Conception, Pregnancy, Fetal Development Flashcards
oogenesis - overview
*differentiation of the ovum
*occurs in the female fetus prior to their birth
oogenesis - steps
- primary oocytes
- begin meiosis 1 during fetal life
- PAUSE (meiosis 1 arrested in prophase 1 for years until ovulation - still a primary oocyte)
- complete meiosis 1 prior to ovulation (now a secondary oocyte)
- meiosis 2 arrested in metaphase 2 until fertilization
- if fertilization does not occur within 1 day, secondary oocyte degenerates
blastocytosis - overview
*transition from a zygote (after fertilization) into a fetus
*zygote (fertilized ovum) → blastomere (2-cell) → morula → blastocyst
*58-cell blastocyst differentiates into 5 embryo-producing cells (inner cell mass) and remaining cells (53 cells) become placental trophoblasts
early fetal development - week 1
*hCG secretion begins upon implantation (usually days 6-10) of the blastocyst
early fetal development - week 2
*bilaminar disc formed (2 layers in week 2- epiblast & hypoblast)
epiblast becomes embryo
hypoblast becomes yolk sac
early fetal development - week 3
*gastrulation: formation of trilaminar disc (3 layers in week 3 - endoderm, mesoderm, ectoderm)
early fetal development - weeks 3-8 (overview)
neural tube** forms; closes by week 4
**organogenesis occurs
*extremely susceptible to TERATOGENS
early fetal development - week 4
*HEART begins to beat
*upper and lower limb buds form
*“4 limbs & 4 heart chambers in week 4”
note - heart beat is not yet detected on ultrasound or doppler
early fetal development - week 6
*cardiac activity on transvaginal ultrasound
recall: heart starts to beat at 4 week, but undetectable until week 6
early fetal development - week 8
*fetal movement begins
early fetal development - week 10
*genitalia female/male characteristics form
important teratogens & susceptibility period
*during the embryonic period (weeks 3-8) the fetus is extremely susceptible
*meds: ACE inhibitors, aminoglycosides, antiepileptic drugs, folate antagonists, isotretinoin, warfarin
*substances: alcohol, cocaine, nicotine, etc
*other: iodine (lack or excess), maternal diabetes, mercury, X-rays
placenta - overview
*primary site of nutrient and gas exchange between mother and fetus
*2 components: fetal & maternal
placenta - maternal component
*aka decidua basalis
*derived from endometrium
*maternal blood is found in the lacunae
placenta - fetal component
- cytotrophoblast - inner layer of chorionic villi
- syncytiotrophoblast - outer layer of chorionic villi
*synthesizes & secretes hormones (hCG)
*lacks MHC-1 expression
diffusion across the placenta
*umbilical vein carries oxygenated blood to the fetus; umbilical artery carries blood from fetus back to mother
*placental villi increase surface area for diffusion
*blood traveling from mother to fetus: high in O2 / nutrients, low in CO2 / waste
*fetal blood returning to mother: low in O2 / nutrients, high in CO2 / waste
umbilical cord - overview
*2 umbilical arteries, carrying deoxygenated blood away from the fetus and back to mom
*1 umbilical vein, carrying oxygenated blood from mom to fetus
*Wharton jelly surrounds the arteries/veins in the umbilical cord to protect them from compression
formation of the umbilical cord
*yolk sac (3rd week) → allantois → urachus
*urachus = duct between fetal bladder and umbilicus
urachus abnormalities
- patent urachus: COMPLETE failure of urachus to obliterate → urine discharge from umbilicus
- urachal cyst: PARTIAL failure of urachus to obliterate → fluid-filled cavity lined with uroepithelium between umbilicus and bladder
- vesicourachal diverticulum: SLIGHT failure of urachus to obliterate
vitelline duct - overview
*connects yolk sac to midgut lumen
*obliterates during the 7th week of gestation
*aka omphalomesenteric duct
vitelline duct abnormalities
- vitelline fistula: failure of vitelline duct to close → meconium discharge from umbilicus
- Meckel diverticulum: PARTIAL closure of vitelline duct (patent to the ileum) → true diverticulum; may have heterotopic gastric/pancreatic tissue → melena, hematochezia, abdominal pain
pregnancy - fertilization & implantation
- fertilization:
-occurs in the ampulla of the fallopian tube (normally)
-within 1 day of ovulation - implantation:
-occurs around day 6 after fertilization
-syncytiotrophoblast releases beta-hCG
(hCG detected in blood 1 wk after conception, in urine 2 wks after conception)
beta-hCG (human chorionic gonadotropin) - overview
*source: syncytiotrophoblast of placenta
