Individualizing the Risk for Preterm Birth

An Overview of the Literature

Melanie van Os; Jeanine van der Ven; Brenda Kazemier; Monique Haak; Eva Pajkrt; Ben W Mol; Christianne de Groot


Expert Rev of Obstet Gynecol. 2013;8(5):435-442. 

In This Article

Abstract and Introduction


Preterm birth is the most important cause of perinatal morbidity and mortality worldwide, and ranks among the top 10 of global causes of burden of disease. Since treatment of threatened preterm delivery has limited effectiveness, the focus is on primary and secondary prevention. Identification of risk indicators in early pregnancy provides the opportunity for preventive measures. To determine the potential impact of individualized risk indicators on the prediction of preterm birth, we reviewed the literature on this topic. Risk indicators for spontaneous preterm birth can be categorized in five groups; characteristics of the individual (ethnicity/race), characteristics of the fetus (fetal gender fetal number and chorionicity), obstetric history (history of preterm birth), modifiable risk indicators (social status, life style, infection) and signs of early labour; potential predictors (sonographic markers, biomarkes). Risk for preterm birth can be seen as a continuous transition from one state to the other. The number of studies that integrate these data is limited.


Preterm birth is the most important cause of perinatal morbidity and mortality in obstetric practice.[1] Preterm birth is traditionally defined as a delivery that occurs before 37 completed weeks of gestation. The preterm birth rate has been reported as an estimated 14.9 million, 11.1% of all live births worldwide, ranging from approximately 5% in some European countries to 18% in several African countries. More than 60% of preterm births take place in south Asia and sub-Saharan Africa, where 52% of the global live births take place. Preterm birth also affects developed countries, USA, for instance is one of the ten countries with the highest numbers of preterm births.[2] 45–50% of preterm births worldwide are estimated to be idiopathic, 30% are related to preterm prelabour rupture of membranes (PPROM) and another 15–20% are ascribed to medically indicated or elective preterm deliveries.[3]

Its impact on public health has resulted in broad attention to this topic in scientific research. Preterm birth was recently ranked in the top 10 causes of global burden of disease, justifying its reduction to become a main goal of the global community.[4]

Treatment of threatened preterm birth has limited effectiveness, as antenatal administration of corticosteroids is the only intervention proven to improve neonatal outcome.[5] Since prevention seems to be more effective than treatment, the medical world is searching for tools to identify women at risk for spontaneous preterm birth. Several prediction models have been proposed including variables such as maternal indicators, for instance age, anthropometry and medical history, pregnancy characteristics like vaginal bleeding, markers early in pregnancy by physical examination and biological markers to predict spontaneous preterm birth.

Although these predictive indicators are usually not classified, we hypothesize that their origin and nature is clearly different. Some indicators are a non-modifiable characteristic of the woman (including ethnicity and medical and obstetric history) or the fetus (including fetal gender, fetal number and chorionicity). Other indicators are modifiable, including smoking, ovarian stimulation, number of embryos transferred, life style and infection. Finally, indicators which are essentially signs of early labor and among which a short cervical length and fetal fibronectin, should be considered. Preterm birth can be the result of three obstetrical circumstances: 1) preterm labor with intact membranes; 2) preterm prelabor rupture of membranes (PROM); and 3) 'indicated' preterm birth, which occurs when maternal or fetal indications require delivery before 37 weeks of gestation.[6] The aim of the current manuscript is to provide an overview of current knowledge on risk indicators for spontaneous preterm birth (1,2), defined as delivery before 37 weeks in singleton pregnancies. Since the multitude of different risk indicators makes it impossible to discuss them all, we decided to make a selection of risk indicators, based on their importance stated in current literature. We subsequently categorized risk indicators into characteristics of the individual women, fetal characteristics and obstetric history as well as modifiable indicators (infection socio-economic status) and signs of early labor; potential predictors. Our general approach was not to repeat searches of the literature, but rather aim to complete existing reviews and discuss the literature from the perspective of impact of individualized risk indicators