PREGNANCY: 1st and 2nd Trimesters

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PREGNANCY 1st and 2nd Trimesters

• (0 24 weeks)

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• General
• Sonography used after 4-5 weeks
• Events prior to this time
• 1. Ovulation
• 2. Fertilization
• 3. Implantation
• 4. Placentation
• 5. Embryonic Development

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II. OVULATION A. Definition a cyclic event
controlled by two hormones (FSH and LH) that
occurs monthly 1. 20 ova begin maturing 2.
Only one completes the maturation process
Phase??
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1st 2nd Trimesters, Ovulation,
cont. 3. After ovulation, ovum moves
into uterine tube 4. If fertilized, the
zygote begins to divide 5.
Implantation begins in 6 days
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III. FERTILIZATION A. Definition
penetration of the ovum by one
spermatozooan 1. Hyaluronidase (from
acrosome) enzyme that allows penetration
2. Lack of acrosome/enzyme infertility 3.
Polyspermy More than one sperm penetrates
ovum
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• 1st 2nd Trimesters, Fertilization cont.
• B. Sperm and ovum are haploid (N)
• C. Genetic material in nuclei fuses to
  form zygote (2N)
• D. Zygote begins cell division (mitosis!)
  immediately

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• 1st 2nd Trimesters, Fertilization cont.
• E. Differentiation prior to reaching uterus,
  zygote has developed into morula
• Cells continue to divide, form
  blastula or blastocyst
• trophoblast
• inner cell mass or blastoderm

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1st 2nd Trimesters, Fertilization, cont. G.
Trophoblast will give rise to placenta H. Inner
cell mass will give rise to the embryo 1.
Ectoderm (outer layer or outer skin) 2.
Endoderm (inner layer or inner skin) 3.
Mesoderm (middle layer or middle skin)
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Primary Germ Layers

• Trophoblast Cells
• Give rise to placenta
• Primary germ layers
• Ecotderm
• Mesoderm
• Endoderm

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• IV. Implantation
• A. Uterus composed of 3 layers
• 1. Perimetrium external layer
• - peritoneum/broad ligament
• 2. Myometrium middle layer
• 3. Endometrium inner layer

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The Uterus
Perimetrium Myometrium Endometrium
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1st 2nd Trimesters, Implantation, cont. a.
Epithelium forms numerous glands - may extend
to myometrium b. Cyclic changes controlled by
hormones - four phases c. If implantation
occurs, endometrium is maintained in secretory
phase
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Implantation

• Implantation begins day 6
• Trophoblast contacts endometrium
• Typically close to fallopian tube
• Trophoblast digests endometrium
• Enters inner cell mass first
• Completed by day 11
• This concludes period of the ovum

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1st 2nd Trimesters, cont. V. Placenta
Fetal Membranes A. Function of membranes
1. house, protect, nourish 2. provide
oxygen to embryo 3. dispose of wastes
for
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• 1st 2nd Trimesters, cont.
• B. Placenta
• Decidua Capsularis
• After implantation, embryo covered by
  endometrial layer
• Maternal tissue

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Placental formation

• Decidua capsularis
• Endometrial tissue
• Covers implanting embryo

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• 1st 2nd Trimesters, Placenta, cont.
• 2. Decidua Basalis (Placentalis)
• a. Endometrial layer between embryo and
  myometrium
• b. Maternal tissue that will be meshed with
  fetal tissue

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Placental formation

• Decidua basalis
• Between embryo and mom
• Gives rise to maternal portion of placenta
• RNA virus DNA???

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1st 2nd Trimesters, Placenta, cont. 3.
Trophoblast develops a second layer (chorion)
during implantation a. Inner layer sprouts
villi b. Villi penetrate decidua basalis c.
Maternal blood seeps into spaces between
villi d. Forms Chorion Frondosum
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Chorion Frondosum

• Chorion frondosum
• Chorionic villi
• Maternal blood

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• 1st 2nd Trimesters, Placenta, cont.
• Placenta has two origins
• a. fetal portion chorion frondosum
• b. maternal portion decidua basalis
• Blood in placental vessels
• a. closely associated with maternal blood
• b. between chorionic villi

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Formation of Umbilical Vessels

• Placental vessels contain fetal blood
• Blood only communicates with moms blood via
  diffusion
• No direct mixing!

