Causes and Risk Factors - a quick look

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Although the cause of preterm birth is often unknown, expectant parents need not leave it purely to chance. There are a number of things a potential or expectant mother should and should NOT do, to limit the chances of preterm birth.


Healthy mother, healthy baby

The cause/s of preterm birth may be due to a number of very different events or triggers. Although there are a lot of risks identified there are no good predictors of preterm birth. This section is intended to give you a guide and a better understanding of the risks, some of which are easier to avoid than others depending on your personal circumstances.
Preemie help is here to help you identify any factors you may be able to avoid.


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Small for gestational age

Small for gestational age, or SGA, is defined as having a birth weight less than the 10th percentile on the standard growth curve for a particular gestational age. Sometimes this is called intrauterine growth restriction (IUGR).

Causes of Growth Restriction

Insufficiency of the placenta

The fetus gets its supply of nutrients and oxygen through the placenta. That means that anything that interrupts the efficient flow of nutrient-rich blood and oxygen through the placenta will affect the growth of the fetus. Placental insufficiency can be caused by illnesses that affect the mother’s circulation, such as preeclampsia, heart disease, and diabetes. Other causes include defects to the placenta, such as placental abruption, a poorly functioning placenta due to malformation or because its small, or one damaged from infection, inflammation, or lack of blood flow and oxygen.

Chromosomal or other congenital abnormalities

Various genetic and congenital abnormalities are associated with fetal growth restriction. For example, Trisomy 21, Trisomy 18, congenital heart disease, diaphragmatic hernia, tracheo-oesophageal fistula.


Some infections can be transmitted to the fetus from the mother if she gets unwell during pregnancy and can affect growth and development, as well as cause other serious problems. Come colds and flu rarely harm the fetus, however some of the common infections that are harmful include, rubella (which causes German measles), herpes, cytomegalovirus (called CMV), toxoplasmosis, and syphilis.

Smoking, drugs, and alcohol

Expectant mothers, who engage in risky behaviours, such as smoking, drinking heavily, or using drugs like cocaine, heroin, and amphetamines, are more likely to have small for gestational age babies.


Poor nutrition in pregnant mothers and those who gain too little weight are also at risk for malnourished and growth restricted infants.

(Avery, Fletcher, & MacDonald, 1999; Thureen, Anderson, & Hay, 2001)

Technical Reference List

Avery, G. B., Fletcher, M. A., & MacDonald, M. G. (1999). Neonatalogy (5 ed.). Philadelphia, Pa: Lippincott Williams & Wilkins. Thureen, P. J., Anderson, M. S., & Hay, W. W. (2001). Small for gestational age. NeoReviews, E139 - e149.



AlbertEinstein_iconOne of the greatest minds in history, Albert Einstein was born preterm.

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Preemie, Premmie, or Prem?

Most babies spend between 38 and 42 weeks in their mother’s uterus. So, technically a preterm birth, preemie, premmie, or prem, is an infant who is born less than 37 completed gestational weeks. 

Read More: Defining Preterm birth



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