When Data Gaps Exist: OB HSV Suppression?

Summary

Podcast Summary:

Dr. Chapa’s OBGYN Clinical Pearls – “When Data Gaps Exist: OB HSV Suppression?”
Released: July 30, 2026
Host: Dr. Chapa
Audience: Medical students, residents, and practicing healthcare providers

Episode Overview

Theme:
Dr. Chapa addresses a practical and clinically relevant question: With current guidelines recommending initiation of antiviral suppression for genital herpes simplex virus (HSV) at 36 weeks gestation, what should clinicians do for patients scheduled for a medically indicated early delivery (e.g., at 37 weeks)? The episode explores where gaps exist in the data and offers evidence-based, logical guidance for best practice when official recommendations are silent.

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Key Discussion Points & Insights

1. Current Guidelines and Their Limitations

• ACOG Recommendations:

  • Antiviral suppression with valacyclovir or acyclovir should start at 36 weeks for individuals with a history of genital HSV ([01:06]).
  • This guidance, originating from Practice Bulletin #82 in 2007 and reaffirmed in Practice Bulletin #220, assumes the patient will deliver at or after term (39–41 weeks).
  • There is no guidance on the minimum effective duration of therapy prior to delivery ([03:20]).
  • "It's not like you take Valtrex immediately and levels drop of HSV shedding immediately. It takes days to do that." (Dr. Chapa, [05:34]).

• Origin of Current Guidelines:

  • Based on three major studies:
    • Watts (2003)
    • Sheffield & Wendell (RCT, 2006)
    • Andrews (2006)
  • In these studies, suppression began at 36 weeks (following guidance), but most study patients delivered at least two weeks or more after starting antiviral medication ([03:50], [08:53]).

2. The Clinical Dilemma: Early Delivery and “Data Gaps”

• Key Question:
  • “What if we have a patient with a history of genital HSV who needs a 37 week medical induction?” ([02:40])
  • Is one week of antiviral suppression enough?
• Data Gap:
  • No published minimum required duration in guidelines or referenced studies.
  • Most trial participants had at least two weeks (and up to five) of antiviral use prior to delivery.
  • "There is nothing about a minimum time of use in ACOG's current guidance or in its original language. It just says, hey, start at 36 weeks." (Dr. Chapa, [05:34])
  • Pharmacokinetic data show it takes about three days to reach steady-state antiviral levels in the serum, but maximal suppression may require longer ([08:53]).

3. Primary vs. Remote HSV Infection: Special Considerations

• Primary First-Episode HSV Infection:
  • For primary first-episode HSV infection in the third trimester (28 weeks+), best practice is:
    • Start antiviral therapy at the time of outbreak and continue through delivery.
    • Consider, via shared decision-making, offering a primary cesarean section due to higher neonatal HSV risk ([06:48]).
  • "If you have a primary first episode in an OB patient in the third trimester... start on a medication at the time of the outbreak so she feels better and then continue that all the way through to delivery." ([06:35])
• Shared Decision-Making:
  • For third-trimester primary outbreaks, discuss possibility of primary cesarean section, as risk is higher and patient should be fully informed ([07:13]).

4. Practical Recommendations on Antiviral Timing for Early-Induction Cases

• Key Takeaways:

  • While starting at 36 weeks is "reasonable in the mass majority of cases," a planned 37-week induction may only provide one week of suppression ([08:53]).
  • "It is totally okay to do that... However, in those pivotal trials, patients had a minimum of two weeks of suppression." ([08:53])
  • No harm in starting earlier; no increased safety concerns with slightly longer antiviral exposures.

• Dr. Chapa's Clinical Pearl:

  • Best practice (in absence of explicit guidance):
    • For scheduled deliveries at 37 weeks, start suppression at 35 weeks to ensure at least two weeks prior to delivery ([09:50]).
    • “Probably two weeks is much better control at ensuring viral suppression... than just a one week span.” ([10:36])
  • Though one week may be "fine," there’s no evidence that such a short course is as effective as what was proven in landmark studies ([10:57]).

