Preterm birth is still the leading cause of death in children under the age of 5. It affects an estimated 13.4 million pregnancies every year – almost 1 in 10 live births. This rate hasn’t changed in the last decade, according to a major WHO and UNICEF report published in 2026.
Some countries did improve. Ten nations, including Spain, reduced their preterm birth rate by more than 5 percentage points over the decade. But even that translates to roughly 0.5 percentage points a year, a pace that makes the global target of cutting preterm birth in half by 2025 look increasingly out of reach.
Gestational Classification: Definitions for Extreme, Very, and Late Preterm Birth
Preterm birth is defined as delivery after 20 weeks and before 37 completed weeks of gestation. Within this range, it is categorized by timing:
- Extremely preterm (<28 weeks)
- Very preterm (28–31+6 weeks)
- Moderately preterm (32–33+6 weeks)
- Late preterm (34–36+6 weeks)
It’s worth noting that late preterm births make up the majority of the burden: roughly 85% of preterm deliveries occur between 32 and 37 weeks. This matters clinically, because outcomes in this group, while better than at earlier gestations, are still vulnerable compared to births at term. Even those born between 37 and less than 40 weeks, although not considered preterm, have a slightly elevated risk of death and an elevated risk of adverse neurodevelopmental outcomes.
Clinical Signs of Preterm Birth: Presentation, Diagnostic Criteria, and Differential Diagnosis
On their own, the signs of preterm labor are easy to miss or misread: regular contractions (sometimes painless), increased vaginal discharge, watery or mucoid leakage, lower back pain or pelvic pressure. Because preterm birth symptoms overlap heavily with normal pregnancy discomfort, differential diagnosis is essential. Contrary to real labor contractions, Braxton Hicks contractions are irregular and don’t intensify over time. Other mimickers that must be actively ruled out include urinary tract infection (dysuria, suprapubic pain), round ligament pain, and placental abruption.
Initial workup typically includes a speculum exam to assess for pooling amniotic fluid, nitrazine and fern testing to evaluate for rupture of membranes, fetal fibronectin (fFN) sampling, a rectovaginal culture for Group B Streptococcus, and a cervical exam to establish dilation, effacement, and consistency. Fetal fibronectin carries a particularly strong negative predictive value: a negative result between 22 and 34 weeks reliably indicates that birth will not occur within 14 days.
Labor definition thresholds and clinical cut-offs
The American College of Obstetricians and Gynecologists (ACOG) defines preterm labor as regular uterine contractions before 37 weeks of pregnancy accompanied by cervical change, or an initial presentation with dilation of 2 cm or more. International guidance from the World Association of Perinatal Medicine and the Perinatal Medicine Foundation (WAPM-PMF) recommends a stricter cut-off of 3 cm, reflecting evidence that labor is unlikely to reverse once that threshold is reached.
Contraction frequency thresholds are similarly inconsistent across the literature, ranging from 4 to 12 contractions per hour. ACOG does not include a fixed number in its definition. WAPM-PMF joint guideline recommends requiring 6 or more contractions per 30 minutes.
Cervical length adds another axis of stratification: measurements of 25 mm or less are associated with significantly increased preterm birth risk, and this measure is one of the two most common tools — alongside fFN — used to risk-stratify symptomatic women. Nevertheless, ultrasound measurement of the cervical length, despite being the gold standard for diagnosing threatened preterm labor, has a low predictive value, with a false positive rate of approximately 70%.
Neonatal Outcomes by Gestational Week: Survival and Morbidity Data for Clinical Counselling
Useful data regarding neonatal morbidity and mortality by gestational age come from a large US cohort covering 23–36 weeks of gestation performed by Manuck et al. (2016). The analysis indicates that neonatal death drops sharply with each extra week. Preterm birth complications include major morbidity (severe intraventricular hemorrhage, necrotizing enterocolitis, and bronchopulmonary dysplasia), which peak at 54.8% among babies born at 25 weeks, then fall. Minor morbidity moves the opposite way, peaking at 81.7% at 31 weeks, as death and major morbidity became less common. Hospital stays shorten too: for babies born between 26 and 32 weeks, each extra week in utero cuts the following NICU stay by at least 8 days.
