USMLE Step 2 CK-OB/GYN

Date created: 12/03/2023

What is Nagele's rule?

due date \= LMP + 9 months + seven days

What is developmental age?

number of weeks and days since fertilization. typically used only in research, as the exact date of fertilization is not commonly known

What is gestational age?

number of wks and days measured from the first day of the LMP.

How else can gestational age be determined?

Fundal height: at 20wks, uterus is at the umbilicus and grows approx 1 cm/wk

Quickening, or appreciation of fetal movt: typically occurs at 17-18 wks

Fetal heart tones: can be heard at 10-12 wks by Doppler

Ultrasound: measures fetal crown-rump length (CRL) at 5-12wks and measured biparietal diameter (BPD), femur length (FL), and abd circumference (AC) from 13 wks. U/S measurement of GA is most reliable during the first trimester

How does renal flow change in pregnancy?

increases 25-50%

How does glomerular filtration rate change in pregnancy?

increases early, then plateaus

How does uterine weight change in pregnancy?

increases from about 60-70g to about 900-1200g

How does body weight change in pregnancy?

average 11kg (25lb) increase

What is the standard for diagnosing pregnancy?

B-hCG

• produced by placenta; peaks at 100,000 mIU/mL by 10wks of gestation

• decreases throughout the second trimester; levels off in the third trimester

• hCG levels double approx every 48hrs during early pregnancy. This is often used to diagnose ectopic pregnancy when doubling is abnormal

What is a quantitative B-hCG used for?

• to diagnose and follow ectopic pregnancy

• to monitor trophoblastic disease

• to screen for fetal aneuploidy

What is a quad screen?

1. Maternal serum alpha-fetoprotein

• produced by the fetus, crosses the placenta in small amounts and enters the maternal circulation

• Elevated: assoc w/ open neural tube defects (anencephaly, spina bifida), abd wall defects (gastroschisis, omphalocele), multiple gestation, incorrect gestational dating, fetal death, and placental abnormalities (e.g. placental abruption)

• Decreased: assoc w/ trisomy 21 and 18, fetal demise, and inaccurate gestational dating.

2. inhibin A

3. estriol

4. B-hCG

What quad screen results suggest Trisomy 18?

ALL four decreased

What quad screen results suggest Trisomy 21

decreased AFP and estriol
Increased B-hCG and inhibin A

How does heart rate change in pregnancy?

gradually increases 20%

How does blood pressure change in pregnancy?

gradually decreases 10% by 34 wks, then increases to prepregnancy values

How does stroke volume change in pregnancy?

increases to maximum at 19wks, then plateaus

How does cardiac output change in pregnancy?

rises rapidly by 20%, then gradually increases an additional 10% by 28wks

How does peripheral venous distention change in pregnancy?

progressive increase to term

How does peripheral vascular resistance change in pregnancy?

progressive decrease to term

How does respiratory rate change in pregnancy?

unchanged

How does tidal volume change in pregnancy?

increases by 30-40%

How does expiratory reserve change in pregnancy?

gradual decrease

How does vital capacity change in pregnancy?

unchanged

How does respiratory minute volume change in pregnancy?

increases by 40%

How does blood volume change in pregnancy?

increases by 50% in second trimester

How does hematocrit change in pregnancy?

decreases slightly

How does fibrinogen change in pregnancy?

increases

How do electrolytes change in pregnancy?

unchanged

How does sphincter tone change in pregnancy?

decreases

How does gastric emptying time change in pregnancy?

increases

What is the recommended amount of weight women should gain in pregnancy?

an additional 100-300 kcal/day; 500 kcal/day during breastfeeding
Excessive gain: \>1.5kg/mo
Inadequate gain:

What are the nutritional guidelines for pregnancy?

folic acid supplements (decrease neural tube defects for all reproductive-age women): 0.4 mg/day
Iron: 30mg/day of elemental iron
Calcium: 1300 mg/day for women

What is PAPP-A?

pregnancy-assoc plasma protein A
recommended at wks 9-14 to detect Down Syndrome and Trisomy 18 risk
combined with ultrasound-determined nuchal transparency (fluid in the fetal neck) + B-hCG

What is CVS?

chorionic villus sampling
recommended at wks 10-12
involves transcervical or transabd aspiration of placental (chorionic villi) tissue

What are the advantages and disadvantages of CVS?

Ads

• diagnostic accuracy comparable to that of amnio, available at 10-12wks

Disads

• carries risk of fetal loss (1-2%); cannot detect open neural tube defects

What are complications of CVS?

limb defects have been assoc w/ CVS performed

How often should prenatal visits occur?

