The Effect of Maternal Age and Duration of Labor on Perinatal and Neonatal Outcomes

Purpose This study aimed to investigate the effect of maternal age and duration of labor on perinatal and neonatal outcomes. Methods From 2016 to 2018, 9,241 parturients (mean age = 29.15 ± 3.41) were included and divided into the age < 28 group (n = 2911), age 28–30 group (n = 3631); and age > 30 years (n = 2699). According to the total duration of labor, the parturients who did not undergo cesarean section (CS) were subgrouped into the < 420 minutes group (n = 4065) and the ≥ 420 minutes group (n = 4094). The perinatal and neonatal outcomes were compared among groups.


Introduction
There has been an increasing trend in childbearing age worldwide in the past few decades [1,2], especially in the developed nations [3,4].China is a developing country with unique socioeconomic characteristics [5].The China fertility survey 2017 demonstrates that from 2006 to 2016, the mean ages at rst marriage and rst birth increased by 2.7 and 2.6 years, respectively [6].The mean age of parturients at rst birth increased from 24.3 to 26.9 years, and the mean age of parturients at second birth increased from 29.2 years (2014) to 30.2 years (2016) [6].In 2016, advanced pregnancies (age ≥ 35 years) accounted for approximately 31% of the total pregnancies in China [7].This trend can partially be attributed to changes in social habits, such as high education, careers, nancial stability, late marriage, use of contraception [8][9][10][11].The Chinese government has relaxed the family planning policy and implemented a universal two-child policy in 2015 to address the country's aging problem [12], which also contributes to advanced pregnancies.Maternal age has been shown to play a crucial role in, pregnancyrelated complications, and adverse obstetric and perinatal outcomes [13][14][15][16][17].However, the studies on maternal age on pregnancy outcome in the Chinese population are relatively limited [18,19].Therefore, the purpose of this study was to investigate the impact of maternal age and total duration of labor on perinatal and neonatal outcomes.

Study subjects
This was a retrospective observation study.A total of 9241 parturients who delivered in the General Hospital of Northern Theater Command of the Chinese People's Liberation Army from January 2016 to December 2018 were included and divided into three groups based on age as follows: age < 28 group (n = 2911), age 28-30 group (n = 3631); and age > 30 years (n = 2699).Meanwhile, according to the total duration of labor, the parturients were subgrouped into the < 420 minutes group (n = 4065) and the ≥ 420 This study was approved by the institutional review board of our hospital (approval no Y(2020)025).
Written informed consent was obtained from the patient.

Data Collection
Data included labor of each stage, labor outcome (delivery method), bleeding amount, use of oxytocin, side cut/forceps during delivery, postpartum fever, 1-min and 5-min Apgar score, the body weight of newborn, the incidences of abnormal fetal heart rate and meconium-stained amniotic uid (MSAF) were collected.

Statistical analysis
Continuous variables were reported with mean ± standard deviation (SD).Means between two groups were compared using Student's independent t-test, for over 3 groups were compared using one-way ANOVA.Categorical variables were presented as number and percentage and were compared using the Chi-square test or Fisher's exact test (if expected value ≤ 5 was found).The multivariate logistic regression model was used to investigate the associations between age/total duration of labor group factors to different postpartum outcomes, including switch to emergency CS, postpartum fever, abnormal fetal heart rate, and MSAF.All analyses were done using IBM SPSS Version 25 (SPSS Statistics V25, IBM Corporation, Somers, New York).The statistical signi cance level for all the tests was set at a P-value < 0.05, two-tailed.

Participant's characteristics among age groups
From 2016 to 2018, a total of 9,241 parturients were included.The mean age was 29.15 ± 3.41 years, the mean gestational age was 29.15 ± 3.41 weeks.The gravidity and parity for all parturients were 1.56 ± 0.87 and 0.17 ± 0.39 times, respectively.Of them, 44.61% of parturients underwent epidural anesthesia in delivery, and the mean cervix dilation at epidural anesthesia was 2.49 ± 0.75 cm.Postpartum Outcomes Among Age Groups

As shown in
The perinatal and neonatal outcomes were compared among the three groups, including duration of labor of each stage, labor outcome (delivery method), bleeding amount, oxytocin using, postpartum fever, Apgar score of newborns at 1st and 5th minute, the body weight of newborn, the occurrence of abnormal fetal heart rate and MSAF.
As shown in Table 2, parturients in the age > 30 group were more likely to have shorter labor at stage 1, 3 and total duration of labor (all P < 0.05).These parturients also had a higher rate of normal spontaneous delivery (NSD) as labor outcome (P < 0.001).Higher age groups were more likely to switch to cesarean section (CS) (P < 0.001).The incidence of postpartum fever was signi cantly higher in age < 28 and 28-30 groups (P = 0.035).The bodyweight of newborn was slightly increased as age increased (P < 0.001).The age 28-30 group was more likely to have abnormal fetal heart rate (P = 0.017).Apgar scores were not different among the three age groups (both P > 0.05).

Participant's Characteristics Between The Two Duration Of Labor Groups
According to the median of the total duration of labor, the parturients were subgrouped into the < 420 minutes group (n = 4065) and the ≥ 420 minutes group (n = 4094).In these analyses, parturients who underwent CS were excluded due to lack of total duration of labor data.As shown in Table 3, the < 420 minutes group (≥ 420 minutes group) had signi cantly younger age, longer gestational age, lower gravidity and parity, higher rate of using epidural anesthesia, and smaller cervix dilation at epidural anesthesia as compared with the < 420 minutes group (all P < 0.05).Postpartum Outcomes Between The Two Duration Of Labor Groups perinatal and neonatal outcomes were also compared between total duration of labor groups.As shown in Table 4, the ≥ 420 minutes group had higher rate of side cut/forceps during delivery, more bleeding volume, higher rate of using oxytocin, postpartum fever, abnormal fetal heart rate, and MSAF as compared with the < 420 minutes group (all P < 0.05).The bodyweight of newborn was also slightly higher in the ≥ 420 minutes group (P < 0.001).Apgar scores did not differ between the two groups (both P > 0.05).