Every week of gestation confers a measurable survival benefit, a principle directly useful in shared decision-making conversations. At a global level, the disparity in access to care is determinant: in high-income countries, roughly 9 in 10 extremely preterm babies (<28 weeks) survive, compared with fewer than 1 in 10 in low-income settings. This is a reminder that outcome data must always be interpreted alongside local level-of-care capacity.
Risk Stratification Tools and Clinical Decision Pathways
Threatened preterm labor puts clinicians in a bind: treatment isn’t free of consequences, yet withholding it carries risk too. Antenatal corticosteroids, routinely given to accelerate fetal lung maturation, have been linked to higher rates of transient respiratory problems, NICU admission, and hypoglycemia in babies whose mothers went on to deliver at term rather than preterm. From the economic side, hospitalizations for threatened preterm labor that ended without delivery in the US from 1999 to 2015 cost the healthcare system $4 billion, with a mean cost of $10,782 per patient.
The scale of the problem is significant. Only 50% of pregnancies with threatened preterm labor actually end in early delivery. Current diagnostic methods’ positive predictive value ranges from just 8% to 30%, producing false-positive rates as high as 70–92%. Part of the issue is that up to 60% of spontaneous preterm births occur in women with normal cervical length, meaning length-based screening alone misses a substantial share of real risk.
This is the gap that biomechanical measurement is designed to close. Cervical length, fetal fibronectin, and the Bishop score all measure the downstream consequences of cervical remodeling. But the cervix begins changing well before any of that becomes detectable: throughout pregnancy, its connective tissue undergoes a gradual reorganization of collagen structure, with declining collagen content and rising hydration, and this altered consistency precedes visible cervical shortening.
A 2025 meta-analysis pooling data from over 4,000 women across 13 studies lends weight to this approach, finding that elastography-based assessment of cervical consistency identified roughly three in four women who would go on to deliver preterm (Angelopoulou et al., 2025). If consistency really does shift earlier than length, it stands to reason that a device measuring stiffness directly could distinguish true labor from false alarms sooner, and with more precision, than tools built around anatomy alone.
CerviSense builds on this principle. It is a handheld, CE-marked, intravaginal probe that generates a torsional wave and converts its propagation into a cervical stiffness reading, in kilopascals, within seconds. The resulting stiffness value feeds directly into an AI-driven risk model to predict threatened preterm labor. Its reproducibility has already been demonstrated in a multicenter Spanish study, reaching excellent intra and interobserver agreement (Molina et al., 2023). We are currently conducting a clinical trial across 18 sites in Germany and Spain to demonstrate whether the Cervisense TPTL device can predict spontaneous preterm birth within 7 days.
Sources
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Bradley E et al. Born too soon: global epidemiology of preterm birth and drivers for change. Reprod Health. 2025 Jun 23;22(Suppl 2):105. doi: 10.1186/s12978-025-02033-x
Griggs KM et al. Preterm Labor and Birth: A Clinical Review. MCN Am J Matern Child Nurs. 2020 Nov/Dec;45(6):328-337. doi: 10.1097/NMC.0000000000000656.
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Lavie A, et al. Threatened preterm labor admissions: A population based study to assess trends and financial effect [35K]. Obstetrics & Gynecology. 2020;135:123S-123S. doi:10.1097/01.AOG.0000664536.04921.dc
Manuck TA et al. Preterm neonatal morbidity and mortality by gestational age: a contemporary cohort. Am J Obstet Gynecol. 2016 Jul;215(1):103.e1-103.e14. doi: 10.1016/j.ajog.2016.01.004.
Molina FS et al. Reproducibility and usability assessment of the novel Fine Birth device for threatened preterm labor diagnosis. Am J Obstet Gynecol MFM. 2023 Jul;5(7):100982. doi: 10.1016/j.ajogmf.2023.100982.