Physiology of Normal Pregnancy Flashcards
Where does the placenta originate from?
The trophoblast cells of the blastocyst that implants into the uterine wall
What are the main hormones secreted from the placenta?
human placental lactogen (HPL)
hCG
Luteinizing hormone releasing hormone (LHRH), TRH, estrogen, and progesterone
What is the structure of HPL?
Solely polypeptide, similar in structure to growth hormone and prolactin
How do HPL levels change throughout pregnancy?
They rise steadily throughout the entirety of pregnancy
Is HPL specific for pregnancy?
No you can see positive titers with bronchogenic carcinoma, hepatoma, lymphoma, and pheochromocytoma and very low titers in trophoblastic disease
What are the actions of HPL?
Promotes lipolysis (as glucose is depleted the maternal body becomes more dependent on fatty acid metabolism) and anti-insulin to provide availabilty of glucose to diffuse to the fetus
T or F. The presence of HPL is required for successful pregnancy
F.
What would be a physiological consequence of switching to fatty acid metabolism during pregnancy?
A normal increased concentration of ketone bodies in urine
Why would pregnancy be so commonly associated with the formation of diabetes (about 10% of pregnancies)?
since HPL leads to insulin resistance, it promotes a diabetogenic state
What might be some complications of gestational diabetes?
- pre term labor
- hypoglycemia of the fetus/newborn due to increased fetal insulin production
- macrosomia
What is the major labor-related complication of macrosomia?
shoulder dystocia- a specific case of obstructed labour whereby after the delivery of the head, the anterior shoulder of the infant cannot pass below the pubic symphysis. Can lead to Erb’s plasy
There can also be more soft tissue damage to the mother, and pelvic floor dysfunction later in life
Describe human chorionic gonadotropin
This is a glycoprotein produced by syncytiotrophoblasts of the placenta containing two non-covalently bonded subunits:
Alpha- similar to FSH, LH, and TSH
Beta- hormone specific unit
What other things may also be associated with increased titers of hCG?
Anything that increases the palcental mass including multiple gestatins, eryhtroblastosis, hydatidiform mole, or a choriocarcinoma
What things may cause an abnormally low titer of hCG during pregnancy?
ectopic pregnancy or SAB
What does hCG do?
- prolongs the life or the corpus luteum early in pregnancy
- increases steroid production
- used as a diagnostic test for the presence of pregnancy via urine or blood
How do hCG levels change throughout normal pregnancy?
You ought to be able to see a fetus on a tranvaginal ultrasound with what level of hCG?
1500 mIU/ml (typically around 5 weeks gestation)
NOTE: On trans-abdominal ultrasound, you should be able to see a fetus when the hCG level is somewhere around 5000-6000 mIU/ml
What are some of the physical changes that are seen in early pregnancies?
There is marked softening and cyanosis of the uterus and the cervix to produce an enlarged uterus with a bluish hue associated with increased vascularity, edema, and hypertrophy and hyperplasia of glands
What is responsible for the physical changes to the uterus and cervix in early pregnancy?
estrogen and an associated physiologic large increase in intravascular blood volume due to veins expanding their capacitance causing plasma oncotic pressure to drop and hydrostatic pressure to increase (as well as the enlarging uterus physically pressing against these vessels causing decreased venous return and thus further increased hydrostatic pressure) and eventually edema follows, first affecting the uterus and cervix, causing them to soften
softening described by Hagar
What causes the blush discolorization of the cervix in early pregnancy (described by Chadwick)?
the extarvasated venous blood is more deoxygenated
When does uterine and cervical softening occur in pregnancy?
Around 6-8 weeks gestation
What happens to endocervical glands during early pregnancy?
Estrogen causes them to extend out over the exocervical surface and there is associated increse in glandular production of mucus causing a physiologic discharge (aka the physiologic leukorrhea of pregnancy)
What is Chadwick’s sign?
This is the appearance of a violet-blue color of the vaginal and cervical mucosa, a presumptive sign of pregnancy
What is the pH of vaginal/cervical physiological secretions?
Acidic (3.5-6.0)
What is the utility of understanding that the normal physiological secretions of the cervix and vagina are acidic?
This can help differentiate from amniotic fluid which are more pathologic and basic in pH
How does the size and thickness of the uterus change during pregnancy?
Typically the size of the uterus will expand primarily due to the weight of products of conception and as it expands it will thin greatly (so that near birth the uterine isthmus may only be a couple millimeters thick at most)
T or F. Uterine contractions throughout the entirety of pregnancy is normal
T.
When does the uterus filled the pelvic cavity aand start to come up into the abdomen?
about 12 weeks gestation
What happens to renin activity in pregnancy?
increases about 5-10x- this is the main mechanism by which intravacular volume increases in pregnancy
What typically happens to BP in normal pregnancy?
It will normally DEcrease. Peripheral resistance drops as well (so its important to note that while renin is elevated in pregnancy to cause fluid retention, its vasoconstrictive properites are somehow blunted)
T or F. Fetal placental vasculature is typically a very low resistance shunt
T.
Describe maternal changes in levels of Calcium related hormones during pregnancy?
- total Ca conc falls but not ionized conc (5% decrease by term)
- increased Vit D hydroxylation and GI Ca absorption
- increased PTH
Describe fetal changes in levels of Calcium related hormones during pregnancy?
