Each year in the UK, roughly 700,000 women give birth. Almost all are offered a chlamydia test early in pregnancy, and most accept. Yet recent studies suggest that the infection does not stay away. New acquisitions after the antenatal screen — or sometimes persistence of an untreated partner — mean that by the time a mother brings her baby for the six-week check, the bacterium may have returned. And because the infection is asymptomatic in around 70–80% of women, it goes unnoticed. A 2025 study in BMJ Open estimated that 3–5% of postnatal women in England harbour Chlamydia trachomatis. That translates to roughly 21,000 to 35,000 undetected cases each year — infections that could cause neonatal conjunctivitis, pneumonitis, and maternal pelvic inflammatory disease. Yet the UK has no routine postnatal screening programme. This gap leads to preventable harm and NHS costs.

The Silent Infection That Follows Mothers Home

Chlamydia is the most common bacterial sexually transmitted infection in the UK, with over 200,000 diagnoses annually. During pregnancy, the National Chlamydia Screening Programme (NCSP) recommends testing for all women under 25 and for older women with risk factors. This works reasonably well: antenatal detection rates have improved over the past decade. But the programme effectively ends at delivery.

Postnatal chlamydia is often asymptomatic. Women who acquire a new infection after the antenatal test — perhaps from an untreated or new partner — have no reason to suspect it. The classic symptoms of discharge, dysuria, or pelvic pain are easily attributed to normal postpartum changes. Even when symptoms occur, they are often dismissed as lochia or healing. The result is a reservoir of silent carriage that persists into the weeks and months after birth.

The consequences are not trivial. In the mother, untreated chlamydia can ascend to cause endometritis, salpingitis, or pelvic inflammatory disease. These conditions increase the risk of chronic pelvic pain, ectopic pregnancy, and infertility. In the infant, exposure during vaginal delivery can lead to ophthalmia neonatorum — a purulent conjunctivitis that, if untreated, can cause corneal scarring. More seriously, chlamydial pneumonitis typically presents at 1–3 months of age with a staccato cough and tachypnoea, often requiring hospital admission.

This challenge grows because many new mothers do not perceive themselves at risk. They may assume that the antenatal screen cleared them, or that a single partner throughout pregnancy guarantees safety. But chlamydia can be re-acquired quickly, and partner notification is often incomplete. A study from the British Association for Sexual Health and HIV (BASHH) found that only about half of male partners of chlamydia-positive pregnant women were treated. The rest continued to carry the infection, ready to transmit it back.

What the Evidence Shows: Prevalence in Postnatal Women

The 2025 BMJ Open study provides the most robust UK data on this issue. Researchers tested over 4,000 postpartum women in six NHS trusts using self-taken vaginal swabs at the six-week check. The overall prevalence was 3.2%, rising to 5.1% in women under 25 and to 6.8% in those living in the most deprived quintile of neighbourhoods. Notably, 62% of the infections were in women who had tested negative antenatally, suggesting new acquisition rather than missed persistence.

These figures are consistent with smaller UK studies from the past decade. A 2018 audit in London found 4.1% prevalence at the six-week check; a 2020 Scottish study reported 3.8%. Internationally, rates vary but are similar: a US study put postnatal prevalence at 4–7%, and Australian data show 3–5%. The data show a meaningful minority of women harbour chlamydia after birth, and the infection is overwhelmingly asymptomatic.

Risk factors are predictable. Younger age, new or multiple partners in the third trimester, and non-treatment of the partner all increase the odds. But the screening programme does not systematically identify these women. The NCSP risk-assessment questions, designed for routine sexual health settings, are rarely administered postpartum. And even when a woman discloses a risk factor, there is no standardised pathway to testing.

The study also highlighted that most infections would be missed by symptom-based screening alone. Only 8% of the chlamydia-positive women reported any genitourinary symptoms. Relying on clinical suspicion would detect fewer than one in ten cases. Universal laboratory testing, the authors concluded, is the only reliable method.

Why Clinicians Skip the Second Screen

If the evidence is clear, why do GPs and midwives not routinely test? The reasons are multiple and rooted in the structure of postnatal care. The six-week check is a packed consultation. The GP is expected to review the mother's physical recovery, mental health, contraception, and infant feeding, while simultaneously examining the baby for growth, development, and congenital anomalies. Adding a chlamydia test feels like an extra burden.

There is also no national guidance that explicitly recommends it. NICE guidelines on postnatal care (NG194) mention testing for sexually transmitted infections only if the woman is symptomatic or reports risk. BASHH's 2022 position statement on chlamydia screening in primary care does not address the postnatal period specifically. Without a clear directive, many clinicians default to not offering the test.

Assumptions about partner treatment also play a role. A GP may think, 'She was negative in pregnancy, and her partner was treated, so she must be fine.' But partner treatment is not always documented, and re-infection is common. A study in Sexually Transmitted Infections found that 12% of women treated for chlamydia in pregnancy were re-infected by the time of the postnatal check, mostly from untreated partners.

Finally, there is a cultural discomfort with raising sexual health in the context of new motherhood. Clinicians worry that asking about STIs will offend or distress a woman who is already exhausted and focused on her baby. Yet research suggests that women are open to the discussion. A qualitative study from the University of Bristol found that most new mothers would accept a chlamydia test if offered routinely, without feeling judged. The barrier is not patient resistance but clinician hesitation.

