Fetal Development Flashcards
Fetal Proportional Growth
Measures of body length (CRL, lemur length) increase faster than measures of width increase (biparietal diameter, abdominal circumference).
Normal Birth Weight
3200 g (7 lbs)
Low Birth Weight
< 2500 g (5.5 lbs)
Fatal Birth Weight
< 500 g (1.1 lbs)
Small for gestational age (SGA)
< 10th percentile in weight for gestational age, but weight for size is normal
in utero growth retardation (IUGR)
< 10th percentile in weight for gestational age and < 2.5th percentile for abdominal circumference. Mortality is 30 times more likely, mental development may be affected.
Preterm birth
< 37 weeks gestational age. Survival 50% at 24 weeks, 90% at 28 weeks. Skin may appear reddish/wrinkly due to paucity of dermal connective tissue. Primary cause of death is respiratory failure.
Fetal fibronectin (fFN) test
test for preterm delivery risk: vaginal swab for placental adhesive glycoproteins
Respiratory distress syndrome (RDS)
Respiratory distress due to underdeveloped lungs
Respiratory distress syndrome (RDS) prenatal treatment
glucocorticoids to promote surfactant secretion in the lung to prevent collapse.
Respiratory distress syndrome (RDS) POST-natal treatment
continuous positive airway pressure (CPAP) to maintain airway patency.
Lecithin-sphingomyelin ratio
test for RDS risk. Lecithin should rise relative to sphingomyelin beginning in the 34th week, 2:1 = low RDS risk. Amniotic fluid sampled by amniocentesis or vaginal swab.
Amniocentesis
sampling amniotic fluid w/ needle guided by ultrasonography. 14-20 weeks for adequate fluid. Fetal calls for karyotyping, fetal metabolites, proteins, hormones, etc.
Chorionic villus sampling (CVS)
biopsy of chorionic villus w/ needle guided by ultrasonography. 10-14 weeks (after 14 wks, amniocentesis preferred). Slightly higher risk (1-2%), less accurate, earlier karyotyping.
Maternal serum screening
identifying fetal markers in maternal blood. Looking for a-fetoprotein and hCG levels. False positives numerous.
a-fetoprotein
fetal marker in maternal blood that can show neural tube defects, GI defects, Down syndrome
hCG
fetal marker in maternal blood used to test for molar pregnancy, ectopic pregnancy, choriocarcinoma, down syndrome.
Fetoscopy (fetendo)
Encoscopic procedure to visualize the fetus. Invasive, high risk (5-10%), used only in extreme casus
Percutaneous Umbilical Cord Blood Sampling (PUBS)
sampling of umbilical vein blood for genetic or metabolic disoreders (also called cordocentesis). > 17 weeks (cord large enough), same risk as CVS (1-2%)
Culdocentesis
extraction of fluid from the peritoneal cavity within the abdomen. Invasive: must penetrate vagina and peritoneum. Looking for blood; indivative of tubal rupture during ectopic pregnancy.
Dilation and curettage (D and C)
dilation of the cervix and removal of endometrium (scraping or suction). Screens for polyps, cancer, ectopic pregnancy. Placental tissue floats in saline, cancer doesn’t. comparison with hCG levels usually necessary.
Vernix caseosa
waxy or cheese-like white substance found coating the skin of newborn human babies. Starts developing on the baby in the womb around 18 weeks into pregnancy.
Lanugo
very fine, soft, and usually unpigmented, downy hair as can be found on the body of a fetusor newborn baby. It is the first hair to be produced by the fetal hair follicles, and it usually appears on the fetus at about 5 months of gestation.
Amniochorionic membrane (ACM)
Formed by fusion of amnion and chrion. Ruptures prior to birth, ‘water breaking’.
Amniotic Band Sundrome (ABS)
Premature rupturing of the ACM. Bands/cords of ACM constrict fetal body parts, may affect development of more distal structures.
Amniotic fluid
500-1000 ml of circulating clear, watery liquid that contains fetal cells, proteins, electrolytes that can be collected via aminocentesis.
Sources of Amniotic fluid
amniotic cells lining cavity, diffusion of maternal tissue fluid, fetal urination.
Amniotic fluid circulation
Enters fetal circulation by being swallowed into GI tract, aspiated into lungs, and absorbed through skin. Returns to maternal circulation through uteroplacental circulation, excretion into amniotic cavity and diffusion into maternal tissue.
Amniotic fluid functions
Cushions, prevents adhesion, permits movement, permits growth, barrier to infections, regulated body temperature, regulates fluid/electrolyte homeostasis.
Polyhdramnios
too much amniotic fluid; >1500 ml. Assoc. w/ severe malformations that prevent swallowing of amniotic fluid.
Oligohydramnios
Too little amniotic fluid; < 400 ml. Assoc. w/ renal agenesis, urinary blockages, premature rupture of ACM (PROM). May lead to slowed growth or oligohydramins sequence.
Oligohydramnios (Potter’s) Sequence
Abnormal appearance due to compression of fetus against uterus, e.g., limb abnormalities, flattened face. Typically caused by bilateral renal agenesis or ACM rupture. Characterized by oligohydramnios, anuria (no urination), pulmonary hypoplasia (under-developed lungs)
Umbilical cord
Attaches fetus to placenta. (55 cm length, 1-2 cm diameter) Contains: 1 umbilical vein (blood: placenta to fetus), 2 umbilical arteries, (blood: fetus to placenta), loops of intestine, yolk sac, vitelline vessels, allantois (waste collection).
long cord
risk of cord prolapse or the cord encircling fetal neck, called nuchal cord.
short cord
restricted fetal movements, early detachment of placenta from uterus during delivery.