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Notable Quotes & Memorable Moments

• “Sometimes there's gaps in the data and we're like, I don't really know what to do with that, but it would make most sense to do this. That's where you get typical and reasonable practice that informs standard of care.”
  — Dr. Chapa ([01:18])

• “All I'm trying to say, guys, and I'm going to do this quick because again, this is all based on logic and based on pharmacokinetics... If you're going to have an induction at 37, I would recommend based on the best logical deduction of the evidence starting at 35.”
  — Dr. Chapa ([09:50])

• “How about that? Isn't that fascinating? So thank you to Autumn, our fantastic resident who brought that up. These are things that you don't really think about, but then you get this in your next clinic patient, and then the question comes up…”
  — Dr. Chapa ([12:36])

• “Michael, let's just end this. We're going to see you all in the next episode of the no Spin podcast. Michael, let's take it home.”
  — Dr. Chapa, wrapping up with humor ([13:31])

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Timestamps for Key Segments

• 01:06 – 03:50: History of HSV suppression recommendations in pregnancy; key studies and guideline origins.
• 05:34 – 08:53: Gaps in current ACOG guidance; pharmacokinetics and real-world clinical challenges for early induction.
• 06:35 – 07:45: Management of primary vs. remote HSV infection in pregnancy; shared decision-making for primary cases.
• 08:53 – 10:36: Logic and data synthesis around minimum duration for suppression; evidence-based recommendation for starting earlier in early induction cases.
• 12:36 – 13:17: Clinical “answer” and summary: Begin HSV suppression at least two weeks before planned delivery.

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Summary Table: Practical Approach

| Scenario | Start HSV Suppression At | |-----------------------------------------------------|-----------------------------| | Usual care, expected term delivery (39–41 wks) | 36 weeks | | Planned early delivery (e.g., 37 weeks) | 35 weeks (get ≥2 weeks use) | | Third trimester, primary first episode HSV | At outbreak – continue thru delivery; discuss cesarean |

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Conclusion

Dr. Chapa’s Clinical Pearl:
When planning early delivery (e.g., 37 weeks) in patients with a history of genital HSV, it is safest and most consistent with the original evidence to start antiviral suppression two weeks in advance (at 35 weeks), even though current guidelines are silent about minimum duration. There is no additional risk with longer use, and “best logical deduction” supports erring on the side of more sustained suppression for optimal results.

This is another example of “filling in the data gap” with reasoning, available evidence, and real-world pharmacology—ensuring both patient safety and adherence to the spirit of evidence-based practice.

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Maintaining Dr. Chapa’s engaging, conversational, and evidence-focused tone throughout.

Transcript

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[Michael]

What do I Do now?

[Dr. Chapa]

Hank Medical guidelines are great because they're very directive, although they don't cover all scenarios like we're going to talk about here. But they do give us some insights to guide us in into best practice. That's the way it should be. However, and we've said this before in other episodes, sometimes there's gaps in the data and we're like, I don't really know what to do with that, but it would make most sense to do this. That's where you get typical and reasonable practice that informs standard of care. All right, now we've mentioned this in the past where ironically, and it's kind of non intuitive, that you would think that standard of care would sometimes follow best practice based on the guidance and but sometimes we don't have guidance and you kind of have to make your own best practice. We're going to touch on that in this episode. We're going to talk about OB HSV viral suppression. Okay, now we know what to do with that. ACOG says and has said since 2007, in a patient with genital HSV, start antiviral suppression with either valacyclovir or acyclovir starting at 36 weeks. Now that makes the assumption that those patients are gonna deliver at full term. I mean, it does. It doesn't give a minimum time of when that medication should be started to get steady state in order to reduce that viral transmission and viral shedding. Okay, you all follow this. Now remember, this goes all the way back to 2007. That was ACOG's first bulletin on the management of herpes in pregnancy and that was really in full formed and directed by three main studies. That was the Watt study in 2003. That was Jean Sheffield. She was phenomenal. She was a fellow when I was a resident. She. And she taught me. She's amazing. Jean Sheffield, in 2006 with the RCT, with Dr. George Wendell, published that data that yes, taking Valtrex or an antiviral medication starting at 36 weeks reduces, but doesn't eliminate. Okay, let's not fool ourselves. It doesn't eliminate HSV shedding or the need for C section, but it does greatly reduce those possibilities. And then there was the Andrews trial also in 2006. All of those went into the shaping of practice bulletin number 82 back in 2007. Now this has been reaffirmed by the college Back in Practice Bulletin 220. So it's a thing, right? The 36 week rule for HSV medication and for suppression. We know what to do with that. That's a no brainer. The question is, what if we have a patient with a history of genital HS also happens to need a 37 week medical induction like for a hypertensive disorder, pregnancy. Y' all get this, right? Is that one week use of antiviral medication, whatever your flavor is, you can do acyclovir or valacyclovir. Is that one week enough? There is no guidance on this. So let me tell you again, this is why we're calling this when data gaps exist. But even though there's no specific guidance on it, we can draw conclusions from pharmacokinetic studies and give a reasonable best practice here to inform standard of care. So let me be very clear. Nothing wrong with starting this at 36 weeks. That is guidance. And doing it for at least one week. However, in those trials that we mentioned, the Watts, Sheffield and Andrews publications, patients had a minimum of two weeks of suppression. You see that? So that's interesting because now we have a gap in the data. But we're going to make it clear and we're going to fill in that gap in the. What did I say? That gap in the data. Did I just mess up those words? Oh my goodness. We're gonna fill the gap in the data. That was weird. And so that we don't. Next time we have this, we don't have to say this.