*maintains corpus luteum (progesterone) during weeks 8-10; acts like LH
*after 8-10 weeks, placenta releases its own estriol & progesterone
-corpus luteum degenerates
-therefore, beta hCG peaks at 8-10 weeks
hPL (human placental lactogen) - overview
*aka chorionic somatomammotropin
*source = syncytiotrophoblast of placenta
*functions:
1. stimulates insulin production
2. increases insulin resistance (shunts carbohydrate metabolism for glucose/amino acids to fetus)
3. increases lipolysis (due to insulin resistance)
*hPL hormone increases throughout the pregnancy
*hPL is the CAUSE OF GESTATIONAL DIABETES
dating criteria - embryonic age
*from date of conception
*embryonic age = gestational age - 2 weeks (accounts for the 2 weeks to ovulation that occur after the last menstrual period)
dating criteria - gestational age
*from date of FIRST DAY of last menstrual period (LMP)
*best predictor for dating
*can vary or “be off”; better if patient has regular, 28-day cycles
fetal heart rate detection
*4 weeks: heart forms, begins to beat (usually do not hear or see it)
*6 weeks: initially seen on ultrasound (transvaginal)
*12 weeks: initially heard on doppler
note - body habitus can affect this; TVUS is better than abdominal US
1st trimester of pregnancy
from conception to 13 weeks 6 days
2nd trimester of pregnancy
from 14 weeks 0 days to 27 weeks 6 days
3rd trimester of pregnancy
from 28 weeks 0 days through the rest of pregnancy
term (early, full term, late, and post) babies - definitions
*term = 37 weeks 0 days and longer; everything in the baby is “fully developed”
*early term = 37w0d - 38w6d
*full term = 39w0d - 40w6d
*late term = 41w0d - 41w6d
*post term = 42w0d +
preterm (extreme, early, late) babies - definitions
*preterm = 20 weeks 0 days to 36 weeks 6 days; baby is not “fully developed”
*extreme preterm = < 28w0d
*early preterm = 28w1d - 33w6d
*late preterm = 34w0d - 36w6d
prenatal visits - timeline
*initial PNV: mid-1st trimester (6-10 weeks)
*subsequent PNVs:
-1st and 2nd trimesters: every 4 weeks
-3rd trimester: every 2 weeks
-once “term” (37w0d): weekly visits until delivery
*typically, about 11-15 total visits
initial prenatal visit - objectives
*determine dating
*determine risk factors
*review pregnancy history
*labs
*genetic testing
*pap (if indicated)
*review vitals
subsequent prenatal visit - objectives
*fundal height (after 20 weeks at umbilicus)
*FHT (after 12 weeks)
*review vitals
*anatomy scan (18-22 weeks)
*genetic testing (if not already done)
*repeat labs @ 28 wks
*GTT (glucose tolerance test) @ 28 wks
*TdaP @ 28 wks
*Rhogam @ 28 wks
*RSV vaccine (32-36 wks); COVID vaccine
*GBS / GC / CT @ 36 wks
key prenatal visits
- initial visit: prenatal labs, fetal heart rate (ultrasound), intake
- 10-12 weeks: fetal heart rate (doppler), cfDNA
- 18-20 weeks: anatomy scan
- 28 weeks: glucose tolerance test, repeat labs, TdaP, Rhogam
- 36 weeks: GBS, GC/CT, position
fundal height
*measured after 20 weeks
*distance from mom’s pubic symphysis to highest point of uterus (fundus) in centimeters = weeks of gestation (after 20 weeks)
important prenatal labs
*CBC (check for anemia, platelet counts)
*infections / immunity: Hep B, Hep C, HIV, syphilis, gonorrhea, chlamydia, group B strep, varicella immunity, rubella immunity
*glucose tolerance test
*urine culture
physiologic adaptations of pregnancy - cardiac output
*goal = increase cardiac output → increase placental and uterus perfusion
*INCREASES: preload & HR
*DECREASES: afterload
physiologic adaptations of pregnancy - anemia
*increases plasma greatly
*increases RBCs
physiologic adaptations of pregnancy - hypercoagulability
*to lower blood loss at delivery
*results in increased risk for DVT or other thromboembolism
physiologic adaptations of pregnancy - hyperventilation
*eliminates fetal CO2
APGAR scores - overview
*APGAR score is checked at 1 min, 5 min, (and sometimes10 mins) after delivery
*low APGARs at later minutes = at risk for long-term neurologic damage
A - appearance
P - pulse
G - grimace
A - activity
R - respiration
APGAR scores - appearance
*score 2 = pink
*score 1 = extremities blue
*score 0 = pale or blue
APGAR scores - pulse
*score 2 = > 100 bpm
*score 1 = < 100 bpm
*score 0 = no pulse
APGAR scores - grimace
*score 2 = cries & pulls away
*score 1 = grimaces or weak cry
*score 0 = no response to stimulation
APGAR scores - activity
*score 2 = active movement
*score 1 = arms & legs flexed
*score 0 = no movement
APGAR scores - respiration
*score 2 = strong cry
*score 1 = slow, irregular
*score 0 = no breathing
