Placentation and Twinning PDF

Placentation and Twinning Lectures delivered to 200 Level MBBS students of FUHSO By Kuma Yandev BSc Anatomy, MBBS  Outline Placentation Preceding events in 2nd and 3rd week Implanta...

Placentation and Twinning Lectures delivered to 200 Level MBBS students of FUHSO By Kuma Yandev BSc Anatomy, MBBS  Outline Placentation Preceding events in 2nd and 3rd week Implantation Decidua reaction and decidua formation Development of lacunar system in trophoblast layer Development of the chorionic villi and formation of the chorion frondosum Formation of the placenta proper Placental membrane Anatomy of the mature placenta Functions of the placenta Placental circulation Fetal membranes and amniotic fluid Umblical cord Twinning Clinical relevance  Implantation About 6 days after fertilization, the blastocyst attaches to the endometrial epithelium, usually adjacent to the embryonic pole, the site of implantation A s so o n as it at t ac h e s t o t h e e n d o me t r ial epithelium, the trophoblast starts to proliferate rapidly and gradually differentiates into two layers A n in n er layer of mon on u c leat ed c ells, t h e cytotrophoblast A highly invasive outer layer of syncytiotrophoblast consisting of a multinucleated protoplasmic mass with no visible cell boundaries  Implantation Fi ng e rl i ke p roc e sse s soon e x te nd f rom the syncytiotrophoblast into and through the endometrial epithelium and invade the connective tissue of the endometrial stroma adjacent to the implantation site By day 9, the blastocyst is more deeply embedded in the endometrium The penetration defect in the surface epithelium is closed by a fibrin coagulum By the 11th to 12th day, the blastocyst is completely embedded in the endometrial stroma The surface epithelium almost entirely covers the original defect in the uterine wall The blastocyst now produces a slight protrusion into the lumen of the uterus Implantation is now complete Implantation  Decidua Reaction Is the characteristic transformation of the functional endometrial stromal CT cells following implantation At the time of implantation, the endometrium is in the secretory phase of the menstrual cycle The syncytiotrophoblast of the implanted embryo soon star ts secreting human chorionic gonadotrophin (HCG) HCG intensif ies the changes/events of the secretory phase causing the stromal cells to further enlarge, va cuo la te a nd beco me f il led up/lo a ded w ith glycogen and lipids in their cytoplasm and become polyhedral. The cells are now called decidual cells  Th e re ac ti on i s i n i ti al l y c on f in e d to th e endometrium near the implantation site but soon spreads throughout the endometrium of the uterus The functional endometrium is now called the decidua or gravid endometrium The primary function of the decidual reaction is to provide nutrition for the early embryo and provide an immunologically privileged site for the conceptus  The decidua is divided into three parts: The decidua basalis is the part that lies deep to the embryo at the embryonic pole to which the villi are anchored/f ixed through the cytotrophoblastic shell It consists of a compact layer of large decidual cells called the decidual plate The decidua capsularis is the part that covers the implanted embryo at the abembryonic pole forming a capsule that separates it from the uterine cavity Decidua parietalis is the rest of the endometrium (excluding the basalis and capsularis).  As the conceptus enlarges, the decidua capsularis bulges into the uterine cavity and becomes greatly stretched It eventually contacts and fuses with the decidua parietalis gradually obliterating the uterine cavity The D,capsularis degenerates and disappears altogether by weeks 22 to 24 due to reduced blood supply to it The chorion laeva/smooth chorion then fuses with the D.parietalis This fusion is not permanent and can be separated potentially reestablishing the uterine cavity space  Second Week of development Lacunar stage of trophoblast development occurs Following implantation, by day 9, vacuoles have appeared in the syncytium and have fused to form large lacunae The lacunae are separated from one another by par tition s of syn cytiu m, w h ich are called trabeculae The syncytiotrophoblast now appears spongelike By the 11th to 12th day, The lacunar spaces in the syncytium have formed an