07 extraembryoner structures

8/6/2019 07 Extraembryoner Structures

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EXTRAEMBRYONER EXTRAEMBRYONER STRUCTURESSTRUCTURES


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PL ACENTA AND FOETAL MEMBRANESPL ACENTA AND FOETAL MEMBRANESPL

ACENTA and FETAL

MEMBRANES Pl acenta: Chorion / Maternal Decidua Chorion: Trophoblasts / Extraembryonic Mesoderm Amnion: Epiblast / Extraembryonic Mesoderm Yolk Sac: Hypoblast / Extraembryonic Mesoderm All antois: Embryonic HindgutP ARTURITIONAMNION SAC AND AMNION FL UID

VITTELL

INE SACALL ANTOIS


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OBJECTIVESDescribe the differentiation of the trophoblastlayer of the blastocyst upon implantation.

Describe the fetal syncytiotrophoblast andcytotrophoblast separate roles in the primitive

placenta.Understand the decidual reaction of theendometrium.Understand the definition of the 3 types of villi

that develop sequentially.Understand the cell layers that separate maternalfrom fetal blood.Understand the nutritive role of the placenta.Understand the maternal and fetal componentsthat can cross the placenta barrier.

Understand the endocrine role of the placenta.Understand abnormalities of placentaldevelopment than can occur.Describe the cause and consequences of erythroblastosis fetalis.


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PL ACENTA: INTRODUCTIONThe placenta (Gk.

plakuos= flat cake) isa materno-fetal organwhich beginsdeveloping atimplantation of the

blastocyst and isdelivered with thefetus at birth.During that 9 month

period it provides

nutrition, gasexchange, wasteremoval, endocrineand immune supportfor the developing

fetus.


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PL ACENTA: GENERAL SP ECIFICATIONThe placenta continues to growand develop throughout

pregnancy and at term is anorgan of about 20cm indiameter , with a thick ness of 3cm and a weight of about500g.The chorionic villi have anenormous area of exchange,reaching 14m2 at term and thecapillaries within them have alength of 50k m.The rate of maternal blood flowto the uterus is in the range of 500-700ml/ min with 80% of that destined to supply the

placenta (Martal and Cdard,1993).

The erosion of the decidua basalis is incomplete uneroded regions called decidual septa.The decidual septa define regions of the placentacalled cotyledon.


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PL ACENTA CL ASSIFICATION

Human plancentationtype is discoid,hemochorial.


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Materna l Surface Cotyledons Form cobblestone

appearance Originally placental septa

formed grooves

Overed with maternal decidua basalis

Fetal Surface Covered with amniotic

membrane attached to

chorionic plate. Umbilical cord attachment. Cord 1-2 cm diameter, 30-

90cm long. Umbilical vessels branch into

chorionic vessels.

Pl acental Anatomy:


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DEC DUADecidual Reaction: stromalcells accumulate glycogenand lipid, called Decidual Cell sDecidua basalis: formsmaternal component of the

placenta; associates with thechorion frondosomDecidua capsularis:Superfical layer overlying theentire embryoblast.

This layer eventually

degenerates; associates withthe chorion laeve

Decidua parietalis: Allremaining parts of theendometrium - not associatedwith the embryo.


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Ear ly Development of the Pl acentaGrowth of the embryoblast outstripsthe trophoblast .As a consequence the former begins

pulling away from later forminganother cavity . This cavity called theamniotic cavityThe next significant step inembryogenesis is separation of embryoblast from trophoblast

This disc will soon come to sit between two sacs; the amniotic sacand yolk sac.Amniotic Sac: Between the epiblast and trophob last,

a slit-like cavity appears and enlargesto form the amniotic sac.

Cells from the epiblast migrateupwards to completely line this newcavity.

P rimary Yo lk Sac The cells of the hypoblast migrate

downwards to line the blastocoele andform the primary yo lk sac.


