IMR Press / CEOG / Volume 48 / Issue 3 / DOI: 10.31083/j.ceog.2021.03.2325
Open Access Original Research
The role of salivary progesterone and cervical length measurement in predicting risk of spontaneous preterm birth
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1 Department of Gynecology and Obstetrics, Maternity and Child Hospital, 42001 Basrah, Iraq
2 Department of Gynecology and Obstetrics, College of Medicine, University of Basrah, 42001 Basrah, Iraq
*Correspondence: maysoonsharief60@yahoo.com (Maysoon Sharief)
Clin. Exp. Obstet. Gynecol. 2021, 48(3), 509–513; https://doi.org/10.31083/j.ceog.2021.03.2325
Submitted: 13 October 2020 | Revised: 28 January 2021 | Accepted: 26 February 2021 | Published: 15 June 2021
Copyright: © 2021 The Author(s). Published by IMR Press.
This is an open access article under the CC BY 4.0 license (https://creativecommons.org/licenses/by/4.0/).
Abstract

Background: Neonatal mortality and neonatal morbidity are increased by preterm birth. Researchers have assessed various biochemical and biophysical markers to predict women at risk for preterm birth in order to decrease its incidence, prevent complications and improve survival rate for infants. Objective: To evaluate the prediction of spontaneous preterm birth by estimation of salivary progesterone levels and by serial measurements of cervical length. Patients and methods: A prospective study was carried out at the Maternity and Child Hospital, Basrah, Iraq. Symptomless women (n = 40) with a single fetus, and with a preterm birth, preterm rupture of membranes, or late spontaneous miscarriage (at 20–28 weeks of pregnancy), were recruited from the outpatient clinic at 24–28 weeks of gestation and were retested after 4 weeks. At each visit, three salivary samples were collected and assessed for their progesterone level using ELISA. Transvaginal sonography was used for cervical length estimation. Results: Of the 40 women, 9 were delivered at term (i.e., after 37 weeks). Their mean pregnancy duration at time of parturition was (38 ± 2) weeks. The other 31 women underwent preterm birth, 13 cases with early preterm (24–34 weeks) and 18 cases with late preterm (>34–37 weeks). The mean levels of salivary progesterone for the term group at the first visit (24–28 weeks) and the 2nd visit (28–34 weeks) were 797.2 pg/mL and 899.4 pg/mL respectively. The mean levels of salivary progesterone in the preterm group at the first visit and 2nd visit were 344.2 pg/mL and 257.3 pg/mL respectively. The difference between the term and preterm birth groups was statistically significant (P = 0.04). There were significant differences regarding cervical length measurement between the preterm delivery groups and the term delivery group. Conclusion: Both low salivary progesterone concentrations and low cervical length can be applied for predicting preterm birth in asymptomatic at-risk women.

Keywords
Cervix
Pregnancy
Preterm birth
Salivary progesterone
1. Introduction

Preterm birth begins with contractions of the uterus, before 37 weeks of pregnancy, that lead to cervical effacement and dilatation [1]. Many developed and developing countries officially record preterm birth as all births with birth weight less than 500 gm [2].

Globally, about 15 million babies are born preterm each year. The rate of preterm birth is less than 10% in many developed countries. Nations with a preterm birth rate more than 15% include Malawi, Congo, Comoros, Zimbabwe, Equatorial Guinea, Mozambique, Goban, Pakistan, Indonesia, Mauritania, and Botswana. The highest number of preterm births are recorded in India, China, Nigeria, Pakistan and Indonesia [3].

The specific cause of preterm birth is unclear. 30–35% of preterm births are iatrogenic due to medico-obstetrical complications, 40–45% are related to spontaneous early labor, and 25–30% to early rupture of membranes [4].

In addition, symptoms of uterine contractions, pelvic pressure, menstrual like cramps, watery vaginal discharge and lower back pain have been empirically associated with impending preterm births [5].

Progesterone promotes uterine preparation for embryo implantation as well as lowered immunity in women during pregnancy. Progesterone production is started by the corpus luteum and after around 8 weeks is maintained by the placenta. Low progesterone concentrations help in fetal birth and induction of milk. Preterm birth takes place when progesterone levels become lower than normal [3, 5] which can be treated by giving progesterone.

The determination of progesterone in saliva can be a more acceptable method than in blood because repeated blood sampling is too stressful and invasive. It has been shown that the salivary steroid hormone reflects the free, unbound part in blood [6, 7, 8]. This free part is considered the biologically active element of the total amount [9, 10, 11]. Therefore, progesterone in the saliva is a good marker of progesterone function.

