Prenatal Care Flashcards
Tests for trisomy 21 and trisomy 18
- Cf-DNA
- First trimester combined test
- Triple screen
- Quad screen
- Sequential screen
- Integrated serum screen
Cf-DNA aneuploidy screen
Cell-free DNA measurement in maternal circulation, thought to be from apoptotic trophoblastic cells (from trophoblastic invasion of endometrial vessels), earliest ~7 wks gestation
This is a highly sensitive (~99%) and specific (~99.8%) test for trisomy 21.
First trimester combined test
- Combination of nuchal translucency on US plus serum PAPP-A and beta hCG
- Can detect trisomy 18 and 21 w/ lower sensitivity than cf-DNA
- First trimester test
Triple screen
- Second trimester serum AFP, hCG, and unconjugated estriol
- Second trimester AND lower sensitivity than most other tests
Quad screen
- Triple screen + Inhibin A
- Also second trimester
- Improves the sensitivity of the triple screen significantly
Sequential screen
- First trimester nuchal translucency and PAPP-A, PLUS
- Second trimester quad screen
- ~93% detection rate for trisomy 21, but still not as sensitive as cf-DNA
Serum integrated screen
- Essentially sequential screen minus nuchal translucency, for when nuchal translucency cannot be assessed.
Most common heritable intellectual disability
Fragile X
Women who need to continue antiepileptic use through pregnancy should take. . .
. . . supplemental folate.
Possible complications of amniocentesis
- 1% risk of miscarriage (higher if before 14 wks gestation)
- Risk of infection
- Risk of amnionic fluid embolism
- Rhesus sensitization
- Increased risk of club foot
Timeframe for amniocentesis vs chorionic villus sampling
- Amniocentesis: After 15 wks gestation
- Chorionic villus sample: Between 11 and 13+6 wks gestation
Interpreting Quad Screen results with relationship to trisomy 21, neural tube defect, and trisomy 18
Note that in the trisomies, AFP is significantly lower
In the neural tube defect, AFP is higher than expected and all other metrics are normal
Following an abnormal non-invasive aneuploidy screening test result, what is the next step in management?
- Invasive diagnostic testing:
- Chorionic villus sampling
- Amniocentesis
Why is the rate of multiple gestation pregnancies increasing as time goes on?
- Increasing average maternal age
- Increased prevalence of assisted fertilization
Risk factors for multiple gestation in a given individual
- Increasing maternal age
- Increasing parity
- FHx of twin pregnancies
- Use of assisted fertility or ovulation techniques
All multifetal gestations infants are at risk of ___, and the effect size of this is proportional to the number of gestations
All multifetal gestations infants are at risk of prematurity, and the effect size of this is proportional to the number of gestations
Complications associated with multiple gestations
- Prematurity
- Preeclampsia
- Congenital abnormalities
- Intrauterine growth restriction
- Placental abruption
Medical complications of multiple gestation pregnancies
- Elevated risk of pre-eclapmsia
- Hyperemesis gravidarum
- Gestational diabetes
- Post-partum depression
When to deliver different chorionicities of monozygotic twins
Note: Mo-mo twins are usually delivered by cesarean section to avoid risk of cord complications. Di-di or Di-mo twins can be delivered vaginally if after 32 weeks eGA, however many will still be delivered cesarean anyway to avoid any other possible complications.
External cephalic version
Guiding an acephalic infant into cephalic position for delivery
Fetal macrosomia
- Fetal mass >4000 g
- Morbidity sharply increases when fetus >4500g
- Causes:
- Maternal: Hx macrosomic pregnancy, excessive pregnancy weight gain, parity, glucose intolerance during pregnancy
- Fetal: Male fetus, Beckwith-Widemann syndrome
- Risks:
- Maternal: Postpartum hemorrhage, vaginal laceration,
- Fetal: Shoulder dystocia, clavicular fracture, lower Apgar score, obesity later in life
- Diagnosis: Combination of fundal height measure and clinical palpation along. Ultasound has high NPV, but poor PPV, so its role is only to rule out macrosomia.
Recommendations regarding delivery of infants w/ fetal macrosomia
- Cesarean section if:
- Fetal weight >5000 g
- Fetal weight >4500 g with diabetes
Fetal growth restriction
- When fetus is <10%ile weight
- Risks:
- Short term: Poor fetal reserve, intauterine failure or failure of delivery
- Long term: Cardiovascular disease, insulin resistance, obesity
- Early onset IUGR has a worse prognosis than late onset due to irreversible changes in early pregnancy (early is hyperplastic growth, late is hypertrophic growth)
Maternal risk factors for early IUGR
- Infection (rubella, CMV, varicella)
- Smoking
- Multiple pregnancies
- Chronic maternal disease
Maternal risk factors for late IUGR
Uteroplacental insufficiency
Uterine artery systolic/diastolic flow
Measured by dopplar ultrasound. Produces a S/D pressure ratio which can be predictive of poor outcomes in intrauterine growth restriction.
