USMLE Obstetrics IV

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  1. Normal adaptations to pregnancy
    • include increases in the glomerular filtration rate, renal blood flow, and renal basement membrane permeability, which causes a decrease in serum blood urea nitrogen and creatinine and an increase in urinary protein excretion.
    • A hypercoagulable state serves to minimize bleeding during delivery. Changes in plasma volume produce a mild dilutional anemia.
  2. Proteinuria in Pregnancy
    • In nonpregnant patients, renal excretion >150 mg of protein is considered abnormal.
    • However, in pregnant patients, due to the increase in the GFR and in renal basement membrane permeability, urinary excretion >300 mg of protein is considered abnormal.
    • Therefore, urine dipstick findings of trace and 1+ protein are normal in pregnancy.
  3. Renal Changes In Pregnancy
    • In a normal pregnancy, both the glomerular filtration rate (GFR) and renal blood flow are increased, which cause the serum blood urea nitrogen and creatinine to become decreased compared to prepregnancy levels.
    • Renal function increases gradually in the first trimester and reaches 40%-50% above the nonpregnant state by midpregnancy, after which it remains unchanged until term.
    • Renal basement membrane permeability is also increased in pregnancy.
    • Due to the increase in renal function during pregnancy, patients on medications that are renally excreted (eg, gabapentin) require close monitoring and dose adjustments as necessary.
    • In addition, a serum creatinine of 1.2 mg/dl may be the upper limit of normal in a nonpregnant woman but is considered renal insufficiency in a pregnant woman.
  4. Increased MSAFP
    • • Open neural tube defects (eg, anencephaly, open spina bifida)
    • • Ventral wall defects omphalocele, gastroschisis)
    • • Multiple gestation
  5. Decreased MSAFP
    • Aneuploidies (eg, trisomy 18 & 21)
  6. osteogenesis imperfecta (0I)
    • type II, an autosomal dominant inherited disease caused by defects in the gene coding for type I collagen.
    • Type I collagen is widely distributed in the body; it is found in bones, tendons, fibrocartilage, skin, eyes, and other structures.
    • OI type II is the most severe form of the disease and is characterized by multiple intrauterine and perinatal fractures as well as restrictive lung disease.
    • It most commonly results in fetal or perinatal death.
    • Characteristic findings include blue sclerae, multiple fractures causing limb deformity, and intrauterine growth retardation.
  7. fetal alcohol syndrome (FAS).
    Findings include subtle craniofacial abnormalities, poor prenatal growth, microcephaly, hypotonia, and poor feeding. As children with FAS age, growth retardation and mild mental retardation are typically present.
  8. luteoma of pregnancy,
    • a benign condition that occurs more frequently in African Americans.
    • Most luteomas are asymptomatic, but -30% of patients experience new-onset hirsutism and acne due to excess testosterone, dihydrotestosterone, and androstenedione.
    • Ultrasound is the gold standard for diagnosing luteomas, which appear as solid ovarian masses (large lutein cells) that are typically 6-10 em in diameter and bilateral in half of patients.
    • Management primarily involves clinical monitoring and ultrasound evaluation as the masses and symptoms regress spontaneously after delivery.
    • However, the patient should be informed that a symptomatic maternal luteoma puts a female fetus at high risk of virilization.
    • In addition, the size of the luteomas should be monitored due to the rare but potential risk of mass effect (eg, hydrocephalus, obstructive labor) and ovarian torsion.
  9. Polycystic ovarian syndrome (PCOS)
    • is the most common cause of hyperandrogenism in nonpregnant women.
    • The classic presentation is a hirsute woman with infertility; infrequent, heavy, prolonged menses; and polycystic ovaries on ultrasound.
    • Clomiphene is the first-line therapy for ovulation induction in PCOS
  10. Theca lutein cysts
    • are benign, multi-septated cystic masses that can be asymptomatic or cause new-onset hyperandrogenism.
    • The cysts arise from high ~-hCG levels, such as in a molar pregnancy or multiple gestation.
    • Suction curettage is indicated when a complete hydatidiform mole is seen on ultrasound (central heterogeneous mass with numerous discrete anechoic spaces), but the associated theca lutein cysts regress spontaneously.
  11. Placenta previa
    • occurs when the placenta implants over the internal cervical os and is a contraindication to labor and vaginal delivery.
    • Patients with placenta previa undergo cesarean delivery at 36-37 weeks.
    • Placenta previa is usually diagnosed during routine prenatal ultrasound at 18-20 weeks gestation by identifying the placenta covering the internal cervical os.
