Women already infected by STIs can conceive and pregnant women can also become infected during their pregnancy, but the complications caused by some STIs can be much more serious.

Most pregnant women undergo STI testing as part of their medical assessment, and it is routine for UK antenatal care to offer tests looking for hepatitis B, syphilis and HIV.

The effects caused by STIs during pregnancy can vary greatly between the different types of infection present:

Bacterial STIs

The most common bacterial STIs include chlamydia, gonorrhoea, syphilis and bacterial vaginosis (BV). They are all caused by unwanted bacteria infecting the body.

Chlamydia, gonorrhoea and BV can all cause similar complications during pregnancy. The potential problems include preterm rupture of the membranes surrounding the baby (also known as waters breaking), premature birth and miscarriage.

Chlamydia and gonorrhoea can also be passed from the infected mother to the newborn baby during vaginal childbirth. This can lead to eye and lung infections.

Untreated syphilis can pose a significant danger to a developing babies and newborn infants. This is because it can cause premature births, stillbirths and death shortly after birth. Untreated newborns can go on to develop multiple organ dysfunction of the brain, eyes, heart, ears, skin, bones and teeth.

Bacterial STIs can usually be treated safely during pregnancy with antibiotics.

Viral STIs

Viral STIs such as herpes, genital warts, HIV and hepatitis can cause pregnancy problems and be passed onto the baby.

The herpes simplex virus (HSV) can be very serious if contracted by the baby. Transmission can occur during pregnancy or after delivery, but it is estimated that up to 90 per cent of cases are passed on during vaginal delivery.

If the mother-to-be has a herpes outbreak at the point of giving birth, a cesarean section may be advised to protect the newborn. This is because the virus can cause blindness, damage to the nervous system, severe learning difficulties and even death.

Genital warts are caused by the human papilloma virus (HPV). If the virus is present during pregnancy the warts may flare-up and become larger physically or in number.

Depending on the location of the warts, they may need to be removed prior to giving birth or else a vaginal delivery might not be possible. HPV can be transferred to the baby and in very rare cases be linked to laryngeal papillomatosis, a benign growth in the baby’s throat.

Genital warts can usually be safely treated during pregnancy but some treatment may be delayed until after the birth.

The human immunodeficiency virus, more commonly referred to as HIV, can be passed from the mother to her child during all stages of pregnancy. However, there are treatments available which minimise the risk. The British HIV Association estimates that the chances of transmitting HIV to your newborn are now less than 2 per cent.

Hepatitis B can be vertically transferred from mother to baby. Unborn babies are most at risk if the infection is caught by the mother close to the time of delivery. Babies that are deemed ‘at-risk’ may be given a vaccine to decrease their chances of developing serious liver disease or liver cancer as they grow older.

Effects on conception and early pregnancy

STIs can be a cause for concern for women trying to conceive. Although the majority of those who have an STI and receive treatment early enough should not experience a problem.

It is still important to note that if left untreated some STIs can lead to fertility complications in both men and women. Women looking to get pregnant might experience difficulty if their fallopian tubes have been damaged.

Some STIs carry the risk of causing miscarriage or ectopic pregnancy. This is because the reproductive organs can be affected if an infection infiltrates the uterus or cervix.

If left untreated, the infection can lead to pelvic inflammatory disease (PID) and permanently damage part of the reproductive system. The STIs commonly associated with PID include chlamydia and gonorrhoea.

During pregnancy

Pregnant women who have STIs may experience symptom flare ups.

Some women might not realise that they have an STI until they are pregnant and the symptoms become noticeable for the first time.

There are symptoms which might be exacerbated by pregnancy and be uncomfortable to experience. In particular new and enlarged clusters of genital warts might form and on rare occasions block the birth canal preventing a vaginal delivery.

Treatment prior to or during pregnancy

Most antibiotic treatments for bacterial STIs can still be used during pregnancy. This includes treatment for chlamydia, gonorrhoea and syphilis.

If you are planning a pregnancy and are taking treatment for an STI then you should speak to your doctor about the best course of action. Your healthcare professional will help you decide what treatment should be started and when.

Safe sexual practices before, during and after pregnancy

Practising safe sex throughout pregnancy is of vital importance. STIs can be contracted and transmitted at any stage of the pregnancy. As we have seen above the complications for pregnant women can be more serious and so getting tested is crucial.

There are treatment options available which can be discussed with your healthcare professional to help ensure a healthy pregnancy and birth.