Reproductive: Obstetrics Flashcards
Menstrual age (AKA gestational age)
Age counting from first day of last menses (embryological age + 14 days, because fertilization is assumed to occur during ovulation)
When does an embryo become a fetus?
After 10 weeks gestation
Menstrual age 0-10 weeks (embryo)
Menstrual age > 10 weeks (fetus)
Vaginal bleeding with a closed cervix in early pregnancy…
Threatened abortion
Cervical dilation in early pregnancy…
Inevitable abortion
Cervical dilation with passage of some products of conception…
Incomplete abortion
Cervix closed without intrauterine products of conception despite documented early pregnancy 1 week prior…
Complete abortion
Missed abortion
When the fetus is dead, but the body does not recognize it (does not try to pass the products of conception), cervix is closed
Positive pregnancy test
Intrauterine gestation
Note: This is the intradecidual sign (small fluid collection covered by echogenic decidua; look for the echogenic stripe of the uterine cavity to pass by the fluid and not stop at it which would suggest just some intracavitary fluid)
Positive pregnancy test
Intrauterine gestation
Note: This is the double decimal sac sign (visualization of both the decidua capsularis, light pink shading, and decidua parietalis, dark pink shading, with a small amount of fluid between, yellow shading)
How can you differentiate an early intrauterine gestation from a small collection of fluid in the endometrial cavity?
Look at the endometrial stripe (which should be continuous and pass right by an intrauterine gestation because those are buried within the endometrium)
Note: If the endometrial stripe stops at a fluid collection, its most likely within the endometrial cavity and not an intrauterine gestation.
What is the first structure visible within the gestational sac?
Yolk sac
What connects the old sac to the embryo?
Vitelline duct
What is the normal size of the yolk sac?
3-6 mm (not larger than 6 mm)
Note: It also shouldn’t be solid or calcified.
What are the layers of the gestational sac?
The embryo is located centrally in the amniotic sac (lined by amnion), which is surrounded by the chorionic space (lined by chorion)
Note: The amnion and chorion typically fuse around 14-16 weeks gestation.
Amniotic band syndrome
When the amnion gets disrupted in the first 10 weeks gestation, allowing the embryo to cross over to the chorionic space where it can get tangled up in fibrous bands resulting in deformities (e.g. limb amputation)
What are these structures?
Arrow: Amniotic sac
White arrowhead: Yolk sac
Black arrowhead: Placenta
Note: This is the “double bleb” sign and the earliest visualization of the embryo (which is flat between the yolk sac and amniotic sac).
When should an embryo be visible on ultrasound?
By 6 weeks gestation
Note: If an embryo isn’t visible by 6 weeks gestation, this is suspicious for pregnancy failure.
When should a yolk sac be visible on ultrasound?
A yolk sac is usually visible by the time the gestational sac reaches 8 mm (on transvaginal imaging)
Anembryonic pregnancy
A gestational sac without an embryo (think very early or non-viable pregnancy)
Pseudogestational sac
A small collection of blood/fluid in the endometrial cavity in the setting of an ectopic pregnancy
Note: This is not a gestational sac, but a fluid collection that looks like one because the ectopic pregnancy is stimulating the decidual endometrium.
What is the most important feature to grade the severity of a subchorionic hemorrhage
The percentage of placental detachment
Note: Hematomas greater than 2/3 the circumference of the chorion has a 2x increased risk of abortion.
Implantation bleeding
A small subchorionic hemorrhage that can cause trace vaginal bleeding when the chorion implants into the endometrium
What ultrasound findings are diagnostic of pregnancy failure?
- Crown-rump length of 7 mm or more and no heartbeat
- Mean sac diameter of 25 mm or more and no embryo
- No heartbeat 2 or more weeks after identifying a gestational sac
- No heartbeat 11 days or more after identifying a yolk sac
Differential for pregnancy of unknown location
- Normal early pregnancy
- Occult ectopic pregnancy
- Complete miscarriage
Note: Recommend serial beta-hCG and follow up ultrasound.
Risk factors for ectopic pregnancy
- Pelvic inflammatory disease
- Tubal surgery
- Endometriosis
- Ovulation induction
- Previous ectopic
- IUD
What is the most common location for an ectopic pregnancy?
Fallopian tube (95%), usually in the ampulla
At what beta-hCG level should you see a gestational sac?
1500-2000 mIU/L
At what beta-hCG level should you see a yolk sac?
~5000 mIU/L
Tubal ring sign
An echogenic rim of Fallopian tube tissue surrounding an unruptred echoic pregnancy
Note: This is ~95% specific for ectopic pregnancy.
Heterotopic pregnancy
When there is both an intrauterine and ectopic gestation
Positive pregnancy test with no intrauterine gestation on ultrasound and a moderate volume of free fluid…
This has a 70% positive predictive value for an ectopic pregnancy (even higher PPV if the free fluid is echogenic)
Positive pregnancy test with no intrauterine gestation on ultrasound and a solid or cystic adnexal structure…
This has a 75-85% positive predictive value for ectopic pregnancy
Note: If there is also moderate free fluid, the PPV increases to 97%.
