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Cover page of the Journal of Health Sciences

 Table of Contents  
Year : 2017  |  Volume : 10  |  Issue : 3  |  Page : 283-287

Analysis of risk factors of late preterm birth: A case-control study

Department of Obstetrics and Gynecology, Jawaharlal Nehru Medical College, Belgaum, Karnataka, India

Date of Web Publication5-Sep-2017

Correspondence Address:
Kamal P Patil
Department of Obstetrics and Gynecology, Jawaharlal Nehru Medical College, Belgaum, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/kleuhsj.ijhs_350_16

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Objective: The aim of this study is to identify the risk factors associated with late preterm births (LPBs).
Methodology: This case-control study was conducted in the Department of Obstetrics and Gynecology, teaching hospital attached to KLE University's Jawaharlal Nehru Medical College, Belagavi during May 2015–April 2016. A total of 918 women were enrolled into the study, 459 in each group. Women who delivered between 34 and 36 weeks 6 days were considered cases and controls were women who delivered from 37 weeks onward immediately after a case occurred. Gestational age was confirmed with ultrasonography before 20 weeks. Data were collected from the history of the patient and the medical records.
Results: Incidence of LPB was found to be 8% among total births. It was found that 55.1% were spontaneous births. The most common risk factor for LPB was hypertensive disorders of pregnancy (gestational hypertension [HTN]–4.8%, chronic HTN–5%, preeclampsia–36%, eclampsia–4.8%) followed by preterm premature rupture of membranes (32.7%), history of prior preterm births (19.2%), gestational diabetes (17.9%), multifetal gestation (16.6%), placenta previa (13.5%), and abruption placenta (9.8%). On analyzing neonatal outcome, sepsis was found in 25%, hyperbilirubinemia in 21.9%, respiratory distress syndrome in 19%, transient tachypnea of newborn in 9%, and patent ductus arteriosus in 2.9% of the neonates.
Conclusion: The indication for the induction or need for termination should be reevaluated in the late preterm gestation. To prevent LPB, identification of the risk factors is necessary and timing of delivery in each risk factor should be reassessed in advance before intended intervention. As LPB constitute the majority of preterm births, it is important to limit late preterm deliveries to clear maternal or fetal indication for delivery.

Keywords: Late preterm birth, preeclampsia, risk factor

How to cite this article:
Patil S, Patil KP. Analysis of risk factors of late preterm birth: A case-control study. Indian J Health Sci Biomed Res 2017;10:283-7

How to cite this URL:
Patil S, Patil KP. Analysis of risk factors of late preterm birth: A case-control study. Indian J Health Sci Biomed Res [serial online] 2017 [cited 2020 Jan 24];10:283-7. Available from: http://www.ijournalhs.org/text.asp?2017/10/3/283/213998

  Introduction Top

Preterm birth is a prime cause of infant morbidity and mortality worldwide. The term “Preterm birth” refers to all births occurring before 37 weeks of gestation or <259 days from the 1st day of the last menstrual period. It is further subclassified into extreme preterm (<28 weeks gestation), very preterm (28–<32 weeks gestation), moderate preterm (32–<34 weeks gestation), and late preterm (34–<37 weeks gestation).[1],[2],[3] The incidence of preterm births in developing countries ranges from 12% to 18% and India recorded the highest number of preterm births in 2010.[1] Neonatal mortality and morbidity associated with preterm births is significantly higher than term births. The frequency of adverse neonatal outcomes increases with decreasing gestational age, this trend is also evident in the gestational window of 34–36 weeks.[4] Mortality rate is seven times higher in moderately preterm and three times higher in late preterm births (LPBs) than term births.[4]

LPBs previously tagged as “near-term” babies contribute to about 70% of the preterm births.[5] It is a major public health concern due to its increasing prevalence, associated neonatal mortality and morbidity. Contrary to our belief that late preterm neonates walk out well similar to term babies, they are at a very high risk of immaturity related complications. Morbidities such as respiratory distress, temperature instability, hypoglycemia, kernicterus, apnea, feeding problems, and rehospitalization after neonatal discharge, neonatal, and postneonatal mortality are reported in LPBs.[4] Respiratory distress, patent ductus arteriosus (PDA), and sepsis are considered common neonatal complications. Furthermore, significantly increased rates of cerebral palsy, and mental retardation, and other major disabilities in the late preterm infant compared with term infant should be of great concern, because of the profound social burden.[6],[7] Prolonged hospitalization, rehospitalization, and long-term sequelae pose great financial and psychological burden on the family.

