Uterine activity during the two hours after placental delivery among low-risk pregnancies: an observational study

Abstract

Objective: The purpose of this study was to describe uterine activity within the first two hours after placental delivery among low-risk pregnant women.

Materials and methods: Participants were 17 low-risk pregnant women who had a singleton birth at midwifery birth centers in Japan. Contractile waves of uterine activity were measured by using an external tocodynamometer.

Results: Spontaneous uterine contraction frequency during the first two hours after the placental delivery decreased over time (F_9, 54=19.7, p < 0.001). The mean contraction intervals were 1.9 ± 0.3 min, 2.4 ± 0.9 min, 4.2 ± 0.7 min and 7.9 ± 2.1 min for the second stage, third stage, and the first hour and second hour after placental delivery, respectively. Uterine contraction frequency increased with oxytocin administration and infant suckling; however, an icepack to cool the uterus did not change the contraction waves. No correlations were found between uterine activity and blood loss or pain.

Conclusion: Contraction of the myometrium is the primary mechanism for hemostasis. The uterine contraction intervals became prolonged over time, and blood loss did not increase. The findings provide insight into the role of myometrium contraction as a hemostasis mechanism.

Keywords:

• Parturition
• uterine contraction
• blood loss
• third stage of labor
• tocodynamometer

Introduction

Postpartum hemorrhage (PPH) is the leading cause of maternal mortality in both developing and developed countries [1]. PPH is defined as blood loss of 500 ml or more within the first 24 h after the delivery of a baby [2]. The incidence of PPH (blood loss ≥ 500 ml) is around 6–10% and, the prevalence of severe PPH (blood loss ≥ 1000 ml) is approximately 1.8%, but it varies depending on the regions of the world [3]. PPH accounted for 19.7% (480 000 95% UI 12.9–28.9) of direct cause of maternal death worldwide [4]. Events that may influence PPH include uterine atony, cervical or vaginal lacerations, retention of the placenta, and coagulation disorders [5,6]. Among these, the most prominent cause of PPH is uterine atony (34.0%) [7]. As a significant medical threat worldwide, effective strategies for the prevention and treatment of PPH is essential to decrease maternal mortality rates.

Given that PPH usually occurs during and after the third stage of labor [3], primary guidelines recommend active management of the third stage of labor, in which the main component is administration of uterotonics as the effective prophylactic management for PPH [2,5,8]. Studies report the effectiveness of some prophylactic management and treatment strategies for PPH, however, some researchers question the necessity for women with low-risk pregnancies [8,9]. To address this, further understanding of the mechanism involved in hemostasis and uterine contraction and retraction without uterotonics is needed.

After the birth of the neonate and placenta, two hemostasis processes are initiated. The primary physiology of postpartum hemostasis involves uterine muscular contractions induced by endogenous oxytocin and prostaglandins. The structure of uterine smooth muscle is spiral in shape and extends in all directions. When the uterine muscles contract, the spiral vessels of the uterus are compressed, and blood flow decreases [10]. Retraction of the muscle assures that the contracted state remains. Moreover, clotting and fibrinolytic factors in the blood of pregnant women increase [11]. The concentrations of all clotting factors, fibrinogen, factor VII, factor X and plasminogen, except for factors IV and VIII, increase during normal pregnancy. Likewise, fibrinogen concentration increases about 50%. The platelets also change; the average blood platelet count decreases to 213 000/μL during pregnancy, but retains the balance of hemostasis [12]. During the third stage of labor the clotting and fibrinogen factors should return to normal supporting the hemostasis process [11].

The uterine activity during early postpartum, including the third stage of labor, has been described in several studies [13–17]. The participants of these studies had labor augmentation with oxytocin, epidural analgesia, and administration of uterotonics in the third stage of labor. In these reports [13–15], the interval of uterine contractions become wider; there is no correlation between the pattern of uterine activity during early postpartum and obstetrical characteristics, such as parity, duration of labor, mode of delivery, or intervention in labor. However, no studies have reported details of uterine activity during the first two hours after the delivery of the placenta among low-risk women with non-pharmacological intervention during the labor and postpartum. Describing the uterine activity during this critical period, while women in labor are at risk for life-threating events as PPH, may help to understand the mechanism for uterine atony, and aid in identifying factors related to PPH brought on by uterine atony.

The purpose of this study was to describe uterine activity within the first two hours after placental delivery among low-risk pregnant women who have undergone no medical treatment during the first to third stages of labor and to explore the relationship between uterine activity and blood loss or pain.