Wks 0-28: every four wks
Wks 29-35: every 2 wks
Wks 36-birth: every wk

What kind of testing should be completed at the initial prenatal visit?

Heme: CBC, Rh factor, type and screen
ID: UA and culture, rubella ab titer, HBsAg, RPR/VDRL, cervical gonorrhea and chlamydia, PPD, HIV, Pap smear (to check for dysplasia)
If indicated: HbA1c, sickle cell screening
Discuss genetic screening: Tay-Sachs, CF

What kind of prenatal testing should be completed at 9-14wks?

offer Triple Screen

• PAPP-A

• nuchal transparency

• free B-hCG +/- CVS

What kind of prenatal testing should be completed at 15-20wks?

Offer Quad Screen

• AFP

• estriol

• B-hCG

• inhibin A +/- amniocentesis

What kind of prenatal testing should be completed at 18-20wks?

ultrasound for full anatomic screen

What kind of prenatal testing should be completed at 24-28 wks?

1hr glu challenge test for gestational diabetes screen

What kind of prenatal testing should be completed at 28-30 wks?

RhoGAM for Rh (-) women (after ab screen)

What kind of prenatal testing should be completed at 32-36wks?

GBS; repeat CBC

What kind of prenatal testing should be compeleted at 34-40wks?

cervical chlamydia and gonorrhea cultures, HIV, RPR in high-risk pts

What is an amniocentesis?

recommended 15-20wks
consists of transabdominal aspiration of amniotic fluid using an ultrasound guided needle and eval of fetal cells for genetic studies

What are the advantages and disadvantages of an amniocentesis?

Ads

• detects ~80% of open neural tube defects, ~85% of cases of Down syndrome, and ~60% of cases of trisomy 18

Disads

• risks: premature rupture of membranes, chorioamnionitis, and fetal-maternal hemorrhage, which can result in fetal loss (0.5%)

When is an amniocentesis indicated?

• women who will be >35yo at time of delivery

• conjunction w/ an abnormal quad screen

• Rh-sensitized pregnancy to obtain fetal blood type or to detect fetal hemolysis

• to evaluate fetal lung maturity via a lecithin-to-sphingomyelin ratio >/=2.5 or to detect the presence of phosphatidylglycerol (done during the third trimester)

What does FDA Risk Category A suggest of drugs used during pregnancy?

adequate and well-controlled studies in women fail to demonstrate a risk to the fetus in the 1st trimester (and there is no risk in later trimesters). Possibility of fetal harm seems remote.

Ex) Vita B6, Vita E, folic acid (w/in recommended daily allowances)

What does FDA Risk Category B suggest of drugs used during pregnancy?

either animal reproduction studies have not demonstrated risk to the fetus but no adequate and well-controlled studies in pregnant women have been reported, or animal reproduction studies have shown an adverse effect that was not confirmed in controlled studies in women in the 1st trimester (and there is no evidence of risk in later trimesters).

Ex) ampicillin, acetaminophen, buproprion

What does FDA Risk Category C suggest of drugs used during pregnancy?

either studies in animals have revealed adverse effects on the fetus but no controlled studies in women have been reported, or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus

Ex) diphenhydramine, rifampin, AZT

What does FDA Risk category D suggest of drugs used during pregnancy?

positive evidence of human fetal risk exists, but the benefits from use in pregnancy women may be acceptable despite risk

Ex) alcohol, phenytoin, tetracycline

What does FDA Risk Category X suggest of drugs used during pregnancy/

studies in animals or humans have demonstrated fetal abnormalities, or evidence exists of fetal risk based on human experience, or both, and the risk in pregnant women clearly outweighs any possible benefit

Ex) isotretinoin, thalidomide, warfarin

What kinds of fetal defects are assoc w/ ACEIs?

fetal renal tubular dysplasia and neonatal renal failure, oligohydramnios, IUGR, lack of cranial ossification

What kinds of fetal defects are assoc w/ alcohol?

FAS

• growth restriction before and after birth

• MR

• midfacial hypoplasia

• renal and cardiac defects Consumption of >6 drinks per day is assoc w/ a 40% risk of FAS

What kinds of fetal defects are assoc w/ androgens?

virilzation of females; advanced genital development in males

What kinds of fetal defects are assoc w/ carbamazepine?

neural tube defects, fingernail hypoplasia, microcephaly, developmental delay, IUGR

what kinds of fetal defects are assoc w/ cocaine?

bowel atresias, congenital malformations of the heart, limbs, face, and GU tract; microcephaly; IUGR, cerebral infarctions

What kinds of fetal defects are assoc w/ DES?

clear cell adenocarcinoma of the vagina or cervix, vaginal adenosis, abnormalities of the cervix and uterus or testes, possible infertility

What kinds of fetal defects are assoc w/ lead?

increased spontaneous abortion (SAB) rate; still births

What kinds of defects are assoc w/ lithium?

congenital heart disease (Ebstein's anomaly)

What kinds of defects are assoc w/ methotrexate?

increased SAB rate

What kinds of defects are assoc w/ organic mecury?

cerebral atrophy, microcephaly, MR, spasticity, seizures, blindness

What kinds of fetal defects are assoc w/ phenytoin?