What are the four measurements of fetal growth taken during second and third trimester ultrasounds?
- Biparietal diameter
- Head circumference
- Abdominal circumference
- Femur length
At what level should the biparietal diameter be measured?
At the level of the thalamus (from the outermost edge of the near skull to the inner table of the far skull)
How would brachycephaly/dolichocephaly change biparietal diameter?
Brachycephaly falsely increases the biparietal diameter
Dolichocephaly falsely decreases the biparietal diameter
Note: Head circumference is less affected by head shape.
At what level should head circumference measurements be taken during second and third trimester ultrasounds?
At the level of the thalamus
Note: It is the circumference of the skull (not including the skin).
At what level should abdominal circumference be measured during second and third trimester ultrasounds?
At the level of the junction of the umbilical vein and left portal vein
Note: This does not include subcutaneous soft tissues.
How should femur length be measured during second and third trimesters?
Longest dimension of the femoral shaft (not including the femoral epiphysis)
How is the estimated fetal weight generated during second or third trimester ultrasounds?
By the machine, based on either:
Biparietal diameter and abdominal circumference
OR
Abdominal circumference and femur length
What is estimated gestational age based on?
First trimester: Crown-rump length (most accurate)
Second/third trimesters: Composite gestational age based on BPD, HC, AC, and FL (less accurate)
How accurate is estimated gestational age?
First trimester: Accurate to 0.5 weeks
Second trimester: Acurate to 1.2 weeks
Third trimester: Accurate to 3.1 weeks
What ultrasound findings are suggestive of intrauterine growth restriction?
- Estimated fetal weights below the 10th percentile
- Femur length:abdominal circumference ratio greater than 23.5
- Umbilical artery systolic:diastolic ratio > 4.0
Estimates fetal weight below the _____ percentile is suggestive of intrauterine growth restriction
Below the 10th percentile
Femur length:abdominal circumference ratio greater than ____ is suggestive of intrauterine growth restriction
FL:AC greater than 23.5
Umbilical artery systolic:diastolic ratio greater than ____ is suggestive of intrauterine growth restriction
Systolic:diastolic greater than 4.0
What is the most common cause of oligohydramnios that develops in the third trimester?
Placental insufficiency
What are the two main categories of intrauterine growth restriction?
- Asymmetric (more common)
- Symmetric
Asymmetric vs symmetric intrauterine growth restriction
Asymmetric IUGR is when there is a normal sized head, but small body (mostly occurs in the third trimester)
Symmetric IUGR is a global growth restriction (does not spare the head, usually present throughout pregnancy)
What are the most salient causes of asymmetric intrauterine growth restriction
- High maternal blood pressure
- Severe malnutrition
- Ehlers-Danlos
Which has a worse prognosis symmetric or asymmetric intrauterine growth restriction?
Symmetric (head and body both small)
Note: This is because the head is not spared (brain doesn’t develop normally). The head is spared in asymmetric IUGR because the body is trying to protect the brain/head.
What are the most salient causes of symmetric intrauterine growth restriction?
- TORCH infections
- Fetal alcohol syndrome/drug abuse
- Chromosomal abnormalities
- Anemia
Where should fetal middle cerebral artery doppler be performed?
At the proximal 1/3 of the vessel
What is the normal spectral waveform of the fetal middle cerebral artery?
High resistance waveform with continuous forward flow (including in diastole)
Note: When the fetal brain becomes hypoxic, there is a brain-sparing reflex that shows up as increased diastolic flow (lower resistance waveform).
Which fetal MCA spectral waveform indicates a problem?
The lower waveform demonstrated increased diastolic flow, which suggests that the brain has experienced hypoxia and initiated the “brain-sparing reflex” that created lower resistance in the MCA (normally fetal MCA flow should be high resistance with low, but still forward, diastolic flow)
What is the best measure of fetal cerebral hypoxia?
Cerebroplacental ratio (ratio of MCA pulsatility to umbilical artery pulsatility)
Note: Cerebral hypoxia leads to a decreased cerebroplacental ratio of < 1.1 because there is decreased MCA pulsatility (due to high MCA diastolic flow from the “brain-sparing reflex”) and increased umbilical artery pulsatility (due to decreased diastolic flow in the umbilical artery from increased placental resistance), creating a lower cerebroplacental ratio.
What is a normal cerebroplacental ratio?
> 1.1
What are the most common causes of fetal anemia?
- Maternal alloimmunization
- Parvovirus infection
Imaging findings of fetal anemia
- Fetal MCA Doppler with increased peak systolic velocities
- Fetal hepatosplenomegaly
Elevated umbilical artery systolic:diastolic ratio…
Think pre-eclampsia or intrauterine growth restriction
What is a normal umbilical artery systolic:diastolic ratio?
2-3 at 32 weeks
At 34 weeks, the ratio should be < 3
Note: The UA S:D ratio should progressively decrease with gestational age (waveform goes from muscle-like to brain-like with higher diastolic flow)
What is the point of a biophysical profile?