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Ear ly Uteroplacental Circu lationEar ly Uteroplacental Circu lationAs the syncytiotrophoblast invades the uterinewall, it erodes into dilated uterine capillariescalled sinusoids.Maternal blood from the sinusoids rushes intothe syncytiotrophoblast cell mass and fillscavities called lacunae.The direct contact of the syncytiotrophoblastwith maternal blood allows for diffusion totake place and forms the beginning of utero-placental circulation.Oxygen and nutrients from maternal blooddiffuse across the trophoblast to supply thedeveloping embryo, while wastes from theembryo diffuse across the trophoblast into thelacunae to be removed by the uterine veins.By day 12, the lacunae form inter-connectionsso that the syncytiotrophoblast (or syncytium)takes on a "spongy" appearance .As the trophoblast grows outward rapidly,cavitations appear within the extraembryonicmesoderm. The cavitations grow larger and eventually

join to form a large cavity that completelysurrounds the embryo all.But at the stalk where it remains attached tothe cytotrophoblast.


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Ear ly Development of the Pl acenta


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Pl acental Development By 8 week s: Chorionic stem villi over the entire surface of the chorionic sacThose villi associated with the decidua

basalis increase in size and more villiform.The villi project into a blood filledintervillous space resulting from the

erosion of the decidua basalis.Endometrial vessels, spiral arteriesand endometrial veinsEnlargement includes further

branching of the anchoring villus;

chorion frondosum.Villi associated with the deciduacapsularis degenerate - this region iscalled the chorion leave


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Structure of the Pl acentaStructure of the Pl acenta P rimary chorionic vill i (L ate Week 2) (Day 13) are solid outgrowths of cytotrophoblast that protrude into thesyncytiotrophoblast.

trophoblastic shell cells syncitiotrophoblasts, cytotrophoblasts frorm finger-like extensions

Secondary chorionic vill i have acore of loose connective tissue,which grows into the primary villiabout the mid-third week (Day 169of development.

Extraembryonic mesoderm grows intovilli; covers entire surface of chorionicsac

Tertiary chorionic vi ll i (L ate ThirdWeek ) (Day 21) contain embryonicblood vessels that develop frommesenchymal cells in the loose

connective tissue core. mesenchyme differentiates into bloodvessels and cells

forms arteriocapi ll ary network fuse with placental vessels developing in connecting stalk


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Pl acental DevelopmentChorionic Vill i Stem or anchoring vill i

cytotrophoblast cells attachedto maternal tissue

Branched or termina l

vill

igrow from sides of stem villiregion of main exchange

surrounded by maternal

blood in intervillous spaces materna l sinusoids


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PL ACENTAL STRUCTURE

OVERVIEW

Chorionic Pl ate Stem vill i extendsfrom this tissueP rimary stem vill i (day 11-13;L ate SecondWeek ): Finger-like protrusions into endometrium -

contains syncytiotrophoblast, cytotrophoblast.Secondary stem vill i (day 16) (Mid ThirdWeek ): Extraembryonic mesoderm invasion into villi

core.Tertiary stem vi ll us (21 day) (Mid ThirdWeek ): Extraembryonic vessels - chorionic arteries and

veins derived from extraembryonic mesoderm.Hemichorial type placenta: Maternal blood baths villiCytotrophob lastic cell column:Terminal villi, solid mass of trophoblastCytotrophob lastic shell : Surroundsembryo; direct contact with maternal

decidual cellsAnchoring Vill i give off cytotrophoblastic extensions anchoring

because they represent the realmaternoembryoner link Floating Vill i (branches off anchoringvilli) suspends freely in maternal blood


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PL ACENTAL CIRCUL ATION

Fetal; Contained within vessels Umbilical Arteries chorionic plate branches to stem villi capillaries in

terminal villi return via - umbilical vein

Materna l; Free-f lowinglak e Spiral arteries open into intervillous space and bath the villi 150 ml of maternal blood in the intervillous space Exchanged; 3-4 times/minute Reduced blood pressure in intervillous space Oxygenated blood to the chorionic plate, return baths the villi