Materials and methods

Study design, setting and population

This observational study was conducted at two midwifery birth centers located in Japanese metropolitan areas. Participants were experiencing a healthy uncomplicated pregnancy, and subsequently had a low-risk singleton birth at term between December 9, 2014 and May 23, 2015. The researcher recruited eligible participants during their prenatal examination of at least 37 weeks’ gestation. Participants were allowed to choose their preference for positioning at birth. Both of the midwifery birth centers performed physiological management at the third stage of labor (no routine administration of oxytocin, late cord clamping, and delivery of placenta spontaneously), and skin-to-skin contact immediately after birth. St. Luke’s International University’s Institutional Review Board approved this research (14-087).

Data collection

Uterine activity

Contractile waves of uterine activity were measured by using an external tocodynamometer (Fetal Actocardiograph MT-325, MT-516, TOITU Co., Ltd., Tokyo, Japan) as a noninvasive method. Although in a previous study [16] researchers used intrauterine pressure catheters, in Japan, monitoring of uterine contractions with external tocodynamometry is daily obstetric practice at most medical facilities. Furthermore, uterine contraction frequency measured by intrauterine pressure catheters and external tocodynamometry were adequately correlated (r = 0.75, p = 0.001) [18]. Thus, external tocodynamometer was adopted for the measurement of uterine activity in this study.

In Japanese guidelines for obstetrical practice, continuous cardiotocography during labor is required [19]. During second stage of labor, midwives placed transducers on the women’s abdomen to detect uterine contractions and the fetal heart rate. After the delivery, the transducer for fetal heart rate was removed. Then, a clinician assessed the fundus of the uterus through abdominal palpation, followed by the placement of a transducer for uterine contraction below the umbilicus fixed with a belt. After the placental delivery, a clinician re-assessed the fundus of the uterus and placed a transducer on the lower abdomen for the first two hours. During early postpartum, maternal position was supine. However, participants were allowed to change their position if requested.

The data pertaining to uterine contractions and their interval, intensity and duration, were obtained from the fetal cardiotocography. The rate of paper feed was three centimeters per minute. Definition of contraction interval was time length (minutes) from the first contraction’s peak to the second one, and contraction duration was the duration (seconds) at the point of one-fifth intensity from baseline. Two midwives (YM the author, and a midwife with 13 years of experience) provided interpretations independently. We resolved discrepancies through discussion.

Other variables

Lost blood, just after delivery of the placenta, was collected in a basin placed under the maternal buttocks and with sanitary pads every 30 min during the first two hours after placental delivery. The blood in the basin and sanitary pads were weighted on a digital scale. The blood loss with sanitary pads was measured by the weight of pads after subtracting the dry pad weight of 20 g. Pain levels ware measured by using a vertical 100-mm visual analog scale at every 30-min intervals during the first two hours after placental delivery. Participants marked their pain level on the 100-mm line indicating pain from none (0) to the most (100). Demographics and obstetrical characteristics were collected from participants’ medical records.

Statistical analysis

The mean contraction parameters were calculated by dividing the data strips into 10 sections, during the last 15 min of the second stage of labor, during the third stage of labor and every 15 min during the first two hours after placental delivery. The data were calculated for the mean contraction’s interval, intensity, and duration of each section. The mean values of each section were compared.

Repeated-measures ANOVA was used for uterine contraction parameters. Spearman’s rank-order correlation coefficient was used to analyze between uterine contraction parameters and blood loss or pain ratings. A two-tailed p value of less than 0.05 was considered statistically significant. The statistical analysis was performed using SPSS software (version 22.0) (IBM Corp., Armonk, NY).

Results

Data for 17 women were available for analysis. No participants were given labor augmentation with oxytocin, epidural analgesia, or prophylactic administration of oxytocin in the third stage of labor. No women complained of discomfort about continuously putting a transducer on the lower abdomen during the observation period. All women delivered in the 15° semi-recumbent position, and maternal position was supine during the first two hours after the placental birth.

Demographics and obstetrical characteristics

The demographics and obstetrical characteristics of the participants are presented in Table 1. After the placental delivery, 10 women underwent a clinical course that could have affected their uterine contractions specifically, six breastfed, two were administered a cooling pack to the uterus and two were administered oxytocin.

Table 1. Demographic and obstetrical characteristics of the study participants.

Characteristics	Total (N = 17)
Maternal age, mean (SD), years	32.1 (5.2)
Parity
0	3
1	10
2	3
3	1
Body mass index, mean (SD), (kg/m^2)	19.1 (1.7)
Gestational age, mean (SD), weeks	39.4 (1.0)
Length of labor, median (range), hours	5.4 (1.9–17.2)
Length of second stage of labor,  median (range), minutes	36 (6–107)
Length of third stage of labor,  median (range), minutes	13 (8–29)
Prelabour rupture of membranes	1
Numberofwomenwithlacerations
Intact	9
First degree	6
Second degree	2
Blood loss, median (range), grams	219 (130–730)
Birth weight, mean (SD), grams	3079.2 (308.1)

Patterns of uterine activity during two hours after birth

Women were categorized into one of four groups based on factors that may have potentially affected the pattern of uterine contractions including, (1) spontaneous progress, (2) breastfeeding, (3) cooling the uterus or (4) oxytocin administration. Breastfeeding was not based on midwives’ judgement, but rather on the need to aid the infant and mother bonding process. Cooling the uterus and oxytocin administration was provided based on midwives’ judgement. When participants had a soft uterus with non-continuous bleeding just after placental birth, cooling the uterus was implemented. In the case of a soft uterus with continuous bleeding, oxytocin was administered.

