Determine whether there is any fetal risk.
• Fetal risk is present only if (1) atypical antibodies are detected in the mother’s circu-lation, (2) antibodies are associated with HDN, (3) antibodies are present at a signifi-cant titer (>1:8), and (4) the father of the baby (FOB) is RBC antigen positive. Fetal blood type may be determined by amniocentesis or percutaneous umbilical blood sampling (PUBS). If the fetus is RBC antigen negative, there is no fetal risk.
• No fetal risk is present if (1) the AAT is negative, (2) antibodies are present but are
NOT associated with HDN, (3) antibody titer is <1:8, or (4) the FOB is RBC antigen negative.
• If the atypical antibody titer is<1:8, management is conservative. Repeat the titermonthly as long as it remains <1:8.
Assess the degree of fetal anemia if the fetus is RBC antigen positive or if fetal blood typing is impossible. This can be done by serial amniocentesis, PUBS, or ultrasound Doppler.
• Amniotic fluid bilirubin indirectly indicates fetal hemolysis because bilirubin accu-mulates as a byproduct of RBC lysis. The bilirubin is plotted on a Liley graph.
• PUBS directly measures fetal hematocrit and degree of anemia.
• Ultrasound Doppler—measurement of peak flow velocity of blood through the fetalmiddle cerebral artery (MCA). As fetal anemia worsens, the peak systolic velocity rises.
This is the procedure of choice since it is non-invasive and has a high correlation with fetal anemia.
Intervene if there is severe anemia. This is diagnosed when amniotic fluid bilirubin is in Lileyzone III or PUBS shows fetal hematocrit to be ≤25% or MCA flow is elevated.
• Intrauterine intravascular transfusion is performed if gestational age is <34 weeks.
• Delivery is performed if gestational age is >34 weeks.
Prevention. RhoGAM is pooled anti-D IgG passive antibodies that are given IM to a pregnantwoman when there is significant risk of fetal RBCs passing into her circulation. The passive IgG antibodies attach to the foreign RBC antigens, causing lysis to occur before the maternal lymphocytes become stimulated.
RhoGAM is routinely given to Rh(D)-negative mothers at 28 weeks, and within 72 h of chori-onic villus sampling (CVS), amniocentesis, or D&C. It is also given within 72 h of delivery of an Rh(D)-positive infant. 300 mcg of RhoGAM will neutralize 15 ml of fetal RBCs or 30 mL of fetal whole blood.
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Rosette test is a qualitative screening test for detecting significant feto-maternal hemorrhage(>10 mL).
Kleihauer-Betke test quantitates the volume of fetal RBCs in the maternal circulation by dif-ferential staining of fetal and maternal RBCs on a peripheral smear. This can assess whether more than one vial of RhoGAM needs to be given when large volumes of fetal–maternal bleed may occur (e.g., abruptio placenta).
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Chapter 8 l Obstetric Complications
PRETERM LABOR
A 24-year-old woman, G2 P1, at 28 weeks’ gestation by dates comes to the birthing unit complaining of regular uterine contractions every 7–10 min. She is a smoker with chronic hypertension. She has had no prenatal care. On examination her fundal height is 35 cm. Her previous pregnancy ended with spontaneous vaginal delivery at 30 weeks’ gestation.
Preterm delivery is the most common cause of perinatal morbidity and mortality. Overall, 12% of pregnancies deliver prematurely. Many patients will have preterm contractions but not be in preterm labor. Three criteria need to be met:
• Gestational age—pregnancy duration>20 weeks, but <37 weeks
• Uterine contractions—at least 3 contractions in 30 min
• Cervical change—serial examinations show a change in dilation or effacement, or asingle examination shows cervical dilation of >2 cm
Preterm Delivery Categories:
• Extreme preterm: <28 weeks
• Very preterm: <32 weeks
• Moderate preterm: 32–24 weeks
• Late preterm: 34–36 6/7 weeks
Risk Factors:
• Most common: prior preterm birth (PTB), short transvaginal (TV) cervical length
<25 mm), PROM, multiple gestation, uterine anomaly
• Others: low maternal pre-pregnancy weight, smoking, substance abuse, and short inter-pregnancy interval <18 months)
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All gravidas should be screened:
• History: previous PTB
• Sonographic cervical length: prior to 24 weeks
Interventions to prevent preterm delivery:
• Singleton pregnancy:
– Weekly IM 17-hydroxy progesterone caproate (17-0H-P) if cervical length >25 mm with prior spontaneous PTB
– Weekly IM 17 -OH-P plus cervical cerclage placement if cervical length <25 mm before 24 weeks with prior PTB
– Daily vaginal progesterone if cervical length <20 mm before 24 weeks but no prior
PTB
• Twin pregnancy: no interventions shown to have any benefit
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OB Triad
Preterm Labor
• Pregnancy 20–36 weeks
• ≥3 contractions in 30 min
• Dilated ≥2 cm or changing
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USMLE Step 2 l Obstetrics
Symptoms. Lower abdominal pain or pressure, lower back pain, increased vaginal discharge,or bloody show. Particularly in primigravidas, the symptoms may be present for a number of hours to days but are not recognized as contractions by the patient.
