Introduction
Preterm birth (PTB) is the most significant cause of neonatal mortality and morbidity. It is called preterm birth if delivery happens in less than 37 weeks of gestation. One of the major steps in preterm birth prevention is risk assessment. The risk stratification includes obstetric history, maternal risk factors, and screening tools. The preventive strategy varies per pregnancy population.
In about two-thirds of cases, preterm birth is spontaneous; in about one-third of cases, it is induced due to medical issues like fetal growth restriction, preeclampsia, etc. Preterm babies are more prone to have short-term morbidities like intracranial hemorrhage, respiratory issues, necrotizing enterocolitis, patent ductus arteriosus, infection, etc. Therefore, PTB prevention is one of the major goals of obstetric care.
What Are the Risk Factors?
The initial step in PTB prevention is accurate risk assessment and proper screening of risk factors.
The risk factors are divided into:
1. Maternal Risk Factors:
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Ethnicity - Some studies suggest ethnic differences in PTB risk.
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Maternal BMI (Body Mass Index) - Extremely low or high pre-pregnancy BMI of the mother increases the risk of PTB.
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Smoking - Smoking during the pregnancy period increases PTB risk.
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The Periodontal Disease of Mother - Maternal periodontal disease is linked to spontaneous PTB. This is due to the hematogenous spread of inflammatory cytokines and pathogens.
2. Obstetric History:
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Previous PTB History - A previous PTB history increases the risk of recurrence.
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Curettage in History - Women who have undergone miscarriages or terminations in the past managed by cervical dilatation and curettage are at greater risk for spontaneous PTB.
3. Maternal History:
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Previous Excisional Cervical Procedures - Women who have undergone excisional procedures for cervical dysplasia are at increased risk of PTM.
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Uterine Anomalies - Women with uterine anomalies like a uterine septum, a bicornuate uterus, etc., are at increased risk of PTB.
4. Issues Related to Current Pregnancy:
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Multiple Gestations - Women with multiple pregnancies are at increased risk.
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Pregnancy Interval - Shorter and longer pregnancy intervals are linked to a greater risk of PTB.
What Are the Screening Tools for PTB Prevention?
Women with singleton pregnancies without a prior history of PTB are at greater risk when compared to women with multiple pregnancies. 60 percent of women with multiple gestations deliver prematurely. Risk stratification is based on risk factors and screening tools that help in the optimal prevention of PTB.
1. Cervical Length:
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In women with a singleton pregnancy with no prior history of PTB, a shorter cervical length during the mid-trimester increases the risk of spontaneous PTB.
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In women with uterine anomalies, a cervical length of fewer than twenty-five millimeters is associated with PTB of less than 35 weeks.
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In women with multiple gestations without prior PTB history, a cervical length of less than 25 mm in mid-trimester is associated with an increased risk of PTB.
2. Bacterial Vaginosis:
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Bacterial vaginosis is an abnormal condition of the vagina due to the overgrowth of certain bacterial species that replace the normal flora. This condition is associated with increased PTB risk.
What Are the Preventive Measures for PTB?
Healthcare providers should inform patients about their risks based on the women’s risk assessment.
1. Progesterone:
Progesterone is a significant hormone for maintaining pregnancy. During the initial stages of pregnancy, progesterone is produced by the corpus luteum. Progesterone administration is done to prevent preterm cervical ripening.
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Women with multiple gestations without prior PTB history- Studies found no significant effect of vaginal progesterone in preventing PTB in women without prior PTB history.
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In women with previous PTB history, vaginal progesterone was found to reduce the recurrence of spontaneous PTB.
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In women with a singleton pregnancy with no prior history of PTB, studies suggested a reduction in PTB.
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No differences in the effectiveness of muscular and vaginal progesterone have been found.
2. Cervical Pessary:
The cervical pessary is a silicone device that is flexible and short. Cervical pessaries prevent premature membrane rupture and premature cervical dilatation. It also acts as an immunological barrier between vaginal microflora and chorion and thus further aids in preventing PTB.
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Only limited evidence is available for PTB prevention in women with a singleton pregnancy, no prior history of PTB, and a short cervix.
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In the case of women with multiple gestations without prior PTB history, studies suggest conflicting results regarding the efficacy of pessaries in PTB prevention.
3. Cerclage:
Cervical cerclage is a surgical intervention that is mostly used for managing pregnancies that are at high risk for PTB. In the procedure, a securing suture is placed around the cervix to prevent cervical shortening.
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There is no evidence of PTB prevention in women with singleton pregnancies with no previous history of PTB.
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In the case of women with multiple gestations without prior PTB history, only limited data are available on PTB prevention using cervical cerclage.
In the case of women with a previous history of PTB, there are two indications for cerclage:
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Primary cerclage/ history-indicated cerclage/ elective cerclage.
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Secondary cerclage/ultrasound indicated cerclage- women with a high risk based on obstetric history and a short cervix benefit from this cerclage.
What Are the Recent Developments in PTB Prevention and Reduction?
The recent developments are:
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Probiotics: Several studies have suggested probiotics as a preventive measure for PTB prevention, but the results are often conflicting. A Norwegian study reported the preventive effect of probiotics (through milk intake) on spontaneous PTB prevention.
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Genetics: Studies suggest genetics is an important risk factor for PTB. Epidemiological studies suggested that mothers who were delivered preterm or had close relatives (siblings, maternal half-sisters, etc.) who had a PTB were at greater risk.
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Biomarkers: Recent research has focused on using biomarkers to screen targets for PTB. Recent research found that some functional proteomic biomarkers are found uniquely in the first trimester in those women who later underwent PTB. These biomarkers help identify the risk groups, and hence these groups benefit from the preventive measures.
What Are the Individual Measures One Can Take To Reduce PTB Risk?
Following a healthy lifestyle includes:
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A balanced diet is rich in folic acid and iron.
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Avoid smoking.
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Avoid alcohol.
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Maintaining proper body weight.
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Stress management.
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Regular physical exercise.
Look out for signs of premature labor, which are:
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Pressure in the pelvic region or vagina.
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Abdominal cramps.
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Lower backache.
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Increased vaginal discharge.
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Bleeding from vagina.
Conclusion
PTB prevention is a significant obstetric goal for reducing infant mortality and morbidity. For optimal PTB prevention, risk stratification must be based on a combination of obstetric history, maternal risk factors, and screening tools.
