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STIs in pregnancy: risks and treatment options

Pauline Handy
Lead Nurse
Sexual Health Services
NHS Newcastle and North Tyneside Community Health
Newcastle upon Tyne

While the incidence of teenage pregnancy fell by 4.9% between 1998 and 2007, it still remains the highest in Europe. Significant numbers of STIs and unintended pregnancies occur in the under-25s, but these have also been noted among mid-life women.

Bacterial vaginosis
Although not an STI, bacterial vaginosis it is an extremely common infection, which is often confused with candida (thrush), leading to inappropriate self-treatment or empirical treatment from a doctor. Symptoms of bacterial vaginosis compared with candida are shown in Table 1.

[[Tab 1 STI]]

As bacterial vaginosis may resolve spontaneously, it is not usually treated if the patient is asymptomatic, ie, an incidental finding. However, treatment is recommended in pregnancy. Adverse outcomes of untreated infection in pregnancy may include:

  • Preterm birth and premature rupture of membranes (PROM).
  • Second trimester miscarriage.
  • Low birth weight.
  • Endometritis.

Risk of preterm birth is increased seven-fold in women with a history of previous premature delivery. Treatment before 20 weeks gestation with oral metronidazole has been shown to reduce the incidence of preterm delivery in infected women.1 The recommended dose of metronidazole is as for non-pregnant women: 400 mg bd for seven days. Meta analyses have shown no evidence linking birth defects to the use of metronidazole in early pregnancy, although larger doses are best avoided.2 In those who are unable to tolerate metronidazole, or where it is contraindicated, clindamycin may be used, but it has not been found to be so effective in reducing preterm delivery.3

One of the most common sexually transmitted infections, chlamydia has been found to be asymptomatic in up to 80% of women. In normal vaginal deliveries, 50-80% of infants will acquire chlamydia if no prophylaxis is given before or immediately after birth.4 However, this can be reduced to 1-2% if the mother is treated before delivery. Infection during pregnancy may result in the following adverse outcomes:

  • Preterm delivery and low birth weight.
  • PROM.
  • Opthalmia neonatorum (a form of conjunctivitis).
  • Neonatal respiratory tract infection/apyrexial pneumonia.5

Opthalmia neonatorum is less severe than gonococcal opthalmia neonatorum, with an overall incidence of 0.65/1,000 live births.6 However, transmission rates can be reduced to 1-2% if appropriate treatment is provided to the mother before delivery. Neonatal symptoms of conjunctivitis usually develop within five to 14 days of delivery.7 

In those with a respiratory tract infection, the nasopharynx is the most frequent site of neonatal infection (70-80%); however, it is usually asymptomatic. It has been suggested that 30% of neonates with nasopharyngeal infection may develop apyrexial pneumonia at around four to 12 weeks of age.

Treatment in pregnancy and breastfeeding is with 1 gm azithromycin stat dose (currently no evidence of adverse pregnancy outcomes - see cautions in the British National Formulary (BNF)) or 500 mg erythromycin bd for 14 days or amoxicillin tds for seven days. Clinicians are advised to perform a test of cure six weeks after treatment if erythromycin has been used.8

Genital warts (human papilloma virus)
Genital warts may increase dramatically in size and number during pregnancy due to an increase in oestrogen/progesterone or as a result of immunocompetence. Vertical transmission in utero is rare. Estimated rates of acquisition during vaginal delivery have been suggested at between 1:80 and 1:1,500.9 Warts do not normally obstruct vaginal delivery and may often regress spontaneously after delivery. Adverse outcomes for the neonate include:

  • Laryngeal papillomatosis (tumours).
  • Anogenital warts.

Perinatal acquisition is the usual cause of anogenital warts in infants under three years of age, with the disease often seen following a history of maternal genital warts at the time of delivery. However, the possibility of child abuse must always be considered.  Although rare, laryngeal papillomatosis can occur via maternal-foetal transmission and may cause significant morbidity in the newborn.10

The aim of treatment is to minimise the number of lesions present at delivery to reduce neonatal exposure to the virus. However, some routine treatments may be contraindicated in pregnancy and breastfeeding. The most commonly used treatment for warts during pregnancy is cryotherapy using liquid nitrogen. Trichloroacetic acid is also safe for use in pregnancy although it is rarely used.
Contraindicated treatments are:

  • Podophyllum and podophyllotoxin (potential teratogenic effects).
  • Imiquimod is not licenced for use in pregnancy.

Genital herpes (herpes simplex virus)
Herpes is associated with high levels of morbidity and mortality if vertically transmitted to the neonate from an infected mother.11 A primary episode during delivery, especially if disseminated or any central nervous system involvement, may result in an 80% mortality rate if untreated.12 Outcomes are less severe if the mother has a recurrence during delivery or immediately before delivery. Neonatal acquisition rates have been suggested at 85% via exposure from infected birth canal, 5% from intrauterine exposure and 10% postnatally.13

Interventions such as invasive foetal monitoring have been found to increase the risk of neonatal herpes and should only be used for defined obstetrical indications.12 Management should be to reduce the morbidity of neonatal herpes by preventing acquisition during delivery.

Treatment recommendations for those who present with a recurrent episode of genital herpes several weeks before delivery is suppressive therapy with aciclovir or valciclovir for the last four weeks of pregnancy (viral cultures should be taken from the 36th week of pregnancy.13 The BNF states that aciclovir is not known to be harmful in pregnancy but manufacturers advise use only when potential benefit out ways any risk.14 Caesarean section is usually recommended for those with a primary attack of herpes at delivery or four weeks before due date.

