The Placenta, Umbilical Cord, & Amniotic Cavity, changes of pregnancy Flashcards
The Placenta
general
Temporary fetal organ that begins developing shortly after implantation
Roles of the placenta:
Facilitating nutrient, and gas and waste exchange between maternal and fetal circulations
Serves as an endocrine organ producing hormones that regulate both maternal and fetal physiology during pregnancy
Placental cells (trophoblasts) invade and start to remodel the uterine vasculature within a few hours after implantation → starts to produce hCG
Placental Structure
Flat, discoid organ measuring 20-25 cm in diameter and 3 cm in thickness
Membranes (fuses into a single membrane by delivery):
Amnion
Chorion
2 sides:
Basal plate (maternal side):
Divided into lobes
Separated by septa
Chorionic plate (fetal side):
Contains branching chorionic villi, providing a massive surface for exchange
Umbilical cord emerges from the fetal side of the placenta
Umbilical cord:
2arteries
1 vein
Placental Circulation
Chorionic villi provide a large surface area for maternal–fetal exchange
Spiralarteries(maternal) fill the intervillous spaces in the decidua basalis layer of the endometrium:
-Bring in oxygenated blood for fetus
-Spiralarteries“rupture” and become large spaces called lacunae
2 umbilical arteries bring deoxygenated blood from fetus to placental chorionic villi
Gas and molecule exchange occurs between the fetal blood in the chorionic villi and the maternal blood in the lacunae, across the placental barrier
1umbilical veintransports oxygenated blood back to the fetus
Maternalveinstake deoxygenated blood back to the maternalcirculation
Maternal and fetal blood never come into direct contact
Functions of the Placenta
Gas exchange
O2-CO2exchange
Occurs via simplediffusion
Fetal hemoglobin has ↑ affinity for oxygen compared to maternal hemoglobin
Nutrient exchange
Provides materials needed for fetal development and growth
Mechanisms of exchange:
Water andsodiumby simplediffusion
Glucoseby facilitateddiffusion
Large molecules (LDLs, peptides,antibodies) by receptor-mediatedendocytosis
Amino acidsby secondaryactive transport
Metabolic functions
Glycogen synthesis
Cholesterolsynthesis
Protein metabolism
Waste product removal
Waste products (urea and CO2) are transported back to the mother
Occurs via simplediffusion
Hormonal secretion
Human chorionic gonadotropin(hCG): Maintains the activity of the corpus luteum required for continuation ofpregnancy
Human growth hormone(hGH)
Human placental lactogen: Stimulates maternal insulin production to ↑ glucose available to the fetus
Chorionic thyrotropin
Chorioniccorticotropin-releasing hormone(CRH)
Progesterone: Maintainspregnancy, preventsmenstruation
Estrogens
Glucocorticoids
Placenta previa
general, Dx, Tx
Abnormal attachment of the placenta in the lower uterine segment
Can obstruct (partially or completely) the internal cervical os
Maternal and fetal hemorrhage can result fromcervical dilation
Classically presents as painless bright red vaginal bleeding
Diagnosed by ultrasound
Treatment:
Pelvic rest (avoiding digital exams and intercourse)
Delivery via C-section prior to the onset oflabor(or emergently if there is clinical bleeding)
Abnormal implantation of the placenta into the uterine wall
dx, tx
Placenta accreta
Chorionic villi invade to the myometrium
Placenta increta
Chorionic villi penetrate deeper into the myometrium
Placenta percreta
Chorionic villi reach the uterine serosa and/or invade other organs
Diagnosed by ultrasound
Treatment:
Delivery via planned C-section, sometimes with concurrent hysterectomy (especially in cases of placenta increta and placenta percreta)
Placental abruption
general, dx, tx
Premature separation of the normally implanted placenta from the uterus
Clinical diagnosis based on a presentation with painful contractions with or without bleeding
Large abruptions may be seen on ultrasound
Treatment
Depends on thegestational ageand size of abruption
Significant abruptions require immediate delivery
The Umbilical Cord
general and length
Connects the fetus to the placenta
Extends from the fetal umbilicus to the fetal surface of the placenta
Cord length:
Depends on amniotic fluid volume and fetal mobility
Average length: 55 cm
≤ 40 cm is considered a short cord
Umbilical cord
structure
Vessels
Contains 2arteriesand 1 vein
Vessels are surrounded by a protective substance called Wharton’s jelly
Counted by sonographic evaluation, with the 3 vessels seen in the 1st trimester
Coiling: the vein andarteriesspiral around each other
Bloodflow
Umbilical vein supplies oxygenated blood to the fetus
Umbilicalarteriestake deoxygenated blood away from the fetus
Umbilical cord structure
Insertion into the placenta:
Normal: central insertion
Variants:
Eccentric: off center
Marginal: the cord inserts on the edge of the placenta
Velamentous: last portion of the umbilical cord lacks the protective Wharton’s jelly, leaving the umbilical vessels exposed
Abnormal insertion
Increases the risk of complications duringlaborand/or delivery
Umbilical cord rupture and/or prenatal hemorrhage
Amniotic Cavity
functions and amnioin
Fluid-filled cavity that encases the developingembryo/fetus
Functions of the amniotic cavity
Protects fetus against trauma
Protects umbilical cord against compression
Nutrientreservoirfor the fetus
Provides space for normal fetal growth and development
Amnion:
An avascular, tough but pliable membrane
1 of the 2 primary fetal membranes
