CRL)
- top of head to bottom of rump
Measuring yolk sac
- measure in 1st trimester
- inner wall to inner wall
- should be 4-6mm
- always assess presence
Measuring gestational sac
- only measure fluid, not chorion
- if embryo present w/ cardiac activity, NOT required
- if no embryo, measure MSD for dating sac
What is MSD?
- mean sac diameter
- MSD = (L + W + H)/3
- MSD + 30 = gestational age (in days)
- 10 mm (MSD) + 30 = 40 days or 5w5d
- MGSD should be at least 5mm bigger than CRL
Measuring heart rate
- don’t measure start to end, measure same point to same point
- be accurate, don’t have to be precise
- measure 1 cycle, some systems measure 3 so adjust accordingly
Dating pregnancy: clinically
- ‘the wheel’
- Naegele’s rule: LMP - 3 months + 7 days = EDD
Dating pregnancy: sonographically
- CRL if embryo present (3 measurements)
- MSD if no embryo present
Other 1st trimester measurements
nuchal translucency
Measuring Nuchal Translucency
- soft tissue posteriorly along embryo cranium/spine
- measurements > 3mm have been associated w/ aneuploidy, esp. Trisomy 21
- sagittal plane of embryo btwn. 11w0d & 13w6d (45-85mm)
- coupled w/ maternal biochemistry for genetic purposes
- STRICT criteria: certification necessary
1st trimester lab values
human chorionic gonadotropin (serum beta-hCG)
hCG values
- ‘discriminatory zone”
- wide range of values for associated gestational age
- TV = 1/2 TA imaging values
- TV = 1800 mIU/mL (1000-2000)
- TA = 3600 mIU/mL (3000-4000)
hCG reporting systems
- different reporting systems
- 1st and 3rd International Reference Preparation (IRP)
- 3rd used at VUMC
- values are almost double the 2IS values for same gest age
Do you need to wait on Beta level results before doing an exam?
No, do not wait since it will put the patient at risk if it’s an ectopic
