@2024 Afarand., IRAN

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ISSN: 2251-8215    Sarem Journal of Reproductive Medicine 2019;3(1):19-23

Background
Preterm labor is a labor before the 37th week of gestation which is the main reason for the death of infants[ 1]. Therefore, about 28% of newborn infants are directly associated with preterm labor[2].
Previous Studies
… [3]. Various studies have been done to find effective factors in preterm labor that based on them maternal factors such as infection, bleeding, uterine and cervical factors, previous pregnancies, demographic factors and factors such as oligohydroaminos and polyhydroaminos, diabetes mellitus and high blood pressure in pregnancy, and fetal factors such as the anomalies of the nervous system have confirmed as effective factors in the occurrence of preterm labor pregnancy[4-8]. Also, some factors such as multiple birth, a small interval between pregnancies and a history of abortion are also considered as proven effective factors in preterm labor[8-10]. According to a study that examined 219868 women from 2004 to 2011, maternal BMI was a major contributor to high labor and high blood pressure and gestational diabetes[11]. In addition, in studies, genitourinary tract infections have been called as an important factor in causing preterm labor[12].
Aim(s)
Considering the importance of preterm labor in mortality and neonatal problems, numerous studies have been carried out in this regard[1, 3]. However, the difference between social factors in different societies, such as the age of marriage and pregnancy, or the type of nutrition during pregnancy, genetic, anatomical and physiological differences in human populations, as well as the existing of anti-conflicting results in previous studies, still requires more extensive studies with a prominent sample. Therefore, this study was conducted to investigate some effective maternal factors in preterm labor.
Research type
This cross-sectional study is descriptive-analytic and retrospective.
Research society, place and time
2432 women were studied as samples.
Sampling method and number
Criteria for entering the study were not having known causes such as fetal abnormalities and genetic problems in these couples, and negative outcome of the leukocyte cross-match test for anti-paternal cytotoxic antibodies (APCA). Accordingly, 61 patients were enrolled in the study.
Used devices&materials
Patients’ demographic information and some of the high risk factors are based on previous studies such as maternal age,, BMI status, history of thyroid disease, history of high blood pressure before pregnancy, history of previous abortion (at least one abortion), Intrauterine Fetal Death (IUFD), history of diabetes, history of ectopic pregnancy, Premature Rupture of Membrane (PROM), incidence of preeclampsia, history of labor or parity, double or multiple pregnancy, and amniotic fluid volume using a researcher-made questionnaire. Data were analyzed using SPSS 22 software. The analysis of maternal risk factors in preterm labor was done using descriptive statistics and Man-Whitney, Fisher’s exact and Chi-square tests.
Findings by Text
The mean age of the studied population was 30.75±3.97 years with a range of age from 19-45 years. The disease was not observed at the age of less than 18 years. The frequency of pregnancies in mothers varied from 1 to 11 cases. In general, 237(%9.75) had preterm labor. 2086 (85.77%) had term labor, and 109 (4.48%) had late labor. The mean age of women with preterm labor was 30.97±4.54 years that was not significantly different from women with term labor with mean age of 30.52±3.9 (p=0.159). The BMI of these women was 11-50 kilogram per square meter with the mean 24.00±3.87 kilogram per meter square. Significant difference was observed between the status of BMI and the occurance of preterm occurrence (p=0.027; Table 1). Frequency of women over 35 years of age with a high prevalence was significantly higher than that of mothers under 35 years of age (p=0.004; Table 1). Other factors include history of thyroid, history of PROM, IUFD, preeclampsia, history of labor or parity, double or multiple pregnancy, and decreased amniotic fluid volume showed a significant correlation with the prevalence of labor (p<0.05). There was no significant relationship with other maternal factors including the history of pre-pregnancy controlled blood pressure, history of abortion, diabetes history, and history of ectopic pregnancy (Table 1).
Main comparison to the similar studies
The prevalence of preterm labor in women was 9.75%. Although some sources, including a study in 2003, evaluated the prevalence of preterm labor as 11.0%[13] and its prevalence was higher in Asia than in Europe, but the global average was estimated to be 6.9%[3]. In some studies in Iran, it has reported a prevalence of 5.5%-8.2%[14] that the reason for high prevalence of preterm labor in this study can be due to the fact that the center of this study (Sarem Specialist Hospital) is reference of patients with more risk factors that their pregnancy problems have been diagnosed in other centers and have referred to this hospital for labor. Various maternal factors are known to affect preterm labor. Previous studies have shown that there is a significant relationship between maternal age and preterm labor[15, 16]. However, there was no a significant relationship between maternal age and preterm delivery in the present study. The reason for this inconsistency with the previous findings is the cultural difference in the gestational age of people in Tehran in one hand, and on the other hand, the referral nature of the Sarem Hospital in terms of the rate of referral of patients with acute problems. In the case of BMI, these factors can also be involved. In this study, there was a significant statistical relationship between PROM and preterm labor which confirms many studies that have identified the premature rupture of membrane as the main effective factor in preterm labor[16, 17]. Having a history of abortion was not significantly correlated with at least one preterm labor that was consistent with the findings of previous study[16, 18]. The significance of differences in this field may be better discussed with higher sample sizes. Based on our findings, there was no significant relationship between the history of hypertension and the high prevalence of labor which was consistent with previous studies in Iran[19]. Also, there was a significant relationship between preeclampsia and preterm labor which confirms the study by Martius et al. and other studies[16, 20, 21].In this study, there was no significant relationship between gestational diabetes and preterm labor which is in contradiction with a series of studies including the study by Heardson et al.[22]. This lack of difference could be due to the type of population referred to Sarem Hospital and the continuous control of diabetes mellitus by patients in Tehran.In our study, there was a significant correlation between amniotic fluid deficiency and preterm delivery which is consistent with the findings of previous studies[23, 24]. In some studies, such as Austolfi et al. there was a correlation between fetal sex and preterm labor[25].
Suggestions
Considering the importance of education of mothers about the factors affecting the occurrence of preterm labor, in order to prevent and control it, study of these cases are emphasized. Therefore, more prospective studies with more sample size and greater efforts are recommended to improve the accuracy of the studies. Considering the maternal condition in terms of age, BMI, as well as the regular monitoring of amniotic fluid volume and other controlled factors of fetus, including the occurrence of preeclampsia, the reduction of multiple risk of multiple birth in applying ARTs, diabetes control and primary hypertension and thyroid disease, and considering the importance of identifying the cause of previous IUFD as a prerequisite for preterm labor in this study, the incidence of this problem in pregnant women can partly be reduced.
Limitations
Our study, although satisfactory in the sample size, was not free of errors due to its retrospective nature and reliability on the medical records of individual.
Conclusions
Maternal factors such as BMI, age (over 35 years), history of thyroid disease, history of PROM, IUDF, preeclampsia, history of labor or parity, two or multiple pregnancies, and amniotic fluid loss are effective on preterm labor.
Acknowledgments
We are grateful to the staff of the Sarem Specialist Hospital who helped us with this research.
Conflict of interest
Non-declared by the authors.
Ethical Permissions
Non-declared by the authors.
Funding Sources
Non-declared by the authors.

TABLES and CHARTS

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