There is strong evidence that transvaginal sonographic estimation of cervical length can be used to diagnose patients at risk for preterm birth in both symptomatic and asymptomatic women [12]. It has been observed that a cervical length less than 20 mm has a 100% predictive value for preterm birth before 28 weeks gestation [13]. In addition, Goldenberg et al. [14] found a cervical length of less than 25 mm at 24 weeks gestation to be a strong indicator of preterm birth. It has been demonstrated that cervical length can be considered as predictive for preterm birth in women with triplet pregnancies [15]. Furthermore, transvaginal sonography is more convenient and efficient for cervical length estimation than transabdominal sonography [16].

Thus, the aim of the present study was to evaluate a marker for spontaneous preterm birth by analyzing salivary progesterone and transvaginal cervical length measurement after 24 weeks of pregnancy.

2. Patients and methods
2.1 Setting

This study was conducted from January 2019 until May 2020 at the Department of Gynecology and Obstetrics in the Basrah Maternity and Child Hospital, Iraq. All women gave informed consent to be involved in the study. Also, the work has been approved by the Ethical Committee of the College of Medicine, University of Basrah, Basrah, Iraq.

2.2 Subjects

Symptomless women (n = 40) with a single fetus at 24–28 weeks of pregnancy, and with a preterm birth, preterm rupture of membranes, or late spontaneous miscarriage (at 20–28 weeks of pregnancy), attending the outpatient clinic were involved in this work. The limitation in sample size was due to failure in follow up for enrolled women especially during quarantine for COVID-19.

Exclusion criteria included cases of multiple pregnancy, congenital disorders of the fetus or uterus, antepartum hemorrhage, women with iatrogenic preterm birth, fetal growth retardation, women with a history of cervical cerclage and patients with vaginal progesterone suppositories. Hypertension, diabetes, nephrotic disease, heart disease, hematological defects, chronic hepatic disease and vaginosis were included. Antidepressants, corticosteroids, progesterone or tocolytic therapy, drug addiction, smoking and any oral abnormality like bleeding gum were excluded.

2.3 Sample collection

Women made their first visit at 24–28 weeks of gestation and they were retested after 4 weeks. Saliva specimens were obtained from women after overnight fasting and washing the oral cavity with water for 10 min. Passive specimens were collected in sterile containers over 2 hours, at 30 min intervals and then were added together. The specimens were kept in a fridge for 30 min and then frozen at -20 C until needed.

2.4 Estimation of salivary progesterone

Specimens were thawed and centrifuged at 1500 g for 5 min. The upper part of the sample was used for salivary progesterone estimation by ELISA according to the manufacturer’s procedures (De Meditec, GmbH, Lise-Meitner-Strasse 2, 24145 Kiel, Germany). The progesterone concentration that was detected in the zero calibrator was low (5 pg/mL) at the 2SD confidence interval. The assay range was 0–5000 pg/mL. Twenty replicate records of 3 saliva specimens within a single run was depended for the intra assay difference. The within assay coefficient of variance was 5.96%, 6.44% and 9.63%. The inter assay difference was assessed by estimations of 3 saliva specimens repeated twice over 10 days.

2.5 Determination of cervical length

The transvaginal scan for cervical length was done at the first visit which was at 24–28 weeks of gestation. The cervical length was determined by a transvaginal transducer probe (LOGI Q 500MD 7 MHz) which was inserted into the anterior fornix of the vagina. The measurement from the external os to the internal os was repeated 3 times. The present study used the shortest estimate. The mean of 2 readings was considered for an angulated cervix.

2.6 Follow up

The two parameters (salivary progesterone and cervical length) were retested after 3–4 weeks. All women in the study were followed up till parturition. Progesterone therapy was avoided during the study. Women with history of pain and a suspicion of preterm delivery were admitted to the clinical ward in the hospital and were given antibiotics and corticosteroid for lung maturity.

2.7 Delivery history record

All the women in the study were followed until delivery. The information recorded included pregnancy age at time of parturition, mode of delivery, the neonatal outcome, Apgar score at 1 and 7 min and history of admission to intensive care unit.

The gestational age is classified as:

(1) Term birth 37 completed weeks of gestation.

(2) Early preterm birth 34 weeks.

(3) Late preterm birth at 34–36+6 weeks.

