RETRACTED ARTICLE: Association between placental site and successful induction of labor among postdate primiparous women

TL;DR

This study found that the placental site does not affect the success of labor induction, while a shorter cervical length is a strong predictor of successful vaginal delivery.

Contribution

The study provides evidence that cervical length, not placental site, is a key factor in predicting successful labor induction.

Findings

Successful induction was achieved in 80.2% of participants.

Cervical length was significantly shorter in women with successful induction.

Placental site had no significant impact on induction success.

Abstract

This study aimed to determine the association between placental site and successful labor induction.

This cross-sectional study recruited all postdate primiparous women undergoing induction of labor. Eligible women were subjected to proper history taking and clinical examination. Vaginal examination to determine the bishop score was done. Routine antenatal scan was done for fetal biometry and the placental site. Transvaginal ultrasound was done for cervical length assessment. Induction of labor was commenced and women were subdivided into those with successful induction (delivered vaginally) and those with failed induction (needed cesarean delivery).

Successful induction was achieved in 73/91 (80.2%) participants. The bishop score was significantly increased among women with successful induction (4.6 ± 0.9 vs 3.9 ± 1.1, p value 0.014). In addition, the cervical length was significantly shorter among those who delivered vaginally (2.6 ± 0.5 vs 4.2 ± 0.5, p value 0.0001). There was no significant difference in the placental site among women with failed or successful induction. The cervical length was the only significant predictor for successful induction of labor (p value 0.0001). The placental site showed a non-significant role in the prediction of successful vaginal delivery (p value 0.280).

The placental site is not associated with the outcome of labor induction. The cervical length was the significant predictor for successful induction of labor.

Full text

What does this study add to the clinical work

Most studies evaluated the association between placental site and adverse pregnancy outcomes. Scarce studies evaluated the role of the placental location and the outcomes of labor with conflicting results.

Introduction

The rate of induction of labor (IOL) has increased over the last years [1]. This was rendered to increased rates of obstetric complications as preeclampsia and gestational diabetes among pregnant women [2]. It is considered a life-saving intervention as continuing pregnancy might pose hazards for the mother or the fetus [3]. It has been linked with increased rates of cesarean delivery [4], while other studies reported contradictory results [5]. Variable results were reported regarding the maternal and fetal outcomes of induction of labor which was rendered to different indications for induction and cervical preparedness among the studied populations [6]. Successful induction of labor has been related to multiple factors including parity, racial variations, gestational age, the estimated fetal weight, maternal weight, and the method of induction itself [7]. The definition of successful IOL is well-defined, while that for failed IOL is less clarified [8]. Failed induction of labor had a wide range of criteria including the mode of delivery and specified time intervals for labor initiation or the commencement of regular uterine contractions [9].

Worldwide, IOL was required for about 20% of pregnancies [10], and cesarean delivery was the final outcome in 20% of these pregnancies [3]. Although, IOL avoids possible maternal and neonatal adverse outcomes, failed IOL requires emergency cesarean delivery with carries multiple maternal and neonatal hazards. These include postpartum hemorrhage, wound infections and other complications, neonatal birth injuries, need for hysterectomy, and even maternal death [11]. It has been reported that cesarean delivery because of failed IOL was associated with greater maternal and neonatal complications than those reported with spontaneous onset of labor [12]. Possible factors contributing to failed IOL included increased maternal age, nulliparous women, decreased bishop score, hypertensive disorders with pregnancy, premature rupture of membranes, and gestational ages > 40 weeks [3].

The placenta is a vital organ between the mother and the fetus. It has multiple functions as nutrient transmission, endocrine functions, and others. It has been associated with adverse perinatal outcomes [13]. Accordingly, an ideal placental position is necessary to enable these important functions to be accomplished [14]. Many studies reported a significant association between placental site and impaired blood supply and pregnancy outcomes [15–18]. Although the underlying mechanism is not elaborated, possible explanation is abnormal trophoblastic invasion associated with abnormal placentation [19]. The availability and ease of ultrasound made the evaluation of fetal biometry and other components of pregnancy as the placenta and the umbilical cord a common practice. However, placental site evaluation was limited to abnormal placentation as placenta previa-accreta spectrum. Few studies reported on the association between placental implantation site and pregnancy outcomes [20, 21]. It has been reported that fundal implantation of the placenta was associated with increased risk of prelabor premature rupture of membranes and accelerated third stage of labor [21]. Labor requires proper interaction between the uterus, the fetus, the placenta, and the cervix. Failure of this harmony leads to impaired labor process [22]. Many studies focused on particular adverse perinatal outcomes with no studies evaluating the association between placental implantation site and successful induction of labor. Accordingly, this study was conducted to determine the relation between placental site and successful induction of labor.

