Podcast Summary: Dr. Chapa’s OBGYN Clinical Pearls

Episode: TWOFER! (Quickie #4): A. Placental Grading, B. GBS Discordant Results

Date: March 25, 2026
Host: Dr. Smith

Overview

This quickie “twofer” episode delivers succinct, evidence-based insights on two real-world OB/GYN clinical dilemmas:

1. Placental Grading: Is it still relevant and what should you do if a preterm patient has a grade 3 placenta on ultrasound?
2. GBS Discordant Results: Management strategies when Group B Strep (GBS) cultures yield conflicting results in pregnancy, particularly with penicillin allergy in play.

Dr. Smith uses a conversational, relatable tone while sharing recent evidence and practice recommendations relevant for medical trainees and clinicians.

1. Placental Grading: Does It Still Matter?

Segment Start: [05:34]

Historical Background

• Placental grading—particularly using the Granum classification (grades 0-3)—was once a widely taught marker in ultrasound training ([05:34]).
  • Grade 0: Homogeneous “snowstorm” placenta, immature.
  • Grade 3: Highly mature, calcified with well-defined cotyledons and septations (“little mountains”).
• The thinking: Early grade 3 (≤34 weeks) implied placental senescence/aging, correlating with increased risk for fetal growth restriction (FGR), distress, and preeclampsia—based on retrospective studies from the 1980s/1990s ([06:25]).

Evidence Update

• 2018 Systematic Review & Meta-Analysis: “To Ignore or Not to Ignore Placental Calcifications on Prenatal Ultrasound”
  • Published in the Journal of Perinatal Medicine ([10:55]).
  • Key finding: Isolated grade 3 placenta does not independently predispose to fetal distress, low Apgar scores, NICU admission, or adverse outcomes.
  • “A grade three placenta may be found with other maternal comorbidities, but in and of itself means nothing.” ([08:55])
• Current Guidelines:
  • ACOG & SMFM have no recommendations for serial growth scans or antepartum fetal surveillance based solely on a preterm grade 3 placenta.
  • Surveillance is only warranted if another risk factor or maternal/fetal/placental pathology raises the stillbirth risk above 0.8 per 1,000 (the false negative rate for biophysical profiles) ([12:55], [14:48]).
    • “A grade three placenta is not an indication for delivery. It's not…an indication in and of itself for antepartum fetal surveillance, but it's reasonable to look for some maternal comorbidities.” ([11:30])

Practical Pearls

• Findings should not be ignored:
  • Reasonable to review for comorbidities (hypertensive disorders, abnormal growth, etc.).
  • Optional: Consider growth ultrasound in 3–4 weeks if concerned, even though not protocolized ([12:30], [14:48]).
• Notable Quote:
  • “If you see a grade three placenta at 28 weeks, even though it's not really a thing and there's no professional guidance, I think it's fine…to track growth and let that be the determining factor.” ([11:15])
  • “Oh, hell, what does that matter? It can matter because the placenta is jank, especially under 30 weeks, you don't want to ignore a potential problem.” ([12:10])
• Bottom Line:
  • "Not a standalone risk factor for adverse neonatal issues. …You can document it. I think that's reasonable…But you don't necessarily have to do surveillance." ([14:48])

2. GBS (Group B Strep) Discordant Results: Which Counts?

Segment Start: [15:42]

Clinical Scenario

• Patient at 36 weeks: Initial GBS rectovaginal culture positive, but sensitivities not requested (penicillin allergy), so sample repeated—second culture negative ([00:47], [15:42]).
  • Dilemma: Which result determines GBS status for delivery management?

Guideline-Based Approach

• Gold Standard for GBS:
  • Rectovaginal culture around 36 weeks.
  • PCR-based testing is not standard for routine screening. Used if a woman presents in labor with no available culture result ([03:13], [16:10]).
• Key Rule:
  • “If that index pregnancy has a positive GBS in any count…that pregnancy is GBS colonized. That's it.” ([17:01])
  • “That second GBS negative culture does not erase the fact that she was a carrier earlier on.” ([17:33])
  • GBS colonization status holds for five weeks; late pregnancy results considered valid for peripartum management ([17:33]).
  • Why so conservative? GBS is “so devastating to the newborn in the early neonatal interval…” ([17:10])

Penicillin Allergy Protocol

• Always clarify the type of allergy when collecting GBS cultures—rash, anaphylaxis, etc ([15:48]).
• If positive for GBS & penicillin allergy:
  • Ideally, send culture for sensitivities during initial collection.
  • Without sensitivities:
    • Vancomycin is the default if high-risk allergy or sensitivities unknown.
    • Clindamycin only if sensitivity proven; otherwise, not advised.
    • Ancef/ampicillin may be used for non-anaphylactic/low-risk reactions ([18:25]).
• Notable Quote:
  • “So yes, having a positive GBS result for the index pregnancy always wins. It does not eliminate that result if it's redone later.” ([19:02])
  • “This is why always ask the patient if she has a penicillin allergy so you can get it with that index culture that first time.” ([17:50])

Recent Evidence

• February 2026, New England Journal of Medicine: “Group B Streptococcal Disease”
  • Reiterates existing best practices—no change to culture-based approach ([16:44], [18:45]).

Key Takeaways

Placental grading

• No longer evidence-based for independent prenatal risk prediction.
• Isolated grade 3 at <34 weeks:
  • Not an indication for increased surveillance or delivery.
  • Reasonable to consider growth scan if additional clinical suspicion.
• Always review for comorbidities; surveillance only if additional risk factors.

GBS discordant results

• Once positive in a pregnancy, always positive—even if repeat is negative.
• Positive GBS status should determine peripartum antibiotics strategy.
• In penicillin allergy, sensitivities should be requested with initial culture.

Memorable Quotes

• On placental grading:
  • “Well, if you're doing that, you pretty much need to stop because it's very historic…sometimes some of the things that are traditional aren't really evidence based.” ([05:47])
  • “It is not an indication for delivery. It's not…for antepartum fetal surveillance, but it's reasonable to look for some maternal comorbidities.” ([11:30])
• On GBS repeat tests:
  • “Once positive, she is positive for that index pregnancy and not having sensitivities, then we either have to be comfortable that she doesn't have high risk anaphylactic reaction…If not, you got to go to vancomycin.” ([17:46])

Notable Timestamps

• [05:34] Placental grading: Historical context and definitions
• [10:55] 2018 systematic review — grade 3 placenta not predictive of adverse outcome
• [12:30] Reasonable but non-mandatory follow-up for grade 3 finding
• [14:48] Stillbirth risk thresholds for initiating antepartum fetal surveillance
• [15:42] GBS: Clinical case and pitfalls of discordant results
• [17:01] “Once positive, always positive” rule explained
• [18:25] Penicillin allergy—implications for GBS management

Tone and Style

Dr. Smith maintains an upbeat, conversational tone, blending humor (“Oh, hell, what does that matter?”) and practical advice (“why don’t we just track growth and let that be the determining factor”). The focus remains solidly on evidence and actionable steps, always returning to what is pragmatic for clinicians.

Bottom Line (For Busy Providers)

• Placental Grading: Document, consider growth scan only if warranted—do NOT use as a sole trigger for surveillance or intervention.
• GBS Culturing: Any positive result = treat as positive all the way through delivery; repeat negatives do not reverse this. Sensitivities matter in allergic patients—get them up front.

This episode exemplifies high-yield, no-nonsense clinical reasoning, providing clear protocols for dilemmas that still arise in daily OB practice.