True knot (umbilical)
fetal hypoxia/anoxia (little/no oxygen); may be fatal
Umbilical cord blood banking
Collection, storage of fetal blood cells. Alternative to bone marrow transplants. Pros: No discomfort, abundant viabble stem cells, minimized host-graft rejection. Cons: expensive, low prob of use.
Placenta
site of nutrient and gas exchange between fetus & mother; produces pregnancy hormones like hCG.
Decidua basalis
maternal part of the placenta, derived from endometrium
Villous chorion
fetal part of placenta, derived from chorion
decidua capsularis
endometrium during pregnancy adjacent to the smooth chorion
decidua parietalis
endometrium during pregnancy not directly associated with the chorion.
Chorion
name for extraembryonic mesoderm plus trophoblast layers
Villous chorion
fetal placenta adjacent to decidua basalis, highly vascular. develops as the cytotrophoblast and extraembryonic mesoderm and grows into the syncytiotrophoblast. NO MIXING OF MATERNAL AND FETAL BLOOD!!
Smooth chorion
less vascular, non-placental region adjacent to decidua capsularis
Placental barrier before 4 months fertilization age
- synctiotrophoblast 2. cytotrophoblast 3. extraembryonic mesoderm 4. endothelial cells lining fetal capillaries.
Placental barrier after 4 months fertilization age
- syncytiotrophoblast 2. endothelial cells lining fetal capillaries. Now increased exchange. Cytotrophoblast cells detach and migrate to lin maternal arteries.
Placental barrier (membrane)
blocks: large, complex molecules, many protein hormones, many bacteria. Allows: gas, nutrient, waste exchange, steroid hormones, some antibodies, most medications/drugs, many viruses.
Preeclampsia
clinical concern > 4 months. Caused by failed migration of cytotrophoblast cells or maternal immune response to invading cytotrophoblast cells. Increases pressure in maternal vessels. Results in maternal hypertension, preoteinuria, slowed fetal growth, potential death.
Eclampsia
follows preeclampsia and is characterized by seizures.
Placenta accreta
placenta attaches to the myometrium of uterus
Placenta increta
placenta invades myometrium of uterus
Placenta percreta
placenta penetrate the uterus and extends into body cavity
DZ twins
dichorionic, diamniotic (DCDA, DiDi): 2 amnions, 2 chorions, 2 placentas. 2 oocytes released at ovulation & fertilized separately, unique DNA, ‘fraternal’.
MZ twins: dichorionic, diamniotic (DCDA, DiDi)
2 amnions, 1 chorion, 1 placenta. 1 oocyte released at ovulation, fertilized by 1 sperm, same DNA, ‘identical’. each blastocyst implants separately in endometrium
MZ twins: monochorionic, monoamniotic (MCMA, MoMo)
1 amnion, 1 chorion, 1 placenta. 1 oocyte released at ovulation, fertilized by 1 sperm. I embryblast at implantation = 1 amnion. 2 epiblasts after implantation = 2 fetuses. 1 trophoblast = 1 chorion, 1 placenta.
Day 1
Spermreach oocyte, pass through CR. Acrosome reaction (male), Zona reaction (female). Sperm fuses with ocyte membrane, oocyte completes M2. Pronuclei fuse to from single diploid nucleus.
Week 1
Cleavage, compaction (day 4), cavitation, hatching, implantation (day 6)
Week 2
uteroplacental circulation, trophoblast differentiation (cytotrophoblast and syncytiotrophoblast.), bilaminar disc formation, chorionic cavity formation, hcG detectable day 8.
Week 2 complications
ectopic pregnancy, placenta previa, molar pregnancy, choriocarcinoma.
Weeks 3-4
Gastrulation, neurulation, NODAL expression, FGF8 expression, hypoblast displaced, body axes established, lateral body folding.
Intermediate mesoderm
forms urogenital system
parietal layer of lateral plate mesoderm
forms connective tissue of body wall and limbs
visceral layer of lateral plate mesoderm
GI/respiratory organs except epithelial lining
Weeks 4-8
somites differentiate (wk 4), myotome differentiation (wk 5), resegmentation (wk 5), organogenesis
week 6
chondrification centers for vertebral column develop
week 7
primary ossification centers for vertebral column develop
week 8
ribs form (sclerotome), tail regresses, limbs rotate/enlongate, digits and face develop,
hox9
produces floating ribs
hox 10
prevents rib formation
sternum formation
from parietal layer of lateral plate mesoderm
Hox11
sacralization of vertebrae
Anencephaly
rostral neuropore doesn’t close
spina bifida
causal neuropore doesn’t close
Caudal dysgenesis
malformed pelvis, underdeveloped lower limbs, 250X more in pregestational diabetics
Sirenomelia
form of CD, mermaid syndrome
Mutation of Hox9
Loss of function: ribcages with all ribs attacted to sternum
Mutation of Hox10
Loss of function: lumbar and sacral vertebrae with ribs. Gain of function: Thoracic vertebrae without ribs
Mutation of Hox 11
LoF: Sacral vertevrae that donot fuse. GoF: vertebrae at various levels fusing
Spondylolysis
fracture of pars interarticularis
Sacralization of L5 vertebra
Hox11 gain of function mutation at L5
Weeks 9+ (fetal period)
bone ossification centers (wk 12), ext genetalia visible (wk 12), swallowing and urine formation (wk 10), respiratory movements (wk 15)
Sound and light recognition
weeks 24 - 28