intercommunicating networks The lacunae networks are more evident at the embryonic pole whilst at the abembryonic pole, the trophoblast still consists mainly of cytotrophoblastic cells  Second Week of development The syncytiotrophoblast continues to penetrate deeper into the stroma and erode the endothelial lining of the maternal capillaries T h es e c a p i l l a r i es , k n o w n a s s i n u s o i d s , a r e congested and dilated and thin-walled The lacunae become continuous with the sinusoids and a mixture of maternal blood and cellular debris from eroded uterine glands enter the lacunar system As the trophoblast continues to erode more and more sinusoids, maternal blood begins to f lo w through the trophoblastic system, establishing the primordial uteroplacental circulation The trophoblast absorbs nutritive f lu id from the lacunar networks,which is transferred to the embryo  Second Week of development By day 13, primary villi formation occurs Each trabecula is initially made up entirely of syncytiotrophoblast Now, cells of the cytotrophoblast proliferate locally and penetrate into the syncytiotrophoblast (trabecula) forming cellular columns surrounded by syncytium These cellular columns with their syncytial covering are known as primary villi The villi are surrounded by maternal blood, filling the lacunar spaces T h e l ac u n ar s p ac e s ar e n o w c al l e d th e intervillous spaces  Third week of development The primary villi begin to branch shortly after they appear Early in the third week, the EESOM lying deep to the cytotrophoblast invades the centre/core of the primary villi and they become the secondary villi These 2 0 villi cover the entire surface of the chorionic sac Some mesoderm (mesenchymal) cells in the villi soon differentiate into capillaries and blood cells and they are now called tertiary chorionic villi  Third week of development The capillaries in the chorionic villi fuse to form arteriocapillary networks, which soon become connected with the embryonic heart through vessels that differentiate in the mesenchyme of the chorion and connecting stalk By the end of the third week, embryonic blood begins to f low slowly through the capillaries in the chorionic villi Oxygen and nutrients in maternal blood in the intervillous spaces diffuse through the walls of the villi and enter the embryo's blood Carbon dioxide and waste products diffuse from blood in the fetal capillaries through the wall of the chorionic villi into the maternal  Third week of development The cells of the cytotrophoblast in the apical region of each villus proliferate and pass across the syncytiotrophoblast to form a continuous layer of cytotrophoblast on the s u r fac e of de c i du a. Th i s l aye r i s c al l e d cytotrophoblastic shell The shell completely cuts off the syncytiotrophoblast from the decidua basalis The villi that attach (anchor) the chorion (fetal part) to the decidua (maternal part) at the cytotrophoblast shell are called anchoring villi (stem chorionic villi)  Third week of development Each anchoring villus consists of a stem (truncus chorii); this divides into a number of branches (rami chorii) which in turn divide into f in er branches (ramuli chorii) The ramuli are attached to the cytotrophoblastic shell T h e an c h orin g v illi also g iv e off n u me rou s branches which grow into the intervillous space as free villi New villi also continue to sprout from the chorionic side of the intervillous space Ultimately, almost the whole intervillous space becomes f illed with villi. As a result, the surface area available for exchanges between maternal and fetal circulations becomes enormous  Third week of development Up until the start of week 8, the villi formed cover the entire surface of the chorion/chorionic sac As pregnancy advances, villi on the embryonic pole in relation to the decidua basalis continue to grow extensively into it and expand, giving rise to the chorion frondosum (bushy chorion) Enlargement of the chorionic sac also causes the villi on the abembryonic pole in relation to the decidua capsularis to degenerate and by the third month this side of the chorion is smooth and is now known as the chorion laeve (smooth chorion)  Placentation Introduction The placenta is a temporary fetomaternal organ formed in the uterus during pregnancy It attaches the fetus through the umblical cord to