Congenital syphilis: when syphilis passes to a baby

Syphilis is caused by the bacterium Treponema pallidum. In an adult it is usually acquired sexually, but the bacteria can also cross the placenta during pregnancy and infect the developing baby. The earlier the mother is infected and the longer the infection goes untreated, the greater the danger to the baby. A pregnant woman may have no symptoms, or only a painless sore that has already healed, so she may not know she has it.

The World Health Organization states that syphilis in pregnancy that is untreated, treated late or treated with the wrong antibiotic results in adverse birth outcomes in between 50 and 80 per cent of cases.

Effects range from pregnancy loss to illness in a baby who appeared normal at birth. The US Centers for Disease Control and Prevention lists miscarriage, stillbirth, prematurity, low birth weight and death shortly after birth. Affected newborns may have bone abnormalities, severe anaemia, jaundice, damage to the brain and nerves including blindness or deafness, and meningitis.

Some babies show no signs at birth and develop serious problems weeks or years later. The CDC mentions cataracts, deafness and seizures as possible later complications. This delayed pattern is the reason all babies born to mothers with syphilis need assessment even when they look well.

• Rashes and inflammation of organs.

• Anaemia and bone problems.

• Sight and hearing loss.

• Developmental delay if untreated.

The NHS offers syphilis screening in pregnancy so that infection can be found and treated before it causes serious problems. A blood test is taken at the start of antenatal care. A positive result prompts referral to a specialist team, usually involving sexual health, obstetric and paediatric services, who arrange treatment, partner testing and a plan for the baby.

The CDC recommends testing at the first prenatal visit and, for some women at higher risk, repeat testing around 28 weeks and at delivery. Screening policies differ between countries, so UK women should follow the schedule offered by their own maternity service.

WHO identifies benzathine penicillin as the only medicine that can prevent mother-to-baby transmission of syphilis. Treatment is started straight away after a positive test, and the infection is monitored with repeat blood tests. Women who are allergic to penicillin may need specialist advice, because alternatives are less reliable in pregnancy.

Sexual partners are traced and tested so that the mother is not reinfected after treatment.

Babies born to mothers with syphilis are examined carefully. The CDC explains that doctors consider the mother's test results and treatment history and may arrange blood tests, a physical examination, a lumbar puncture or X-rays. WHO notes there is no single diagnostic test specific to congenital syphilis, so assessment combines clinical examination and laboratory tests at birth with follow-up evaluations.

A baby diagnosed with congenital syphilis is treated promptly with antibiotics in hospital, typically over about ten days according to the CDC, although some cases need only a single injection. Follow-up visits check that treatment has worked.

Prevention rests on early testing, prompt treatment and reducing the risk of infection through condoms or mutually monogamous relationships. The CDC reports that cases in the United States have more than tripled in recent years, and WHO has a global initiative to eliminate mother-to-child transmission of syphilis, HIV and hepatitis B together. In countries with comprehensive antenatal screening the condition is uncommon, but it has not disappeared.

A woman who has had unprotected sex with a new partner, or whose partner has been diagnosed with syphilis, can attend a sexual health clinic for testing at any time, including during pregnancy; no GP referral is usually needed and attendance is confidential. Anyone who is pregnant and notices a genital sore, rash on the palms or soles, or other worrying symptoms should contact their midwife or a sexual health clinic promptly.