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Flashcards in Fetal Development Deck (83)
1

Fetal Proportional Growth

Measures of body length (CRL, lemur length) increase faster than measures of width increase (biparietal diameter, abdominal circumference).

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Normal Birth Weight

3200 g (7 lbs)

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Low Birth Weight

< 2500 g (5.5 lbs)

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Fatal Birth Weight

< 500 g (1.1 lbs)

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Small for gestational age (SGA)

< 10th percentile in weight for gestational age, but weight for size is normal

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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.

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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.

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Fetal fibronectin (fFN) test

test for preterm delivery risk: vaginal swab for placental adhesive glycoproteins

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Respiratory distress syndrome (RDS)

Respiratory distress due to underdeveloped lungs

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Respiratory distress syndrome (RDS) prenatal treatment

glucocorticoids to promote surfactant secretion in the lung to prevent collapse.

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Respiratory distress syndrome (RDS) POST-natal treatment

continuous positive airway pressure (CPAP) to maintain airway patency.

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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.

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Amniocentesis

sampling amniotic fluid w/ needle guided by ultrasonography. 14-20 weeks for adequate fluid. Fetal calls for karyotyping, fetal metabolites, proteins, hormones, etc.

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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.

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Maternal serum screening

identifying fetal markers in maternal blood. Looking for a-fetoprotein and hCG levels. False positives numerous.

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a-fetoprotein

fetal marker in maternal blood that can show neural tube defects, GI defects, Down syndrome

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hCG

fetal marker in maternal blood used to test for molar pregnancy, ectopic pregnancy, choriocarcinoma, down syndrome.

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Fetoscopy (fetendo)

Encoscopic procedure to visualize the fetus. Invasive, high risk (5-10%), used only in extreme casus

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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%)

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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.

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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.

22

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.

23

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.

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Amniochorionic membrane (ACM)

Formed by fusion of amnion and chrion. Ruptures prior to birth, 'water breaking'.

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Amniotic Band Sundrome (ABS)

Premature rupturing of the ACM. Bands/cords of ACM constrict fetal body parts, may affect development of more distal structures.

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Amniotic fluid

500-1000 ml of circulating clear, watery liquid that contains fetal cells, proteins, electrolytes that can be collected via aminocentesis.

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Sources of Amniotic fluid

amniotic cells lining cavity, diffusion of maternal tissue fluid, fetal urination.

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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.

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Amniotic fluid functions

Cushions, prevents adhesion, permits movement, permits growth, barrier to infections, regulated body temperature, regulates fluid/electrolyte homeostasis.

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Polyhdramnios

too much amniotic fluid; >1500 ml. Assoc. w/ severe malformations that prevent swallowing of amniotic fluid.

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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.

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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)

33

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).

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long cord

risk of cord prolapse or the cord encircling fetal neck, called nuchal cord.

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short cord

restricted fetal movements, early detachment of placenta from uterus during delivery.

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True knot (umbilical)

fetal hypoxia/anoxia (little/no oxygen); may be fatal

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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.

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Placenta

site of nutrient and gas exchange between fetus & mother; produces pregnancy hormones like hCG.

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Decidua basalis

maternal part of the placenta, derived from endometrium

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Villous chorion

fetal part of placenta, derived from chorion

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decidua capsularis

endometrium during pregnancy adjacent to the smooth chorion

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decidua parietalis

endometrium during pregnancy not directly associated with the chorion.

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Chorion

name for extraembryonic mesoderm plus trophoblast layers

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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!!

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Smooth chorion

less vascular, non-placental region adjacent to decidua capsularis

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Placental barrier before 4 months fertilization age

1. synctiotrophoblast 2. cytotrophoblast 3. extraembryonic mesoderm 4. endothelial cells lining fetal capillaries.

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Placental barrier after 4 months fertilization age

1. syncytiotrophoblast 2. endothelial cells lining fetal capillaries. Now increased exchange. Cytotrophoblast cells detach and migrate to lin maternal arteries.

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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.

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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.

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Eclampsia

follows preeclampsia and is characterized by seizures.

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Placenta accreta

placenta attaches to the myometrium of uterus

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Placenta increta

placenta invades myometrium of uterus

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Placenta percreta

placenta penetrate the uterus and extends into body cavity

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DZ twins

dichorionic, diamniotic (DCDA, DiDi): 2 amnions, 2 chorions, 2 placentas. 2 oocytes released at ovulation & fertilized separately, unique DNA, 'fraternal'.

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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

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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.

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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.

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Week 1

Cleavage, compaction (day 4), cavitation, hatching, implantation (day 6)

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Week 2

uteroplacental circulation, trophoblast differentiation (cytotrophoblast and syncytiotrophoblast.), bilaminar disc formation, chorionic cavity formation, hcG detectable day 8.

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Week 2 complications

ectopic pregnancy, placenta previa, molar pregnancy, choriocarcinoma.

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Weeks 3-4

Gastrulation, neurulation, NODAL expression, FGF8 expression, hypoblast displaced, body axes established, lateral body folding.

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Intermediate mesoderm

forms urogenital system

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parietal layer of lateral plate mesoderm

forms connective tissue of body wall and limbs

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visceral layer of lateral plate mesoderm

GI/respiratory organs except epithelial lining

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Weeks 4-8

somites differentiate (wk 4), myotome differentiation (wk 5), resegmentation (wk 5), organogenesis

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week 6

chondrification centers for vertebral column develop

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week 7

primary ossification centers for vertebral column develop

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week 8

ribs form (sclerotome), tail regresses, limbs rotate/enlongate, digits and face develop,

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hox9

produces floating ribs

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hox 10

prevents rib formation

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sternum formation

from parietal layer of lateral plate mesoderm

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Hox11

sacralization of vertebrae

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Anencephaly

rostral neuropore doesn't close

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spina bifida

causal neuropore doesn't close

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Caudal dysgenesis

malformed pelvis, underdeveloped lower limbs, 250X more in pregestational diabetics

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Sirenomelia

form of CD, mermaid syndrome

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Mutation of Hox9

Loss of function: ribcages with all ribs attacted to sternum

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Mutation of Hox10

Loss of function: lumbar and sacral vertebrae with ribs. Gain of function: Thoracic vertebrae without ribs

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Mutation of Hox 11

LoF: Sacral vertevrae that donot fuse. GoF: vertebrae at various levels fusing

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Spondylolysis

fracture of pars interarticularis

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Sacralization of L5 vertebra

Hox11 gain of function mutation at L5

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Weeks 9+ (fetal period)

bone ossification centers (wk 12), ext genetalia visible (wk 12), swallowing and urine formation (wk 10), respiratory movements (wk 15)

83

Sound and light recognition

weeks 24 - 28