Isoimmunization, Multifetal Gestation & Fetal Growth Abnormalities Flashcards
1
Q
What is the average “menstrual or gestational” age of a developing fetus?
A
40 weeks (FDLMP to due date)
2
Q
What is the average gestational age for twins?
A
35 weeks
3
Q
What is the average gestational age for triplets?
A
33 weeks
4
Q
What is the average gestational age for quadruplets?
A
29 weeks
5
Q
What are the common complications of preterm delivery?
A
- low birth weight
- respiratory distress syndrome
- neurologic impairment
- intraventricular hemorrhage
- necrotizing enterocolitis
- retinopathy of prematurity
6
Q
What are the complications of multiple gestations?
A
- preterm complications
- fetal growth restriction
- preeclampsia/gestational DM
- abruptio placentae
- rupture of membranes leading to preterm delivery.
- congenital anomalies
- cerebral palsy
7
Q
On what day after ovulation does the zygote (blastocyst) implant in the endometrial lining?
A
day 8
8
Q
With what does maternal blood come into direct contact?
A
the CHORION
9
Q
** What 2 layers comprise the sac that the baby grows in?
A
- INNER AMNION (water bag).
- OUTER CHORION
10
Q
*** What are DIZYGOTIC twins?
A
- twins resulting from two separate fertilizations by two genetically dissimilar sperm with 2 genetically dissimilar oocytes.
- aka you get 2 genetically different babies (FRATERNAL twins).
11
Q
*** How are the membranes arranged for DIZYGOTIC twins?
A
- each has their own INNER AMNION and OUTER CHORION.
* Dichorionic-Diamniotic placentation!
12
Q
*** What are MONOZYGOTIC twins?
A
- twins resulting from ovulation and fertilization of a SINLGE OOCYTE with subsequent division (cleavage) of the zygote.
- aka IDENTICAL twins
13
Q
** What determines the membrane division of monozygotic twins?
A
the TIMING of zygote cleavage.
14
Q
** Are dizygotic twins ALWAYS dichorionic-diamniotic?
A
YES!!!
15
Q
*** What is the placentation result of zygote cleavage (MONOZYGOTIC twins) within 4 days of fertilization, while still in the fallopian tube?
A
- dichorionic-diamniotic
16
Q
** What is the placentation result of zygote cleavage (MONOZYGOTIC twins) between days 4-8 after fertilization (typically while the blastocyst is in the uterine cavity)?
A
- MONOchorionic-diamniotic
17
Q
If you do an ultrasound and see a MONOchorionic-diamniotic placenta, what do you absolutely know?
A
- babies are 100% MONOZYGOTIC twins
* aka identical twins
18
Q
If you do an ultrasound and see a dichorionic-diamniotic placenta, what do you know?
A
- babies could be either dizygotic or monozygotic.
19
Q
** What is the placentation result of zygote cleavage (MONOZYGOTIC twins) between days 8-12 after fertilization?
A
- MONOchorionic- MONOamniotic
* these babies have a higher rate of cord entanglement and complications.
20
Q
*** What happens if zygote cleavage (MONOZYGOTIC twins) occurs after day 13 (after formation of the bilaminar disc)?
A
conjoined twins :(
21
Q
*** Are all monochorionic twins identical?
A
YES
22
Q
*** Are all dichorionic twins always dizygotic?
A
NO, could be monozygotic if division occurs within 4 days of fertilization.
23
Q
*** Are all dizygotic twins always dichorionic?
A
YES
24
Q
*** Can monochorionic twins be dizygotic?
A
NEVER, these are always identical twins.
25
Are most twins di- or mon-zygotic?
- most are dizygotic
26
What type of placentation are most MONOzygotic twins?
- 65%= MONOchorionic-diamniotic
- 34%= dichorionic-diamniotic
- 1%= MONOchorionic-MONOamniotic
27
**** How do you tell chorionicity/amnionicity?
1. count the # of placentas (if 2, then DC; if 1, then DC or MC).