the mother’s uterine wall It is highly vascular and endocrine in nature Shape: Circular and discoid Purpose: Is largely to provide oxygen and n u tr i e n ts to; re m ov e w as te p rod u c ts of m e tab ol i s m from th e fe tu s an d s e c re te important hormones necessary for maintenance of pregnancy  Placentation Formation: It has two parts with distinct origins: Fetal part; Develops from the chorion frondosum Maternal part; Develops from the decidua basalis Fo r ma ti o n i s pr eceded by cer ta i n events including Implantation Development of lacunae system in the trophoblast Decidua reaction and decidua formation Development of the chorionic villi and formation of the chorion frondosum  Placentation Formation of the placenta proper Following the formation of the anchoring villi, in the 4 th and 5 th months, a number of septae grow inwards from the uterine endometrium, projecting into the intervillous spaces These decidual septa divide the forming placenta into 15 – 20 lobes called Cotyledons but do not reach the chorionic plate Each cotyledon consists of 2 to 3 anchoring villi  Placentation Each decidual septum consists of a core of maternal tissue but their surface is covered by a layer of syncytial cells Th is is so design ed su ch th at at all times a syn cytial layer separates matern al blood in intervillous lakes from direct contact with fetal tissue of the villi Also because the septa do not extend all the way to the chorionic plate, contact between the intervillous spaces is maintained Endometrial (spiral) arteries and veins pass freely through gaps in the cytotrophoblastic shell and open into the intervillous space  Placentation Due to the continuous growth of the fetus and expansion of the uterus, the placenta also enlarges Growth in the size and thickness of the placenta continues rapidly until the fetus is about 18 weeks The increase in its surface area roughly parallels that of the expanding uterus Throughout pregnancy it covers approximately 15 to 30% of the internal surface of the uterus It must be noted that increase in thickness of the placenta results from arborization of existing villi an d n ot c au sed by fu r th er pen etration in to maternal tissues  Placentation Placental membranes/barriers These are membranes that separates maternal and fetal blood within placenta Thus, there is no mixing of maternal and fetal blood in the placenta Exchange of gases, nutrients and waste between the fetal and maternal blood also occurs across the barrier Sources of blood within the placenta are: Maternal blood in the intervillous spaces derived f ro m e n d o m e t r i a l a r t e r i e s a n d d ra i n e d b y endometrial veins Fetal blood flowing within the fetal blood vessels in the chorionic villi  Placentation Until the 20 week, the placental membrane th consists of four layers and is about 0.025mm thick. The layers from the maternal to the fetal side are: Syncytiotrophoblast Cytotrophoblast Mesoderm of the villus Endothelium of fetal capillaries After the 20 week, each of the layers progressively th thins out and the cytotophoblast disappears altogether T he m e m b rane re d uc e s i n thi c kne ss to ab o ut 0.002mm The thinning allows more ef fic ient transport of  Placentation Anatomy of the mature/term placenta Shape: Discoid Dimensions: Diameter of 15-25cm about 3cm thick Weight: About one sixth of the fetal weight (500 -600grams) Surfaces: Fetal surface; Is covered entirely by the chorionic plate It is smooth an d sh in y covered by amn iotic membrane The umblical cord is attached at its centre  Placentation Maternal surface; Has a cobble stone appearance due to 15-20 rounded elevations formed by the cotyledons and separated by grooves formed by decidua septa It is covered by a thin layer of decidua basalis Internal structure Deep to the amnion lining the chorionic plate are chorionic vessels surrounded by thinned out layers of mesoderm and syncytiotrophoblast These are continuous with vessels in the umblical cord  Placentation The villi are surrounded by intervillous spaces into which placental septa extend forming incomplete partitions The intervillous spaces are supplied and drained by endometrial arteries and veins passing from the decidua plate to open into the spaces  Placentation Functions of the Placenta The placenta has three main functions: Metabolism Endocrine secretion