2.8 Statistical analysis

The collected data were statistically analyzed using Statistical Package for the Social Sciences (SPSS). Chi-square test (X2) and t-students test were applied to compare clinical variables. Pearson correlation was used to assess the relationship between cervical length and salivary progesterone. P < 0.05 was the significance value.

3. Results

Forty women who met the inclusion criteria were included in the study.

There was a significant difference between the preterm group and the term group with regard to age (P = 0.0034). 62.5% of the preterm group were between 20–30 years old. Also, there was a significant difference with regard to parity. 60% of the preterm group has parity between 1–4 and 17.5% of them were multiparous (>4) (P = 0.005) (Table 1). There were no significant differences with regard to socioeconomic state and residence between the groups (Table 1).

Nine women out of the 40 were delivered at term (i.e., after completed 37 weeks). Their mean pregnancy age at time of parturition was (38 ± 2) weeks. The gestational age for the early preterm group (13 women) was 30 ± 1 weeks in comparison to 34 ± 3 weeks for the late preterm group (18 women) (Table 1).

The mean levels of salivary progesterone in the preterm group at the first visit (24–28 weeks) and the 2nd visit (28–34 weeks) were 344.2 pg/mL and 257.3 pg/mL respectively (Table 2). The mean levels of salivary progesterone in the term group at the first and second visits were 797.2 pg/mL and 899.4 pg/mL respectively. The mean salivary progesterone for the term group was statistically higher than the preterm group at both the first visit (P = 0.04) and the second visit (P < 0.05) (Table 2).

The relationship between salivary progesterone concentrations and serial measurements for cervical length by transvaginal ultrasound in both groups are shown in Table 3.

There was a significant difference between the level of progesterone in the preterm subgroups (early and late preterm) and the term group. Furthermore, there is significant difference in the measurement of cervical length in both subgroups of preterm birth when compared to the term birth group (Table 3).

In general, the salivary progesterone values as well as the cervical length measurements were lower among preterm group in relation to term group. They were statistically significant (Table 3).

Table 1.Demographic features of both groups.
Characteristic features Group 1 Group 2 P value
Preterm birth Term birth
n = 31 n = 9
77.5% 22.5%
Age (years) 0.0034
<20 0 0
20–30 25 (62.5%) 5 (12.5%)
30–40 6 (15%) 4 (10%)
Socioeconomic state 0.4
upper 4 (10%) 1 (2.5%)
middle 22 (55%) 5 (12.5%)
lower 5 (12.5%) 3 (7.5%)
Residency 0.2
urban 20 (50%) 6 (15%)
rural 11 (27.5%) 3 (7.5%)
Parity 0.005
1–4 24 (60%) 7 (17.5%)
>4 7 (17.5%) 2 (5%)
Gestational age at time of labor (weeks) late preterm: 34 ± 3 38 ± 2 0.05
early preterm: 30 ± 1
Previous miscarriage 0.1
0 28 9
1 3 0
2 and more 0 0
Table 2.The value of salivary progesterone concentrations in both delivery groups.
Mean salivary progesterone for preterm group Mean salivary progesterone for term group P value
n = 31 n = 9
1st visit: (24–28 weeks) 344.2 pg/mL 747.2 pg/mL 0.04
2nd visit: (28–34 weeks) 257.3 pg/mL 899.46 pg/mL <0.05
Table 3.Comparison of salivary progesterone levels and cervical length by TVS between the three delivery groups.
Groups No. of subjects Mean Mean P value
1st visit: (24–28 weeks) 2nd visit: (28–32 weeks)
Salivary progesterone Term 9 747.2 pg/mL 899.4 pg/mL 0.01
Early 18 301.5 pg/mL 245.3 pg/mL 0.04
Late 13 344.246 pg/mL 301.3 pg/mL 0.02
Cervical length Term 9 30 mm 28 mm 0.01
Early 18 20 mm 18 mm 0.08
Late 13 22 mm 20 mm 0.001
4. Discussion

Women at risk for preterm birth could potentially be identified by biochemical and biophysical markers so that patients can be followed and appropriate care given. Early diagnosis might keep pregnant women away from preterm birth and increase fetal lung maturity. At the same time, identifying women at low risk could minimize their hospital stay and antenatal requirements. Many markers have been investigated but a specific one for preterm birth still uncertain [17]. Assessment of salivary progesterone as a marker has value because it is non-invasive and saliva can easily be collected and stored.