Methods

This cross-sectional study was conducted at the labor and delivery ward at Suez Canal University hospital from 20th November 2022 to 20th November 2023. The study recruited all postdate primiparous women undergoing induction of labor according to certain inclusion and exclusion criteria. The inclusion criteria were (a) women aged 18–45 years, (b) singleton pregnancy, (c) cephalic presentation, (d) gestational age ≥ 40 weeks, and (e) living fetus. The exclusion criteria were (a) previous uterine surgeries as myomectomy, (b) prelabor premature rupture of membranes, (c) antepartum hemorrhage, (d) medical disorders with pregnancy as diabetes and hypertensive disorders with pregnancy, (e) fetal anomalies, (f) women with unreliable dates, and (g) fetal distress indicating cesarean delivery.

Eligible women were subjected to:

• Clinical evaluation including age, height, weight, and body mass index (BMI).
• Obstetric history including date of last menstrual period (LMP), gestational age, and any medical disorders. The gestational age was confirmed by an early ultrasound.
• Vaginal examination to determine the bishop score [23].
• Routine laboratory investigations as complete blood count, Rh, coagulation profile, and group and save.
• An ultrasound was done for fetal evaluation including fetal biometry, estimated fetal weight (EFW), amniotic fluid index (AFI), and the placental site. Placental implantation site was divided into anterior, posterior, fundal, and lateral implantation sites. Ultrasound was done at 36–37 weeks.
• A transvaginal ultrasound was done for measuring the cervical length, at 36–37 weeks [24].

Women with a bishop score > 6 were managed by artificial rupture of membranes. If regular uterine contractions did not ensue within 2 h, labor augmentation with oxytocin was started.

For women with a bishop score < 6, induction of labor was done using intravaginal prostaglandin E1 pessary (Vagiprost, 25 µcg tablets ADWIA pharmaceuticals, Amiria, Cairo, Egypt). The patients were assessed every 6 h, and repeated doses were allowed if needed for a maximum of 4 doses [10]. Amniotomy was done if needed. The amniotic fluid was evaluated for the presence of meconium. The vaginal insert was removed in case of rupture of membranes, initiation of labor pains, or abnormal fetal heart monitoring.

The primary outcome measure was the event of successful vaginal delivery. Women were divided into 2 groups; those who had successful vaginal delivery and those who had cesarean delivery due to failed induction or failure of labor progression.

Failed induction was defined as failure to establish labor pains after 24 h of intravaginal prostaglandin ± 3 h of oxytocin infusion [25]. Failure to progress is defined as failure of the presenting part to proceed down in the birth canal despite the presence of good uterine contractions [26].

Adverse perinatal outcomes included a) cesarean delivery because of fetal distress, b) meconium aspiration syndrome (MAS), diagnosed by the presence of meconium-stained amniotic fluid with respiratory difficulties or the presence of widespread coarse infiltration with over-inflation of the lungs by X-ray [27], and c) neonatal intensive care unit (NICU) admission.

Statistical analysis

Data were statistically described in terms of mean and standard deviation, frequencies (number of cases), and percentages when appropriate. P values less than 0.05 were considered statistically significant. All statistical calculations were done using the computer program SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) release 23 for Microsoft Windows. The Chi-square test was used for categorical variables, and the (t) test was used for continuous variables with normally distributed data. Non-normally distributed data were tested using Fisher’s exact for categorical variables, and Mann–Whitney U tests for continuous variables. Logistic regression was performed to determine the predictors for successful vaginal delivery.