Placental transfer  Placentation Metabolism Involves synthesis of Glycogen Cholesterol and Fatty acids They serve as sources of nutrients and energy  Placentation Endocrine secretion:protein Endocrine secretion: steroid hormones hormones Human chorionic Progesterone gonadotrophin (hCG) Estrogen Human chorionic so mato mammo t ro pi n o r human placental lactogen Human chorionic thyrotropin Human chorionic corticotropin  Placentation Placental transfer refers to the transport or exchange of substances across the placental barrier/membrane between the fetal and maternal blood It thus occurs in both directions Tran s p or t i s b y th e f ol l ow i n g tran s p or t mechanisms: simple diffusion facilitated diffusion active transport and pinocytosis  Placental transfer Substances transported from Substances transported from maternal to fetal blood fetal to maternal blood Oxygen Metabolic waste: Nutrients Carbondioxide (CHO, Amino acids, lipids, Water electrolytes, vitamins, iron and trace Urea elements) Uric acid Hormones Bilirubin Antibodies (IgG) Hormones Transferrin RBC antigens Harmful substances Drugs, alcohol, poisons and CO Viruses (Rubella, Cytomrgaloviruses) Protozoa (Toxoplasma gondii)  Placental circulation There are two types of circulation in the p l ac e n ta: M ate r n al an d F e tal p l ac e n tal circulation Maternal Placental Circulation Blood circulation in the intervillous spaces begins as early as on ninth day of pregnancy About 80–100 spiral arteries and number of veins of uterine endometrium (decidua basalis) open into the intervillous spaces  Placental circulation Maternal Placental Circulation Blood enters the intervillous spaces through spiral arteries, and under the pressure of blood in arteries, the blood reaches right up to the chorionic plate It then slowly passes around the branches of villi for exchange across the very thin placental membrane The blood from the intervillous space is drained by the veins of decidua basalis In fully formed placenta, the intervillous space contains 150 ml of blood, which is replaced every 15–20 seconds (3–4 times per minute)  Placental circulation Fetal Placental Circulation The fetal blood comes to placenta through the umbilical arteries These arteries after entering the placenta ramify freely in the chorion and their branches enter the chorionic villi The veins from the chorionic villi drain into the umbilical vein that carries blood rich in oxygen (O2) and nutrients to the fetus from placenta  Fetal membranes Formation of the fetal membranes also called amniochorionic membrane is preceded by the following events: Formation of the amniotic cavity and amnion Formation of the chorionic sac and chorion Formation of decidua capsularis and parietalis Formation of chorionic villi Enlargement of the chorionic sac causing the villi in relation to the decidua capsularis to degenerate forming the chorion laeve (smooth chorion)  Fetal membranes The amniotic sac/cavity enlarges faster than the chorionic sac Initially, it obliterates the chorionic sac, as a result, the amnion and smooth chorion soon fuse to form the amniochorionic membrane Further enlargement of the amniotic sac also obliterates the uterine cavity This composite membrane then fuses with the decidua capsularis temporarily The decidua capsularis soon disappears and the membrane adheres to the decidua parietalis  Fetal membranes The amniochorionic membrane surrounds the amniotic cavity with its contained fluid It bulges into the cervical canal during labor and helps to dilate it Rupture of the membranes (breaking of the waters) is also a sign that labor has begun When the membrane ruptures, amniotic f lu id escapes through the cervix and vagina to the exterior After the child is delivered, the placenta and the membranes, along with all parts of the decidua, separate from the wall of the uterus and are expelled from it  Amniotic fluid Is the clear watery f lu id within the amniotic cavity Derived from the M ate r n al b l ood by d i f f u s i on ac ros s th e amniochorionic membrane from the decidua parietalis Secretion by amniotic cells Placenta: by diffusion across the chorionic plate from blood in the intervillous space Secretion by the fetal respiratory tract (lung) Secretion from the fetal kidney as urine Secretion by the fetal gastrointestinal tract  Volume: 30mls at 10 weeks 450mls