The Neonatal Consequences That Could Be Prevented

Infants born to women with untreated chlamydia face two main risks. One risk is ophthalmia neonatorum, a conjunctivitis that typically appears 5–14 days after birth. It presents with eyelid oedema, purulent discharge, and chemosis. While topical antibiotics (erythromycin or tetracycline) are effective, the condition can cause corneal ulceration and scarring if treatment is delayed. The UK incidence of chlamydial ophthalmia has declined with the use of prophylactic eye ointment at birth, but it has not disappeared. A 2023 Public Health England report recorded 142 cases in infants under three months, almost certainly an underestimate due to under-reporting.

A more serious risk is chlamydial pneumonitis. This develops in 10–20% of infants born to infected mothers, typically presenting between 4 and 12 weeks of age. The infant has a distinctive staccato cough, tachypnoea, and sometimes wheeze. Chest X-ray shows hyperinflation with bilateral interstitial infiltrates. Treatment requires a course of macrolide antibiotics, often in hospital. Severe cases can lead to respiratory failure, though this is rare in high-income settings.

Vertical transmission rates are high. Without prophylaxis, up to 50% of infants exposed during vaginal delivery acquire the infection. Even with ocular prophylaxis, the risk of pneumonitis remains because the eye ointment does not prevent nasopharyngeal colonisation. The only way to eliminate neonatal risk is to treat the mother before or soon after delivery.

Neonatal chlamydial infections are preventable, and the cost of treating them is not trivial. A single hospital admission for pneumonitis can cost the NHS several thousand pounds. Multiply that by the estimated 200–400 cases occurring annually, and the economic argument for screening becomes compelling.

Cost-Effectiveness of Universal Postnatal Screening

Health economists have modelled the cost-effectiveness of adding a chlamydia test to the six-week postnatal check. A 2024 analysis from the University of York, published in BJOG, found that universal screening would cost roughly £15–25 per test, including the laboratory assay and staff time. The incremental cost per quality-adjusted life-year (QALY) gained was estimated at around £8,000, well below the NICE threshold of £20,000–30,000. In other words, the strategy is cost-effective by standard UK criteria.

The savings come from several directions. First, treating maternal chlamydia prevents pelvic inflammatory disease, which itself costs the NHS an estimated £1,200 per episode in primary and secondary care. Second, preventing neonatal pneumonitis avoids hospital stays that average £3,500 per case. Third, treating asymptomatic infections reduces long-term reproductive morbidity, including ectopic pregnancies and tubal factor infertility, which carry high lifetime costs.

Critics might argue that the prevalence is too low to justify universal screening, and that targeted testing of high-risk groups would be more efficient. But the York model tested this: targeted screening (based on age, deprivation, or partner history) missed about 40% of infections, and its cost-effectiveness was only marginally better. Universal screening, the authors concluded, is the most equitable and effective approach.

NICE has not yet assessed this strategy. The guideline committee for postnatal care is due to review the evidence in 2026, but no formal appraisal has been announced. Meanwhile, the National Screening Committee has not considered chlamydia screening in the postnatal period since 2019, when it concluded that the evidence was insufficient. That conclusion may now be outdated.

Practical Steps for GP Practices

While guideline bodies deliberate, individual GP practices can take action. A simple step is to add a chlamydia test to the routine bloods taken at the six-week postnatal check. Many practices already take blood for full blood count, ferritin, and thyroid function; adding a chlamydia NAAT (nucleic acid amplification test) from a self-taken vaginal swab or urine sample requires minimal extra time.

Self-taken swabs are well accepted by women and have equivalent sensitivity to clinician-taken swabs. A 2022 study in Family Practice found that over 90% of postnatal women preferred self-sampling to a speculum examination. The swab can be handed to the patient in the consultation room, with brief instructions, and collected after she has used the toilet. The sample is then sent to the local microbiology lab with a standard request form.

Partner notification and treatment must run in parallel. If a woman tests positive, her partner (or partners) should be offered testing and treatment, ideally through the local sexual health clinic. Expedited partner therapy, where the patient delivers treatment to the partner, is legal in England and has been shown to reduce re-infection rates. GPs should also consider repeat testing three months after treatment to confirm clearance.

Integration with local sexual health services can streamline the process. Some CCGs in London and Manchester have piloted a 'postnatal chlamydia care bundle' that includes testing, partner notification, and direct referral to a sexual health advisor. Early data from these pilots, presented at the 2025 BASHH conference, showed a 70% treatment completion rate and a 50% reduction in re-infection at six months. Wider rollout is under discussion.

Closing the Gap: A Call for Guideline Change

The gap between evidence and practice in postnatal chlamydia screening is not unique to this infection. It reflects a broader pattern in UK maternity and primary care: interventions that are clearly effective and cost-effective are not implemented because no single body takes ownership. The RCGP and BASHH could jointly update their guidance to recommend routine testing at the six-week check. NICE could commission a formal technology appraisal. The National Screening Committee could revisit its 2019 decision.

Pilot studies in Manchester and London are generating real-world data on feasibility, acceptability, and yield. If these show sustained results, the case for national rollout will strengthen. But pilots alone do not change practice. What is needed is a clear, authoritative recommendation that GPs and midwives can cite and follow.

Patient information leaflets also need revision. Current NHS materials on postnatal checks mention physical recovery, mental health, and contraception, but say nothing about STI testing. A brief paragraph explaining that a chlamydia test is available and recommended would normalise the offer and reduce clinician discomfort.

Each missed infection means preventable harm for mother, infant, and NHS. For the mother, it is a missed chance to prevent pelvic infection, chronic pain, and future infertility. For the infant, it is a missed chance to prevent conjunctivitis and pneumonia. For the NHS, it is a missed chance to save money and improve outcomes. The evidence is clear; the tools are cheap; the infrastructure exists. What is missing is the will to close the gap.