Fetal Fibronectin (fFN):
fFN is a protein matrix produced by fetal cells that acts as a biological glue binding the tropho-blast to the maternal decidua. It “leaks” into the vagina if PTB is likely and can be measured with a rapid test using a vaginal swab.
• Prerequisites for testing: gestation 22-35 weeks, cervical dilation <3 cm, and mem-branes intact.
• Interpretation: main value of the test is a negative, since the chance of PTB in the next 2 weeks is <1%. With a positive result, the likelihood of PTB is 50%.
Intravenous Magnesium Sulfate for Fetal Neuroprotection:
OB Triad
Preterm Contractions
• Pregnancy 20–36 weeks
• ≥3 contractions in 30 min
• Dilated <2 cm and no change
OB Triad
Magnesium Toxicity
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• Preterm labor tocolysis
• Respiratory depression
• Muscle weakness
Matemal IV MgSo4 may reduce the severity and risk of cerebral palsy in surviving very preterm neonates.
• Start infusion if PTB is anticipated <32 weeks gestation regardless of the anticipated route of delivery.
• It takes 4 hours of infusion to achieve steady state of Mg in the fetus.
Antenatal Corticosteroid therapy:
• A single course of corticosteroids is recommended for pregnant women with gesta-tional age 24–34 weeks of gestation who are at risk of preterm delivery within 7 days.
• A complete course is two IM 12-mg doses of betamethasone given 24 hours apart OR four IM 6-mg doses of dexamethasone given 12 hours apart.
• Neonates whose mothers receive antenatal corticosteroids have significantly lower severity, frequency, or both of respiratory distress syndrome, intracranial hemorrhage, necrotizing enterocolitis and death.
Tocolytic Contraindications. These are conditions under which stopping labor is either danger-ous for mother and baby or futile (makes no difference in outcome). Examples include the fol-lowing:
• Obstetric conditions—severe abruptio placenta, ruptured membranes, chorioamnion-itis.
• Fetal conditions—lethal anomaly (anencephaly, renal agenesis), fetal demise or jeop-ardy (repetitive late decelerations).
• Maternal conditions—eclampsia, severe preeclampsia, advanced cervical dilation.
Tocolytic Agents. Parenteral agents may prolong pregnancy but for no more than 72 h. Thisdoes provide a window of time for (1) administration of maternal IM betamethasone to enhance fetal pulmonary surfactant and (2) transportation of mother and fetus in utero to a facility with neonatal intensive care. Oral tocolytic agents are no more effective than placebo.
• Magnesium sulfate is a competitive inhibitor of calcium. Clinical monitoring is basedon decreasing but maintaining detectable deep tendon reflexes.
– Side effects include muscle weakness, respiratory depression, and pulmonary edema. Magnesium overdose is treated with IV calcium gluconate.
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– Contraindications include renal insufficiency and myasthenia gravis.
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Chapter 8
• b-Adrenergic agonists include terbutaline. Tocolytic effect depends on theb2-adrenergicreceptor myometrial activity.
– Cardiovascular side effects (hypertension, tachycardia) are from b1 receptor cardio-vascular activity. Other side effects are hyperglycemia, hypokalemia, and pulmo-nary edema.
– Contraindications include cardiac disease, diabetes mellitus, uncontrolled hyperthyroidism.
• Calcium-channel blockers decrease intracellular calcium (e.g., nifedipine).
– Side effects include tachycardia, hypotension, and myocardial depression.
– Contraindications include hypotension.
• Prostaglandin synthetase inhibitors decrease smooth muscle contractility by decreas-ing prostaglandin production (e.g., indomethacin).
– Side effects include oligohydramnios, in utero ductus arteriosus closure, and neona-tal necrotizing enterocolitis.
– Contraindications include gestational age >32 weeks.
l Obstetric Complications
OB Triad
Beta Agonists
• Preterm labor tocolysis
• Hypokalemia
• Hyperglycemia
OB Triad
Calcium Channel Blocker
• Preterm labor tocolysis
• Hypotension
• Myocardial depression
Management:
• Confirm labor using the 3 criteria listed earlier.
• Rule out contraindications to tocolysis using criteria listed above.
• Initiate IV hydration with isotonic fluids.
• Start IV MgSo4 for fetal neuroprotection (if <32 weeks) at least 4 hours before antici-pated birth.
• Start tocolytic therapy with terbutaline, nifedipine or indomethacin (if <32 weeks) for no longer than 48 hours to allow for antenatal steroid effect.
• Obtain cervical and urine cultures before giving IV penicillin G (or erythromycin) for group B b Streptococcus sepsis prophylaxis.
• Administer maternal IM betamethasone to stimulate fetal type II pneumocyte surfac-tant production if gestational age is <34 weeks.
Prevention. Weekly intramuscular injections of 17a-OH progesterone caproate starting at20 weeks’ gestation has been shown to decrease preterm deliveries in women with a history of previous idiopathic preterm deliveries.
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