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PL ACENTAL CIRCUL ATIONPL ACENTAL CIRCUL ATION


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PL ACENTAL CIRCUL ATIONPL ACENTAL CIRCUL ATION


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FOETAL CIRCUL ATIONFOETAL CIRCUL ATION

There are essentially 3 separate aortic/venous circulatory systems: Umbilical, systemic and vitelline. The umbilical system is is lost at birth, The vitelline contributes to the portal system

And the systemic (embryonic) matures into the cardiovascular system.


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PL ACENTAL BARRIERS Placental barrier decreases withgestationPl acental Barrier:

syncytiotrophoblast + basal lamina, basal lamin+ fetal capillaryendotheliumSyncytiotrophoblasts manymicrovilli, no major histocompatibilityantigens


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CHORIONChorionic cavity

(extraembryonic coelom)-lined with extraembryonicmesodermChorionic cavity expandsseparating amnion fromcytotrophoblastChorionic sac consist of: Cytotrophoblastic layer Syncytiotrophoblastic layer Extraembryonic somatic

mesodermThe Chorion / maternal

endometrium forms the placentaChorion forms stem villi


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STEM VILL I Chorionic Pl ate Stem vill i extendsfrom this tissueP rimary stem vill i (day 11-13): Finger-like protrusions into endometrium -

contains syncytiotrophoblast, cytotrophoblast.Secondary stem vill i (day 16): Extraembryonic mesoderm invasion into villi

core.Tertiary stem vi ll us (21 day): Extraembryonic vessels - chorionic arteries and

veins derived from extraembryonic mesoderm.Hemichorial type placenta: Maternal blood

baths villiCytotrophob lastic cell column:Terminal villi, solid mass of trophoblastCytotrophob lastic shell : Surroundsembryo; direct contact with maternaldecidual cells Anchoring Vill i give off

cytotrophoblastic extensions anchoring because they represent the realmaternalembryo link

Floating Vill i branches off anchoringvilli dangles freely in maternal blood


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UMBL ICAL CHORDUMBL ICAL CHORDOne umbilical vein, two umbilical arteriesWhartons jell y mucoid connective tissue surrounding vesselsAllantoisYolk Stalk (vitelline duct) and vitelline vessels (early)Intestinal loop umbilical hernia (late)


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UMBL ICAL CHORDUMBL ICAL CHORD


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Pl acental FunctionMain functions of the placenta are(a ) exchange of metabolic and

gaseous products betweenmaternal and fetal bloodstreamsand

Exchange of gasses Exchange of Nutritients and

Electrolytes

Transmission of MaternalAntibodies(b) production of hormones. hCG Chorionic somatomammotropin Chorionic adrenocorticotropin

(cACTH) Estriol Progesteron Relaxin Human Placental Lactogen


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The endocrine role of the placentaP rogesterone: Progesterone plays an important part in maintaining pregnancy. At conception progesterone production in the corpus luteum is increased

(Bassett et al., 1969), this secretion of progesterone inhibits the norma l oestruscycle and all ows pregnancy to continue.

Progesterone production is continued by the corpus luteum for about 50 daysafter which time the cytotrophoblast and syncytiotrophoblast of the placentatake over the production of progesterone (Martal and Cdard, 1993).

Progesterone levels continue to increase during pregnancy but there is a markedspecies variation in progesterone levels around parturition. In some species there is a marked drop in the levels of progesterone just

before the beginning of parturition , e.g. the ewe (Thorburn and Challis,1979).

In summary , it seems that in most species there is evidence that a drop in progesterone levels precedes parturition, this led to the hypothesis that a drop in

progesterone levels was needed for the uterine contractions associated with parturition to occur (Numan, 1994). However in primates there is no clear evidence that a drop in progesterone

levels is needed for parturition to occur, it should be noted however, that themeasurement of plasma levels of hormones may not be indicative of their levelsat the site of action.

