1. primary oocytes 2. begin meiosis 1 during fetal life 3. PAUSE (meiosis 1 arrested in prophase 1 for years until ovulation - still a primary oocyte) 3. complete meiosis 1 prior to ovulation (now a secondary oocyte) 4. meiosis 2 arrested in metaphase 2 until fertilization 5. if fertilization does not occur within 1 day, secondary oocyte degenerates

Conception, Pregnancy, Fetal Development Flashcards by Kyra Porter

oogenesis - overview

*differentiation of the ovum
*occurs in the female fetus prior to their birth

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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

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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

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early fetal development - week 1

*hCG secretion begins upon implantation (usually days 6-10) of the blastocyst

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early fetal development - week 2

*bilaminar disc formed (2 layers in week 2- epiblast & hypoblast)

epiblast becomes embryo
hypoblast becomes yolk sac

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early fetal development - week 3

*gastrulation: formation of trilaminar disc (3 layers in week 3 - endoderm, mesoderm, ectoderm)

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early fetal development - weeks 3-8 (overview)

neural tube** forms; closes by week 4
**organogenesis occurs
*extremely susceptible to TERATOGENS

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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

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early fetal development - week 6

*cardiac activity on transvaginal ultrasound

recall: heart starts to beat at 4 week, but undetectable until week 6

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early fetal development - week 8

*fetal movement begins

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early fetal development - week 10

*genitalia female/male characteristics form

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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

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placenta - overview

*primary site of nutrient and gas exchange between mother and fetus
*2 components: fetal & maternal

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placenta - maternal component

*aka decidua basalis
*derived from endometrium
*maternal blood is found in the lacunae

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placenta - fetal component

cytotrophoblast - inner layer of chorionic villi
syncytiotrophoblast - outer layer of chorionic villi
*synthesizes & secretes hormones (hCG)
*lacks MHC-1 expression

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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

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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

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formation of the umbilical cord

*yolk sac (3rd week) → allantois → urachus
*urachus = duct between fetal bladder and umbilicus

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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

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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

1. initial visit: prenatal labs, fetal heart rate (ultrasound), intake 2. 10-12 weeks: fetal heart rate (doppler), cfDNA 3. 18-20 weeks: anatomy scan 4. 28 weeks: glucose tolerance test, repeat labs, TdaP, Rhogam 5. 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