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1st 2nd Trimesters, cont. C. Fetal
structures 1. Amnion a. Inner fetal
membrane b. Produces amniotic fluid c.
Cushions embryo d. Contains enzymes for
development
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Fetal membranes

• Amnion
• Outer fetal membrane
• Folds around embryo on all sides
• Forms amniotic fluid

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1st 2nd Trimesters, Fetal structures,
cont. 2. Yolk Sac a. Provides initial
nourishment -connects to fetal gut b.
develops from endoderm c. produces first
blood cells d. forms part of primitive
gut e. gives rise to allantois
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Fetal membranes

• Yolk Sac
• Formed from endoderm
• Minimal nourishment
• Provides umbilical vessels

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1st 2nd Trimesters, Fetal structures,
cont. 3. Umbilical Cord a. Point of
fetal/maternal communication b.
Formed from amnion, yolk sac, and body
stalk c. Allantois Contributes blood
vessels to cord This concludes period of
embryo (8 weeks)
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Umbilical Cord

• Vessels arise from yolk sac and forming placenta
• O2 blood in umbilical veins
• - O2 blood in fetal veins
• /- blood in fetal, umbilical arteries

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1st 2nd Trimesters, cont. VI.
Anomalies A. Meckels Diverticulum of the
Ileum p. 137 1. Persistence of proximal end
of yolk sac 2. Blind pouch
a. usually lt10 cm b. terminates at
umbilicus c. occurs in 2 of population
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Meckels Diverticulum

• Meckels diverticulum of the Ileum
• May undergo torsion
• May form fistulas
• Sx mimic appendicitis

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1st 2nd Trimesters, Anomalies, cont. B.
Polyhydramnios 1. Volume of amniotic fluid gt
2 liters 2. Associated with G.I. Tract
obstruction or atresia 3. Causes a.
Diabetes Mellitus b. Viral infection in
utero c. Rh incompatibility
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1st 2nd Trimesters, Anomalies, cont. C.
Oligohydramnios 1. Volume of amniotic fluid lt
1/3 liter 2. May cause amniotic band
syndrome 3. May be due to renal agenesis
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1st 2nd Trimesters, Anomalies,
Oligohydramnios, cont. 4. May indicate fetal
demise, premature rupture of
membranes 5. Causes a. IUGR (Intrauterine
Growth Restriction) b. Pulmonary
Hypoplasia lungs fail to develop properly
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• 1st 2nd Trimesters, cont.
• Hydatidiform or Vesicular Mole
• 1. Occurs when embryo blights and
  chorion persists
• 2. Associated with Theca Lutein cysts in
  1/3 of cases
• 3. Chorionic villi transform into vesicles
• 4. Benign tumor, may become huge (molar
  pregnancy)

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• 1st 2nd Trimesters, Anomalies, cont.
• Omphalocele
• 1. Results when intestines fail to retract
  from umbilical cord
• 2. Zipper at linea alba fails to zip
• 3. External portion covered with skin of
  abdomen

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Omphalocele

• Associated with various trisomies and increased
  AFP levels
• Internal organs covered with peritoneum and
  amnion
• Normal till 10 weeks
• High fetal mortality rate

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1st 2nd Trimesters, Anomalies, cont. F.
Ectopic Pregnancy 1. Implantation of embryo
outside uterus 2. Ampulla is most common
site 3. May implant on mesentery,
omentum, other sites 4. Rarely reach maturity
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Ectopic Pregnancy

• 99 are tubal pregnancies
• Other sites
• Ovary
• Mesentery
• Cul-de-sac
• Spleen
• Liver

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1st 2nd Trimesters, Anomalies, cont. G.
Metastatic Carcinomas 1. Spread via lymph
circulation a. Cervix drains into internal
and external nodes b. Body of uterus
drains into superficial inguinal nodes
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1st 2nd Trimesters, Anomalies, cont.
c. Fundus of uterus, fallopian tubes, and
ovary drain into para-aortic nodes at
L-1 d. Vagina drains into two directions
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1st 2nd Trimesters, Anomalies, cont. 1.
Lower 1/3 and vulva drain into
superficial inguinal nodes 2. Upper 2/3
drain to sacral, external internal iliac
nodes 2. Cancers may penetrate bladder or
rectum wall
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1st 2nd Trimesters, Anomalies,
cont. H. Rectouterine Pouch (of Douglas) or
cul-de-sac 1. Lowest point in abdominal
cavity 2. Ectopic
pregnancies, metastases often found here
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1st 2nd Trimesters, Anomalies, cont. 2.
Collects excess fluid in peritoneal cavity
a. May be drained via posterior fornix b.
Instruments may inadvertently penetrate 1.
Enter peritoneal cavity 2. May cause
peritonitis
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1st 2nd Trimesters, Anomalies, cont. I.
Hydrocephaly 1. Due to stenosis or blockage
a. cerebral aqueduct b.
foramina of Luschka or Magendie 2. CSF
cannot circulate 3. Collects in and expands
ventricles
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Hydrocephalus