IUGR, MR, microcephaly, dysmorphic craniofacial features, cardiac defects, fingernail hypoplasia

What kinds of fetal defects are assoc w/ radiation?

microcephaly, MR, medical dx radiation delivery

What kinds of fetal defects are assoc w/ streptomycin and kanamycin?

hearing loss; CN VIII damage

what kinds of fetal defects are assoc w/ tetracycline?

premanent yellow-brown discoloration of deciduous teeth; hypoplasia of tooth enamel

What kinds of fetal defects are assoc w/ thalidomide?

bilateral limb deficiencies, anotia, microtia, cardiac and GI anomalies

What kinds of fetal defects are assoc w/ Trimethadione and paramethadione?

cleft lip or clef palate, cardiac defects, microcephaly, MR

What kinds of fetal defects are assoc w/ valproic acid?

neural tube defects (spinal bifida); minor cranial defects

What kinds of fetal defects are assoc w/ vitamin A and derivatives?

increased SAB rate, thymic agenesis, cardiovascular defects, craniofacial dysmorphism, microphthalamia, cleft lip, or clef phrase, MR

What kinds of fetal defects are assoc w/ warfarin?

nasal hypoplasia and stippled bone epiphyses, developmental delay, IUGR ophthalmologic abnormalities

What are common sequelae of maternal-fetal infxns?

premature delivery, CNS abnormalities, anemia, jaundice, hepatosplenomegaly, growth retardation

What are the TORCH infxns?

most common pathogens causing maternal-fetal infxns

• Toxoplasmosis

• Other (parvovirus, varicella, Listeria, TB, malaria, fungi)

• Rubella

• CMV

• Herpes

• HIV

• Syphilis

What kinds of animals should pregnant women avoid?

cats
they shouldn't change a cat's litterbox

Which is more common, toxo during the first or third trimester?

1st trimester: less common, more severe
3rd trimester: more common, less severe

How does toxoplasmosis affect pregnant women?

transplacental transmission w/ primary infxn occuring via consumption of raw meat or contact w/ cat feces.
Specific findings: hydrocephalus, intracranial calcifications, chorioretinitis, ring-enhancing lesions on head CT

How does rubella affect pregnant women?

transplacental transmission in the 1st trimester.
Specific findings: purpuric "blueberry muffin" rash, cataracts, MR, hearing loss, patent ductus arteriosus (PDA)

How does CMV affect pregnant women?

most common congenital infxn
primarily transmitted transplacentally
specific findings: petechial rash (similar to "blueberry muffin" rash) and periventricular calcifications

How does herpes affect pregnant women?

intrapartum transmission if the mother has active lesions
Causes skin, eye, and mouth infxns or life-threatening CNS/systemic infxn

How does HIV affect pregnant women?

Transmission can occur in utero, at the time of delivery, or via breast milk
Occurs in 13-39% of births to infected mothers
Combination of AZT tx (prenatally, intrapartum, and neonatally for the first six wks of life) and C-section can lower transmission to 2%.
Newborns w/ congenitally acquired HIV are often ASx, failure to thrive, bacterial infxns w/ common organisms, and an increased incidence of upper and lower respiratory diseases may appear early or may be delayed for months to years. HIV + mothers should not breastfeed

How does syphilis affect pregnant women?

Primarily intrapartum transmission
Specific findings: maculopapular skin rash, lymphadenopathy, hepatomegaly, "snuffles" mucopurulent rhinitis, osteitis
Childhood findings: saber shins, saddle nose, CNS involvement and Hutchinson's traid: peg-shaped upper central incisors, deafness, and interstitial keratitis (photophobia, lacrimation)

What is the definition of SAB?

loss of products of conception prior to the 20th wk of pregnancy.

Approx 60% of chemically evident pregnancies and 15-20% of clinically dx pregnancies terminate in a SAB. More than 80% occur in first trimester

What are the risk factors for an SAB?

