Dr. Chapa’s OBGYN Clinical Pearls

Episode: TWOFER! (Quickie #4): A. Placental Grading, B. GBS Discordant Results
Host: Dr. Smith
Date: March 25, 2026

Episode Overview

This fast-paced "Quickie" episode is a twofer focused on two clinically relevant, real-world conundrums often encountered in OB/GYN practice:

1. Placental Grading—Does it still matter, and what should we do with an incidental grade 3 placenta, especially preterm?
2. GBS Discordant Results—How to handle conflicting Group B Streptococcus (GBS) culture results, particularly in the context of penicillin allergy and intrapartum prophylaxis.

Throughout the episode, Dr. Smith brings a no-nonsense, evidence-driven approach and frequently emphasizes clinical practicality, focusing on what’s relevant for trainees and practicing providers.

1. The Role of Placental Grading (Grade 3 Placenta Preterm)

Segment begins: [05:30]

Background and Historical Practice

• Placental grading, popularized by the Granum classification (grades 0–3), was core training for many clinicians during ultrasound rotations.
• Grade 0: Homogeneous, immature appearance.
• Grade 3: Highly mature with characteristic indentations (cotyledons), septations, and calcifications (“looks like a snowstorm” or “stippling like a breast mammogram”).
• Early belief (1980s–’90s): Preterm grade 3 placentas signaled placental senescence/aging, potentially predicting higher risk for fetal growth restriction, fetal distress, or maternal hypertensive disorders.

Key Insight: Outdated and Unsupported by Current Evidence

• These earlier associations were drawn from retrospective studies, often complicated by existing maternal-fetal pathologies.
• In 2018, a systematic review and meta-analysis (Journal of Perinatal Medicine, Federation of Asia and Oceania Perinatal Society) debunked this:

  “A grade three placenta did not predispose to fetal distress, low APGAR, need for resuscitation, or NICU admission as an isolated standalone finding.” – Dr. Smith [07:54]

• Placental grading “died” in the early 2000s among most practitioners but persists in some radiology reports.

Current Recommendation

• Seeing a grade 3 placenta preterm:
  • No professional society (ACOG/SMFM) recommends any intervention solely for a grade 3 finding.
  • No indication for antepartum fetal surveillance or “serial growths” purely based on grade 3, unless comorbid conditions exist (e.g., hypertension, prior fetal growth restriction, gestational diabetes).
  • Reasonable (but not required) to consider a repeat growth ultrasound in 3-4 weeks as a conservative measure—especially “if the placenta is looking kind of jank.”
• Memorable quote:

  “If you see a grade three placenta at 28 weeks… we’re not going to put you on surveillance… But, you know, it’s fine, it’s reasonable, if the placenta is looking kind of jank, why don’t we just track growth?” – Dr. Smith [10:10]

• Don’t ignore possible comorbid conditions—“look for something else”—but grade 3 alone ≠ action.

Clarification on Fetal Surveillance Thresholds

• Only begin antepartum fetal surveillance if the maternal/fetal/placental condition confers a stillbirth risk exceeding 0.8 per 1,000, matching the false-negative rate of biophysical profile (BPP) testing.

  “If you’re ever asked what’s the cutoff stillbirth risk… to do antepartum fetal surveillance, it’s 0.8 per 1,000.” [14:46]

2. GBS Discordant Results in Pregnancy

Segment begins: [14:46]

Clinical Scenario

• Patient has a GBS rectovaginal swab at 36 weeks—result: positive.
• Penicillin allergy status not assessed ± culture not sent for sensitivities.
• Repeat culture for sensitivities—result: negative.
• Clinical dilemma: Which result “counts”? Does a later negative invalidate the earlier positive?

Key Discussion Points:

• Always ask about penicillin allergy when taking the initial GBS swab—this guides whether to order sensitivities up front.
• The standard of care for GBS screening is culture-based rectovaginal swab; PCR is only a point-of-care option for term patients with unknown GBS status at the time of delivery.

  • “PCR, while very, very good… is not the standard of care… It is still rectovaginal culture-based.” [15:50]

• If cultures conflict, once positive = always positive for the index pregnancy.
  • The negative repeat does not “erase” earlier colonization; colony status is considered valid for ~5 weeks after a positive culture.

    • “That second GBS negative culture does not erase the fact that she was a carrier earlier on. GBS culture is good for five weeks. And yes, it can be transient, so it may be transiently negative now, but it may be positive when she delivers. So once positive, she is positive for that index pregnancy…” [16:58]

• If sensitivities are missing in a penicillin-allergic patient, you may have to default to vancomycin (if high risk) or to alternative agents if not high-risk (consider cephalosporins/Ampicillin if not anaphylactic; clinda only if proven sensitive).

  • “If not a high-risk allergy, then something like an Ancef or Ampicillin could be considered if the patient is okay with that.” [17:56]

• Recent reference: February 2026 New England Journal of Medicine overview echoes this—no big changes, but more awareness.

Notable Quotes & Memorable Moments

• On placental grading:

  “If you’re doing that, you pretty much need to stop because it’s very historic… sometimes some of things that are traditional aren’t really evidence based.” [05:34]

• On what to do with an incidental finding:

  “A grade three placenta is not an indication for delivery. It’s not an indication in and of itself for antepartum fetal surveillance.” [10:43]

• On GBS discordant results:

  “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 to penicillin... or else you have to go directly to vancomycin.” [17:34]

• On clinical decision-making:

  “Having a positive GBS result for the index pregnancy always wins. It does not eliminate that result if it’s redone later. I found that kind of interesting, so I wanted to put that out there.” [18:07]

Key Takeaways & Practical Pearls

Placental Grading

• Placental grading is a historical practice—not a modern standard.
• No evidence that an isolated grade 3 placenta preterm predicts bad outcomes.
• No indication for fetal surveillance unless there are other maternal or fetal risk factors.
• Conservative follow-up with a single growth ultrasound is reasonable but not required.

GBS Testing

• Always check penicillin allergy status when ordering GBS cultures (send for sensitivities as indicated).
• If GBS is ever positive in the index pregnancy, treat as positive throughout.
• If sensitivities aren’t available and patient is high risk for anaphylaxis, treat with vancomycin.
• Recent major OB references (ACOG, NEJM 2026) confirm these standards.

For More: See referenced systematic review (Journal of Perinatal Medicine 2018) and New England Journal of Medicine, Feb 2026—“Group B Streptococcal Disease.”