    • Most patients are asymptomatic but at significant risk of painless but severe antepartum hemorrhage.
    • Although placenta previa may resolve spontaneously by the third trimester due to growth of the lower uterine segment and/or placental growth toward the fundus, pelvic rest and abstinence from intercourse (due to potential penile contact with the cervix) are recommended for all patients once the diagnosis of placenta previa is made.
    • Clinicians should refrain from digital cervical examination as cervical penetration can potentially disrupt the placenta.
    • Labor and vaginal delivery are also contraindicated.
    • Cesarean delivery is scheduled for 36-37 weeks gestation as cervical changes and uterine contractions can cause partial placental detachment from the cervix. Should a follow-up ultrasound show resolution of the placenta previa, the plan of care can be modified accordingly and the pelvic rest restriction can be lifted.
  12. vasa previa
    • fetal blood vessels covering the cervical os, which is often associated with resolved placenta previa.
    • Vasa previa is characterized by fetal blood vessels that cross the fetal membranes between the fetus and the internal cervical os.
    • It also presents as painless antepartum hemorrhage but is associated with rapid deterioration of the fetal heart tracing as the hemorrhage is of fetal origin.
    • This patient has a normal fetal heart rate tracing.
  13. Placenta accreta
    • occurs when uterine villi attach directly to the myometrium instead of the decidua.
    • Risk factors for placenta accreta include a prior cesarean delivery, a history of dilation and curettage, and maternal age >35.
    • Placenta accreta is typically diagnosed by antenatal ultrasound findings that include irregularity or absence of the placental-myometrial interface and intraplacental villous lakes.
    • Antenatally diagnosed placenta accreta is delivered by planned cesarean hysterectomy.
    • Undiagnosed placenta accreta presents as difficulty with placental delivery. The placenta does not detach from the uterus, and this often results in cord avulsion and necessitates a manual extraction, which is then complicated by placental adherence and severe hemorrhage.
  14. Postpartum endometritis
    • an infection of the uterine decidua, is the most common etiology of puerperal fever.
    • Postpartum endometritis typically presents with fever >24 hours postpartum, purulent lochia, and uterine tenderness.
    • Risk factors include prolonged rupture of membranes, operative vaginal delivery, prolonged labor, and cesarean delivery.
    • Postpartum endometritis is the result of the inoculation of the uterine cavity by vaginal flora during labor or delivery and is a polymicrobial infection.
    • Treatment of this polymicrobial infection requires broad-spectrum antibiotics; the most appropriate therapy is clindamycin plus gentamicin.
    • Treatment should be continued until the patient is afebrile for >24 hours.
    • Neither blood nor endometrial cultures are required for diagnosis, but further evaluation is indicated if there is no clinical improvement after 48 hours of antibiotic therapy.
  15. Postpartum hemorrhage (PPH)
    • is an obstetrical emergency and a major cause of maternal mortality.
    • Hemostasis after placental delivery is achieved by clotting and by compression of the placental site blood vessels by myometrial contraction. Disruption of either of these processes can lead to PPH.
    • Primary PPH occurs <24 hours after delivery and is most commonly caused by uterine atony.
    • Atony occurs when the uterus becomes fatigued (eg, prolonged labor), over-distended (eg, fetal weight >4000 g [8.8 lb), multiple gestation), or unresponsive to oxytocin from oxytocin receptor saturation.
    • Other risk factors for atony include operative (eg, forceps assisted) vaginal delivery and hypertensive disorders.
    • The uterus fails to contract and is soft ("boggy") and enlarged (eg, above the umbilicus) on physical examination.
  16. Postpartum uterine atony
    • Risk Factors
    • • Uterine fatigue from prolonged or induced labor
    • • Chorioamnionitis
    • • Uterine over-distension (multiple gestation, polyhydramnios)
    • • Retained placenta
    • Clinical features
    • • Most common cause of postpartum hemorrhage
    • • Enlarged, soft, boggy, poorly contracted uterus
    • Treatment
    • • Bimanual uterine massage
    • • Intravenous fluids, oxygen
    • • Uterotonic medications (eg, oxytocin, methylergonovine, carboprost, misoprostol)
  17. Methylergonovine
    is an uterotonic drug that causes smooth muscle constriction, uterine contraction, and vasoconstriction. Because vasoconstriction can cause hypertension, a history of hypertension is a contraindication to methylergonovine.