- Placenta is active in Ca and PO4 metabolism
- Active transport of Ca to fetus probably occurs
- Newborn levels of calcium exceed maternal
- PTH may facilitate Ca transport to fetus but PTH and calcitonin do not cross
- 25 hydroxy vitamin D crosses placenta while 1,25 dihydroxy vitamin D does not cross
Describe thyroid levels in a pregnant woman
- TSH decreases slightly early in pregnancy (due to hCG increase) and returns to normal later
- The thyroid may be enlarged but functions normally
- TBG capacity ↑ leading to T4 resin uptake ↓
- Thyroid hormones increase but free hormone levels unchanged
Do thyroid hormones cross the palcenta typically?
- Little T4 and T3 cross placenta
- TSH does not cross placenta
How does GH levels change during pregnancy?
The pituitary gland enlarges and GH levels lower during and after delivery
How do prolactin levels change during pregnancy?
They increase and decrease following delivery
How do prolactin levels change during pregnancy?
Plasma levels increase with gestational age
How do the maternal adrenal glands change during pregnancy?
There is expansion of the zona fasiculata and increased glucocorticoid production as well as production of corticosteroid binding globulins (but free plasma cortisol levels still rise- increased production and decreased clearance)
Cortisol is typically increased up to 3x by delivery
T or F. Maternal deoxycorticosterone increases during pregnancy
T
- Does not respond to ACTH stimulation or dex suppression
- Probably comes from fetoplacental unit
- DHEAS decreased
How are the kidneys affected by pregnancy?
The kidneys both increase in size (right more than the left), GFR increases, RBF increases until about 16 weeks then falls, and
BUN decreases secondary to increased GFR (creatinine clearance increases as well- max at the end of the first trimester)
T or F. Glucosuria is common in pregnancy
T. In addition to insulin resistance, glucose transporters become saturated and glucose ends up in the urine
How do the ureters react to pregnancy?
They dilate, elongate, and increase in tortuosity in response to the uterus growing and urine flow decreases due to progesterone decreasing muscle tone (more likely to have upper UTI infections!!)
How long after pregnancy does ureter function take to return to normal?
•Changes resolve by 6 – 8 weeks postpartum
How do the lungs react to pregnancy?
- Total lung capacity actually decreases from 4200 to 4000 mL in pregnancy
- Level of diaphragm is pushed up 4 cm (thus, Diaphragmatic excursion actually increases)
- Subcostal angle widens (Does not prevent reduction in residual volume from elevated diaphragm)
Increased tidal volume in pregnancy (increases 30-40% at expense of expiratory reserve volume which falls 20%)
How do the VC and IRV change in pregnancy?
they dont
What happens to minute ventilation in pregnancy?
It increases due to an increase in tidal volume, which results in increased PAO2 and decreased pACO2, which helps facilitate the CO2 gradient between the fetus and mother
What would be the pH of the blood during pregnancy?
It might be slightly basic because increasing the tidal volume pushes off a lot of CO2, which produces an alkotic state (note: it is compensated by getting rid of HCO3-)
Again, what happens to functional residual capacity and residual volume during pregnancy?
They decrease secondary to an elevated diaphragm. This might produce an increased awareness of the desire to breath and is commonly interpreted by women as dyspnea
Why are murmurs so common in pregnant women?
There is always a physiologic anemia of pregnancy contributing to these murmurs- red cell content wont increase with increased intravascular volume, leading to anemia. 85% of women will present with a widely split S1 and an S3
90% will have a soft, mid-systolic flow murmur
How does CO change in pregnancy?
It increases with little change after the first trimester and peaks at 30-32 weeks
Why/how does CO increase in pregnancy?
There is increaseb both heart rate and stroke volume, as well as decreased total peripheral resistance
How do RBCs change during pregnancy?
They have a decreased life span during the latter half of pregnancy, as well as decreased O2 affinity. So, some things you will see later in pregnancy on a CBC include increased reticulocyte counts, increased red cell volumes, and increased EPO levels
What causes increased EPO levels in pregnancy?
hPL
Iron supplementation is needed during pregnancy to prevent maternal iron deficiency. How much is needed?
Typically 1000mg daily- 500mg to increase RBC mass, 300 mg to the fetus, and 200 mg lost daily
NOTE: The fraction of iron absorbed increases with increased needs (20-40% absorbed in pregnancy)
T or F. Iron is actively transported to the fetus
T.
How does a WBC vary during pregnancy?
- 3,000 – 10,000 in first trimester
- 6,000 – 16,000 in 2nd and 3rd trimester
- 30,000 in labor
How do caog factors change during pregnancy?
- Fibrinogen, Factors VII – X, and XII increase (II, V normal)
- Hypercoaguable state of pregnancy does not seem to be due to these changes but rather increased thromboembolism incidence
How does the liver change during pregnancy?
There’s no change in morphology, hepatic blood flow, and bilirubin but:
- Alk Phosphatase doubles
- plasma albumin and cholinesterase decreases
How does the gallbaldder change in pregnancy?
there is distension, a hypotonic state develops, and thickening of bile
How does the spine change during the pregnancy?
Lordosis is prominent- Keeps center of gravity over legs. The enlarging uterus would otherwise shift center of gravity anteriorly
- Hegar’s sign- 6 weeks
- Lower uterine segment softening
- Chadwicks sign- 6-8 weeks
- Bluish discoloration
- Goodell’s sign- 8 weeks
- Cervical softening
