Sep 30, 2026 03:14pm

By Sabina Gaspirc

Under Fertility

5 min read

Antivirals and Pregnancy: What You Need to Know

It's the happy time of finding out you're pregnant (or planning to become), but there are surely questions that comes to mind when you're throwing your herpes diagnosis in. So, let's go when are you recommended in taking the antivirals during pregnancy.

Please note that we are not doctors - these are general guidelines for antivirals in pregnancy.

Another note - antivirals are never a must. It's your decision. They are recommended to take during the last few weeks in pregnancy and the benefit is in our opinion, totally worth it. Alexandra took them in her second pregnancy, despite not feeling the best afterwards. But the benefit outweighed the risk.

But when it comes to 'regular' outbreaks during pregnancy, you don't need to take them, if you don't want to. Some women experience a lot more outbreaks than before when they are in their 1st, 2nd or 3rd trimester. It's nothing to worry about - it's your hormones that are acting in a different way.

Ok, let's dig in.

Why Consider Antivirals in Pregnancy

The main concern with herpes during pregnancy is neonatal herpes—a rare but serious infection that can be passed to a baby during vaginal delivery if the mother has an active outbreak.

Here's the risk breakdown:

Primary infection (first-ever outbreak) near delivery: 30% to 50% risk of transmission to the baby
Recurrent herpes with active lesions at delivery: 1% to 3% risk
Recurrent herpes with suppressive therapy and no active lesions: substantially lower risk

The goal of antiviral therapy in pregnancy is simple: prevent outbreaks around the time of delivery, so you can have a safe vaginal birth and protect your baby.

General Guidelines: Suppressive Therapy

If you have a history of genital herpes, major medical organizations recommend suppressive antiviral therapy starting in late pregnancy.

Standard Recommendations (ACOG & CDC)

Start at 36 weeks of gestation
Continue until delivery
Typical doses:
- Acyclovir 400 mg three times daily
- OR Valacyclovir 500 mg twice daily

Note: Because pregnancy increases kidney clearance, the doses used for suppressive therapy in pregnancy are higher than those for non-pregnant women.

Updated UK Guidelines (2024)

In the UK, the BASHH/RCOG guidelines were updated to recommend starting suppressive therapy earlier—at 32 weeks instead of 36 weeks. This is because 23% of neonatal herpes cases occur between 32 and 36 weeks.

For women at significantly higher risk of preterm delivery, the guidelines recommend starting as early as 22 weeks.

What If You Have a First Episode During Pregnancy?

A first-episode (primary) genital herpes infection during pregnancy is treated differently because the risk to the baby is higher.

First Trimester or Second Trimester

You'll receive treatment-dose antivirals for the acute episode
Then you'll start suppressive therapy at 36 weeks

Third Trimester

You'll receive treatment-dose antivirals (acyclovir 400 mg three times daily or valacyclovir 1,000 mg twice daily for 5–10 days)
Continuing antiviral therapy until delivery may be considered
Cesarean delivery may be offered because of the possibility of prolonged viral shedding, even if lesions have resolved

Are Antivirals Safe During Pregnancy?

Yes. The data is reassuring.

No increased risk of birth defects: Studies have not found an increased chance of birth defects with acyclovir or valacyclovir, including over 1,500 exposed infants reviewed
No increased risk of miscarriage: Studies have not found an increased chance of miscarriage
No increased risk of preterm delivery: Clinical case reports have not reported increased chances of preterm delivery

Acyclovir has the most pregnancy safety data—it's been studied extensively and is considered the first-line choice. Valacyclovir is also considered safe and is commonly used.

Important note: The background risk of birth defects in any pregnancy is about 3%. Taking antivirals does not appear to increase this risk.

Delivery Planning

Vaginal Delivery (Recommended When...)

No active genital lesions or prodromal symptoms (tingling, burning, pain) at the time of labor
You've been on suppressive therapy

Cesarean Delivery (Recommended When...)

Active genital lesions or prodromal symptoms are present at the time of labor
You've had a primary or first-episode infection in the third trimester (may be offered even if lesions have resolved)

What About Lesions on the Thigh or Buttock?

Vaginal delivery is still recommended. These nongenital lesions can be covered with an occlusive dressing, and you can give birth vaginally.

Important: Membrane rupture duration does not eliminate the indication for cesarean if active lesions are present.

A Note on Routine Screening

Routine herpes screening of all pregnant women is not recommended. The U.S. Preventive Services Task Force reaffirmed a Grade D recommendation against routine serologic screening in 2023, as harms outweigh benefits.

However, if you have symptoms or a known history, testing and treatment are absolutely appropriate.

Key Takeaways

Suppressive therapy from 36 weeks (or 32 weeks in the UK) is standard for women with a history of genital herpes
Antivirals are safe in pregnancy—decades of data show no increased risk of birth defects
First-episode infections in the third trimester carry the highest risk and may require cesarean delivery
If you have no active lesions at delivery, vaginal birth is safe
Talk to your healthcare provider early—they can help you create a plan that's right for you and your baby

Years ago, when Alexandra was pregnant with her first baby, she interviewed her OBGYN, and this interview is such a great way to get some information and reassurance about your decisions.

INTERVIEW WITH OBGYN

Footnotes

https://mothertobaby.org/fact-sheets/acyclovir-zoviraxvalacyclovir-valtrex-pregnancy/#1#1 https://podcasts.apple.com/ng/podcast/when-data-gaps-exist-ob-hsv-suppression/id1412385746?i=1000779099638

https://www.guidelinecentral.com/guideline/308315/#1