STI Testing During Pregnancy: What You Need to Know

STI testing during pregnancy is a standard part of antenatal care in the UK. For the majority of women, pregnancy is a healthy and straightforward experience, and routine screening is offered as a precautionary measure to support the wellbeing of both mother and baby.

Many women are surprised to learn that certain sexually transmitted infections are screened for as part of their initial antenatal blood tests. This is not because infection is expected — it is because early identification, where relevant, allows appropriate management well before delivery.

Most infections detected during pregnancy can be managed effectively, and many women with treated infections go on to have entirely healthy pregnancies and deliveries. The purpose of screening is reassurance and early action, not alarm.

This guide explains which STI tests are routinely offered in UK pregnancy care, why testing matters, and what happens if a result is positive. It also covers situations where additional private testing may be considered.

Is STI Testing Routine During Pregnancy in the UK?

Yes. As part of standard NHS antenatal care, several blood-borne infections are screened for during early pregnancy. These tests are typically offered at the booking appointment, which usually takes place between 8 and 12 weeks of pregnancy.

The routine antenatal blood screening panel in the UK includes:

• HIV — all pregnant women in the UK are offered HIV screening. Uptake is high, and routine testing has been instrumental in reducing mother-to-child transmission to very low levels
• Syphilis — screening for syphilis is included in the standard antenatal blood panel. Syphilis can be effectively treated during pregnancy if detected early
• Hepatitis B — screening identifies women who carry the hepatitis B virus, allowing preventive measures to be offered to the baby after birth

Chlamydia screening is not universally included in antenatal blood tests but may be offered depending on age, risk factors, or local screening programmes. In England, the National Chlamydia Screening Programme targets sexually active individuals under 25.

It is important to note that NHS antenatal screening is thorough and well-established. Private STI testing is not a replacement for this pathway but may be considered as an additional option in certain circumstances.

Why STI Testing Matters During Pregnancy

STI testing during pregnancy is recommended because some infections, if left undetected and untreated, have the potential to affect the pregnancy or the health of the newborn. However, the level of risk varies considerably depending on the infection, the stage of pregnancy, and whether treatment is provided.

Key points to understand:

• Some infections can be transmitted from mother to baby — this can occur during pregnancy, during delivery, or, in some cases, through breastfeeding. The likelihood depends on the specific infection and whether it has been identified and managed
• Early detection allows timely management — most bacterial STIs can be treated safely during pregnancy with appropriate antibiotics. Viral infections such as HIV can be managed with antiviral therapy to significantly reduce the chance of transmission
• Many women with treated infections have healthy pregnancies — a positive test result does not mean that complications are inevitable. With appropriate care, outcomes are generally very positive

The aim of screening is not to cause anxiety but to ensure that any infection is identified early enough for effective management.

Which STIs Are Most Relevant During Pregnancy?

Not all STIs carry the same implications during pregnancy. The following infections are considered most clinically relevant in the context of antenatal care.

Chlamydia

Chlamydia is one of the most common bacterial STIs in the UK. In many cases, it produces no symptoms. If chlamydia is present and untreated at the time of delivery, there is a possibility that it can be passed to the baby during vaginal birth, potentially causing eye or respiratory infections in the newborn.

Chlamydia can be treated safely during pregnancy with a course of antibiotics. Testing is straightforward and usually involves a urine sample or swab.

Gonorrhoea

Gonorrhoea is less common than chlamydia in the UK but carries similar considerations during pregnancy. If untreated at the time of delivery, gonorrhoea can affect the newborn's eyes — a condition known as ophthalmia neonatorum. This is preventable with appropriate treatment before or at the time of birth.

Like chlamydia, gonorrhoea can be treated with antibiotics during pregnancy.

HIV

All pregnant women in the UK are offered HIV screening as part of routine antenatal care. If HIV is detected during pregnancy, antiviral treatment can be started promptly. With effective treatment, the risk of mother-to-child transmission is reduced to very low levels — in many cases below 1%.

Management of HIV in pregnancy involves close collaboration between sexual health specialists and obstetric teams. Decisions about delivery method and infant feeding are made on an individual basis.

For more information about recognising HIV, see our guide on early symptoms of HIV.

Syphilis

Syphilis screening is a routine part of antenatal blood testing in the UK. If syphilis is detected and treated early in pregnancy, the risk to the baby is significantly reduced. Untreated syphilis during pregnancy can, in some cases, lead to complications — which is precisely why routine screening is offered.

Treatment with antibiotics is safe and effective during pregnancy.

Herpes

Genital herpes (HSV) is most relevant in the context of pregnancy if active lesions are present near the time of delivery. If a woman has a first episode of genital herpes during the third trimester, there may be considerations around delivery method to reduce the risk of neonatal transmission.

For women with a known history of genital herpes, antiviral medication may be recommended in the final weeks of pregnancy to reduce the likelihood of an outbreak at the time of delivery. Recurrent herpes in women with an established infection carries a much lower risk to the baby than a new primary infection.

For more on recognising herpes symptoms, see our guide on what herpes looks like.

Can STIs Harm Your Baby?

This is understandably one of the most common concerns among pregnant women. The answer depends on the specific infection, whether it has been detected, and whether treatment has been provided.

Some key points:

• Bacterial infections such as chlamydia, gonorrhoea, and syphilis can potentially be passed to the baby during delivery if untreated. However, all three are treatable with antibiotics during pregnancy, and early detection through screening significantly reduces any associated risks
• HIV can be transmitted during pregnancy, delivery, or breastfeeding if untreated. With appropriate antiviral therapy, the risk of transmission is reduced to very low levels. The UK has one of the lowest rates of mother-to-child HIV transmission in the world, largely due to effective screening and treatment programmes
• Herpes is primarily a concern if active lesions are present at the time of delivery. For women with a known history, management plans are put in place during late pregnancy to minimise any risk
• Hepatitis B can be transmitted at the time of birth, but vaccination and immunoglobulin given to the newborn shortly after delivery are highly effective at preventing infection

The important message is that early detection and appropriate management make a significant difference. The vast majority of women who receive timely treatment during pregnancy go on to have healthy babies.