In the human placenta progesterone is derived from maternal cholesterol bound

to low-density lipoprotein (LDL) (Martal and Cdard, 1993).


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The endocrine role of the placentaOestrogen:Oestrogen play an important role in implantation and in mammary g landdevelopment as well as in the release of prolactin at parturition.In the ewe the amount of osteogen in the mothers plasma rise slowly untilday 145-150of pregnancy when there is a sharp increase in the level.In humans, the levels of oestrogen in maternal plasma appear to risethroughout pregnancy, but as with progesterone there is a difference of

opinion as to what happens prior to parturition.In some species oestrogen are produced entirely in the placenta by synthesisfrom C21 steroid precursors (e.g. pregnenolone and progesterone), however,in man, who lacks the necessary enzymes for this pathway, oestrogen are

produced from androgens secreted by the fetal adrenal gland (Wooding andFlint, 1985).Man is therefore said to posses a 'fetoplacental unit' because both the fetusand the placenta are required to complete the steroidogenic pathway.


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The endocrine role of the placenta

Pl acental lactogen:Placental lactogen (PL) (also known as chorionicsomatomammotropin) is a member of the growthhormone and prolactin family of hormones.

At the amino acid level human placental lactogen (hPL)shows an 85% homology to human growth hormone(hGH) and a 67% homology to prolactin (PRL) (Martaland Cdard, 1993), because of this, and the fact that

hPL binds to both hGH and PRL receptors most of thework done on the role of hPL in pregnancy hasexamined processes that are regulated by growthhormones and PRLs. (Ogren and Talamantes, 1994).


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The endocrine role of the placentaThese include: i. The regulation of materna l intermediary metabo lism:

PL is thought to play a role in some of the lipid and carbohydrate metabolism changes that occur in themother during the third trimester of pregnancy.These include increases in the basal and glucose stimulated insulin secretion, development of insulinresistance by some tissues, impaired carbohydrate tolerance and an increase in lipid mobilization.The net effect of these changes being to free-up maternal glucose for the fetus.

ii. Stimulation of fetal growth:The potency of PL in promoting growth is very low.This led early researchers into this field to believe that the main role of PL was the regulation of maternal intermediary metabolism (Ogren and Talamantes, 1994).

Recently, it has been found that hPL plays a role in regulating growth-associated processes in severalfetal tissues, for example, hPL stimulates amino acid uptake, thymine incorporation and insulin-likegrowth factor-1 (IGF-1) production in fibroblast and skeletal muscle myoblasts (Hill et al., 1986)

iii.Stimulation of mammary gland secretary differentiation:The predominant role of hPL in the human mammary gland would appear to be to stimulate cell

proliferation rather than secretion although hPL stimulates lactogenesis in non-primate species. (Thiscould be because of the similarity between hPL and the animals own PRL)

iv.The regulation of steroidogenesis:Human PL stimulates an increase in basal lipolysis (Williams and Coltart, 1978) as well as stimulatingglucose uptake and utilisation

Human placental lactogen is produced in the syncytiotrophoblast from the 5th week of pregnancy and is secreted into the maternal bloodstream.

The seretuary rate of hPL increases gradually until term at which time the placenta may be producing between 0.3 and 1.0 g/day (Martal and Cdard, 1993).


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Growth Hormone: A variant of human growth hormone (hGH) hGH-V which differs in 15

amino acid positions from hGH has been found in the placenta. Its role appears to be similar to pituitary growth hormone in that it has a

somatogenic activity and during the second half of pregnancy it mayregulate many of the processes normally regulated by pituitary growthhormone in non-pregnant individuals (Ogren and Talamantes, 1994).

Examination of the levels of hGH-V and insulin-lik e growth factor-1(IGF-1) during pregnancy have shown a correlation between their levelssuggesting a possible role for hGH-V in regulating IGF-1 production in thesecond half of pregnancy (Caufriez et al., 1990).