Results

Ninety-seven women were eligible for the study. Five women declined to participate in the study, and one woman had cesarean section (CS) due to fetal distress and was excluded. This resulted in the recruitment of 91 women (Fig. 1). The study population was divided into 2 groups according to the mode of delivery. Women who delivered vaginally were in the successful induction group (73/91) (80.2%) and those who delivered by CS were in the failed induction group (18/91) (19.8%).Fig. 1. Patients’ flow chart

There was no significant difference in the main demographic data between both groups but for the BMI which was significantly increased among those who had failed induction (30.2 ± 3.7 vs 24.6 ± 2.7, p value 0.0001) (Table 1).Table 1. Basic demographic data of the studied population (N = 91)Failed induction (18/91, 19.8%)Successful induction (73/91, 80.2%)P valueAge (years) (mean ± SD)25.7 ± 3.424.3 ± 3.00.115^a^Occupation N (%) Housewife15 (83.3%)50 (68.5%)0.212^b^ Employee3 (16.7%)23 (31.5%)Residence N (%) Urban15 (83.3%)50 (68.5%)0.155^b^ Rural3 (16.7%)23 (31.5%)BMI, kg/ht^2^ (mean ± SD)30.2 ± 3.724.6 ± 2.70.0001^a^^a^Independent t test, ^b^Chi-square test

The bishop score was significantly increased among women with successful induction (4.6 ± 0.9 vs 3.9 ± 1.1, p value 0.014). In addition, the cervical length was significantly shorter among those who delivered vaginally (2.6 ± 0.5 vs 4.2 ± 0.5, p value 0.0001). The fetal weight was significantly increased among women with failed induction (3815.9 ± 299.3 vs 3348.7 ± 299.5, p value 0.0001). There was no significant difference in fetal gender and the placental site among women with failed or successful induction (Table 2).Table 2. Obstetric data of the studied populationFailed induction (18/91, 19.8%)Successful induction (73/91, 80.2%)P valueNumber of days after 40 weeks (mean ± SD)6.8 ± 5.05.9 ± 3.40.376^a^Bishop score (mean ± SD)3.9 ± 1.14.6 ± 0.90.014^a^Cervical length (cm) (mean ± SD)4.2 ± 0.52.6 ± 0.50.0001^a^EFW (g) (mean ± SD)3815.9 ± 299.33348.7 ± 299.50.0001^a^Fetal gender N (%) Male8 (44.4%)39 (53.4%)0.495^b^ Female10 (55.6%)34 (46.6%)Placental site N (%) Anterior12 (66.7%)33 (45.2%)0.145^b^ Posterior6 (33.3%)31 (42.5%) Fundal0 (0%)9 (12.3%)^a^Independent t test, ^b^Chi-square test

There was no significant difference in neonatal outcome in both groups. MAS was diagnosed in 3/18 (16.7%) and 13/73 (17.8%) neonates, in those with failed and successful induction, respectively (p value 0.909). NICU admission was required in 6/18 (83.3%) and 10/73 (82.2%) neonates, in those with failed and successful induction, respectively (p value 0.050).

The cervical length was the only significant predictor for successful induction of labor (p value 0.0001). The placental site showed a non-significant role in the prediction of successful vaginal delivery (p value 0.280) (Table 3).Table 3. Regression analysis for the predictors of successful induction of laborΒ95% CI (Lower–upper)P valueAge– 0.009 – 0.027 to 0.0090.325Number of days after 40 weeks– 0.003 – 0.019 to 0.0120.679Occupation– 0.007 – 0.131 to 0.1160.909BMI– 0.008 – 0.031 to 0.0150.515Bishop score– 0.070 – 0.143 to 0.0030.062Cervical length– 0.349 – 0.478 to – 0.2200.0001EFW0.0000.000 to 0.0000.098Placental site0.047 – 0.039 to 0.1320.280Fetal gender0.022 – 0.097 to 0.1410.715

Discussion

Successful induction was achieved in 80.2% participants. Another study reported a success rate of 73.7% among term nulliparous women undergoing indicated induction of labor [6]. An earlier one reported a CS rate of 52.2% among nulliparous women undergoing induction of labor. They reported an overall success rate of 84% [28]. Different rates of successful induction were explained by different gestational age of the recruited women, BMI, parity, race and ethnicity, and the method of induction [6]. Prostaglandins were associated with increased rate of successful induction than oxytocin [29]. The current study used prostaglandins mainly for induction of labor. In addition, increased gestational age at induction was associated with increased odds of successful induction [28], with the current study recruiting women after 40 weeks gestation.

