·
Fetal cardiac
output is approximately 200 mL/kg/min,
whereas an average adult's cardiac output is 70 mL/kg/min.
Fetal oxygen consumption is approximately 8 mL/kg/min,
whereas adult oxygen consumption is approximately 3 mL/kg/min. both are 3 times more than adult.
·
Maternal virilizing tumor during pregnancy (luteoma
of pregnancy): This condition may result in masculinization
of the female fetus. The clinical picture and therapy are similar to those
for the maternal ingestion of androgenic substances. Psychological development
and mental capacity are consistent with chronologic age. Reproductive potential
is not adversely affected, and the patient can become pregnant.
·
Glucose
is transported across the placenta via facilitated transport. Iron is transported via endocytosis.
Amino acids are transported via active
transport. Carbon dioxide passively
diffuses across the placenta.
·
Placenta accreta
refers to the absence of the decidua and the direct
attachment of the placenta to the myometrium.
There is no plane of separation between the placental villi
and the myometrium. It is an important cause of
postpartum hemorrhage because the placenta fails to separate from the myometrium at the time of labor. The hemorrhage can be
life-threatening, and a total hysterectomy is the treatment of choice.
·
In the membranaceous
placenta, all fetal membranes are covered by villi
and the placenta develops as a thin membranous structure. This type of placenta
is also known as placenta diffusa.
·
A delay in fetal
pulmonary maturation is observed in pregnancies complicated by
maternal diabetes or erythroblastosis fetalis. A risk of RDS of 40% exists with an L/S ratio
of 1.5 to 2; when the L/S ratio is <1.5, the risk of RDS is 73%.
When the L/S ratio is >2, the risk of RDS is slight. However, when
the fetus is likely to have a serious metabolic compromise at birth (e.g.,
diabetes or sepsis), RDS may develop even with a mature L/S ratio (>2.0).
This may be explained by lack of PG, a phospholipid
that enhances surfactant properties. The identification
of PG in amniotic fluid provides considerable reassurance (but not
an absolute guarantee) that RDS will not develop. Moreover, contamination of amniotic fluid by blood, meconium,
or vaginal secretions will not alter PG measurements.
·
Fetal malformations are more common with velamentous insertion of the umbilical cord. When fetal
vessels cross the internal os (vasa previa), rupture of membranes may be accompanied
by rupture of a fetal vessel, leading to fetal exsanguination.
An increased risk of premature rupture of membranes and of torsion of the
umbilical cord has not been described in association with velamentous insertion of the cord.
·
Fraternal or DZ twins arise from the fertilization
of two separate ova.
Superfecundation
refers to fertilization of different ova in the same menstrual cycle, at two
separate episodes of intercourse.
Superfetation occurs when
two ova are fertilized during separate menstrual cycles, i.e., the second
ovulation occurred after the first pregnancy was established; this is rare.
·
The incidence of
monozygotic twinning is constant at a rate of one set per 250
births around the world. It is unaffected by race, heredity, age, parity, or
infertility agents.
·
The Kleihauer-Betke (KB) test
will tell you the percentage of fetal cells in the maternal circulation.
Generally we assume that the maternal blood volume is 5 L during pregnancy.
Multiplying your KB result by 5000 cc will give you the amount of fetal blood
in the maternal circulation. For example, a KB of 0.2% should be calculated as
.002 × 5000 = 10 cc of fetal blood. If more than 30 cc of fetal blood has
passed into the maternal circulation, then more than one vial of anti-D
globulin is required.
·
The Liley graph is a plot on
semi-logarithmic paper between the change in optical density at 450 nm (delta
OD450) of the amniotic fluid bilirubin plotted
against gestational age between 27 and 41 weeks. The graph is divided into
three zones. Zone 1 indicates an unaffected fetus, Zone 2 is an affected fetus,
and Zone 3 indicates a fetus that is at risk for intrauterine death. Prior to
27 weeks, data have been published for the extrapolation of the curve.
·
CVS removes placental tissue and has been
associated with increased
risk of limb reduction abnormalities.
·
IUGR is a prenatal
term, whereas SGA is used for neonates.
·
Note that fetal macrosomia is not a contraindication to an attempt at
vaginal delivery following cesarean section.
·
Second-trimester oligogyhydramnios
can lead to fatal pulmonary hypoplasia.
·
The layer of fibrinoid
degeneration between the invading trophoblasts and
the decidua basalis is
called Nitabuch's layer.
·
If there is widespread extravasation
of blood into the uterine musculature and beneath the serosa,
giving the uterus a bluish color at the time of laparotomy,
this is termed a Couvelaire uterus. Such collections of blood
rarely disrupt uterine contraction enough to cause postpartum hemorrhage and
are not an
indication for hysterectomy.
·
In Placenta Abruption, Ischemic necrosis of the kidney may take
the form of acute tubular necrosis (ATN) or bilateral cortical necrosis.
Both ATN and bilateral cortical necrosis are characterized by oliguria or anuria. However,
bilateral cortical necrosis results in death from uremia within 1-2 weeks
unless dialysis is instituted, whereas ATN usually resolves spontaneously.
·
Absent or reversed end-diastolic flow in Doppler velocimetry studies is concerning and warrants inpatient
surveillance or delivery.
·
Fetal heart rate
accelerations signify normal fetal pH and an intact CNS.
·
Decelerations are
characterized based on timing with contractions-early (head compression), late
(uteroplacental insufficiency), variable (cord
compression).
·
The knee-chest
position is sometimes more useful than the left lateral position when there is
a nonreassuring fetal heart rate pattern, especially
a severe variable deceleration.
·
Susceptibility of the conceptus to teratogenic
agents depends on the developmental stage at the time of exposure:
- Resistant period. From day 0 to day 11 of gestation (postovulation), the fetus exhibits the â??all or noneâ? phenomenon with regard to major anomalies.
- Maximum susceptibility (embryonic period). From days 11 to 57 of gestation, the fetus is undergoing organ differentiation and, at this time, is most susceptible to the adverse effects of teratogens.
- Lowered susceptibility (fetal period). After 57 days (8 weeks) of gestation, the organs have formed and are increasing in size. A teratogen at this stage may cause a reduction in cell size and number.
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