  18. Carboprost
    is a synthetic prostaglandin that stimulates uterine contraction. Carboprost causes bronchoconstriction, and asthma is a contraindication to its use.
  19. Post Term Pregnancy
    • Pregnancies at 41 weeks or beyond are defined as late-term (41 weeks to 41 weeks and 6 days gestation) or postterm (2:42 weeks gestation) from the last menstrual period.
    • Risk factors include nulliparity, history of prior postterm pregnancy, maternal obesity, and fetal anomalies (eg, anencephaly).
    • An induction of labor can be considered for late-term pregnancy and is recommended for postterm pregnancies to prevent complications
    • Antepartum fetal testing may be started at 41 weeks gestation to assess fetal well-being.
    • Oligohydramnios (single deepest vertical pocket of amniotic fluid s2 cm or an amniotic fluid index of s5 em on transabdominal ultrasound) is a common complication of prolonged pregnancies.
    • An aging placenta may have decreased fetal perfusion, resulting in decreased renal perfusion and decreased urinary output from the fetus.
    • The diagnosis of oligohydramnios is an indication for delivery even if antepartum fetal testing is normal.
  20. Magnesium sulfate
    • Is the treatment of choice for the prevention of eclamptic seizures.
    • It is also administered to patients for whom preterm delivery is imminent as it decreases the risk for cerebral palsy in premature infants.
    • Common adverse effects of magnesium sulfate Include headache, nausea, fatigue, and diaphoresis.
    • Signs of magnesium toxicity include loss of deep tendon reflexes, somnolence, and respiratory depression.
    • Because magnesium is solely excreted by the kidneys, a common risk factor for magnesium toxicity is renal insufficiency, as seen in this patient.
    • Patients with an elevated serum creatinine may need a lower magnesium dose and close observation.
    • Magnesium levels should be checked after initiation of the infusion and the infusion rate adjusted accordingly.
    • Calcium gluconate is the first-line treatment for magnesium toxicity
  21. Eclampsia
    • is defined as the occurrence of seizures in a patient with preeclampsia (eg, hypertension, proteinuria) and is the most common cause of new-onset seizures in pregnant patients.
    • The risk factors for eclampsia are similar to those of preeclampsia (eg, history of preeclampsia, maternal age >40, history of hypertension).
    • Eclamptic seizures are typically tonic clonic, generalized, and brief, lasting several minutes.
    • The seizures are frequently preceded by severe headaches, visual disturbances (eg, blurry vision, photophobia, loss of vision), and epigastric/right upper quadrant pain.
    • Patients typically have hypertension (systolic blood pressure more than or equal to 140 mm Hg or diastolic blood pressure 2:90 mm Hg) and proteinuria but no focal neurologic defects.
    • During the postictal phase of an eclamptic seizure, patients are typically fatigued and sleepy.
    • Administer magnesium sulfate
    • Administer antihypertensive agent
    • Deliver the fetus
    • If magnesium sulfate does not control eclamptic seizures, then diazepam or phenytoin would be indicated as a second choice.
  23. Preeclampsia with Severe Features
    • SBP more than or equal to 160 mm Hg or DSP more than or equal to 110 mm Hg (2 times measured 4 hours apart)
    • • Thrombocytopenia
    • • Increased Creatinine
    • • Increased Transaminases
    • • Pulmonary edema
    • • Visual or cerebral symptoms
  24. Management of Preeclampsia
    • without severe features: delivery at ≥37 weeks
    • • With severe features: delivery at ≥34 weeks
    • • Magnesium sulfate (seizure prophylaxis)
    • • Antihypertensives ( Hydralazine IV, labetalol IV or nifedipine PO )
    • The first-line drugs for maternal hypertensive crisis include intravenous labetalol (beta blocker with alpha-blocking activity), intravenous hydralazine (vasodilator), and oral nifedipine (calcium channel blocker). Intravenous labetalol is fast acting and safe in pregnancy. Labetalol causes bradycardia.
  25. Mode of Delivery In Preeclampsia
    • After 37 weeks gestation, the risks associated with prematurity are minimal and preeclampsia is an indication for delivery.
    • If both mother and fetus are stable and with no contraindications (eg, breech presentation), labor induction for a vaginal delivery is preferred.
    • Cesarean delivery is indicated for obstetrical indications (eg, failed induction) or for a nonreassuring fetal status (eg, heart rate abnormalities)
  26. Methyldopa In Pregnancy
    • It has a long history of safety in pregnancy but is used to treat chronic hypertension rather than hypertensive emergencies.