Human growth hormone variant is produced by the syncytiotrophoblastcells and is found in the materna l blood from about week s 21 to 26, itsconcentration increases until about week 36 and then remains constantfor the remainder of pregnancy (Caufriez et al., 1990).

It is possible that hGH-V is in the maternal blood system from week 9 atlow levels since mRNAs for hGH-V are present in placenta from that time(Liebhabner et al., 1989).

The endocrine role of the placenta


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Pl acental Abnorma lities placenta accreta

abnormal adherence, withabsence of decidua basalis placenta percreta

villi penetrate myometrium placenta previa

placenta overlies internal osof uterusabnormal bleedingcesarian delivery


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AMNIONAMNION Amnionic membrane is two cell l ayers 1) epiblast derived extraembryonic

ectoderma l l ayer 2) thin non-vascular extraembryonic

mesodermAs the amnion enlarges it encompassesthe embryo on the ventral side, mergingaround the umbilical cord.Amnion forms the epithelial layer of the

umbilical cordWith embryo growth the amnionobliterates the chorionic cavityAmnionic sac is fluid filled calledamnionic fluid: the embryo is bathed inthe fluid.


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AMNIONIC FL UIDUp to week 20 - fluid is similar to fetalserum (keratinization)

After 20 week s Contribution from urine,maternal serum filtered thru endothelium of nearby vessels, filtration from fetal vesselsin cord.Near birth - can contain fetal feces calledmeconiumNear birth: A mnionic fluid (500-1000 ml)exchanges every 3 hrs

1) across the amnion exchange withmaternal fluids.

2) fetal swallowing (20 ml/hour) to gut adsorption by fetus out the umbilicalcord to placenta.

Hydraminos Excess fluid (>2000 ml),esophageal atresiaOligohydramnios Insufficient fluid(


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AMNION FUNCTION

Mechanical protection: hydrostatic

pressureAll ows free movement - which aidsin neuromuscular developmentAntibacteria lAll ow for fetal growthP rotection from adhesions


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YOLK SAC - VITELL INE SACHypoblast - the primary yolk sac or Heuser's membrane.

Day 12- Second wave of cell migration - forms definitive yolk sacComposed of extrembryonicendodermEarly nutrition (2-3 weeks) for the

embryo - later shrinking -nonfunctional Meck elsdiverticulum (outpocketing of smallintestine)Connects to midgut via the yolk sacstalk

Derivatives: Early blood cells forms from blood

islands Primordial germ cells The early gut, epithelium of the

respiratory and digestive tracts


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ALL ANTOISEndoderma l origin; caudaloutpocketing of the yolk sacInvades the connecting stalk (extraembryonic mesoderm) thatsuspends the embryo in the chorioniccavityInvolved in early hematopoiesis (upto 2 months)The allantois blood vessels - arteryand vein becomes the umbilicalvesselsRemnants of All antois becomes theurachus ligament that connects the

belly button to the bladder


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FOETAL MEMBRANES


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P ARTURITION Fetal Growth First Trimester (1-12 weeks) embryonic and early fetal Second Trimester (13-24 weeks) organ development and

function, growth

Third Trimester (25-40 weeks) organ function and rapidgrowthFetus to neonate involves three phases Transition P hases L ate gestation P arturition

processes needed to establish independent homoeostatic regulationafter separation from the placenta.Phases are regulated by a series of fetal and placental endocrineevents .