at 20 weeks and 800-1000mls at term (37 weeks ) The volume of amniotic f luid is replaced every 3 hours  Amniotic fluid is in balance with the fetal circulation The water content of amniotic f luid changes every 3 hours. Large amounts of water pass through the amniochorionic membrane into the maternal tissue fluid and enter the uterine capillaries An exchange of f luid with fetal blood also occurs through the umbilical cord and across the fetal surface of the placenta Amniotic f luid is swallowed by the fetus and absorbed by the fetus's respiratory and digestive tracts. Towards the end of pregnancy, the fetus swallows up to 400mL of amniotic f luid per day. The f luid passes into the fetal bloodstream and the waste products in it cross the placental membrane and enter the maternal blood in the intervillous space Excess water in the fetal blood is excreted by the fetal kidneys and returned to the amniotic sac through the fetal urinary tract. In late pregnancy, about 500 mL of urine is added daily  Composition of Amniotic Fluid
Amniotic f luid is an aqueous solution in which undissolved material desquamated fetal epithelial cells Organic and inorganic salts Organic component: Half protein and half other substances including carbohydrates, fats, enzymes, hormones, and pigments In advanced pregnancy, fetal excreta: fetal feces called meconium and fetal urine.  Significance/function of amniotic fluid Amniotic fluid plays a major role in fetal growth and development. Its functions include: Permits symmetric external growth of the embryo and fetus Acts as a barrier to infection Permits normal fetal lung development Prevents adherence of the amnion to the embryo and fetus Cushions the embryo and fetus against injuries by distributing impacts the mother receives Helps control the embryo's bodytemperature by maintaining a relatively constant temperature Enables the fetus to move freely, there by aiding muscular development in the limbs Assists in maintaining homeostasis of fluid and electrolytes Forms a hydrostatic bag (bag of waters) that helps in dilatation of the cervix at the beginning of the labor  Umblical cord The umbilical cord is a long cord-like structure by which fetus is attached to the uterine wall via placenta At full term/birth: it is about 50–55 cm in length and 1–2 cm in breadth one end is attached to the center of anterior abdominal wall of fetus (umbilical region) and the other end is attached to the center of fetal surface of the placenta. It is covered by glistening amniotic membrane Is also twisted and presents false knots because the umblical vessels are longer than  Umblical cord Formation of the umblical cord involves: Formation of the connecting stalk Formation of the allantoic diverticulum Folding of the embryo (craniocaudal folding) causing the stalk to lie ventrally in the umblical region Incorporation of remnant parts of the yolk sac, its vitello-intestinal duct and the allantois into the stalk Development of blood vessels in the stalk Mucoid generation in the mesoderm of the stalk to form whartons jelly Amnio tic sac enlarges and o bliterates the extraembryonic coelom and forms a tubular sleeve around the umbilical cord lined externally by amnion  Umblical cord Contents of the Umblical cord are: Two umbilical arteries One umbilical vein Wharton’s jelly Remains of allantoic diverticulum Remains of vitellointestinal duct and yolk sac Function of the Umblical cord The umblical vein conveys oxygenated blood from the placenta to the fetus and Umblical arteries carry deoxygenated blood from the fetus to the placenta  Twinning Mu lt ip le p reg n an c ies/g est at ion refers to a pregnancy that nurtures two or more fetuses When there are two fetuses its called twins Multiple births have become commoner due to the wider access to fertility treatments However, certain regions have been known to have a high incidence of twins occurring naturally. Example is the South western city of Igbo-Ora, in Oyo State where nearly every family has twins or other multiple birth Multiple gestations are associated with higher risks; the risks increases with the number of fetuses  Twinning Twinning is the conception/bearing of twins There are two types of twins: Monozygotic or identical twins and Dizygotic or fraternal twins  Twinning Monozygotic twins form from splitting of single fertilized ovum/zygote at