What If You Test Positive During Pregnancy?

Receiving a positive STI result during pregnancy can feel worrying, but it is important to know that effective management options exist for most infections.

If you test positive, the following steps are typically taken:

• Confidential discussion with your healthcare team — your midwife, GP, or specialist will explain the result, what it means for your pregnancy, and the recommended next steps
• Safe treatment where appropriate — most bacterial STIs can be treated with antibiotics that are considered safe during pregnancy. Viral infections such as HIV are managed with antiviral medication in coordination with specialist services
• Ongoing monitoring — your clinical team will monitor your progress and may recommend follow-up tests to confirm that treatment has been effective
• Coordination with obstetric care — where relevant, your sexual health team and maternity team will work together to ensure a coordinated approach to your care during pregnancy and delivery

A positive result does not define your pregnancy. With appropriate care, the outlook is generally very positive, and many women in this situation go on to have straightforward deliveries and healthy babies.

Should You Consider Private STI Testing During Pregnancy?

NHS antenatal screening provides comprehensive testing for the most clinically significant infections during pregnancy. However, some women choose to seek additional private STI testing for a variety of reasons:

• New sexual partner during pregnancy — if you have had a new partner since your antenatal booking tests, additional screening may provide reassurance
• Symptoms that have developed since initial screening — such as unusual discharge, pain, or skin changes
• Previous STI history — if you have had a previous infection and would like to confirm your current status
• Concerns that were not fully addressed — if you feel that specific tests were not included in your antenatal screening and would like additional coverage
• Testing for infections not routinely included — such as chlamydia (if not offered), herpes (in the absence of symptoms), or mycoplasma genitalium

Some individuals choose additional testing for personal reassurance. Private STI testing is not a replacement for NHS antenatal care but can complement it in specific circumstances.

Any testing during pregnancy should be discussed with your midwife or obstetrician to ensure it is appropriate and that results are interpreted in the context of your overall maternity care.

When Is the Best Time to Test During Pregnancy?

The timing of STI testing during pregnancy depends on the circumstances:

• At the booking appointment (8–12 weeks) — this is when routine NHS antenatal screening takes place, covering HIV, syphilis, and hepatitis B
• If a new exposure occurs during pregnancy — if you have had sexual contact with a new partner, testing after the appropriate window period is advisable
• If symptoms develop at any stage — symptoms such as unusual discharge, sores, or pain should be assessed promptly, regardless of the stage of pregnancy

Window period considerations still apply during pregnancy. For example, chlamydia and gonorrhoea tests are generally reliable from 7 to 14 days after exposure, while HIV testing is most reliable from 18 to 45 days (4th generation test). For more on symptom timelines, see our guide on when STI symptoms appear.

If you have any concerns about a potential exposure during pregnancy, discussing them with your midwife or a sexual health professional promptly is always the best course of action.

Frequently Asked Questions

Is STI testing safe during pregnancy?

Yes. STI testing during pregnancy is safe and non-invasive. Blood tests, urine samples, and swabs pose no risk to the pregnancy. Routine antenatal screening is recommended for all pregnant women in the UK and is a standard part of maternity care.

Can chlamydia affect pregnancy?

Chlamydia, if untreated, may be associated with complications such as premature delivery in some cases, and can potentially be transmitted to the baby during vaginal birth. However, chlamydia is easily treatable with antibiotics that are safe to use during pregnancy. Early detection through testing allows prompt treatment.

Is HIV testing mandatory in pregnancy?

HIV testing is not mandatory in the UK — it is offered as part of routine antenatal screening, and women have the right to decline any test. However, uptake is strongly encouraged because early detection allows effective treatment that significantly reduces the risk of mother-to-child transmission.

What happens if you refuse antenatal STI screening?

You have the right to decline any test offered during pregnancy. If you choose not to be screened, your midwife will discuss the implications with you and document your decision. Declining screening does not affect your access to maternity care, but it does mean that certain infections may go undetected.

Can I breastfeed if I have an STI?

This depends on the specific infection. Most bacterial STIs such as chlamydia, gonorrhoea, and syphilis are not transmitted through breast milk, and breastfeeding is generally considered safe after treatment. For HIV, the recommendation in the UK is to formula-feed rather than breastfeed, as the virus can be present in breast milk. Your healthcare team will provide individualised guidance based on your situation.

When Should You Seek Medical Advice Urgently?

While most STI-related concerns during pregnancy can be managed through routine appointments, you should seek prompt medical advice if you experience:

• Fever accompanied by a rash — which may suggest a systemic infection requiring assessment
• Severe abdominal or pelvic pain — which could indicate a complication that needs urgent evaluation
• Unusual vaginal discharge — particularly if it is accompanied by pain, odour, or a change in colour
• Painful genital ulcers or sores — which may require swab testing and clinical assessment

These symptoms do not necessarily indicate a serious problem, but prompt assessment ensures that appropriate care is provided without delay.

Confidential STI Testing in Pregnancy

If you would like confidential STI testing during pregnancy, appointments are available at our UK clinic. Testing decisions should always consider your individual medical history and timing within pregnancy.

Whether you are looking for additional reassurance, testing following a new exposure, or screening for infections not included in routine antenatal care, our team can advise on appropriate options. Book a confidential appointment at a time that suits you.