Previous research and available literature on LPBs focused to cluster the short-and long-term outcome. Less is known about the medical indications for late-preterm delivery. Recent rise in the LPB rates by 25% raises the question as to whether the indications for these births are justified.[5],[8] Evidence suggested that 32% of these deliveries were medically indicated.[4] It is important to know which medical indication is a major contributor in late-preterm delivery as the neonatal outcomes likely differ depending on the underlying pathophysiology of the complication.[9] The timing of delivery in such cases ought to balance the maternal and newborn risk with the risk of continuation of pregnancy, and however, evidence to guide the timing of delivery in certain conditions is limited.

Few indications can be expectantly managed with delivery ≥37 weeks to decrease the risk of neonatal morbidity and mortality without a significant increase in stillbirth. Thus, in many cases, it is possible to prevent LPB without negatively affecting the outcome.[9],[10] To identify these possible preventive measures, a better knowledge of the risk factors leading to LPB is essential. Defining risk factors aid in identifying at-risk women and early initiation of risk specific treatment.

As LPBs contribute to nearly two-thirds of preterm births, there is a paramount need to evaluate the risk factors leading to the same and identify the associated neonatal morbidities in these seemingly healthy neonates. With this background, we set our objective to assess the risk factors associated with LPB.

  Methodology Top

This case-control study was conducted for 1 year from May 2015 to April 2016 at KLES Dr. Prabhakar Kore Hospital and Medical Research Centre, Belgaum. Sample calculation was done, and it was found that we need to study 140 individuals in each arm. We have sufficiently crossed the statistically significant upper limit for the sample size. The technique used to calculate the sample size was - N = 2 (Zalpha+ Zbeta) PQ/(P0− P1).

Cases were 459 women who delivered at 34–36 weeks 6 days period of gestation and controls were 459 women who gave birth at 37 weeks onward immediately after a case occurred. Gestational age in both groups was confirmed by an ultrasound before 20 weeks of gestation. Women without an ultrasound before the 20th week of gestation were excluded from the study.

Cases and controls who met the inclusion criteria were identified and data were collected by direct interviewing with women and their relatives and from the records. Details regarding the neonate were collected at the time of discharge from the records. The study was approved by the Ethical and Research Committee, Jawaharlal Nehru Medical College, Belgaum, and ethical clearance was obtained before the commencement of the study.

A data collection instrument was designed which consisted of information regarding following;

  • Sociodemographic data
  • Maternal characteristics
  • Current pregnancy
  • Mode of delivery
  • Newborn condition and complications.

Statistical analysis

Data obtained were coded and entered into Microsoft Excel Worksheet. Association of each risk factor with LPB was obtained by Chi-square test. The values of P < 0.05 were considered statistically significant. Univariate logistic regression analysis was performed to identify one-to-one relationships between each risk factor, and LPB and measure of association were calculated by unadjusted odds ratio (OR) with corresponding 95% confidence interval.

  Results Top

The data were analyzed and the final results and observations were interpreted as follows.

Among the 459 cases, 55.1% were spontaneous in onset and 44.9% were induced/iatrogenic for either maternal or fetal indication, whereas among the controls 20.7% were induced and 79.3% were spontaneous births. Two hundred and fifty-six cases and 81 controls underwent a cesarean section and 203 cases and 378 controls delivered vaginally. The majority of the cases were 36 weeks (200) and 159 of them were 35 weeks at the time of delivery.