Ultimately fuses with the chorion
Functions of the amnion:
Involved in solute and water transport required for amniotic fluidhomeostasis
Produces bioactive compounds
Amniotic cavity
Amniotic fluid
Normal fluid index/oligo/poly
Amniotic fluid:
Liquid that surrounds theembryoand fetus during its development
As the fetus grows, it “creates” amniotic fluid via urination, and continually “recycles” the fluid byswallowingit
Congenital defects inswallowingand/or the renal/urinary system can lead to abnormalities in amniotic fluid volume
Normal amniotic fluid index: 5-25 cm of fluid
Oligohydramnios: less than 5 cm
Polyhydramnios: greater than 25 cm is considered
Β-hCG
Peaks around week 9
Produced by the placenta
Maintains to activity of the corpus luteum until ~12 weeks
Estrogen (estriol)
Produced by the corpus luteum → placenta
Increases throughout pregnancy; drops drastically just before birth
Prepares the maternal body for delivery
Progesterone
Produced by the corpus luteum → placenta
Increases throughout pregnancy; drops drastically just before birth
Maintains the uterine lining
Smooth muscle relaxant
changes during pregnancy
Uterus
Increased uterine size
Hypertrophy of the uterine wall - ↑ fibrous and elastic tissue
Growth is initiated by ↑estrogenlevels
By term, the uterus is 5x its normal size
By 28 weeks, uterine growth slows and theuteruscontinues to stretch and become thinner
Fundal height measurements
Increase blood flow
Muscle contraction
Uterus is maintained by ↑ levels ofprogesterone
Braxton-Hicks contractions
Irregular contractions that donotcause cervical change
More noticeable as the pregnancy progresses
Uterine involution
Return of theuterusto its pre-pregnant state in the 1st several weeks postpartum
changes during pregnancy
Cervix
Cervix softens (Goodell’s sign)
and can becomebluish (Chadwick sign)due to:
Increased vascularization
Hypertrophy and hyperplasia of the cervical glands
May undergo eversion:
Glandular cells normally lining the cervical canal become visible on the surface of the cervix
Can cause benign bleeding
All bleeding in pregnancy should be fully evaluated
Endocervical mucosal cells produce amucus plug (operculum), an immunological barrier for uterine contents
changes during pregnancy
Ovaries
Follicle-stimulating hormone (FSH) ceases its activity due to the increased levels of estrogen and progesterone secreted by the corpus luteum → placenta
Corpus luteum
Enlarges during early pregnancy
May even form a cyst on the ovary
Suppliesprogesteroneduring the 1st part of pregnancy to help maintain the lining of the endometrium
10-12 weeks of pregnancy, the placentais developed enough to take over production of progesterone
changes during pregnancy
breasts
Changes result form estrogen and progesterone production
Breast fullness that continues throughout pregnancy
Increased size
Hyperplasia of mammary alveoli and fat deposits
Hyperpigmentation and enlargement of the areola
Enlargement of the Montgomery glands
Sebaceous glands of the areola
Secrete an antibacterial oil that moistens and protects the nipple during breastfeeding
Surface vessels may become prominent due to ↑ circulation
Bluish tint to the breasts
Colostrum production
Occurs by week 16
Precursor of breast milk
Thin, watery, yellowish secretion with high protein content
Thickens as pregnancy progresses
changes during pregnancy
integumentary system
Alterations in hormonal balance and mechanical stretching are responsible for several changes in the integumentary system
Hyperpigmentation:
Face (melasma or “mask of pregnancy”)
Brownish hyperpigmentation of the skin over centrofacial-malar area due to ↑ melanocyte-stimulating hormone, estrogen, and progesterone
Begins at ~16 weeks of pregnancy and gradually increases
Exacerbated by sun exposure
Usually fades after delivery
Umbilicus
Areola of the nipples
Perineum
Linea nigra
Dark line that runs from the umbilicus to the symphysis pubis and may extend as high as the sternum
After delivery, the line begins to fade, but may never completely disappear
Stretch marks (Striae gravidarum)
Separation within underlying connective tissue of the skin
Occurs over areas of maximal stretch…the abdomen, buttocks, thighs, and breasts
Fade after delivery, but never completely disappear
Sweat Glands
↑ activity throughout the body leading to profuse perspiration during pregnancy
Other common cutaneous changes:
Spider angiomas
Palmar erythema
Worsening of varicosities
Nail changes:
Brittle nails
Beau’s lines
Arrest ofnail growth at the area under the cuticle and will present as indentations in the nails
changes during pregnancy
heme/anemia
Blood volume:
Increased plasma volume gradually by 30-50% (1500 ml to 3 units)
↑ estrogen → stimulation of the renin-angiotensin system → ↑ levels of circulating aldosterone; aldosterone promotes renal Na+ reabsorption and water retention
Results in decrease concentration of red blood cells and hemoglobin
Dilutional anemia = fatigue, shortness of breath
Diagnosis of anemia if the hemoglobin falls below 10.5 g/dL and the hematocrit drops below 30%
Hypervolemia of pregnancy compensates for material blood loss at delivery
Average loss:
400-500 cc for vaginal delivery
1000 cc caesarean delivery
RBC mass:
Human placental lactogen (human chorionic somatomammotropin) produced by the placenta promotes erythropoiesis by enhancing the effects of erythropoietin → RBC production
↑ utilization of iron
Reason women need iron in pregnancy!