Absent or reversed diastolic flow on dopplar is an indication for delivery.
MCA dopplar
Reflects fetal adaptation to poor blood supply (ie, when there is decreased placental perfusion, you should see increased MCA dopplar flow). If MCA flow is normal to decreased in the setting of retrograde diastolic flow on uterine artery ultrasound, this is a very bad sign
Definition of post-term pregnancy
Pregnancy reaching or extending beyond 42 weeks eGA
Definition of late-term pregnancy
Pregnancy that reaches between 41+0 days and 41+6 days
Most common etiology of post-term pregnancy
Inaccurate estimation of eGA
Maternal and fetal complications of post-term pregnancy
- Maternal:
- Increased risk of maternal vaginal trauma
- Increased need for cesarean delivery (w/ inherent risks of infection, bleeding, visceral injury, thromboembolic event)
- Fetal:
- Increased risk of macrosomia
- Post-maturity syndrome
- Meconium aspiration syndrome
- Oligohydramnios
Post-maturity syndrome
- Complicates 10-20% of post-term pregnancies
- Due to aging placenta
-
Decreased subcutaneous fat and lack of vernix and lanugo, resulting in wrinkly, peeling skin and lean body habitus
- Vernix: waxy, cheese-like substance that protects a fetus’s skin while in utero
- Lanugo: Thin, soft, unpigmented, downy hair on the body of a fetus and newborn that functions to hold the vernix to the skin. Replaced by vellus hair a few weeks after birth.
Meconium passage
- Incidence increases w/ prolonged pregnancies
- Risk of meconium aspiration syndrome:
- Severe respiratory distress from mechanical obstruction of small and large airways as well as meconium chemical pneumonitis
Oligohydramnios in the setting of post-term pregnancy
- Rates increase w/ prolonged pregnancies
- Decreased urine production due to shunting of blood away from the kidneys and towards the brain to preserve brain nutrient supply
- Ultimately caused by decreased placental flow in the setting of post-term pregnancy
Membrane sweeping
- Intervention associated with decreased risk of late-term and post-term pregnancies.
- OB provider gently sweeps the amniotic sac away from the uterine wall at the level of the cervix
- Releases prostaglandins that increase the incidence of spotaneous labor
Antepartum surveillance
Begins at 41 weeks given increased risk of intrauterine demise
Induction of labor should occur between 41-42 weeks eGA if spontaneous labor does not occur.
Risk of RhD isoimmunization if Rhogam untreated Rh- mother has a full term delivery with a Rh+ infant
10% at full term
Best way to assess for fetal anemia
MCA flow
Fetal hydrops
Diffuse edema. Every form of effusion you can imagine. Worse than anasarca.
Seen in severe fetal anemias, like alpha thalassemia major and anti-RhoD hemolytic anemia
How do you know how much Rhogam to administer to someone who needs it?
With a Kleihauer-Betke (KB) test!
Measures the amount of fetal blood in maternal circulation.
Lewis antibodies
These are AB!
Don’t worry about these. Occasionally ACOG and USMLE will try to confuse you into thinking that Lewis antibodies are anti-Rh. They are anti-A or anti-B and are IgM, so they have no effect on the fetus.
Ferritin in the amniotic fluid is suggestive of. . .
. . . impending spontaneous pre-term delivery
Bilirubin in the amniotic fluid is suggestive of. . .
. . . fetal hemolytic anemia
How can you treat an infant with hydrops from RhD disease?
Intrauterine intravascular fetal transfusion with matched Rh- blood
Mom is Rh- and her screen picks up antibodies. What is the next step?
Determine dad’s Rh status.
ONLY IF dad’s status is Rh+ would we consider screening the fetus.
Determining how much Rhogam you need
x mL of fetal blood in maternal circulation requires 10x micrograms of Rhogam
Quad screen for Patau syndrome
Just elevation in AFP, all the other markers are normal.
This makes it quite similar to NTD on quad screen.
Quad screen for Turner’s syndrome
Low AFP with very high hCG and inhibin A
Very similar to Down’s, but hCG and inhibin A will be even higher than in someone with Down’s.
Quad screen for Down’s
“What does someone with Down’s say? HI-yA!”
HCG, Inhinbin A are elevated
Everything else is depressed
Quad screen for Edward’s
Low AFP, much like Down’s
However, unlike Down’s, beta hCG will be very low and inhibin A will be normal
NTD on quad screen
High AFP, but normal everything else
Same as Patau’s
“MOM” in reference to alpha fetoprotein
“multiples of median”
2.5 is the upper limit of normal, and anything above this suggests open neural tube defect.
PAPP-A
Pregnancy-associated plasma protein A
Decreased in abnormal pregnancies, such as the three trisomies (21, 18, 13)
First step in management of an abnormal triple or quad screen
Ultrasound to assess whether the EGA is correct and to exclude fetal demise
First step in management if alpha fetoprotein comes back high
High-res ultrasound to assess EGA and for presence of neural tube defect
Amniocentesis to assess amniotic alpha fetoprotein is also an option, however this is more invaisve.