2. check gender (if different, then DC; if same, then DC or MC)
3. check for LAMBDA SIGN= as two chorions come together they form a triangular appearance on US which is an intervening membrane that separates the 2 babies (always dichorionic-diamniotic).
4. check for T-SIGN= no triangle appearance like lambda sign, but membrane goes straight in and is more consistent with monozygotic (MONOchorionic-diamniotic) preganancy.
5. check membrane thickness (dichorionic-diamniotic makes a THICK membrane; MONOchorionic-diamniotic makes a THIN membrane, usually less than 2 mm).
28
If you don't see an intervening membrane on US, but do see 2 separate yolk sacs, what can you infer about placentation?
- MONOchorionic-diamniotic
29
What can you infer if you see 2 embryos, with 1 yolk sac on US?
- MONOchorionic-MONOamniotic
30
What is considered advanced maternal age?
age 33= increased risk of fetal aneuploidy (down syndrome).
31
Is the likelihood of having a baby with down syndrome in a trichorionic-triamniotic pregnancy the same parental age as a parent with a singleton pregnancy?
NO, age drops to 28
32
What is used more now instead of amniocentisis?
- analyze the fetal DNA in the maternal serum :)
33
What is the management of dichorionic-diamniotic twins?
- US every 4-6 weeks
- serial nonstress testing during 3rd trimester (weekly)
- deliver by 38 weeks
34
What is twin-to-twin transfusion syndrome (TTTS)?
- abnormal blood vessel connections in the placenta allow blood to flow unevenly between the babies; occurs in MONOchorionic-diamniotic twins
35
If one baby dies in a MONOchorionic-diamniotic or MONOchorionic-MONOamniotic, is there a risk of neurologic impairment (cerebral palsy) of the surviving twin?
YES
36
What is the management of MONOchorionic-diamniotic twins?
- US every 2 weeks to rule out TTTS.
- US every 4 weeks to evaluate interval fetal twin growth.
- serial nonstress testing during 3rd trimester
- deliver by 34-36 weeks
37
What is the management of MONOchorinoic-MONOamniotic twins?
- US every 2-3 weeks
- come in daily for 4 hours for fetal non-stress monitoring.
- deliver at 32 weeks via cesarean section (give MgSO4 and dexamethasone to reduce complications).
38
What is the most common variety of conjoined twins?
- thoracopagus, followed by omphalopagus
39
Do most conjoined twins spontaneously miscarry?
YES
40
What are the complications of an incompatible blood transfusion?
- hemolysis
- renal failure
- shock
- death
41
What is the most common blood type?
O+
42
**** What is the INDIRECT antiglobulin test (IAT)? (TEST QUESTION)
- maternal antenatal antibody screen
| * aka how a pregnant mom is evaluated to determine whether or not she has antibodies to her RBCs or Rh
43
What happens if a mother is Rh- and the fetus is Rh+?
if the RBCs cross the placenta, the antibodies can attack the Rh+ RBCs of the fetus causing hemolysis, anemia, heart failure, and even death of the fetus.
44
What is Rh sensitization?
- in the first pregnancy of an Rh- mom with an Rh+ dad, the mom is exposed to the Rh + factor of the baby for the first time during delivery, causing her to develop antibodies to this Rh factor antigen. First baby is fine.
- in the second pregnancy of an Rh+ baby, the mother's IgG antibodies will cross the placenta and attack the fetal RBCs causing erythroblastosis fetalis (rhesus sensitization).
45
In what does erythroblastosis result?
- hemolysis
- hyperbilirubinemia (due to lysis of RBCs= bilirubin).
- fetal anemia
- high output heart failure
- pallor
- hepatosplenomegaly
46
**** What is RHOGAM (Anti-Rh(D) immunoglobulin)?
- medication that prevents the maternal immune system from recognizing fetal Rh+ RBCs.
- give at 28 weeks gestation to Rh- moms and then again (within 72 hours) to mother after delivery if baby is Rh+.
47
When does Rh sensitization occur?
- delivery (vaginal or cesarean section).
- prenantal diagnosis (CVS or amniocentesis).