The BMI was significantly increased among women who had failed induction. In an earlier study, the BMI was significantly lower among women who had vaginal delivery after induction of labor [28], in accordance with the current study. Another study reported that obese women had the same opportunity for successful induction as normal weight women; however; the rate of emergency CS was significantly increased among women with increased BMI [30]. However, different estimations of weight gain among studies would result in contradicting results. Some studies reported on the weight recorded before delivery, others used self-report of pre-pregnancy weight which may be subjected to bias [31]. It has been mentioned that obese women have increased head–perineum distance and slower fetal head descent against cervical dilatation [32], explaining failed induction. In addition, the changed definition of the start of the active phase of labor > 6 cm rather than > 4 cm, resulted in weak differences between obese and non-obese women as obese women had slower progression from 4 to 6 cm [33]. The current study used cervical dilatation of 4 cm as the start of the active phase of labor. Increased rate of failed induction among obese women was due to insufficient myometrial contractility, impaired cervical ripening, and improper placental preparation for labor [34]. This effect was mediated by increased cholesterol level, adipokines, and inflammatory cytokines in obese women [35].

The cervical length was significantly shorter among women with successful induction. This was in accordance with previous results as the cervical length was significantly longer among women who delivered by CS [36]. Another one reported non-significant difference in the cervical length between multiparous women who delivered vaginally or by CS, but the difference was significant in nulliparous women [37]. This finding might be rendered to the fewer number of multiparous women recruited.

Other factors as the bishop score and fetal weight differed significantly between both the groups. However, this contradicted previously reported results where the bishop score and fetal weight showed non-significant difference between women who had vaginal and cesarean delivery after induction of labor [28]. This might be rendered to their recruitment of multiparous and nulliparous women undergoing induction for variable causes as post-term pregnancy, medical disorders with pregnancy, and rupture of membranes. Another study reported increased fetal weight was associated with increased rates of CS due to labor arrest; however; this study recruited women with estimated fetal weight ≥ 4000 gm and < 4000 gm [38].

There was no difference in the placental site between patients who had successful or failed induction. This agreed with previous results where the placental site did not differ significantly among women with failed or successful induction [39]. Contradicting results reported anterior placentation being significantly evident among women with failed induction. While women with successful induction had more fundal and posterior placentation [22]. The effect of placental site on labor progression was rendered to its effect on myometrial contractility and impulse generation [40]. Anterior placentation was associated with impaired uterine contractility [41]. In addition, anterior placentation was associated with neonatal respiratory distress, delayed onset of labor, increased rates of induction of labor, increased CS rates, and increased postpartum complications [42]. Conflicting results could not be explained, as the effect of placental site on labor progression remains to be elucidated.

The cervical length was the only predictor for successful induction. The placental site had no significant predictive role. In previous results, maternal age and the bishop score were significant predictors for successful induction of labor [43]. The cervical length was reported to be more effective in predicting successful vaginal delivery [44, 45] and in predicting successful induction of labor [46]. An earlier one reported a significant association between elongated cervix and cesarean delivery [47]. Contradicting results were reported by Khandelwal et al., as the cervical length did not predict successful induction of labor [48]. This discrepancy was rendered to different definitions of successful induction between studies [49]. In another study, multiparity and lower BMI were associated with increased chances of successful induction of labor. In addition, increased fetal weight and gestational ages < 37 weeks were associated with increased rates of CS [28], contradicting our results. Contradicting results would be explained by different parity, gestational age, indication for induction, ethnicity, and outcomes between studies.

Strength and limitations: We recruited primiparous women with postdate gestations to avoid possible medical disorders that might affect the outcome of induction. The study was conducted prospectively. The study did not evaluate the rate of induction of labor. It was conducted in a single tertiary center which limits the generalizability of data. A comparison with multiparous women would be more informative. Evaluation of the association between placental site and pregnancy outcome is recommended.

Research implications: Evaluation of the relation between placental site and pregnancy outcomes is recommended. Comparison between nulliparous and multiparous women would be fruitful.

Conclusion: The placental site is not associated with the outcome of labor induction. The cervical length was the significant predictor for successful induction of labor.