Mean age among cases was 24.4 and in controls was slightly less (23.8), and however, maternal age did not reveal statistical association as a risk factor. The majority of the cases were Primipara in both groups, 240 and 251 in cases and controls, respectively. Among the risk factors analyzed, maternal age, parity, and induced abortion did not show any association with LPB. Nonetheless, few of them showed significant association with LPBs. Their comparison with controls, P value, and OR with 95% confidence interval are shown in [Table 1]. Among the 459 cases, an overwhelming number of them had hypertensive disorders of pregnancy, followed by preterm premature rupture of membranes (PPROM). History of prior preterm birth (PTB) was the strongest risk factor with OR of 26.98, and placenta previa and multifetal gestation also showed high association with OR of 14.1 and 14.9, respectively. Other noteworthy variables included gestational diabetes mellitus (GDM) with OR of 9.8, Preeclampsia (PE) with OR of 8, abruption (OR– 5.4), and other hypertensive disorders of pregnancy.
Table 1: Risk factors analyzed

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Prevalence of neonatal complications and admission to intensive care unit was 80% in cases and 10% in controls. As cited in [Table 2], 25% of them had sepsis and 21.9% had hyperbilirubinemia, 9% and 19% had transient tachypnea of newborn (TTN) and respiratory distress syndrome (RDS), respectively. About 2.9% had PDA and 2.3% had intraventricular hemorrhage (IVH). Nearly 83.4% of cases delivered newborns with birth weight <2.5 kg. Along these lines, sepsis, hyperbilirubinemia, and RDS were the frequent complication in this gestational window. Neonatal mortality was found to be 6%.
Table 2: Neonatal complications and late preterm births

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  Discussion Top

The majority of studies in the past have studied risk factors for preterm births. Previous research on late preterm neonates focused on their physiologic immaturity with associated higher morbidities and mortality compared to neonates born ≥37 weeks gestation. Our study analyzed the risk factors for LPB, a population much different from the overall preterm births.

The incidence of LPB in our study was 8% of total births consistent with the review article published on LPB in 2010.[11] The percentage distribution of LPB in the present study was 21.78%, 34.64%, and 43.57% at 34, 35, and 36 weeks, respectively, similar to an Indian study conducted at Pune in 2015.[12] PPROM was found in 32.7% and it was found that 55.1% were spontaneous births and 44.9% were induced/iatrogenic LPBs. A retrospective study conducted in Texas concluded maternal age <17 and >35 increased the risk of late preterm, whereas our study did not show any significant association between maternal age and LPB.[13] In our study, no significant association was found with parity similar to results of a case-control study in Italy which quoted no association between parity and LPB in contrast to study at Melamed which concluded that there was a significantly increased prevalence of LPB among nullipara.[4],[14] In agreement with other available studies, history of previous preterm birth was seen in 19.2% of cases, 15% had previous one PTB, and 4.2% had previous 2 PTB and it was one of the strongest risk factors (OR-26.98) for LPB.[4]

In accord to a study conducted in Italy which reported hypertension (HTN) to be strongly associated with LPB, hypertensive disorders of pregnancy were another strong risk factor in the present study with PE (OR-8) and eclampsia (OR-3.8) comprising major input.[4] Similar results were acquired in various studies.[5],[8],[9],[12] In a retrospective cross-sectional analysis which analyzed routine delivery data from all births in San Antonio/Bexar County, Texas variables associated with an increased risk of LPB were black race, age <17, age ≥35, gestational HTN, chronic HTN, and diabetes.[13] The study had similar results with gestational HTN, chronic HTN, and diabetes as risk factors. Our study did not show any association between the previous history of induced abortion and LPB in contrast to Sandeep et al. study which suggested that induced abortions increased the risk of preterm delivery in subsequent pregnancies.

Multifetal pregnancy, placenta previa, and abruption placenta have been recognized as a risk factor for preterm births, the same is evident even in late preterm gestation. Our study had 16.6% of multifetal gestation, 13.5% of placenta previa, and 9.8% of abruption placenta. Each of them had a trivial association with LPBs comparable to the conclusion of Pune 2015 study and review article 2010.[11],[12]

On the subject of the neonatal outcome, the current study showed the momentous difference between the neonatal outcome of the term and LPBs. Among a range of neonatal morbidities studied, sepsis (25%), hyperbilirubinemia (21.9%), RDS (19%), and TTN (09%) were noteworthy with major contribution. PDA (2.9%) and IVH (2.3%) were other morbidities noted. Sepsis, hyperbilirubinemia, and RDS were of a greater magnitude. Comparable results were reported in available studies.[2],[7],[11],[12]

  Conclusion Top

Risk factors of LPB found in the current study were a history of prior PTB, gestational HTN, chronic HTN, PE, GDM, eclampsia, multifetal gestation, abruption, placenta previa, PPROM, and intrauterine device. History of prior preterm births and hypertensive disorders of pregnancy were major contributors. Neonatal mortality and morbidity is higher in LPB compared to term births. Sepsis, hyperbilirubinemia, and RDS were the frequent morbidities noted.

