5.2 Placental Disorders, Bleeding in Pregnancy & Isoimmunization
Key Takeaways
- Ectopic pregnancy typically presents with abdominal pain, amenorrhea, and vaginal bleeding; a beta-hCG above the discriminatory zone with an empty uterus on ultrasound is diagnostic.
- Placenta previa presents as painless, bright red vaginal bleeding in the third trimester; digital vaginal exams are strictly contraindicated until ultrasound rules it out.
- Placental abruption involves painful, dark red bleeding with a hypertonic, woody uterus and is heavily associated with maternal hypertension and trauma.
- Rh-negative, unsensitized mothers must receive Anti-D immune globulin at 28 weeks and within 72 hours of delivering an Rh-positive infant to prevent alloimmunization.
- Middle cerebral artery (MCA) Doppler peak systolic velocity is the preferred non-invasive test to detect fetal anemia in sensitized Rh pregnancies.
Placental Disorders, Bleeding in Pregnancy & Isoimmunization
Obstetrical hemorrhage remains a leading cause of maternal and fetal morbidity and mortality. Any vaginal bleeding during pregnancy requires rapid, methodical clinical evaluation. On the SMLE, candidates are expected to differentiate causes of early pregnancy loss (ectopic, spontaneous abortion, gestational trophoblastic disease) from late pregnancy bleeding (placenta previa, placental abruption, vasa previa) and master protocols for Rh alloimmunization prevention.
First-Trimester Bleeding & Early Pregnancy Complications
Vaginal bleeding affects approximately 20-25% of pregnancies in the first trimester. Immediate diagnostic priority is ruling out ectopic pregnancy.
Ectopic Pregnancy
- Definition & Anatomy: Extrauterine implantation of a fertilized ovum. Over 95% occur in the fallopian tube (most commonly the ampulla).
- Clinical Triad: Amenorrhea, pelvic/abdominal pain, and vaginal bleeding.
- Diagnostic Algorithm:
- Quantitative Serum beta-hCG: The discriminatory zone is the beta-hCG level above which an intrauterine pregnancy (IUP) should be visible on transvaginal ultrasound (TVUS) (typically 1,500 to 2,000 mIU/mL).
- Transvaginal Ultrasound (TVUS): If beta-hCG is above the discriminatory zone and TVUS demonstrates an empty uterus, ectopic pregnancy is highly probable. Identification of an adnexal mass or ectopic gestational sac confirms diagnosis.
- Management:
- Medical Management (Methotrexate): Folate antagonist. Candidates must be hemodynamically stable, compliant, with an unruptured adnexal mass <3.5-4.0 cm, no fetal cardiac activity, and baseline serum beta-hCG <5,000 mIU/mL. Relative contraindication: Presence of fetal cardiac motion.
- Surgical Management: Indications include hemodynamic instability, signs of tubal rupture (peritonitis, fluid in pouch of Douglas), contraindications to Methotrexate, or failed medical therapy. Options: Laparoscopic Salpingostomy (fertility-preserving) or Salpingectomy (removal of tube; preferred if severe damage or uncontrolled bleeding).
Spontaneous Abortion (Miscarriage) Categories
Defined as involuntary pregnancy loss prior to 20 weeks of gestation (or fetal weight <500 grams).
| Classification | Vaginal Bleeding | Cervical Os Status | Ultrasound & Tissue Findings | Management Protocol |
|---|---|---|---|---|
| Threatened Abortion | Present (mild/spotting). | CLOSED | Viable intrauterine fetus with positive cardiac activity. | Reassurance, expectant management, pelvic rest. |
| Inevitable Abortion | Present (moderate/heavy). | OPEN | Products of Conception (POC) at or near os; no tissue passed yet. | Medical (Misoprostol) or Surgical (D&C/D&E). |
| Incomplete Abortion | Present (heavy + clots). | OPEN | Partial expulsion of POC; retained tissue remaining in uterus. | Suction Curettage or Misoprostol to clear retained tissue. |
| Complete Abortion | Minimal/subsiding. | CLOSED | Complete expulsion of all POC; empty uterine cavity. | Observational follow-up; monitor beta-hCG drop. |
| Missed Abortion | Absent or brownish discharge. | CLOSED | Non-viable fetus (no fetal cardiac activity) retained in utero. | Medical (Mifepristone + Misoprostol) or D&C. |
| Septic Abortion | Foul-smelling purulent discharge. | OPEN (usually) | Retained POC + systemic infection (fever, leukocytosis, peritonitis). | Broad-spectrum IV Antibiotics (Ampicillin + Gentamicin + Clindamycin) + Urgent D&C. |
Gestational Trophoblastic Disease (Hydatidiform Mole)
- Complete Mole (46,XX): Fertilization of an empty egg by a single sperm that duplicates. No fetal tissue. Marked by markedly elevated beta-hCG (>100,000 mIU/mL), hyperemesis gravidarum, early preeclampsia (<20 weeks), and hyperthyroidism. TVUS: Classic "snowstorm" pattern or "bunch of grapes".
- Partial Mole (69,XXX / 69,XXY): Fertilization of a normal egg by two sperm. Fetal tissue present.