Postpartum Outcomes In Multivariate Models
To investigate the association between age/total duration of labor groups to postpartum outcomes, the signi cant variables among groups (Tables 1 and 3) were adjusted in a multivariate logistic regression model.For the age groups, participant's gestational age, gravidity, and parity were adjusted; For the total duration of labor groups, the adjusted covariates were age, gestational age, gravidity, and parity.
As shown in Table 5, as age increased, the rates of switch to emergency CS and abnormal fetal heart rate also increased (all P < 0.01); parturients with longer total duration of labor (≥ 420 minutes group) had signi cantly higher risk of postpartum fever and MSAF (both P < 0.01).

Discussion
In this study, we investigated the effect of maternal age and total duration of labor on perinatal and neonatal outcomes.The results showed that higher age groups were more likely to switch to emergency CS.The incidence of postpartum fever was signi cantly higher in the age < 28 and 28-30 groups.The age 28-30 group was more likely to have abnormal fetal heart rate.The ≥ 420 minutes group had higher rate of side cut/forceps during delivery, more bleeding volume, higher rate of using oxytocin, postpartum fever, abnormal fetal heart rate, and MSAF as compared with the < 420 minutes group.The multivariate logistic regression analysis showed that as age increased, the rates of switch to emergency CS and abnormal fetal heart rate also increased, while parturients with longer total duration of labor had higher risk of postpartum fever and MSAF.
Higher maternal age would increase the risk of obstetric complications, such as gestational diabetes, preeclampsia, placenta previa, placental abruption [15,20,21].As a result, it is well-known that the cesarean section rate increased with increasing maternal age [22][23][24].Advanced pregnant women are more likely to undergo cesarean section due to scarred uterus, a history of adverse pregnancy, di cult pregnancy, unwilling to vaginal trial delivery, psychological pressure, lack of con dence in vaginal trial delivery.In addition, with the increase of gravidity, the incidences of abdominal wall relaxation, breech position, transverse position and other abnormal fetal position also increase.Since vaginal delivery has many uncertain factors, advanced pregnant women tend to expand the surgical indications, thus increasing the cesarean section rate.Accumulating evidence has suggested that the prolonged duration of labor increases adverse maternal and neonatal outcomes [30,31].Our results showed that the parturients with a duration of labor ≥ 420 min had a signi cantly higher incidence of postpartum fever than those with a duration of labor < 420 min.In addition, the multivariate logistic regression model adjusted for the confounding factors including age, gestational age, gravidity, and parity showed that parturients with prolonged duration of labor had a 3.05-time higher risk of postpartum fever.This observation is in agreement with a meta-analysis by Pergialiotis et al. that included 13 studies and 337.845 parturients and demonstrated that prolonged second stage was associated with higher incidences of postpartum fever [32].
Prolonged duration of labor is a risk factor for passage of meconium in utero [33].MSAF is also regarded as a sign of fetal distress and fetal asphyxia and its precise etiology is still unclear [34].Cheng et al. have reported that prolonged second stage of labor increases the incidence of MSAF [35,36].Lee et al. also con rmed that the longer the duration of labor ( rst stage, second stage, or total), the higher the frequency of MSA [37].Supporting this notion, our results showed that the risk of MSAF slightly elevated (1.17 times) in parturients with a longer duration of labor ( rst stage, second stage, and total).
It should be noted that this study was limited by its retrospective nature.Some confounding factors were not excluded, such as whether the puerpera used other labor inducing drugs except for oxytocin, and different time of labor analgesia.A well-designed prospective trial should be conducted to validate the ndings of this study.
In summary, our results showed that maternal age was an independent factor associated with switch to emergency CS and abnormal fetal heart rate, while total duration of labor was an independent factor associated with postpartum fever and MSAF.

Declarations
Not applicable.

Table 3
Participant's characteristics between total labor time groups

Table 5
The logistic regression results of age/total labor time group factors to clinical postpartum outcomes The multivariate models of age group were adjusted with gestational age, gravidity, and parity.The multivariate models of total labor time group were adjusted with age, gestational age, gravidity, and parity.
[29]17]al.havedemonstratedthatadvancedmaternalage is an independent risk factor of emergency CS due to nonreassuring fetal heart rate or arrest disorder[25].Our previous study showed that maternal age is an independent risk factor associated with conversion to an emergency cesarean section in the failed trial of labor[26].Attali et al. also reported that advanced maternal age is an independent risk factor for intrapartum Cesarean delivery[13,17].Consistent with these ndings, this study showed that maternal age is an independent factor associated with switch to emergency CS.The parturients with age of 28-30 had a 1.58 -time higher risk of switch to emergency CS as compared with those under age of 28.For those over age of 30, the risk elevated to 1.87 times.In this study, maternal age was also an independent risk factor for abnormal fetal heart rate, which is one sign of fetal distress[27].Compared to parturients under age of 28, those with age of 28-30 and those above age of 30 had 1.20-time and 1.38-time higher risk of fetal heart rate abnormality, respectively.In line with this observation, Cavazos-Rehg, et al. have revealed that both younger and older parturients have an increased risk of fetal distress [28].Ngowa et al. also reported that multiparous advanced parturients had an increased incidence of fetal distress[29].