Childbirth P arturition ( L. parturitio = chi ldbirth)

expelling the fetus, placenta and fetal membranesprobably initiated by fetus not mother

L aboruterine contractions and dilation of cervixprocess under endocrine regulation

Pl acenta and Feta l Membranessecundina (L. following)expelled after birth


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L ABOR STAGESL ABOR STAGES stage 1- dilatationuterine contractions 10 minutes apartfunction to dilate cervix

fetal membranes rupture releasing amnion7 -12 hours (longer for first child )

stage 2- expulsionuterine contractions push fetus through cervix andvaginauterine contractions 2-3 minutes apart

20 - 50 minutes

stage 3- placentalfollowing child delivery contractions continue toexpel placentahaematoma separates placenta from uterine wallseparation occurs at spongy layer of decidua basalis15 minutes

stage 4- recoverycontinued myometrial contraction closes spiralarteries

2+ hours


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DEL IVERY


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CHIL D BIRTH1. About 9 Months (about 270 Days) after Fertilization, at the end of a Full Term Pregnancy,the Fetus is ready for Birth. By this time, it hasusually moved so that its Head is against the Cervix.2. When it is time? A Hormone known asOXYTOCIN is released from the Pituitary Gland,that affects a group of large Involuntary Musclesthat surrounds the Uterus.3. WEAK, Irregular Contractions may occur for Several Weeks before birth. (False Labor).4. As these Muscles are stimulated, they begin aseries of Rhythmic Contractions knows as L ABOR that Expands the opening of the CERVIX so that itwill be large enough (about 10 cm) to allow the

baby to pass through it.5. As contractions continue, they become morePowerful (PAINFUL) and more Frequent, occurringonce every minute or two.6. Little by little, in a process (LABOR) that lastfrom 2 to 20 hours, the baby is FORCED toward theVagina as labor continues.


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CHIL D BIRTH7. The Amniotic Sac Breaks (BreakingWater), and the fluid it contains rushesout of the Vagina.8. The baby is finally Forced out of theUterus and the Vagina, Head First, stillattached to its mother by the UmbilicalCord.9. The Baby will begin to cough or cry inorder to rid its lungs of the fluid withwhich they have been filled. Breathingstarts almost immediately.10. The Umbilical Cord is clamped andcut, leaving a Scar known as Navel or Belly Button.11. In the final contractions the Placenta,Amniotic Sac and the Uterine Lining,collectively called AFTER BIRTH areexpelled from the mother's body about 10minutes after the baby is born.12. The process of Childbirth iscomplete.


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CL INICAL CORREL ATIONSMultiple P regnancy Dizygotic Fraternal) twinsare derived from two

zygotesthat were fertilizedindependently (i.e., twooocytes and twospermatozoa).

Consequently, they areassociated with twoamnions, two chorions,and two placentas, whichmay (65%)

or may not (35%) be fused. Dizygotic twins are only as

closely geneticall y relatedas any two siblings.


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MUL TIPL E P REGNANCY

Monozygotic twins(30%) are derived from one zygote that splits into twoparts .

This type of twins commonly has two amnions, one chorion, and one placenta.If the embryo splits ear ly in the second week after the amniotic cavity has formed,

the twins will have one amnion, one chorion, and one placenta.Monozygotic twins are geneticall y identical , but may have physical differences due

to differing developmental environments (e.g., unequal division of placentalcirculation).


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CONJOINED (SIAMESE) TWINS


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FETUS P AP YRACEUS & TWINSTRANSFUSION SYNDROME


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CL INICAL CORREL ATIONS

Erythrob lastosis Fetalis Some erythrocytes produced in the fetus routinely escape into the mothers systemic

circulation. When fetal erythrocytes are Rh positive but the mother is Rh negative, the mothers

body can form antibodies to the Rh antigen, which cross the placental barrier anddestroy the fetus.

The immunological memory of the mothers immune system means this prob lem ismuch greater with second and subsequent pregnancies.


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CL INICAL CORREL ATIONS

Oligohydramnios: Deficiency of amniotic fluid (less than 400 ml inlate pregnancy). It can result from rena l agenesis because the fetus is unable to contribute

urine to the amniotic fluid volume.