- Management: Suction curettage followed by weekly quantitative serum beta-hCG monitoring until undetectable for 3 consecutive weeks, then monthly for 6 months. Strict contraception mandatory during monitoring to rule out progression to Gestational Trophoblastic Neoplasia (Choriocarcinoma).
Late Pregnancy Bleeding (Antepartum Hemorrhage - APH)
Antepartum hemorrhage is defined as vaginal bleeding occurring after 20 weeks of gestation. The two major causes—Placenta Previa and Placental Abruption—must be rapidly differentiated.
Placenta Previa vs. Placental Abruption
| Feature | Placenta Previa | Placental Abruption (Abruptio Placentae) |
|---|---|---|
| Pathophysiology | Placenta implants over or adjacent to the internal cervical os. | Premature separation of a normally implanted placenta from uterine wall. |
| Bleeding Character | Painless, bright red blood. | Painful, dark red blood (may be concealed behind placenta). |
| Uterine Tone | Soft, non-tender, relaxed uterus. | Tender, rigid, hypertonic ("woody") uterus. |
| Fetal Distress | Usually absent initially (unless maternal shock). | Common & Severe (fetal bradycardia, late decelerations). |
| Associated Risk Factors | Prior C-section, prior previa, multiparity, advanced maternal age. | Maternal Hypertension / Preeclampsia, Cocaine use, Smoking, Abdominal trauma. |
| Maternal Complications | Severe hemorrhage, placenta accreta spectrum. | Disseminated Intravascular Coagulation (DIC), hypovolemic shock. |
| CRITICAL Management Rule | NO DIGITAL VAGINAL EXAM until ultrasound rules out previa! | Rapid resuscitation; urgent C-section if fetal distress present. |
| Definitive Management | Pelvic rest; scheduled Cesarean delivery at 36-37 weeks. | Emergent delivery if maternal/fetal compromise; trial of labor if stable & term. |
Vasa Previa
Catastrophic condition where fetal blood vessels cross the membranes over the internal os unsupported by placenta or cord. Presentation: Painful or painless bleeding immediately following rupture of membranes (spontaneous or artificial), rapidly followed by severe fetal bradycardia or sinusoidal heart pattern. Cause: Fetal exsanguination. Treatment: Emergent STAT Cesarean section.
Rh Isoimmunization (Alloimmunization)
Occurs when an Rh-negative mother (lacking D antigen) carries an Rh-positive fetus. Fetal red blood cells cross into maternal circulation (fetomaternal hemorrhage), inducing maternal anti-D IgG antibody production. In subsequent Rh-positive pregnancies, maternal IgG anti-D antibodies cross the placenta and destroy fetal RBCs, leading to Hemolytic Disease of the Fetus and Newborn (HDFN), severe fetal anemia, Hydrops Fetalis (high-output heart failure, pericardial effusion, ascites, edema), and intrauterine fetal death.
Prevention Protocol (RhoGAM / Anti-D Immune Globulin)
Anti-D immune globulin neutralizes fetal Rh-positive RBCs before the maternal immune system can generate antibodies.
- Routine Administration: Given to ALL unsensitized Rh-negative women at 28 weeks of gestation.
- Postpartum Dose: Administered within 72 hours of delivery if the newborn is confirmed to be Rh-positive.
- Indication for Extra Doses: Administered following any potential fetomaternal hemorrhage event (e.g., miscarriage, ectopic pregnancy, amniocentesis, CVS, abdominal trauma, external cephalic version, antepartum bleeding).
- Kleihauer-Betke (KB) Test: Quantifies the volume of fetomaternal hemorrhage to calculate if additional doses of RhoGAM beyond the standard 300 mcg dose are required.
Management of Sensitized Rh-Negative Pregnancies
If maternal Anti-D antibody titer is positive and critical (≥1:16), RhoGAM is ineffective. Fetal monitoring is mandatory:
- Non-Invasive Standard of Care: Doppler ultrasound assessment of Middle Cerebral Artery (MCA) Peak Systolic Velocity (PSV). Elevated velocity reflects hyperdynamic circulation driven by fetal anemia.
- Treatment: If severe anemia is detected, Intrauterine Blood Transfusion (IUT) via umbilical vein under ultrasound guidance.
A 30-year-old G3P2 at 32 weeks of gestation presents to the emergency department with sudden-onset, severe abdominal pain and dark red vaginal bleeding. On examination, the uterus is firm, tender, and hypertonic. Fetal heart rate monitoring reveals a baseline of 165 bpm with recurrent late decelerations. Which of the following is the most likely diagnosis?
A 24-year-old G1P0 at 8 weeks of gestation presents with vaginal spotting and mild pelvic cramping. Her cervical os is closed on examination. Transvaginal ultrasound shows a viable intrauterine gestation with a normal fetal heart rate. What is the most appropriate management?
An Rh-negative, unsensitized 29-year-old G2P1 woman at 28 weeks of gestation is seen in the clinic. Her first child is Rh-positive. She has had an uncomplicated pregnancy thus far with no vaginal bleeding or trauma. What is the next best step in her management regarding Rh isoimmunization?