[Michael]

What do I do now, Hank?

[Dr. Chapa]

I don't know who Hank is, but I found that interesting and funny. What do I do now, Hank? We're gonna deliver at 37 weeks. There's a gap in the data.

[Michael]

What do I do now, Hank?

[Dr. Chapa]

I think I've set it up enough or going to answer that question. Is one week of antiviral suppression for HSV enough? If we're planning an early medically indicated delivery, or should we likely start that medication sooner? We're going to get into it coming up next. We're just trying to fulfill our life calling and our mission. This is Dr. Chapa's OBGYN no Spin podcast. All right, Mike, we can't get any stupider on this show. Let's do that one more time. One more time.

[Michael]

What do we do now, Hank?

[Dr. Chapa]

All right, so now that we've covered that nonsense, let's get to the data. There is nothing about a minimum time of use in ACOG's current guidance or in its original language. It just says, hey, start at 36 weeks. Because she's probably going to deliver, you know, sometime around 39 weeks or so. But it doesn't say how long that should take to be effective. It's not like you take Valtrex immediately and levels drop of HSV shedding immediately. It takes days to do that. It has to reach stead state and then keep the medication in use to keep suppression at bay. To keep suppression in effect, rather. So there is a gap here. And then one of my residents actually brought this up. It's an interesting point. Hey, we have a patient who's going to be 37 week induction, but she has history of HSV genitally. Should we actually start this at 36 weeks or start before gap in the data? All right, now this is for the patient who has a remote history of genital hsv. Let me just make this caveat on the side. If a patient has first episode primary herpes, first episode primary, that means she comes in with a lesion. She's like, something hurts down there, you swabby, swabby. It comes back out, the PCR returns as HSV, you know, whatever, type 2. And you're like, okay, so you've got herpes and your antibody that you draw at the same time, because that's when you draw serum antibodies to correlate with a lesion, and those are negative. That's called primary first episode. Right? So if you have a primary first episode in an OB patient in the third trimester, so 28 weeks and beyond, it is best practice to start on a medication at the time of the outbreak so she feels better and then continue that all the way through to delivery. Because those patients have a much higher risk of suppression compared to somebody who has a remote history of genital Herpes. All right, so that's not what we're talking about here. We're talking about a patient who has a remote history, maybe has it for two to three years or longer. And this is just about starting prophylactic routine suppression. Okay. Oh, also, by the way, for any patient who has a primary first episode HSV in the third trimester, some make the case, although it's not standard. You don't have to do this. But it is shared decision making with a patient to offer a primary C section for that very reason, because they have a very high rate of shedding. You don't have to do that, but you have to discuss it with the patient because if something happens, the patient shouldn't be able to come back and say, you never told me about a C section. So primary first episode in the third trimester, start suppression at the time of the outbreak and continue all the way through and offer as shared decision making the possibility of primary elective C section. Just because the rate of shedding is so high in those cases, because the shedding lasts for weeks after the initial outbreak.