In the present study, the explanation for the significant differences between the delivery groups with regard to age and parity might be because of the small sample size, especially for the term group. In this study, the preterm deliveries are mostly in the younger age group. This result would confirm a previous study which observed that preterm birth was more common in the younger age group (20–30 years) [18]. Social class, residency and history of previous abortions were not found to have any significant association.

In the present study, salivary progesterone concentrations were lower in the preterm group when compared to the term group. In the pre-term group, progesterone levels decreased significantly from the first to the second visit and the decrease was more noticeable in early preterm group compared with late preterm group. This finding has confirmed the theory that progesterone levels are significantly lower in women who have preterm labor than those delivered at term [19]. These results are in agreement with other workers [20, 21]. However, others have reported that the levels of plasma progesterone in women with preterm birth were identical to that of women with term birth [22].

The present study indicates that there is an inverse correlation between cervical length and gestational age. There was a similar correlation between progesterone concentrations and the shorten cervical length which was noticed in women who delivered before 34 weeks of pregnancy.

The mean cervical length at the first visit in the preterm group was significantly shorter (P = 0.04) in comparison with the term group. It was also observed that cervical length had decreased by the second visit for both groups (18–20 mm ± 2) in the preterm and 28 mm in the term group respectively. In addition, it was noticed that there was a decrease in the length of cervix for all the studied groups (early, late preterm and term) over visits.

Progesterone has anti-inflammatory properties and is important for maintaining pregnancy and enhancing uterine relaxation by reducing prostaglandin synthesis and increasing cellular calcium binding [23]. Progesterone treatment is widely prescribed as a preventive measure in women at risk for preterm birth [23]. Other workers have investigated the role of serum neopterin [24] and also neopterin/creatinine ratio, C-reactive protein and chitotriosidase in serum of pregnant women [25] but they have recommended further studies to evaluate these markers in clinical practice. Therefore, given the unavailability of these markers in the developing countries, the advantage for the present study is the availability of progesterone which can be measured in saliva as a non-invasive test among asymptomatic at-risk pregnant women.

In conclusion, low salivary progesterone concentrations and low cervical length can predict preterm birth in asymptomatic at-risk women. Therefore, measurement of saliva hormone and cervical length can be strongly recommended for use in clinical practice at 24–34 weeks of pregnancy.

Author contributions

Both authors involved in samples collection, data analysis and writing up the manuscript.

Ethics approval and consent to participate

All participants gave informed consent and agreed to be involved in the study. The work has been approved by the Ethical Committee of the College of Medicine, University of Basrah, Basrah, Iraq, code 59 dated 16th December 2018 in accordance with ethical standard of the Arab Board of the Medical Specialization.

Acknowledgment

We would like to thank Dr. Asaad Al-Yaseen, Department of Community Medicine, College of Medicine, Basrah, Iraq for his help in doing the statistical analysis.

Funding

This research received no external funding.

Conflict of interest

The authors declare no conflict of interest.