Chromosomal abnormalities

Maternal factors

• maternal trauma, increased maternal age, infxn, dietary deficiencies

• inheritied thrombophilias: Factor V Leiden, prothrombin, antithrombin, proteins C and S, methylene tetrahydrofolate reductase (hyperhomocysteinemia)

• immunologic issues: antiphospholipids abs, alloimmune factors

• anatomic issues: uterine abnormalities, incompetent cervix, cervical conization, loop electrosurgical excision procedure, cervical injury, DES exposure, anatomical abnormalities of the cervix

• endocrine issues: DM, hypothyroidism, progesterone deficiency

Environmental factors: Tabacco, alcohol, caffeine, toxins, drugs, radiation

Fetal factors: anatomic malformation

How is SAB dx?

decreasing level of hCG

U/S: identify the gestational sac 5-6 wks from LMP, a fetal pole at six wks, fetal cardiac activity 6-7wks; accurate dating, a small, irregular intrauterine sac w/o fetal pole on transvaginal U/S is diagnostic of abnormal pregnancy

Maternal Rh type should be determined and RhoGAM given if the type is Rh neg

What is included in a normal obstetric exam?

1. Leopold's maneuvers: determine fetal lie (longitudinal or transverse) and if possible, fetal presentation (breech or cephalic)

2. Cervical examination: evaluate dilation, effacement, station, cervical position, cervical consistency. Use Bishop score. Confirm or determine fetal presentation. Determine fetal position through palpation of the fetal sutures and fontanelles. Conduct a sterile speculum exam if rupture of membranes is suspected

What is the Bishop score?

used to evaluate the favorability of delivery and the probability of succeeding w/ an induction. Scoring:
0-4: indicates 45-50% chance of failure. Give prostaglandins for induction
5-9: points to a 10% chance of failure. Give pitocin for induction
10-13: assoc w/ very high probability of success. There is no need for intervention for induction

What are the different types of SAB?

• Complete

• Incomplete

• Threatened

• Inevitable

• Missed

• Septic

• Intrauterine fetal demise

• Recurrent

What is a complete SAB?

POC is expelled. Pain ceases, but spotting may persist.
CLOSED OS
U/S shows empty uterus
POC should be sent to pathology to confirm fetal tissue

No further intervention needed

What is an incomplete SAB?

some POC expelled, bleeding/mild cramping. Visible tissue on exam.
OPEN OS
U/S shows retained fetal tissue

Intervention: manual uterine aspiration (MUA) or D&C

What is a threatened SAB?

No POC expelled. Uterine bleeding +/- abd pain
CLOSED OS
intact membranes, fetal cardiac motion on U/S

Intervention: pelvic rest for 24-48hrs and follow-up U/S to assess the viability of conceptus

What is an inevitable SAB?

No POC expelled. Uterine bleeding and cramps
OPEN OS +/- ROM

Intervention: MUA, D&C, misoprostol, or expectant mgmt

What is a missed SAB?

No POC expelled, No fetal cardiac motion, No uterine bleeding. Brownish vaginal discharge
CLOSED OS
No fetal cardiac activity, retianed fetal tissue on U/S

Intervention: MUA, D&C, or misoprostol

What is a septic SAB?

endometritis leading to septicemia. Maternal mortality is 10-15%
Hypotension, hypothermia, increased WBC count

Intervention: MUA, D&C, IV abx

What is an intrauterine fetal demise?

absence of fetal cardiac activity
Uterus is small for GA; no fetal heart tones or movt on U/S

Intervention: induce labor; evacuate the uterus (D&E) to prevent DIC at GA \>16wks

What is recurrent SAB?

Early pregnancy: often due to chromosomal abnormalities
Late pregnancy: due to hypercoagulable states (SLE, factor V Leiden, protein S deficiency)
Incompetent cervix: should be suspected w/ hx of painless dilation of cervix and delivery of a normal fetus btw 8 and 32 wks

Karyotype both parents. Hypercoagulability work-up in mom. Evaluate for uterine abnormalities

Intervention: surgical cerclage procedures to suture the cervix closed until labor or ROM occurs w/ subsequent removal prior to delivery. Restrict activities

what is the medical procedures for a first trimester therapeutic abortion?

1. oral mifepristone (low dose) + oral/vaginal misoprostol UP TO 49 days GA

2. IM/oral methotrexate + oral/vaginal misoprostol UP TO 49 days GA

3. vaginal or sublingual or buccal misoprostol (high dose), repeated up to three times UP TO 56 days GA

What is the surgical procedure for a first trimester therapeutic abortion?

1. manual aspiration

2. D&C w/ vacuum aspiration

BOTH UP TO 13 wks GA

What is the obstetric mgmt for a second trimester therapeutic abortion?

induction of labor (typically w/ prostaglandins, amniotomy, and oxytocin)
UP TO 13-24 wks GA (depending on state laws)

What is the surgical option for a second trimester therapeutic abortion?

D&E

UP TO 13-24 wks GA (depending on state laws)