Spontaneous progress

Seven women were analyzed. Of these, only one was a primipara. The median blood loss was 219 g (range: 130–510 g), and only one woman had PPH (blood loss exceeded 500 g).

Spontaneous uterine activity even during the first two hours after the birth of the placenta exhibited a noticeable pattern of contractions. Contraction frequency decreased (F_9, 54=19.7, p < 0.001) with progression over the different stages. The mean contraction intervals were 1.9 ± 0.3 min (second stage), 2.4 ± 0.9 min (third stage) and 4.2 ± 0.7 min for the first hour, and 7.9 ± 2.1 min for the second hour after placental birth. Intensity of contractions did not show a marked change across the stages (F_{3.45, 20.75}=2.63, p = 0.07). The mean intensities were 59.0 ± 22.2 mmHg (second stage), dropping to 33.6 ± 6.4 mmHg, 56.1 ± 13.3 mmHg (third stage) and rising again to 50.8 ± 18.5 mmHg for the first hour and second hour after placental birth. Duration of contractions gradually became longer (F_{3.59, 21.55}=6.75, p = 0.001). The mean durations were 50.2 ± 16.1 s (second stage), 54.4 ± 20.9 s (third stage), 83.3 ± 11.2 s (first hour) and 102.7 ± 25.9 seconds for second hour after placental birth. Figure 1 displays an example of spontaneous uterine activity.

Figure 1. This 37-year-old multiparous woman exhibited good uterine contraction. The measured total blood loss was 261 g. The period within the first two hours after the delivery of the placenta showed a uterine contraction frequency that slightly decreased over time. The rate of paper feed was 3 cm/min.

Breastfeeding

Six women were analyzed (two primiparous, four multiparous). Their median blood loss was 182.5 g (range: 150–305 g). The timing and duration of suckling by the infants was varied.

The mean contraction frequency before breastfeeding was calculated during the last 15 min before the start of suckling; contraction frequency after breastfeeding was calculated during the first 15 min following the end of suckling. Contraction interval with breastfeeding appeared to be shorter than without breastfeeding, but there was no statistical significance (F_{1.15, 4.6}=2.18, p = 0.20). The mean contraction intervals were 4.4 ± 1.1 min before breastfeeding, 2.6 ± 0.3 min during breastfeeding, and 3.6 ± 0.2 min after breastfeeding. There were no differences in intensity or duration of contractions with or without breastfeeding. Figure 2 shows an example of uterine activity in a woman who breastfed.

Figure 2. Time of the placental delivery was 8:39. This 33-year-old primiparous woman had good uterine contractions and her measured total blood loss was 201 g. This woman had skin-to-skin contact with her baby during the first hours after birth. Around 30 min after the delivery of placenta, breastfeeding was initiated. During breastfeeding, her contraction intervals become frequent. The rate of paper feed was 3 cm/min.

Cooling the uterus

The method of cooling the uterus comprised of putting an icepack (270 × 170 × 27 mm, 1100 g of nonfreezing gel in a plastic bag) wrapped with a cloth on the women’s abdomen to cool the uterine smooth muscle through the abdominal wall during two hours after the delivery of the placenta.

Two multiparas were evaluated; one had blood loss of 537 and the other 689 g just after delivery but neither had continuous bleeding. There was no difference in contractile waves of uterine activity between using cooling of the uterus and spontaneous uterine contractions. Contraction frequency was slightly decreased, and intensity and duration of contractions showed no change.

Administration of oxytocin

Two multiparas had continuous bleeding just after the delivery of the placenta, and boggy uterus through abdominal palpation. One women lost 483 g and the other 730 g of blood. Thus, they were treated with intravenous infusion of oxytocin (5 IU in 500 ml, 150 ml per hour). Uterine contractions were frequent, induced by oxytocin and the mean contraction interval was 3.5 ± 2.0 min.

Correlation of uterine activity with blood loss, or with pain

No correlation was found between blood loss and contraction frequency (p = 0.21, p = 0.40), intensity (p = −0.05, p = 0.84), duration of contractions (ρ = 0.07, p = 0.76). Likewise, no correlation was found between the mean pain ratings and contraction frequency (ρ = 0.39, p = 0.11), intensity (ρ = 0.24, p = 0.34), duration of contractions (ρ = 0.08, p = 0.75).