different stages of its development into two daughter cells, each developing into a separate embryo/fetus A 3 of twin pregnancies are monozygotic. They rd are of three types depending on the stage of splitting: 1. Early splitting of the zygote at the two cell stage result two fetuses, each implanting separately and having its own chorionic sac , placen ta an d amn iotic s ac (Dichorionic diamniotic twins) Occurs in about 35% of MZ twins Splitting of 2 cell zygote forms Dichorionic diamniotic twins  Monozygotic twins 2. Splitting of the zygote at the early blastocyst stage such that the inner cell mass splits into two separate groups of cells within the same blastocyst cavity. The two embryos have a common chorionic sac and placenta but separate amniotic cavities (Monochorionic diamniotic) Splitting of inner cell mass forms monochorionic diamniotic twins  Monozygotic twins 3. Splitting at the bilaminar germ disc stage, just before the appearance of the primitive streak results in formation of two partners with a single placenta and chorionic sac and a common amniotic sac (Monochorionic monoamniotic) It is rare MZ twins are characterized by being the same sex, genetically identical, and very similar in physical appearance Physical differences between MZ twins are environmentally induced  Twinning Dizygotic twins result from simultaneous shedding of two oocytes and their fertilization by different spermatozoa It makes up 2/3 of twin pregnancies rds The two zygotes have totally different genetic constitutions therefore the twins have no more resemblance than any other brothers or sisters They may or may not be of different sex The zygotes implant individually in the uterus and usually each develops its own placenta, amnion, and chorionic sac Sometimes, however, the two placentas and the walls of the chorionic sacs are so close together that they fuse  Twinning Monozygotic twins Dizygotic twins Form from single zygote Form from two zygotes Incidence is less Incidence is more common common Genetically not identical Genetically identical Twins maybe of the Twins are of the same same or different sex sex Resemblance is just like any other two siblings Resemblance is similar Mostly have two Mostly diamniotic, amnions, two chorions, monochorionic, with and two placentas single placenta  Clinical Relevance Labor or parturition is the process of expulsion of the fetus and placenta from the uterus It is characterized by regular uterine contractions that cause progressive cervical dilatation It is divided into three stages First stage: Onset of uterine contractions to full cervical dilatation (@ 10cm) Second stage: Is from full cervical dilatation until delivery of the infant Third stage: Is from delivery of the infant to delivery of the placenta  Clinical Relevance The placenta is delivered in the third stage of labour normally within 15 to 30 minutes of delivery of the fetus In this stage, the placenta is gradually separated from the uterine wall due to: Reduction in the surface area of the placental site due to uterine muscle retraction/shrinkage with each successive contraction Haematoma formation in the placental bed due to venous occlusion and vascular rupture. Massive b l e e d i n g i s h o w e v e r p re v e n t e d b y u t e r i n e contraction that closes off the exposed spiral arteries after detachment  Clinical Relevance Uterotonic agents like oxytocin is administered just after delivery of the fetus to promote this separation Signs of separation/detachment include Lengthening of the cord Uterus rises in the abdomen Uterus becomes more globular in shape and firmer A gush of blood occurs Controlled cord traction with counter traction on the uterus is then employed to deliver the placenta  Clinical Relevance Placental abruption or abruptio placentae Is premature separation of the placenta from the uterine wall It is associated with bleeding and haematoma formation behind the placenta called the retroplacental clot Presents with Vaginal bleeding, abdominal or back pain Decreased fetal movements Uterine tenderness Shock Treatment : Resuscitation, delivery of fetus  Clinical Relevance P re e c l am p si a i s a c o n d i t i o n i n p re g n an c y characterized by high blood pressure, protein in urine (proteinuria) and fluid retention (edema) Eclampsia is convulsions occurring in a woman diagnosed with preeclampsia