Serum screening “window” for detecting trisomies during pregnancy
15 to 21 weeks
ACE inhibitor teratogenic effects
Fetal renal tubule dysgenesis and resulting oligohydramnios, skull and limb defects, miscarriage
If AFP is found to be elevated, but no etiology is found, the pregnancy is at increased risk for. . .
. . . stillbirth, growth restriction, pre-eclampsia, and placental abruption
For this reason, close following of the pregnancy with serial ultrasounds and BPPs is standard.
Prenatal diagnosis and management of vasa previa
Best made by color Dopplar ultrasound
Management is Cesarean delivery before rupture of membranes
Bleeding with placenta previa vs abruption
Bleeding with placenta previa is usually painless and does not lead to coagulopathy.
Bleeding with abruption is often quite painful, associated with contractions, and may lead to coagulopathy.
Managing placenta previa
- First bleeding is not a huge concern, though it is often the presenting symptom that leads to diagnosis. Often postcoital spotting.
- Expectant management at early stages
- Often, the second or third episodes of bleeding are what force delivery
- The lower uterine segment is poorly contractile, and so postpartum hemorrhage is very common in placenta previa since the spiral arteries are not well compressed
- Cesarean section at 34 weeks best balances the risks of prematurity and the maternal benefit of delivery
What is the order of examinations for a patient at 34 weeks gestation with moderate vaginal bleeding and no uterine contractions
- Ultrasound: to rule out placenta previa
- Speculum exam: to rule out laceration
- Digital exam
If someone has low-lying or maginal placenta previa at 22 weeks, you should plan to. . .
. . . re-assess at 32 weeks
If a placenta previa is marginal or simply low-lying in the second trimester, it may correct itself in the third trimester. A Cesarean section at 34 weeks may not be necessary if the previa has resolved.
Placenta increta and percreta are usually diagnosed. . .
. . . during Cesarean delivery
Why is ultrasound a poor modality for diagnosing placental abruption?
Because coagulated blood has the same sonographic texture as the placenta itself, and it is not possible to dinstinguish them by this modality.
What condition is shown in this image?
Couvelaire uterus
When placental abruption occurs and the bleeding is into the myometrium itself. The discoloration is from coagulated fetal and maternal blood.
Coagulopathy in placental abruption is primarily due to. . .
. . . hypofibrinoginemia
All of the clotting happening within the uterus consumes the body’s fibrinogen stores
An important consequence of this is that fibrinogen can be useful to predict whether or not a patient with abruptio placentae is likely to bleed. Bleeding usually occurs only when fibrinogen is below 150 mg/dL.
Typical management for abruptio placentae
Delivery
Although there is no true contraindication to vaginal delivery, C section is usually performed in order to avoid potential complications.
Most common cause of antepartum bleeding with coagulopathy
Hypofibrinoginemia due to placental abruption
Risk factors for placenta accreta
- Previous uterine scar (from myomectomy, C section, curretage, and in a dose-dependent manner, ie more C sections means more likely to have placenta accreta)
- Placenta previa
- Implantation in the lower uterine segment
- Fetal Down syndrome
- Age > 35 yr
Usual management of placenta accreta
Hysterectomy
Attempts to remove the placenta or to pack the uterus often lead to excess mortality compared to immediate hysterectomy. In a young patient who still desires fertility, this option may rarely be maintained.
Diagnosing placenta accreta
While the clinical definition of placenta accreta is the abnormal adhesion of the placenta to the uterus, the true diagnosis requires histology demonstrating a defect in the decidua basalis.
When the placenta is retained in an otherwise uneventful labor, an obstetrician may attempt a manually extract the placenta by looking for a cleavage plane between the placenta and uterine wall. In placenta accreta, no such cleavage plane is found.
Time window for cf-DNA screen
10 weeks EGA to delivery
If by 41 weeks EGA a patient has still not delivered, then at the 41 week prenatal visit the practitioner should . . .
. . . offer induction
The single most reliable way to assess estimated fetal age
Crown-rump length measurement by ultrasound during first trimester (6 to 12 weeks)
Least invasive mode of therapeutic abortion
Mifepristone and misoprostol
Effective up to 9 weeks EGA
Possible therapies for cervical insufficiency
- Circlage
- Vaginal progesterone (indicated only if previous singleton pre-term infant based on current evidence)
- Abdominal circlage (difficult procedure, significant morbidity, usually last resort)
Dichornionic and monochorionic twins in the case of singleton fetal demise
- In dichorionic twins, the other twin is unaffected
- In monochorionic twins, the other twin will have its blood siphoned into the low pressure cardiovascular system of the failed twin (whose heart is not pumping). It is thus at risk for neurologic injury or stillbirth.
Uric acid in preeclampsia
Prognostic, but not diagnostic