This may be passed to the neonate from an infected mother during delivery and suggested adverse outcomes are:

  • Preterm delivery.
  • Low birth weight.
  • PROM.
  • Endometritis.
  • Gonococcal opthalmia neonatorum.15

Opthalmia neonatorum is a notifiable disease in the UK. It has been found to occur in 30-50% of those born to infected mothers during birth.15 Symptoms generally present within two to five days of delivery and without treatment may extend to the subconjunctival connective tissue and cornea, leading to ulceration and possible blindness.16
Treatment in pregnancy is as follows:

  • Ceftriaxone 250 mg IM stat dose; or
  • Cefotaxamine 500 mg IM stat dose; or
  • Ampicillin 2 g plus probenecid 1 g orally stat dose.
  • Pregnant women should not be treated with quinolone or tetracycline antimicrobials.17

All pregnant women are now routinely tested for HIV at antenatal visits. If found to be positive, care should be provided by a multidisciplinary team involving an obstetrician, HIV specialist, midwife and paediatrician. The highest risk of transmission to the neonate occurs during delivery and post partum (breastfeeding) with ante partum (transplacental) spread uncommon. It is thought that mother to child transmission accounts for 90% of HIV infection in children worldwide.18 
Adverse outcomes include:

  • Small increase in spontaneous abortion.
  • Possible low birth weight and preterm delivery.
  • HIV infected neonate.

Viral load is an important predictor of transmission. However transmission has been reported when maternal viraemia was not detected.19 The use of appropriate highly active antiretroviral treatment (HAART) has been found to reduce transmission at all levels of maternal viraemia when given before the third trimester. Elective caesarean sections are advised for HIV-positive women on no antiretroviral treatment (or only on zidovudine) as studies have shown this to reduce the risk of vertical transmission.20 Mothers should be advised to avoid breastfeeding (HIV reported in 14% of at risk infants).21

With optimised antenatal/postnatal care and effective timely HAART treatment, transmission rates can be decreased to

Along with HIV, syphilis is now routinely tested for during antenatal care. Although rare in the UK, maternal syphilis results in abortions, stillbirths and congenital syphilis and remains an increasing problem in many countries of sub-Saharan Africa.22 Untreated syphilis may be fatal or have several adverse outcomes which vary dependent upon the stage of pregnancy, including:

  • Spontaneous abortion.
  • Premature delivery.
  • Intrauterine growth restriction.
  • Stillbirth.
  • Serious sequalae in live born infected children.

Infection has been reported from the ninth week of gestation but is most likely to arise after the 18th week. In pregnant women with early untreated syphilis, 70-100% of infants will be infected, with stillbirths reported in up to a third.23
Categorised as early syphilis (symptoms within first two years of life) or late syphilis (symptoms after two years usually near to puberty), manifestations are listed below.
Early syphilis:

  • Failure to thrive.
  • Mucosal lesions with pharyngeal and nasal involvement (snuffles).
  • Skin lesions, rashes, condylomata lata (wart-like growth) around anus and genitals, sparse hair and brittle atrophic nails.
  • Hepatosplenomegaly (enlargement of liver and spleen) and lymphadenopathy.
  • Osteochondritis (cartilage/bone fracture).

Late syphilis:

  • Frontal bossing (bulldog appearance).
  • "Saddle nose" deformity, conical and notched incisors (Hutchinson's teeth).  
  • Moons/mulberry molars - domed first lower molars.
  • Interstitial keratitis (eye inflammation).
  • Clutton's joints (effusion of knee joints).
  • Gumma of the nasal septum, palate and throat.
  • Neurosyphilis.

Treatment in early syphilis is with benzathine penicillin 2.4 g IM stat dose in the first and second trimester, with a second dose if treated during the third trimester after one week. Retreatment of those with a past history of syphilis should be considered if there is any doubt about efficacy of past treatment if there has not been a fourfold drop in Venereal Disease Research Laboratory test (VDRL).24

In early syphilis, Jarisch-Herxheimer (a nonspecific acute febrile illness) reaction to treatment with IM benzathine penicillin may cause uterine contractions, foetal distress and preterm labour especially if the foetus is infected. Research has shown that around 40% of pregnant women treated with penicillin will suffer such a reaction.25 Patients must be carefully informed of the potential for this reaction following treatment with advice to contact their doctor if they experience any symptoms.

Management of the pregnancy must be in conjunction with midwives, obstetricians and paediatricians. Referral for ultrasound to evaluate foetal involvement is recommended after 26 weeks gestation.24

Women should be made aware of the risks of a sexually transmitted infection during pregnancy so that they are able to make an informed decision about testing. Should an infection be found during pregnancy, careful monitoring and medical advice are essential. Information regarding a past history of herpes simplex (either oral or genital) should be recorded in the patient's notes.

Healthcare professionals should remember that some women may embark upon pregnancy already having an undiagnosed STI with many infections remaining asymptomatic. Some women may have a change in partner during their pregnancy with the associated risks of acquiring an STI. The offer of STI screening (ie, self-taken swab for gonorrhoea and chlamydia) at a first antenatal visit or at a later date if indicated together with the routine serology for HIV and syphilis may help reduce any potential adverse outcomes.

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