    • Its use is limited by its slow onset and comparative weakness, which necessitates high doses that can cause sedation.
  27. Preeclampsia
    • is defined as new-onset hypertension with proteinuria after 20 weeks gestation.
    • This patient's new-onset, severe hypertension at 37 weeks gestation, headache with visual symptoms, increased ankle clonus. and thrombocytopenia are
    • strongly suggestive of preeclampsia with severe features.
    • Her elevated lactate dehydrogenase and anemia are consistent with microangiopathic hemolysis, a known feature of preeclampsia.
    • Risk factors for preeclampsia include nulliparity and maternal age <18.
    • The pathophysiology of preeclampsia likely involves abnormal placental development and function, which puts the fetus at risk for chronic uteroplacental insufficiency .
    • Uteroplacental insufficiency can lead to fetal growth restriction/low birth weight (ie, small for gestational age infant) even if the neonate is delivered at term.
    • Maternal complications from preeclampsia include abruptio placentae, disseminated intravascular coagulation, and eclampsia.
  28. Acute uteroplacental insufficiency
    • leads to hypoxic brain injury
    • Abruptio, Labor stress
  29. Influenza Vaccination in pregnancy
    • Pregnancy is associated with an increased risk for influenza-associated morbidity and mortality (eg, pneumonia, acute respiratory distress syndrome).
    • Therefore, all pregnant women without contraindications should receive the inactivated influenza vaccination as soon as it becomes available.
    • The inactivated influenza vaccine is safe during every trimester of pregnancy and while breastfeeding.
    • The live attenuated intranasal vaccine is contraindicated during pregnancy due to the risk of congenital infection but is safe during breastfeeding.
    • In addition to preventing influenza in the mother, vaccination also provides passive neonatal immunity and has been shown to decrease the frequency and severity of influenza in newborns.
  30. cell-free fetal DNA testing (cffDNA)
    • Indications
    • • Maternal age >35
    • • Abnormal maternal serum screening test
    • • Sonographic findings associated with fetal aneuploidy
    • • Previous pregnancy with fetal aneuploidy
    • • Parental-balanced Robertsonian translocation
    • Applications
    • • Screening for trisomy 21 , 18, 13 & sex chromosome aneuploidies
    • • Fetal sex determination
  31. Cell-free fetal DNA testing
    • Women age more than or equal to 35 are at increased risk of fetal aneuploidy and should be offered cell-free fetal DNA testing (cffONA) of maternal plasma.
    • This noninvasive test can be performed at <::10 weeks gestation and has -99% sensitivity and specificity for detecting trisomy 21 (Down syndrome), >92% sensitive for trisomy 18 (Edward syndrome), and >80% sensitive for trisomy 13 (Patau syndrome).
    • It can also identify the fetal sex and detect some sex chromosomal disorders.
    • Normal results are generally reassuring and reduce the rate of invasive diagnostic procedures.
    • Abnormal cffDNA results can be confirmed by fetal karyotyping via chorionic villus sampling in the first trimester or amniocentesis in the second trimester.
  32. First trimester Combined Test
    • Patients who do not meet high-risk criteria for cffDNA can undergo screening during the first trimester with the combined test (pregnancy-associated plasma protein A, beta-hCG, and ultrasound nuchal translucency), which has a detection rate of -85% for Down syndrome.
    • In the second trimester, the quadruple screen includes maternal serum a fetoprotein, beta-hCG, unconjugated estriol, and inhibin A levels. The detection rate for Down syndrome using the quadruple screen is -80%.
  33. Management of Preterm labor
    • 34 0/7 to 36 6/7 weeks
    • • +/- Betamethasone
    • • Penicillin if GBS positive or unknown
    • 32 0/1 to 33 6/7weeks
    • • Betamethasone
    • • Tocolytics
    • • Penicillin if GBS positive or unknown
    • <32 weeks
    • • Betamethasone
    • •Tocolytics
    • • Magnesium sulfate
    • • Penicillin if GBS positive or unknown
  34. MgSo4 In Preterm Labor
    • magnesium sulfate administration at <32 weeks gestation lowers the risk of neonatal neurological morbidities (eg, cerebral palsy).
    • Although magnesium sulfate has weak tocolytic properties, it is used primarily for fetal neuroprotection in patients at <32 weeks gestation who are expected to deliver within the next 24 hours.
    • Magnesium sulfate can be administered concurrently with indomethacin .
  35. management of Preterm Labor with Breech Presentation
    • In the absence of contraindications to vaginal delivery, patients who present in preterm labor at more than or equal to 34 weeks gestation can be managed expectantly.