Placenta actively transports iron from the mother to the fetus, so the fetus is generally not anemic
Hypercoagulability:
50% ↑ in blood coagulation factors
I, II, VII, VIII, X, and XII
changes during pregnancy
cardio
Heart displacement:
Heart rotates in response to uterine enlargement and diaphragmatic elevation
Left-upward displacement (15-20 degree shift to the left on electrical axis)
Apical beat (point of maximum intensity) shifts laterally
Cardiac output:
CO = SV x HR
↑ CO of 30-50% in the 1st & 2nd trimester to accommodate hypervolemia
SV ↑ and reaches maximum at 12-24 weeks gestation
Position dependent: supine ↓ SV
HR ↑ after 20 weeks…average increase of ~10 beats/min
Venous return:
↓ venous return because of vena caval obstruction by the enlarging gravid uterus → CO ↓
Supine hypotensive syndrome:
10% of patients (3rd trimester)
Sensitive to caval compression
Hypotension, bradycardia, syncope
Encourage lateral positioning
Peripheral vascular resistance:
↓ in the first trimester due to smooth muscle-relaxing effects of progesterone and ↑ production of vasodilators (prostaglandins, nitric oxide, etc.)
At the time of delivery ~40% decrease
Blood pressure:
Arterial pressure
↓ in systolic (4-6 mm Hg) and diastolic (8-15 mm Hg) pressure with a maximum by 20-24 weeks
Most often returns to normal by term
↑ BP may be an indicator of preeclampsia
Venous pressure
Progressive ↑ in the lower extremities due to compression of the vena cava by the gravid uterus → edema and varicosities
↓ in the lower extremities immediately after delivery
Blood flow distribution:
Increased flow
Uterus
↑ in a gestational age-dependent manner
Kidneys
Skin
Particularly the hands and feet to help dissipate heat produced by metabolism
Breasts
Strenuous exercise:
Diverts blood flow to large muscles → ↓ uretoplacental perfusion
Exercise plans should be discussed providing physician
changes during pregnancy
murmurs, heart sounds, rhythm
Murmurs:
Low-grade systolic ejection murmurs detected in up to 90% of patients
Diastolic murmurs should NOT be considered normal in pregnancy
Heart Sounds:
Normal findings
Second heart sound splitwith inspiration
S3gallop (third heart sound) after mid-pregnancy
Rhythm:
↓ threshold for reentry supraventricular tachycardia
Normal findings
Sinus tachycardia
Sinus bradycardia
Isolated atrial and ventricular premature contractions
changes during pregnancy
pulmonary system
Changes occur due to increased oxygen demand of the mother and fetus
Primarily mediated by progesterone
Thorax enlargement:
Changes due to uterine enlargement
Diaphragm is elevated ~4-5 cm
Rib cage is displaced upward creating a ~2 cm diameter and 6 cm circumference increase in the lower thorax
Lung Volume & Capacities:
↓ total lung capacity and functional residual capacity due to elevation of the diaphragm
Relaxation of the musculature of the conducting airways (pregnancy-induced bronchodilation)
Slight ↑ tidal volume and inspiratory capacity
Respiratory rate:
↑ to 18-20/minute resulting from ↑ maternal oxygen consumption…demands from the uterus, placenta, and fetus
Hyperventilation
Progesterone creates an increased sensitivity to CO2
↓ arterial PCO2 = what acid-base disturbance?
Compensation by ↑ renal excretion of bicarbonate