To look for acute and chronic hypoxia
How long should you scan for before calling a biophysical profile abnormal?
30 minutes (e.g. if you don’t get normal fetal movement in 30 min you can call it abnormal)
What is a normal score for a biophysical profile?
8-10
Note: You get 2 points for every normal category and 0 for every abnormal category.
What are the components of a biophysical profile?
- Amniotic fluid
- Fetal movement
- Fetal tone
- Fetal breathing
- Non-stress test
What is considered normal amniotic fluid on a biophysical profile?
At least 1 pocket measuring > 2 cm deep in a vertical plane
Note: Failing this is a sign of chronic hypoxia.
Which component of the biophysical profile is the only one that evaluates for chronic hypoxia?
Amniotic fluid
What is considered normal fetal movement on a biophysical profile?
3 discrete movements (within a 30 min period)
Note: Failing this is a sign of acute hypoxia.
What is considered normal fetal tone on a biophysical profile?
1 episode of fetal extension from flexion (within a 30 min period)
Note: Failing this is a sign of acute hypoxia.
What is considered normal fetal breathing on a biophysical profile?
1 episode of “breathing motion” lasting at least 30 seconds (within a 30 min period)
Note: Failing this is a sign of acute hypoxia.
What is considered a normal non-stress test on a biophysical profile?
2 or more fetal heart rate accelerations of at least 15 bpm for 30 seconds or longer (within a 30 min period)
Note: Failing this is a sign of acute hypoxia.
What is the most common cause of fetal macrosomia?
Maternal diabetes (usually gestational, but could be type 2 also)
Major complications of fetal macrosomia
- Delivery complications (e.g. shoulder dystocia, brachial plexus injuries)
- Neonatal hypoglycemia
- Meconium aspiration
Think right-sided Erb’s palsy (brachial plexus upper trunk, C5-C6, injury)
Note: Aplastic/hypoplastic humeral head/glenoid in a kid.
What is injured in Erb’s palsy?
The upper trunk of the brachial plexus (C5-C6)
Note: This is usually caused during delivery with shoulder dystocia (common in fetal macrosomia).
Common causes of oligohydramnios
- Renal dysfunction (not making urine)
- Placental insufficiency
Common causes of polyhydramnios
- GI dysfunction (not swallowing amniotic fluid)
- Maternal diabetes
What is the amniotic fluid index?
A sum of the deepest fluid pocket in each quadrant of the uterus
What is a normal amniotic fluid index?
5-20
Note: AFI < 5 is oligohydramnios and AFI > 20 is polyhydramnios.
Definition of polyhydramnios
Amniotic fluid index > 20
OR
Any fluid pocket deeper than 8 cm
Definition of oligohydramnios
Amniotic fluid index < 5
What should be the distance between the choroid plexus and the medial wall of the lateral ventricle?
Less than 3 mm
Note: Greater than 3 mm indicated ventriculomegaly.
What is the normal width of the fetal cisterna magna?
2 mm - 11 mm
Note If < 2 mm think Chiari II and if > 11 mmm think Dandy Walker.
Measurement is 0.66 cm
Think ventriculomegaly
Note: Choroid plexus-lateral ventricle distance should be less than 3 mm.
Measurement is 1.3 mm
Think Chiari II
Note: Cisterna magna should be 2-11 mm.
Measurement is 13 mm
Think Dandy-Walker
Note: Cisterna magna should be 2-11 mm.
Ultrasound of upper lip
Philtrum of upper lip (normal anatomy, not a cleft lip)
Why is this lung hyperechoic?
Normal finding (on fetal ultrasound, the lungs are usually homogeneously echogenic, similar in appearance to liver)
Fetal ultrasound
Echogenic foci in the ventricles are common on fetal ultrasounds (usually due to normal calcification of papillary muscles)
Note: This is usually a normal finding, but is also associated with Downs syndrome (look hard for other findings).
Two vessel umbilical cord (single umbilical artery)
Note: Normally you should see two arteries adjacent to the bladder.
What is the normal diameter of fetal bowel?
Less than 6 mm
Note: If larger, consider bowel obstruction.
Fetal echogenic bowel (associated with trisomy 21/Down syndrome, CMV infection, and intrauterine growth restriction)
Note: Bowel can be moderately echogenic in the 2nd and 3rd trimester, but should never be more echogenic than bone.
What is the outlined structure in this fetal ultrasound?
Adrenal gland
Note: The adrenal glands are huge in newborns (20x their relative adult size).
Two vessel cord
Note: Normally there should be 3 vessels (2 arteries and 1 vein).
Normal rhombencephalon
Note: The rhombencephalon appears as a cystic structure in the posterior fossa around 6-8 weeks gestation (do NOT call this a Dandy-Walker malformation).
When does physiologic midgut herniation occur?
9-11 weeks gestation
Physiologic midgut herniation (occurs during gestational weeks 9-11)
Note: This is a normal finding (do NOT call this an omphalocele/gastroschesis).
