Fetus & Placenta

·         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.

·         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:

1. 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.
2. 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.
3. 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.

·         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.