Should I screen for syphilis when I find out I’m pregnant? Because it’s important to block mother-to-child transmission in the early stages!

Author: Wang Linghang, Chief Physician, Beijing Ditan Hospital, Capital Medical University

Reviewer: Zhang Yu, researcher at Chinese Center for Disease Control and Prevention

Syphilis is a sexually transmitted disease caused by Treponema pallidum, which is mainly transmitted through sexual intercourse and mother-to-child transmission. It is very rare for it to be transmitted through blood products, because Treponema pallidum is difficult to survive for more than 48 hours under the current storage conditions of blood banks.

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Syphilis screening is currently included in routine prenatal checkups. If a woman is infected with syphilis and becomes pregnant, the risk of transmission to the fetus is relatively high. Given the serious impact of syphilis on the fetus, syphilis screening should be performed during early pregnancy checkups.

1. What impact does syphilis have on the fetus?

If a pregnant woman has syphilis, the chance of transmitting it to the fetus is about 50% for primary syphilis and about 40% for primary latent syphilis. The transmissibility of late syphilis is significantly lower, about 10%. Therefore, if a woman becomes pregnant in the early stages of syphilis infection, the risk of transmitting it to the fetus is relatively high.

Pregnant women with syphilis have active Treponema pallidum in their bodies. Treponema pallidum is particularly delicate and can easily invade the placenta, causing edema and swelling of the placenta, which may lead to miscarriage. The miscarriage rate is about 40%.

If a pregnant woman has syphilis, she can transmit the Treponema pallidum to the fetus from the 9th to the 10th week of pregnancy. At this time, the fetus's immune system is not fully developed and there may not be any abnormalities. After 20 weeks, the fetus's immune system develops to a certain extent and can respond to the invading syphilis. B-ultrasound can observe fetal abnormalities. If the fetus is infected with syphilis in utero, the entire appearance and organ function will be affected, such as tibial lordosis, hepatosplenomegaly, etc., and the skin and mucous membranes will also be affected to varying degrees.

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This is why syphilis screening is performed during the first prenatal check-up. In order to avoid false negatives or missed diagnoses, the test should be repeated after 20 and 28 weeks of pregnancy.

2. If syphilis is discovered during pregnancy, can it be prevented from being transmitted to the fetus?

Early detection of syphilis after pregnancy and active treatment can greatly reduce the risk of transmitting syphilis to the fetus, which can be reduced to 1%-2%.

If syphilis is discovered too late after pregnancy, for example, at 36 weeks of pregnancy, the treatment will be very rushed; or the pregnant woman's syphilis titer level is particularly high, and although the load of Treponema pallidum in the body is greatly reduced after treatment, the fetus may still be infected with syphilis, so early detection and early treatment are necessary.

In addition, if you know that you have syphilis, it does not mean that you cannot get pregnant. Early intervention and treatment can reduce the load of Treponema pallidum in your body to the lowest level. Pregnancy at this time can avoid transmission to the fetus.

3. How to intervene and treat syphilis if it is diagnosed during pregnancy?

There are now specific treatments for syphilis, and penicillin is the preferred treatment drug. As long as you are not allergic to penicillin, actively using penicillin to treat syphilis after it is discovered can achieve clinical cure.

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Penicillin is an antibiotic that pregnant women can use, and it has been proven to be safe through a lot of clinical practice. However, some pregnant women may be allergic to penicillin. In this case, you can choose alternatives, such as azithromycin, which pregnant women can also use, but the effect is not as good as penicillin. If you want to use penicillin for treatment, you can use desensitization treatment, and then you can use penicillin after desensitization treatment.

After a child is born, a serological screening for syphilis is usually performed. Newborn babies carry antibodies passed down from their mothers. A positive antibody test does not determine whether the child is infected with syphilis or the antibodies were passed down from the mother. However, if the child's syphilis titer is more than 4 times that of the mother, then it is suspected that the child has been infected with syphilis. We need to dynamically observe whether the child has clinical manifestations related to syphilis, and observe changes in the titer level, and recheck every 3 and 6 months.

If it is confirmed that the child is infected with syphilis and requires intervention treatment, penicillin can also be used for treatment to reduce the load of Treponema pallidum in the body and will not affect the organ function.