The actual cause is unknown but it is thought to be due to disordered placentation among other factors It is commoner in f irst pregnancies and multiple gestation It can be deadly to both the mother and fetus if not managed promptly and properly The def in itive treatment of preeclampsia and prevention of eclampsia is delivery of the baby and placenta  Clinical Relevance Variation in the shape of the placenta Bilobed (bidiscoidal) placenta: consists of two lobes Multilobular placenta: Has more than two lobes Diffuse placenta: is thin and not disc shaped due per s i s ten ce o f ch o r i o n i c v i l l i a l l a ro u n d th e blastocyst Placenta succenturiata: a small part of the placenta is separated from the main (rest) part of the placenta, but remains connected through blood vessels and placental membranes Placenta fenestrata: a hole is present in the placental disc Circumvallate placenta: the peripheral edge of the placenta is covered by a circular fold of the decidua  Clinical Relevance Variation in the placenta due to abnormal attachment of the cord; Marginal (Battledore) placenta: When the cord is attached to the margin of the placenta Furcate placenta: When blood vessels of umbilical cord divide before reaching the placenta Velamentous placenta: When the umbilical blood vessels are attached to amnion and ramify there before reaching the placenta  Clinical Relevance C ord prolapse; w h en t h e c ord prolapses or protrudes through the cervix during labour and gets compressed between the fetal head and pelvic wall of the mother causing hypoxia in the fetus Prolonged cord may encircle the neck of the fetus and strangle it during delivery Shortened cord may pull of the placenta during delivery of the fetus causing premature seperation of the placenta from the uterus True knots formed in the cord may cause reduce blood supply and cause hypoxia and even death in the fetus  Clinical Relevance Conjoint or Siamese twins is a condition that occurs in MZ twins when the splitting of the embryo is incomplete The fetuses are joined together by a tissue bridge The different types based on site and extent of fusion are: Craniophagus: Fusion of heads Thoracophagus: Fusion of thorax Cephalothoracophagus: Fusion of head and thorax Pygophagus: Fusion of sacral regions The conjoint twins can be separated only if they have no vital parts in common  Clinical Relevance Twin twin transfusion syndrome O c c u rs in MZ t w in s w h e n t h e re is u n e qu al distribution of blood from the shared placenta to either twin One twin receives too much blood and is larger while the other receives too little blood and is smaller. It can even cause death in one or both twins Vanishing twin refers to the death of one twin usually in the first or second trimester of pregnancy. The dead twin is resorbed and disappears or remains as a compressed dehydrated mass re se mb lin g p arc h me n t p ap e r c alle d F e t u s papyraceous  Drugs and their metabolites can cross the placenta and affect the fetus Drugs like alcohol can cause major congenital anomalies Drugs like heroin taken in pregnancy can cause fetal drug addiction and the newborns can experience withdrawal symptoms after birth Drugs used in labor or obstetric surgeries like sedatives, opioid analgesics and anaesthetic agents can cross the placenta and respiratory depression in newborns depending on the dose and duration of exposure  Amniocentesis: Is a procedure to take a sample o f a mni o ti c f lui d o f ten under ul tra s o und guidance Studies of cells in the amniotic f lu id permit diagnosis of chromosomal abnormalities such as trisomy21 (Down syndrome) and cer tain genetic and other disorders High levels of alpha fetoprotein usually indicate the presence of a severe neural tube defect Low levels of alpha fetoprotein may indicate chromosomal aberrations such as trisomy 21  Hydramnios or polyhydramnios is an excess of amniotic fluid (1500–2000 ml) Associated with maternal diabetes and fetal anomalies of the CNS (anencephaly) and GIT (oesophageal atresia) Oligohydramnios refers to a decreased amount (less than 400 ml) Associated with premature rupture of amnion and can lead to clubfoot and lung hypoplasia Tears in the amnion can form amniotic bands that may encircle part of all of the fetus causing ring constrictions or even amputation of a limb THANK YOU FOR YOUR TIME