References
[1]
American College of Obstetricians and Gynecologists. “Preterm (premature) labour and birth” [Internet]. Washington, DC: American College of Obstetricians and Gynecologists. 2016. Available at: https://www.acog.org/womens-health/faqs/preterm-labor-and-birth (Accessed: 13 August 2018).
[2]
World Health Organization. Managing complications in pregnancy and childbirth-abdominal pain in later pregnancy. 2003. Available at: https://apps.who.int/iris/bitstream/handle/10665/255760/9789241565493-eng.pdf;jsessionid=F317D52A024B07E2E800568C158D04CF?sequence=1 (Accessed: 9 September 2019).
[3]
World Health Organization. Born Too Soon: The Global Action Report on Preterm Birth. Geneva: WHO. 2012.
[4]
Offiah I, O’Donoghue K, Kenny L. Clinical risk factors for preterm birth. Preterm Birth-Mother and Child. 1st ed. InTech, Open Access Publisher. 2012: 73–94.
[5]
Cunningham FG, Leveno KI, Bloom SI, Spong CY, Dashe JS, Hoffman BI, et al. Preterm Labour. In: Williams Obstetrics. 25th edn. McGraw: Hill Education. 2018.
[6]
Buxton IL, Singer CA, Tichenor JN. Expression of stretch-activated two-pore potassium channels in human myometrium in pregnancy and labor. PLoS ONE. 2010; 5: e12372.
[7]
Blickstein I. Does assisted reproduction technology, per se, increase the risk of preterm birth? BJOG: an International Journal of Obstetrics and Gynaecology. 2006; 113: 68–71.
[8]
Ouyang DW, Economy KE, Norwitz ER. Obstetric complications of fibroids. Obstetrics and Gynecology Clinics of North America. 2006; 33: 153–169.
[9]
Visintine J, Berghella V, Henning D, Baxter J. Cervical length for prediction of preterm birth in women with multiple prior induced abortions. Ultrasound in Obstetrics & Gynecology. 2008; 31: 198–200.
[10]
Royal College of Obstetricians & Gynecologists. The Care of Women Requesting Induced Abortion. [(National Evidence-Based Clinical Guideline No. 7]. RCOG. 2011. Available at: https://www.rcog.org.uk›guidelines›the-care-of-wo (Accessed: 15 September 2019).
[11]
Jakobsson M, Gissler M, Paavonen J, Tapper A. Loop electrosurgical excision procedure and the risk for preterm birth. Obstetrics & Gynecology. 2009; 114: 504–510.
[12]
Honest H, Bachmann LM, Coomarasamy A, Gupta JK, Kleijnen J, Khan KS. Accuracy of cervical transvaginal sonography in predicting preterm birth: a systematic review. Ultrasound in Obstetrics and Gynecology. 2003; 22: 305–322.
[13]
Skentou C, Souka AP, To MS, Liao AW, Nicolaides KH. Prediction of preterm delivery in twins by cervical assessment at 23 weeks. Ultrasound in Obstetrics and Gynecology. 2001; 17: 7–10.
[14]
Goldenberg RL, Iams JD, Mercer BM, Meis PJ, Moawad A, Das A, et al. The Preterm Prediction Study: toward a multiple-marker test for spontaneous preterm birth. American Journal of Obstetrics and Gynecology. 2001; 185: 643–651.
[15]
Guzman ER, Walters C, O’reilly-Green C, Meirowitz NB, Gipson K, Nigam J, et al. Use of cervical ultrasonography in prediction of spontaneous preterm birth in triplet gestations. American Journal of Obstetrics and Gynecology. 2000; 183: 1108–1113.
[16]
Committee on Practice Bulletins—Obstetrics, The American College of Obstetricians and Gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol. 2012; 120: 964–973.
[17]
Goldenberg RL, Goepfert AR, Ramsey PS. Biochemical markers for the prediction of preterm birth. American Journal of Obstetrics and Gynecology. 2005; 192: S36–S46.
[18]
Arbyn M, Kyrgiou M, Simoens C, Raifu AO, Koliopoulos G, Martin-Hirsch P, et al. Perinatal mortality and other severe adverse pregnancy outcomes associated with treatment of cervical intraepithelial neoplasia: meta-analysis. British Medical Journal. 2008; 337: a1284.
[19]
Brown AG, Leite RS, Strauss JF 3rd. Mechanisms underlying “functional” progesterone withdrawal at parturition. Annals of the New York Academy of Sciences. 2004; 1034: 36–49.
[20]
Kenyon S, Boulvain M, Neilson J. Antibiotics for preterm rupture of membranes. Cochrane Database of Systematic Reviews. 2003; 2: CD001058.
[21]
Lachelin GC, McGarrigle HH, Seed PT, Briley A, Shennan AH, Poston L. Low saliva progesterone concentrations are associated with spontaneous early preterm labour (before 34 weeks of gestation) in women at increased risk of preterm delivery. BJOG: an International Journal of Obstetrics and Gynaecology. 2009; 116: 1515–1519.
[22]
Morris JM, Roberts CL, Bowen JR, Patterson JA, Bond DM, Algert CS, et al. Immediate delivery compared with expectant management after preterm pre-labour rupture of the membranes close to term (PPROMT trial): a randomised controlled trial. Lancet. 2016; 387: 444–452.
[23]
Zakar T, Hertelendy F. Progesterone withdraw key to parturition. American Journal of Obstetrics and Gynecology. 2007; 196: 289–296.
[24]
Navolan DB, Vladareanu S, Lahdou I, Ciohat I, Kleist C, Grigoras D, et al. Early pregnancy serum neopterin concentrations predict spontaneous preterm birth in asymptomatic pregnant women. Journal of Perinatal Medicine. 2016; 44: 517–522.
[25]
Navolan DB, Stoian DL, Bohiltea RE, Crainiceanu Z, Craina ML, Cretu O, et al. Comparison of early pregnancy serum concentration of neopterin, neopterin/creatinine ratio, C-reactive protein, and chitotriosidase, in pregnant women with birth at term and spontaneous preterm birth. Experimental and Therapeutic Medicine. 2020; 20: 2449–2454.
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