    • However, due to an increased risk for fetal injury and asphyxia, a vaginal delivery is contraindicated for a singleton breech fetus.
    • Consequently, the best option for managing this patient's preterm labor is cesarean delivery.
    • Active labor is a relative contraindication for external cephalic version.
    • Regardless of delivery route, patients in preterm labor at <37 weeks gestation are candidates for betamethasone, which can reduce the incidence of neonatal respiratory distress syndrome.
    • All patients in preterm labor who are either group B Streptococcus (GBS) positive or unknown and who will deliver vaginally should receive intravenous penicillin to prevent the vertical transmission of GBS.
    • Patients at <37 weeks who will deliver by cesarean require penicillin only if they are GBS positive or unknown and have ruptured membranes.
  36. Evaluation of Patient with Preterm Delivery
    • The strongest risk factor for preterm delivery is preterm delivery in a prior pregnancy.
    • Other important risk factors include multiple gestation and a history of cervical surgery.
    • In particular, removal of part of the cervix by cold knife conization for cervical intraepithelial neoplasia can cause cervical scarring/stenosis and incompetence.
    • The first step in evaluating the risk of preterm delivery is transvaginal ultrasound (TVUS) measurement of cervical length in the second trimester.
    • A short cervical length is a strong predictor of preterm labor.
    • Fetal fibronectin (FFN) levels are high until 20 weeks gestation, are low during the mid-second and third trimesters, and increase again at term, when contractions disrupt the decidual-chorionic interface.
    • Elevated levels prior to term are used as an indicator for increased risk of preterm delivery.
  37. Evaluation Of Patient at risk for Preterm Delivery
    • A short cervix ≤2 cm without a history of preterm birth or ≤2.5 cm with a history of preterm birth) on transvaginal ultrasound (TVUS) during the second trimester is a strong predictor for preterm delivery.
    • During pregnancy, progesterone maintains uterine quiescence and protects the amniotic membranes against premature rupture.
    • Supplementation with exogenous progesterone decreases the rate of preterm delivery in patients with short cervices or a history of preterm birth.
    • Patients with short cervices and no history of preterm delivery should be offered vaginal progesterone.
    • Patients with a history of preterm delivery receive intramuscular progesterone starting in the second trimester and undergo serial TVUS for cervical length measurements.
    • If TVUS reveals a short cervix, cerclage may be indicated.
  38. Risk Factors for Preterm Delivery
    • Prior cervical surgery, particularly cold knife conization, is a risk factor for preterm delivery, possibly due to cervical scarring and loss of cervical stroma.
    • A loop electrode excision procedure (LEEP) may or may not confer a risk of preterm delivery
    • cervical laser ablation does not increase that risk.
    • Other risk factors for preterm delivery include obesity in vitro fertilization and advanced maternal age.
    • Tobacco use is a modifiable risk factor for preterm delivery.
    • However, all of these factors are less significant than a history of prior spontaneous preterm delivery.
  39. premature rupture of membranes(PROM)
    • Membrane rupture prior to the onset of labor is PROM
    • PROM at <37 weeks gestation is preterm PROM (PPROM).
    • The diagnosis of membrane rupture can be confirmed with the nitrazine or fern tests or with a speculum examination showing vaginal pooling of clear fluid or fluid emerging from the cervix.
    • PPROM risk factors are similar to those for preterm delivery (eg, history of prior preterm delivery, multiple gestation) but also include a history of prior PPROM, genital tract infection (eg, bacterial vaginosis), and tobacco use.
    • Complications of PPROM include chorioamnionitis/endometritis, cord prolapse, and abruptio placentae
  40. Management of PPROM
    • is dependent on gestational age and clinical presentation with the goal of minimizing prematurity risks and the risks of prolonged membrane rupture (eg, infection).
    • At <34 weeks gestation, fetuses are at greatest risk of prematurity-related morbidity (eg, lung immaturity, intraventricular hemorrhage).
    • Patients with PPROM at <34 weeks gestation with no signs of infection or fetal compromise should be managed conservatively so that in utero fetal growth can continue.
    • This patient should be hospitalized for observation and receive corticosteroids (eg, betamethasone) to decrease the risk of neonatal respiratory distress syndrome.
    • Antibiotics should also be administered to increase the interval between membrane rupture and delivery.
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USMLE Obstetrics IV
2017-08-27 07:47:12

Normal Changes in Pregnancy
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