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[Dr. Chapa]

So all to say is While starting at 36 weeks is reasonable in the mass majority of cases, the practical issue is that what if you have a 37 week induction that only leaves one week time for medication to be used. Now it is totally okay to do that. As we said in the intro, the pharmacokinetics say that while it takes about three days for steady state and then continuance and thereafter to maintain that a week is probably fine. However, if we want to be true to the data, which we've already referenced before, the Watts Jean Sheffields and then the Andrews publication, that's not what happened those patients. And by the way, it's not like they had, oh, you need to take this for a minimum of this time, then deliver. No, they just started at 3.6 and then patients delivered. But in those cohorts, the vast majority delivered at 38 weeks or beyond, meaning they had anywhere from two weeks at a minimum up to five weeks because some patients delivered at 41 weeks of use. So significantly more than the one week duration. Do you all get this? Guys, isn't this fascinating? So again, let's just rephrase this here. Rephrase this here. There's a patient who has genital herpes. She's going to be out at 37 weeks. Guidelines say to start at 36 weeks. Is that enough? Maybe. But that's not reflected in the main data pieces that informed the original practice bulletin when it came out in 2007. Right. Watts, Sheffield and Andrews. So if we take a look at those and we can then infer that the minimum time used in those which the medication did work to suppress viral transmission and reduce the need for C section for herpetic indications, it was two weeks of use. All I'm trying to say, guys, and I'm going to do this quick because again, this is all based on logic and based on pharmacokinetics of this and those three main publications that went into the practice bulletin. If you're going to have an induction at 37, I would recommend based on the best logical deduction of the evidence starting at 35, it is possibly okay to just let her on at one week of suppression. But there is no safety or risk with doing Valtrex for longer. Remember, if a patient has primary first episode at 28 weeks, she's going to take that all the way through until the delivery anyway. It's not a harmful medication. Now, can you start before the two weeks for sure, but probably two weeks is much better control at ensuring viral suppression and reducing the risk of shedding than just a one week span. I really wish that ACOG's practice bulletin on management of HSV in pregnancy said, hey, we don't really have a minimum time of use, but it would seem reasonable based on pharmacokinetic data and those studies published. But it doesn't get into that much detail. All right, so what's the clinical implication here for a 37 week induction? We're gonna start wrapping this up. While one week is likely enough, it is definitely a shorter duration than what was studied in in those pivotal trials. Now, while acyclovir and valacyclovir do achieve therapeutic levels relatively quickly, there's no direct evidence that says that that shorter duration provides equivalent reduction in viral shedding as what was seen in those trials because those patients delivered longer than a week after exposure. Okay, so again, we're doing this because we're getting ready, obviously launching into the fall and Abog applicants are going in for their oral boards. This is a great question. I mean, this is a good one to ask as an oral examiner is how. What is the minimum time necessary to reach suppression? The answer is, well, we don't really know. I mean, it goes up fast in the serum. It does work relatively quickly, but there was no minimum set in any of the guidelines or in the trials. But we're gonna be true to the trials. Those patients received at least two weeks, some longer, up to five weeks of medication. So it would be safest to to start earlier since there is no concern for safety or risk of exposure with these medications. How about that? Isn't that fascinating? So thank you to Autumn, our fantastic resident who brought that up. And something. These are things that you don't really think about, but then, you know, you get this in your next clinic patient, and then the question comes up, what

[Michael]

do I do now, Hank?

[Dr. Chapa]

Well, Hank, we've answered that question for you. You should probably start at least two weeks prior to planned delivery. Podcast family, as always, we're thankful for you. We're glad you're part of our podcast community.

[Michael]

What do I do now, Hank?

[Dr. Chapa]

That is so stupid. Michael, let's just end this. We're going to see you all in the next episode of the no Spin podcast. Michael, let's take it home. This is Dr. Chapma's OBGYN no Spin podcast. Sam.