- blunt trauma to gravid abdomen (ex. car accident).
- antenatal hemorrhage
- ectopic pregnancy
- vaginal bleeding
48
What is the first thing we do at a mother's first prenatal appointment?
- ABO blood type and INDIRECT Coombs (IAT) antibody screen.
| - If Rh- and no evidence of sensitization, then she is managed as a routine pregnancy.
49
Do we give RHOGAM if mother is already sensitized?
NO, because this is just to prevent sensitization.
50
In the event of a fetal-maternal hemorrhage, will one dose of RHOGAM (anti-Rh(D) immunoglobulin) prevent Rh sensitization?
YES :)
51
What will the Rosette test tell you after delivery?
- tests for significant amount of fetal-maternal hemorrhage (more than 30 cc's).
52
What must you also do if Rosette test is +?
perform Kleihauer-Betke stain= tells you how much fetal blood is in the maternal circulation
53
What do we do if the mom is already Rh sensitized?
- titrate the amount of Rh antibodies in her serum (ex. 1:1 not bad, but 1:56 is bad).
54
What is the critical Rh titer?
- the level at which the mother is significantly sensitized that she may be producing enough antibodies to cause fetal anemia from fetal hemolysis.
* 1:16 is typical critical level
55
What must we do once the critical Rh(D) antibody level is reached?
- determine father's (paternal) zygosity.
- if he's heterozygous, then perform amniocentesis to evaluate fetal Rh(D).
- if he's homozygous, then fetus is at risk
56
What happens as a result of fetal anemia do to Rh sensitization of the mother?
- blood viscosity increases, causing the heart to pump harder (increasing CO and velocity).
57
How do we evaluate blood viscosity?
- US color doppler of middle cerebral artery to calculate peak systolic velocity.
58
How many vessels are in an umbilical cord?
2 arteries and 1 vein usually.
59
**** What do we do if the fetus is anemic?
- intrauterine vascular TRANSFUSION of 80% packed RBCs
60
Are there other minor RBC antigens and antibodies?
YES. If mom has any of these, we follow her the same way we would follow Rh disease= titer testing every 4 weeks until 24 weeks, and then every 2 weeks thereafter (or until she hits the critical threshold).
61
Is there any medication to prevent anemia from a minor RBC antigen?
NO, only for Rh disease.
62
What is fetal/neonatal alloimmune thrombocytopenia?
- mom has antibody against a platelet antigen that the father has given to the fetus. The fetus can spontaneously bleed and die.
63
**** How do you manage minor RBC antigen problems? (TEST QUESTION)
- you can do in vitro fertilization by transferring only those embryos that don't have the minor antigen (only if father is HETEROZYGOUS).
- if HOMOZYGOUS, then you can use a gestational carrier, but make sure the mom carrying the baby doesn't have antibody against the minor antigen.
64
What is the average fetal (embryonic age) age?
- 38 weeks (266 days)
65
What is Naegle's rule for assessment of gestational age?
FDLMP - 3 months + 7 days= due date
66
What can you do after 20 weeks of pregnancy to evaluate fetal size?
- measure the maternal abdomen (FUNDAL HEIGHT in cm from the pubic symphysis correspond to number of weeks pregnant).
Ex. 28 cm = 28 weeks pregnant.
67
What is Leopold's maneuver?
- way to assess the size of the baby and fetal presentation.
* not very accurate
68
How does US in OB compare to other US modalities?
- 2-12 million cycles/sec compared to normal US of 20,000 cycles/sec
69
How does US work?
- by applying an electrical potential to Piezoelectric crystals in the US transducer (probe) that causes crystals to mechanically deform, and this deformation results in formation of an acoustic wave.
- each piezoelectric crystal functions as both a transmitter and receiver of mechanical energy.
- the piezoelectric crystal waits to receive the returning echoes, which it converts back to electrical energy.
- display of these returning electrical signals (echoes) creates images.
70
*** How does frequency of US compare to wavelength?
the higher the frequency the shorter the wavelength, and the greater the image resolution (but lower penetration).