• Means water in the head
• Usually due to a blockage in the CSF circulatory
  pattern
• May be corrected in utero

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1st 2nd Trimesters, Anomalies, Hydrocephalus,
cont. 4. Causes usually viral
a. Toxoplasmosis (Valley Fever) b.
Rubella (3-day measles) c. Treponema pallidum
(syphilis) d. Herpes virus infection e.
CMV infection (cytomegalovirus)
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1st 2nd Trimesters, cont. Anomalies,
continued J. Anencephaly 1. Lack of
cerebral hemispheres 2. Brainstem is
intact 3. Basic functions are present
(breathing, heart beat)
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1st 2nd Trimesters, Anomalies, cont. K.
Porencephaly 1. Cysts or cavities in cerebral
hemispheres 2. Cysts communicate with
ventricles
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1st 2nd Trimesters, Anomalies,
Porencephaly, cont. 3. Hydranencepaly
a. an extreme form b. cerebral
hemispheres nearly absent 4. Developmental
anomaly, or ischemic infarction in utero
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Doppler U/S of the Circle of Willis in utero

• Circle of Willis

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Fetal circle of Willis 3D U/S
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1st 2nd Trimesters, Anomalies, cont. L.
Spina Bifida 1. Defect of the spinal
column 2. Due to failure of vertebral arches
to close 3. Meninges, neural tissue
exposed 4. May be associated with severe
latex allergy
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Ultrasound-guided Prenatal Diagnosis

• Amniocentesis and CVS

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1st 2nd Trimesters, cont. VII. First
Trimester Bleeding A. Abortion (threatened or
spontaneous) 1. Distorted irregular
gestational sac 2. Common during first
pregnancy a. Most women unaware b. Up
to 50 may abort
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1st 2nd Trimesters, First trimester bleeds,
cont. B. Blighted ovum 1. embryonic
membranes and chorion develop
2. no gestational sac C. Incomplete
Abortion embryo expelled, POC retained
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• 1st 2nd Trimesters, cont.
• Molar gestation
• 1. Embryo blights
• 2. Chorionic villi become hydropic
• 3. Often accompanied by theca lutein cysts

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• 1st 2nd Trimesters, cont.
• Ectopic pregnancy
• 1. Tubal implantation most common
• 2. Rupture results in bleeding
• F. Pelvic masses
• 1. Uterine leiomyoma (fibroid)
• 2. Corpus luteum cysts

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• 1st 2nd Trimesters, cont.
• VIII. Uterine Anomalies
• - usually result from fusion abnormalities of
  Mullerian ducts
• - embryonic tubular structures that give rise
  to fallopian tubes, uterus
• A. Arcuate uterus saddle-shaped

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Uterine Anomalies
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1st 2nd Trimesters, Uterine anomalies,
cont. B. Capped uterus muscle of fundus is
contracted C. Couvelaire uterus 1.
blood in myometrium 2. indication
of placental abruption D. Uterus acollis
uterus lacking a cervix
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1st 2nd Trimesters, Uterine anomalies,
cont. E. Uterus bicornis (duplex uterus,
bifid uterus, uterus bifidis) uterus
divided in two 1. Uterus bicornis
unicollis bifid uterus with one
cervix 2. Uterus bicornis bicollis
bifid uterus with two cervices
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Uterine Anomalies, cont
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Uterine Anomalies, cont
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1st 2nd Trimesters, Uterine anomalies,
cont. F. Uterus biforis (uterus subseptus)
1. single uterine body 2. divided by
short septum G. Uterus bilocularis (septate
uterus, bipartite uterus, uterus septus)
- uterus is divided by a complete
anterior-to-posterior septum
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Uterine Anomalies, cont
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• 1st 2nd Trimesters, Uterine anomalies, cont.
• H. Uterus didelphys double uterus, each
  with own cervix
• Uterus incudiformis (uterus triangularis)
  uterus bicornis with broad, flat fundus
• J. Uterus parvicollis normal uterus with
  abnormally small cervix
• K. Uterus unicornis only one half of the
  uterus exists

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Uterine Anomalies, cont
Uterus didelphys
Uterus unicornis