Is a mother’s infection or virus a risk factor for low birth weight or prematurity? Are there any other medical conditions that can cause it?

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Yes, for certain infections and viruses. We estimate that one third of all premature births are caused by infections. Among those studied are malaria, syphilis, gonorrhea, urinary tract infections, vaginal bacterial infections, toxoplasmosis, trichomoniasis, and gum infections. 

To learn more about the consequences of prematurity and low birth weight, click here.

Other medical factors can put the baby at risk of low birth weight or prematurity. These risk factors are grouped in the following table.

Medical factors Low birth weight Prematurity
Untreated bacterial infections and viruses X X

(pregnancy hypertension)

Diabetes X X
Uterineabnormalities X X
Placental abnormalities X X
Medications X X
Infertilityandin-vitrofertilization X X
Trauma(pelvic fracture,severe cranial injury, etc.) X X


Vaginal bacterial infections are frequent during pregnancy (12 to 22%) and are associated with greater prematurity (average age of less than 32 weeks). These bacterial infections can arise from sexually transmitted diseases that can happen even during pregnancy. Certain infections such as chlamydia, gonorrhea, syphilis, and trichomoniasis can be treated with antibiotics. However, in the case of certain viruses such as herpes, HIV, or hepatitis B, they cannot be treated. The treatment of vaginal bacterial infections during pregnancy can reduce the risk of prematurity. Babies born prematurely often have a low birth weight and certain infections can cause complications during pregnancy. Other infections can also have a negative impact, especially urinary tract infections and gum infections. Both are associated with an increased prematurity risk.

It is important to get tested, even in the absence of symptoms, for sexually transmitted diseases, as well as other infections in the presence of symptoms. These symptoms include fever, burning sensations, or vaginal discomfort, vaginal discharge, or swelling of the lymphatic nodes.

To avoid infection risk, it is recommended to be in a long-term monogamous relationship and to use adequate contraceptive methods.


Preeclampsia is associated with an increased risk of low birth weight or prematurity, probably due to the decreased blood flow of the fetus. The quantity of oxygen and nutrients that the baby gets to develop is diminished and can thus cause decreased fetal growth. Thanks to medical improvement and frequently performed prenatal tests, the chances of fetal survival despite this condition are now better.


Pregnant women who are diabetic (existing or gestational diabetes) are at higher risk of preeclampsia or to give birth prematurely, spontaneously or provoked. The risk is increased when the diabetes is not well controlled.


Certain placental abnormalities, such as placenta prævia (placenta found in the inferior portion of the uterus) is associated with greater risk of prematurity, which in turn increases the risk of low birth weight. In certain cases of placenta prævia, spontaneous premature birth can occur, and a provoked premature labor can be indicated for the security of the infant and the mother.


Certain medications can cause intra-uterine growth retardation. The biological causes include loss of appetite, linked to certain medications, with direct effects on growth, and many malformation syndromes. A pregnant woman must always inform her doctor and pharmacist of her pregnancy. Certain natural health products can also increase the risk of premature labor. Pregnant women should ask a doctor before taking natural health products.


Infertility is frequently associated with in-vitro fertilization. In-vitro fertilization is linked to prematurity and low birth weight, as it predisposes to a multiple pregnancy and other risk factors, such as advanced age or pre-pregnancy overweight. More than 50% of twins are born prematurely and this rate increases with the amount of fetuses.

To learn more on how to avoid or decrease certain risk factors, click here.

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Ananth, C.V., Demissie, K., Smulian, J. C. & Vintzileos, A. M. (2001). Relationship among placenta previa, fetal growth restriction and preterm delivery: A population-based study. The American College of Obstetricians and Gynecologists, 98(2), 299-306.

Centers for Disease Control and Prevention. (2016). STDs during pregnancy – CDC Fact sheet.

Hillier, S.L., Nugent, R.P., Eschenbach, D.A. et coll. (2015). Association between bacterial vaginosis and preterm delivery of a low-birth-weight infant. New England Journal of Medicine, 333 (26), 1737-1742.

Institut canadien d’information sur la santé. (2009). Nés trop vite et trop petits : Étude sur les bébés de faible poids au Canada.

Institute of health economics. (2008). Alberta, Canada. Determinants and prevention of low birth weight: a synopsis of the evidence. Alberta : Institute of health economics.

Robinson, J. N. & Norwitz, E. R. (2016). Preterm birth: Risk factors and interventions for risk reduction. UpToDate.



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