Discussion

This study aimed at characterizing uterine activity during the first two hours after the placental delivery among low-risk pregnant women by using an external tocodynamometer. The main findings include: (1) spontaneous uterine contraction frequency during the two hours after the placental delivery slightly decreased over time, (2) uterine contractions were frequent when induced by oxytocin administration and suckling by the baby; however, the contraction waves did not change by cooling the uterus and (3) no correlations were found between uterine activity and blood loss or pain.

To our knowledge, this study is the first to characterize spontaneous uterine activity in low-risk pregnant women who have not undergone pharmacological intervention. In a previous study, women with augmentation of labor and administration of oxytocin for two hours after birth, the uterine contraction interval was three times per 10 min periods just after placental delivery, and two times per 10 minute periods during the second hour of delivery [14]. Comparing the postpartum uterine contraction patterns of previous studies [14,15], the uterine contraction intervals were shorter with oxytocin, the tendency to decrease in frequency over time among low-risk pregnant women without intervention during the labor stages was similar to women who had oxytocin and epidural analgesia. The uterine contraction intervals become prolonged over time, and blood loss did not increase. In this study, no correlation was found between blood loss and uterine activity parameters. This result is in line with those of previous studies [15,20]. It is important to acknowledge that the mechanism involved in hemostasis includes not only contraction of the myometrium, but also coagulation factors. Although this finding could apply to low-risk women without PPH, further studies need to be undertaken that include consideration of coagulation factors.

Contraction frequency during breastfeeding was increased, and contraction intervals with breastfeeding were shorter than without breastfeeding. Similarly, previous studies [14,21] noted the effectiveness of breastfeeding for postpartum uterine activity in women with administration of prophylactic oxytocin and reported increasing uterine activity with breastfeeding. Nipple stimulation caused by the baby’s suckling releases oxytocin [22], leading to oxytocin induced contraction of the myometrium and decrease blood flow [23]. While in this study there was no correlation between blood loss and uterine contraction frequency, which was also in agreement with a previous study [20], blood loss and duration of breastfeeding was shown to be correlated in an experimental study [24]. Breastfeeding over a fixed time-period might decrease the mean blood loss, but a randomized controlled study showed suckling in the third stage of labor did not significantly decrease the incidence of PPH and mean blood loss [25]. Therefore, future high-quality research is necessary that takes into account the duration of breastfeeding to examine the effect of breastfeeding for prophylactic management of PPH.

Cooling the uterus is one of the unique non-pharmacological prophylactic management strategies for PPH in Japan. It is understood that cold compress may help contract the myometrium, but a description of the mechanism of uterine contraction by cold compress is limited. A previous study [26] reported a relationship between cooling the uterus and uterine contraction and described it as a potential strategy as a prophylactic or a form of treatment management for PPH. Cold therapy helps blood vessels constrict and decrease the blood flow [27]. Blood vessels in the skin are affected by cold, resulting in somato-visceral reflex and subsequent vasoconstriction of relevant internal organs [27]. Cold therapy and the somato-visceral reflex decrease the blood flow of the uterus; thus, cooling the uterus could prevent PPH. However, the results of this study do not provide support for an effect of cooling the uterus on the contraction of the myometrium. The previous study [26] was observational in design, and therefore, confounding factors may have affected the results. Furthermore, the number of subjects was very small. Further studies focused on examining the role of cooling the uteruses on blood flow with larger sample size and improved research design is necessary.

This study had several limitations. Participants requiring emergency action for PPH were excluded. Thus, the uterine activity of woman with PPH could not be described. Also, despite the recording of uterine activities, some of the contractile waves were not identifiable. The reason for this is not clear; either they had no uterine contractions or the external tocodynamometer could not measure them. Uterine contraction frequency measured by external tocodynamometry has been shown to have good correlation with intrauterine pressure catheters [18]. However, the external tocodynamometer does not detect intensity of contractions with precision when compared with intrauterine pressure catheters [18]. A negative correlation has been shown between BMI and sensitivity of uterine activity measured by external tocodynamometry [28]. External tocodynamometry had better sensitivity to detect uterine activity among non-obese women than obese women (BMI > 35 kg/m²) [28]. While external tocodynamometer is an appropriate method to measure uterine activity in Japanese women because of their small build, consideration of the measuring device may be needed to clarify the mechanism of uterine atony.

While we believe our findings provide insight into improved understanding of the relationships between myometrium contractions and blood loss and between pain, further research should be undertaken in a larger sample size to include the consideration of coagulation factors and improved methods for uterine activity measurement.

Declaraton of interest

The authors have no conflict of interest.

Acknowledgements

This study was supported by JSPS KAKENHI Grant Number 26670993 and the Japan Academy of Midwifery’s Research Fund.