Assessing the Risk of Preterm Birth: Strategies for Early Detection and Prevention
1. Introduction
1.1. Introduction to Preterm Birth: Global Impact and Definitions
A normal pregnancy lasts 37 to 42 weeks. Preterm birth (PTB) is defined as the occurrence of birth before 37 completed weeks of gestation (1). Around 15 million babies are born preterm each year globally, reflecting a worldwide preterm birth rate of approximately 11% (2). More disappointingly, an estimated 1 million children lose their lives each year as a result of complications associated with PTB, with 60% of these cases occurring in developing countries (3).
1.2. Adverse Outcomes of Preterm Birth
PTB is linked to both immediate and long-term complications. It is a leading cause of mortality among children under five, accounting for one-third (33.1%) of neonatal deaths and 15.9% of all under-five child fatalities worldwide (1). Also, PTB poses a heightened risk for developmental disabilities and growth issues, accounting for 75% of perinatal deaths and 50% of neurological abnormalities. It contributes to short-term and long-term complications, including motor development delays, behavioral impairments, and diminished academic performance in later life. Beyond the substantial health impact on the infant, PTB also results in economic burdens for families, communities, and the nation (3).
PTB is also linked to significant economic costs during infancy and later in life. A study utilizing national data from 39 countries with a very high human development index, estimated that US$3 billion annually could be saved by preventing 58,000 preterm births. Additionally, research from Australia in 2013 indicated that the average annual hospitalization costs for infants decreased by 10–25% with each additional week of gestational age (4, 5).
2. Key Risk Factors for Preterm Birth
2.1. Non-Modifiable Risk Factors: Focus on High-Risk Pregnancies
Various clinical factors play a significant role in the occurrence of PTB, some of which are non-preventable and could be considered as factors that need extra care. Some of these key risk factors for a first preterm birth include chronic hypertension, gestational diabetes (GDM), early menarche (before the age of 12), and a history of miscarriage. For all instances of PTB, the primary risk factors encompass a previous history of preterm birth, early menarche, lack of a partner, chronic hypertension, gestational diabetes, and asthma. Notably, PTB is less likely to occur in subsequent pregnancies and among women with a university degree compared to those with only a high school diploma (Figure 1) (1).
Figure 1. The key risk factors for PTB and their associated odds ratios (OR). This visualization highlights both the risk factors for first PTBs and all PTBs, as well as protective factors such as subsequent births and higher education.
Additional factors contributing to PTB risk include extreme maternal age (under 20) (6), pregnancy-induced hypertension (PIH), antepartum hemorrhage (APH), multiple pregnancies, short intervals between births, premature rupture of membranes (PROM), chronic medical conditions, and HIV-positive status in mothers (3). Women with a birth interval of less than two years face a 2.96-fold increased likelihood of experiencing PTB compared to those with longer intervals. Furthermore, women who develop anemia during pregnancy are 4.20 times more likely to experience PTB than those without anemia. Mothers with PIH have odds that are 3.13 times higher for developing PTB compared to those without this condition (3).
2.2. Modifiable Risk Factors: Opportunities for Intervention
Conversely, some risk factors can be modified to reduce the likelihood of preterm birth and its adverse outcomes. For instance, having more than four antenatal care (ANC) visits significantly decreases the risk of PTB. These sessions provide essential care aimed at promoting low-risk pregnancies. It is crucial for women to be aware of the risk factors associated with PTB and to seek adequate prenatal care. While the history of conditions leading to PTB is not modifiable, understanding these factors can enhance the quality of care provided to high-risk women. Consequently, a comprehensive medical history is vital at the onset of ANC. Inquiring about previous instances of PTB or PROM is essential; women who have experienced PROM are 3.57 times more likely to have PTB compared to those who have not. Additionally, a lack of dietary supplementation during pregnancy has been associated with a 2.43-fold increase in the odds of PTB (3). Urogenital infections are significant risk factors for PTB, and many of these infections can be prevented through proper personal hygiene during pregnancy (6).
Ensuring adequate nutrition through at least four meals a day and supplementary feeding under the Integrated Child Development Scheme (ICDS), is crucial (7).
Various lifestyle and health-related factors have been identified to significantly increase PTB risk. Experiencing a stressful life event during the final month of pregnancy is associated with a 2.62 times higher risk of PTB. Dissatisfaction with one’s health increases the risk by 2.54 times, highlighting the importance of mental well-being during pregnancy (8).
Physical exertion, specifically standing for more than 2.5 hours during the third trimester, also increased the likelihood of PTB by 1.91 times. This may be due to reduced blood flow to the placenta, potentially triggering labor (8). Women employed in labor-intensive occupations had a 20% higher risk of preterm delivery compared to those working as legislators or managers (9). Prolonged standing at work for seven or more hours a day, working in hot environments, commuting, walking, lifting heavy objects, and night shifts have all been linked to an increased risk of pregnancy loss and PTB, particularly in women with compromised nutritional status. Additionally, counseling can help promote afternoon rest for two hours and encourage a minimum of four ANC visits during pregnancy (7).
On the other hand, abstaining from sexual activity for seven days in the later stages of pregnancy is protective, reducing the risk of PTB by 54%. This is likely linked to avoiding factors such as increased uterine pressure, membrane rupture, and the effects of prostaglandins present in seminal fluids (8).