The indication for the induction or need for termination should be reevaluated in the late preterm gestation. To prevent LPB, identification of the risk factors is necessary and timing of delivery in each risk factor should be reassessed in advance before intended intervention. However, further research is considered necessary evaluating genitourinary infections leading to PPROM and spontaneous LPB. Nonevidence-based LPB deliveries should be avoided, cutting down unwarranted induction of labor in late preterm gestation, and close survey for infections followed by treatment provides a scope to prevent LPB.

As LPB constitute the majority of preterm births, it is important to limit late preterm deliveries to clear maternal or fetal indication for delivery. Screening for patients with aforementioned risk factors and modification of the same will further help in better outcome of the pregnancy.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

WHO. Preterm Birth; 2012. Available from: http://www. Who. Int. [Last accessed on 2015 Jan 30].  Back to cited text no. 1
Engle WA, Tomashek KM, Wallman C; Committee on Fetus and Newborn, American Academy of Pediatrics. “Late-preterm” infants: A population at risk. Pediatrics 2007;120:1390-401.  Back to cited text no. 2
Committee on Obstetric Practice. ACOG Committee Opinion No 404 April 2008. Late-preterm infants. Obstet Gynecol 2008;111:1029-32.  Back to cited text no. 3
Mandruzzato GP, Calì G, Chiaffarino F, Dal Pozzo G, Danti L, Gerosa V, et al. Risk factors for late preterm births: A case control study. J Gynecol Obstet 2013;3:182.  Back to cited text no. 4
Barton JR, Barton LA, Istwan NB, Desch CN, Rhea DJ, Stanziano GJ, et al. Elective delivery at 340/7 to 366/7 weeks' gestation and its impact on neonatal outcomes in women with stable mild gestational hypertension. Am J Obstet Gynecol 2011;204:41-5.  Back to cited text no. 5
Available from: https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pretermbirth.htm. [Last accessed on 2017 Jun 26].  Back to cited text no. 6
Jain L. Morbidity and mortality in late-preterm infants: More than just transient tachypnea! J Pediatr 2007;151:445-6.  Back to cited text no. 7
Reddy UM, Ko CW, Raju TN, Willinger M. Delivery indications at late-preterm gestations and infant mortality rates in the United States. Pediatrics 2009;124:234-40.  Back to cited text no. 8
Laughon SK, Reddy UM, Sun L, Zhang J. Precursors for late preterm birth in singleton gestations. Obstet Gynecol 2010;116:1047-55.  Back to cited text no. 9
Rubaltelli FF, Dani C, Reali MF, Bertini G, Wiechmann L, Tangucci M, et al. Acute neonatal respiratory distress in Italy: A one-year prospective study. Italian Group of Neonatal Pneumology. Acta Paediatr 1998;87:1261-8.  Back to cited text no. 10
Loftin RW, Habli M, Snyder CC, Cormier CM, Lewis DF, Defranco EA. Late preterm birth. Rev Obstet Gynecol 2010;3:10-9.  Back to cited text no. 11
Sandeep T, Chaya V, Sandhya K. Early morbidities and mortality in late preterm birth and associated maternal risk factors: A tertiary care experience. Int J Recent Sci Res 2016;7:9118-24.  Back to cited text no. 12
Carter MF, Fowler S, Holden A, Xenakis E, Dudley D. The late preterm birth rate and its association with comorbidities in a population-based study. Am J Perinatol 2011;28:703-7.  Back to cited text no. 13
Melamed N, Klinger G, Tenenbaum-Gavish K, Herscovici T, Linder N, Hod M, et al. Short-term neonatal outcome in low-risk, spontaneous, singleton, late preterm deliveries. Obstet Gynecol 2009;114(2 Pt 1):253-60.  Back to cited text no. 14


  [Table 1], [Table 2]

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