Hydraminos: Excess fluid (>2000 ml), esophageal atresia


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P RENATAL DIAGNOSIS


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P renata l DiagnosisThe perinatologist has several

approaches for assessinggrowth and development of thefetus in utero, includingultrasound, maternal serumscreening, amniocentesis , andchorionic villus sampling .

In combination, thesetechniques are designed todetect malformations, geneticabnormalities, overall fetalgrowth, and complications of

pregnancy, such as placental or uterine abnormalities.The use and development of in

utero therapies have heralded anew concept in which the fetusis now a patient.


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UltrasonographyU ltrasonography is a relativelynoninvasive technique that uses high-frequency sound waves reflected fromtissues to create images.The approach may be transabdominal or transvaginal, with the latter producingimages with higher resolution.Important parameters revealed byultrasound include characteristics:

Fetal age and growth; Presence or absence of congenital

anomalies; Status of the uterine environment ,

including the amount of amniotic fluid; Pl acental position and umbilical blood

f low; Multiple gestationsare present


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Ultrasonography

Fetal age and growth are assessed by crown-rump length during the5th to 10th weeks of gestation. After that, a combination of measurements; including the biparietal

diameter (BPD) of the skull, femur length , and abdominal circumference are used

Congenital malformations that can be determined by ultrasoundinclude:

The neural tube defects anencephaly and spina bifida; Abdominal wall defects, such as omphalocele and gastroschisis; Heart and facial defects, including cleft lip and palate.


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Materna l Serum ScreeningA search for biochemical markers of fetal statusled to development of maternal serumscreening tests .One of the first of these tests assessed serum a-

fetoprotein (AFP) concentrations.AFP is produced normally by the fetal liver,

peaks at approximately 14 week s, and leaksinto the maternal circulation via the placenta.Thus, AFP concentrations increase in maternalserum during the second trimester and then

begin a steady decline after 30 weeks of gestation.In cases of neura l tube defects and severalother abnormalities, including omphalocele,gastroschisis, bladder exstrophy , amnioticband syndrome, sacrococcygeal teratoma,and intestinal atresia, AFP levels increase inamniotic fluid and maternal serum.

In other instances, AFP concentrationsdecrease, as, for example, in Down syndrome,trisomy 18, sex chromosome abnormalities,and triploidy.These conditions are also associated with lower serum concentrations of human chorionic

gonadotropin (hCG) and unconjugated estriol .


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AmniocentesisDuring amniocentesis, a needle is insertedtransabdominally into the amniotic cavity andapproximately 20 to 30 mL of fluid iswithdrawn.Because of the amount of fluid required, the

procedure is not usuall y performed before 14week s gestation, when sufficient quantities areavailable without endangering the fetus.The risk of fetal loss as a result of the procedureis 1%, but it is less in centers skilled in thetechnique.The fluid itself is analyzed for biochemical factors, such as AFP and acetylcholinesterase.In addition, fetal cells, sloughed into theamniotic fluid, can be recovered and used for metaphase k aryotyping and other geneticana lyses.With special stains (Giemsa) and high-resolution techniques, chromosome banding patterns can be determined.Furthermore, now that the human genome has

been sequenced, more sophisticated molecular analyses using polymerase chain reaction(P CR) and genotyping assayswill increase thelevel of detection for genetic abnormalities.


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Chorionic Vill us SamplingChorionic villus sampling (CVS) involves

inserting a needle transabdominally or transvaginally into the placental mass andaspirating approximately 5 to 30 mg of vill us tissue.The risk of fetal loss from CVS isapproximately twofold greater than withamniocentesis, and there have beenindications that the procedure carries anincreased risk for limb reduction defects.Generally, these prenatal diagnostic testsare not used on a routine basisIndications for using the tests include thefollowing:

(1) advanced maternal age (35 years andolder);

(2) previous family history of a genetic problem, such as the parents having had achild with Down syndrome or a neural tubedefect;

(3) the presence of maternal disease, such asdiabetes;

(4) an abnormal ultrasound or serumscreening test.


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07 extraembryoner structures

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