These findings emphasize the importance of focusing on modifiable behaviors to lower the risk of PTB and preventive measures to reduce preterm birth should prioritize addressing modifiable factors while enhancing healthcare quality for individuals with unmodifiable risk factors.
| Non-modifiable Risk Factors | Modifiable Risk Factors |
| History of Preterm Birth Chronic Hypertension Gestational Diabetes (GDM) Early Menarche History of Miscarriage Lack of Partner Asthma Extreme Maternal Age Pregnancy-Induced Hypertension (PIH) Antepartum Hemorrhage (APH) Multiple Pregnancies Short Intervals Between Births Premature Rupture of Membranes (PROM) Chronic Medical Conditions HIV-Positive Status | Antenatal Care Visits Awareness of Risk Factors Dietary Supplementation Stress Management Mental Well-Being Physical Activity Management Employment Conditions Rest and Recuperation Sexual Activity Abstinence Urogenital Hygiene |
3. The Importance of Early Risk Identification
Early identification of pregnancies at risk for adverse outcomes is a fundamental aspect of maternity care, enabling timely intervention and management to improve maternal and neonatal health. The early prediction of pregnancies at heightened risk for PTB primarily relies on evaluating maternal and obstetric history, with a previous occurrence of PTB recognized as the most influential risk factor. However, the impact of environmental and lifestyle factors on PTB occurrence should not be neglected. It has become increasingly clear that PTB represents the outcome of various underlying pathologies. As a result, a uniform approach to prediction and prevention across all pregnancies is impractical (10).
4. Assessing Cervical Length for Early PTB Prediction
The clinical identification of women at risk for PTB primarily relies on nonspecific factors, such as socioeconomic status, a prior history of preterm birth, or the presence of a short cervix. Although a prior PTB is the strongest predictor, this does not apply to many pregnancies—40% occur in nulliparous women, and only 7.2% of multiparous women have a history of PTB. Cervical shortening is observed in about 1–2% of the general population, but its predictive value for PTB in both nulliparous and multiparous populations is modest (11).
Guidelines recommend that women with identified risk factors for PTB could benefit from an opportunistic cervical length measurement during the first-trimester anomaly scan, typically conducted between 12 and 14 weeks of gestation (11, 12). However, this is specified for high-risk pregnancies and there is no valid method to predict PTB in low-risk and non-symptomatic pregnancies. As mentioned in the previous sections, there is a wide variety of lifestyle and environmental risk factors with noticeable reported odds ratios which can be used to design a risk assessment tool to predict the risk of PTB in the current pregnancy in both the first and second half of the pregnancy and in low and high-risk cases.
5. March Health Risk Assessment Tool: A Proactive Approach
This self-assessment tool is designed to provide a comprehensive evaluation of risk for PTB based on established evidence in the field of obstetrics. It systematically assesses both environmental factors and medical conditions, allowing for a nuanced understanding of individual risk profiles about gestational age. The questions are thoughtfully tailored to take into account personal medical history, particularly focusing on whether a previous preterm birth has been experienced—one of the most critical risk factors associated with PTB. By considering a range of influences, including lifestyle choices, existing health conditions, and social determinants, this tool aims to deliver a holistic view of risk. Additionally, the self-assessment offers insights into how specific factors may interact with one another, providing a clearer picture of overall vulnerability to preterm birth. After the assessment is completed, personalized feedback and recommendations for further action will be provided, which may include discussions with healthcare providers about preventive measures and appropriate prenatal care. This proactive approach empowers individuals to make informed decisions about their pregnancies and enhances the ability to seek timely interventions if necessary.
6. References
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2. Walani SR. Global burden of preterm birth. International Journal of Gynecology & Obstetrics. 2020;150(1):31-3.
3. Abadiga M, Wakuma B, Oluma A, Fekadu G, Hiko N, Mosisa G. Determinants of preterm birth among women delivered in public hospitals of Western Ethiopia, 2020: Unmatched case-control study. PloS one. 2021;16(1):e0245825.
4. Chang HH, Larson J, Blencowe H, Spong CY, Howson CP, Cairns-Smith S, et al. Preventing preterm births: analysis of trends and potential reductions with interventions in 39 countries with very high human development index. The Lancet. 2013;381(9862):223-34.
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6. Chiabi A, Dobgima W, Achuh W, Niba L, Teke G. Prevalence, Risk Factors, and Hospital Outcome of Preterm Births in a Regional Hospital in Cameroon. Dates. 2022;2:1-9.
7. Salunkhe AH, Salunkhe JA, Mohite VR, More U, Pratinidhi AK, Kakade SV. Development of risk scoring scale tool for prediction of preterm birth. Indian Journal of Community Medicine. 2019;44(2):102-6.
8. Peiris D, Jayaratne K, de Alwis Seneviratne R. Risk factors of preterm birth in Sri Lanka: case-control study. Journal of the College of Community Physicians of Sri Lanka. 2023;29(2).
9. Park JH, Lim S, Lim J, Kim K, Han M, Yoon IY, et al. An overview of the Korean longitudinal study on health and aging. Psychiatry investigation. 2007;4(2):84.
10. Ramachandran A, Clottey KD, Gordon A, Hyett JA. Prediction and prevention of preterm birth: Quality assessment and systematic review of clinical practice guidelines using the AGREE II framework. International Journal of Gynecology & Obstetrics. 2024.
11. Branch DW, VanBuren JM, Porter TF, Holmgren C, Holubkov R, Page K, et al. Prediction and Prevention of Preterm Birth: A prospective, randomized intervention trial. American Journal of Perinatology. 2023;40(10):1071-80.
12. Munim S, Islam Z, Zohra N, Yasmin H, Korejo R. Guidelines on prevention of preterm birth. The Journal of Maternal-Fetal & Neonatal Medicine. 2022;35(25):9527-31.