*OB uses 2-12 MHz
71
Does oligohydramnios make US easier or harder?
- harder, because US waves go more easily through fluids, an oligohydramnios has little fluid around the fetus.
72
What is the timetable for US visible structures in a developing fetus?
- 4.5-5 weeks= gestational sac.
- 5 weeks= yolk sac within that sac.
- 5.5-6 weeks= cardiac activity and embryo (measurable crown rump length).
73
When do you change the "due date" based on US discrepancy with FDLMP?
- if less than 9 weeks, must have 5 days or more difference in US date.
- if 9-14 weeks, must have 8 days or more difference.
74
What is the most accurate measure for dating by US?
- crown rump length measurement (CRL)
75
**** What do we use to estimate fetal size and date when baby is at 14-22 weeks gestational age?
1. HEAD CIRCUMFERENCE (most predictive US parameter at this point).
2. biparietal diameter
3. abdominal circumference
4. femur length
76
**** What US measurement is best for evaluating gestational age in the third trimester?
FEMUR LENGTH
77
What is fetal macrosomia?
- large fetus (4500 grams) and morbidity significantly increases.
78
**** What are the major complications of fetal macrosomia? (TEST QUESTION)
- shoulder dystocia= the anterior shoulder of the infant cannot pass the pubic symphysis, leading to brachial "Erb-Duchenne" palsy.
- neonatal hypoglycemia
- metabolic syndrome
- impaired glucose tolerance and obesity.
79
What is the amount of time that you should delivery a baby after the head is out?
- 5 mins max
80
**** What are the risk factors for fetal macrosomia?
- DM (because the placenta makes hormones that make her carbohydrate intolerant, leading to the fetus's response of increased insulin production, which acts as a growth factor).
- prior Hx of fetal macrosomia
- weight gain prior to or during pregnancy
- multiparity (babies tend to get larger for subsequent pregnancies).
- male
- ethnicity
- gestation greater than 40 weeks.
- positive 1 hr glucose tolerance test (GTT) with normal 3 hour GTT.
81
What are the maternal risks of fetal macrosomia?
- protracted/arrested labor
- operative vaginal delivery (forceps for vacuum assisted).
- Cesarean delivery
- genital tract lacerations
- postpartum hemorrhage
82
**** How do you manage fetal macrosomina? (TEST QUESTION)
- AVOID operative vaginal delivery (FORCEPS, VACUUM)
- consider elective CESAREAN SECTION if over 5,000 grams or 4,500 (with DM).
- consider cesarean section for fetuses with small head circumference/abdominal circumference (HC/AC ratio).
83
What is fetal growth restriction?
small baby (less than 10th percentile).
84
What does growth velocity (fetal abdominal growth of less than 10 mm over 2 weeks) reflect?
- decreased abdominal adipose tissue and decreased hepatic size related to decreased glycogen storage in the liver.
85
Does perinatal mortality go up as birth weight goes down?
YES
86
Why do we look at the fluid when a fetus is not growing well?
- amniotic fluid is fetal urine. If the baby is not being appropriately oxygenated, the kidneys are not being adequately perfused, and are therefore making less urine (amniotic fluid)= BAD.
87
What happens when the placenta is not functioning well?
- it becomes progressively more difficult for the baby to get blood flow back to the placenta so that it can be adequately re-oxygenated.
* do a doppler eval of the umbilical artery to see how difficult it is (resistance of blood flow) for the baby to get blood flow back to the placenta.
88
Are most babies under the 10th weight percentile normal?
YES, but 20% are pathologic.
89
Of the 20% of pathologic cases of babies under the 10th weight percentile, what are the causes?
- 75%= extrinsic (placental)
| - 25%= intrinsic (chromosomal, infection, anomaly).
90
Is there less vascularization of the maternal bed to the placenta in fetal growth restriction or pre-eclampsia?
YES
91
**** What happens if the fetus is not getting adequate oxygenation due to fetal growth restriction?
it shunts blood flow to the brain, causing increased end diastolic velocity. This can be evaluated with doppler of the middle cerebral artery!
