15.3 Physiologic Adaptations during Labor and Birth

Vital Signs

The laboring person’s heart rate increases during contractions, and the baseline can increase or decrease. Sustained increases in heart rate warrant an investigation for possible signs of infection and excessive blood loss.

Blood pressure (BP) increases during contractions and returns to baseline between contractions. Slow increases in BP can be noted with the experience of pain; however, significant increases (>140/90 mm Hg) should be investigated for the presence of hypertensive disorders of pregnancy, which can occur during pregnancy, labor, birth, and the postpartum period (ACOG, 2020). Any hypotension should be investigated as possible infection, anesthesia side effects, or a sign of a concealed hemorrhage.

The laboring person’s temperature can increase with exposure to misoprostol (Cytotec) as well as epidural anesthesia, but any increase above 100.4° F (38° C) warrants investigation for possible infection.

The respiratory rate can increase, especially in unmedicated labor due to breathing techniques used as a coping mechanism.

The laboring person’s oxygen saturation can decrease with epidural anesthesia, especially if the medication gets above recommended levels, or when magnesium sulfate is administered for preeclampsia.

Fetal Descent

The pregnant person’s body continues to facilitate the labor process with contractions causing downward pressure on the presenting fetal part, which leads to descent through the pelvis. This typically occurs with internal rotation of the fetus combined with the physical pressure of uterine contractions and changes in pelvic diameters through maternal positioning in labor. During the first stage, the fetus is typically not engaged in the pelvis with a station of −1 to −3, but can be lower if fetal head engagement occurred prior to labor or rapidly during labor (see Figure 15.3(c)).

Cardiovascular

Cardiac output increases an additional 10 percent to 15 percent in the first stage of labor (Martin et al., 2022). This is likely related to increased stroke volume from the sensation of pain and/or the work of the body even when adequate anesthesia is present. The body is also protecting vasodilation around the uterine muscle to allow for perfusion of the fetus during the work of labor, which will need to abruptly switch to vasoconstriction after birth.

Musculoskeletal

Pelvic floor anatomy is stretching to accommodate the descent of the fetus in labor. The pelvis is affected by relaxing and position changes to increase diameters and allow passage of the fetus (Cohen & Friedman, 2023). The sacrum will often become more pronounced, especially when the laboring person is in an upright position, as the presenting part of the fetus engages into the pelvis and places internal pressure on the sacrum.

Gastrointestinal

Gastric emptying and motility are further slowed during labor. Slowed gastrointestinal function combined with intense pain and abdominal pressure can increase the likelihood of nausea and vomiting in labor, especially in the active phase of the first stage of labor. This can explain why many people in labor without anesthesia do not have the desire to eat, but those with epidural anesthesia may experience hunger. The physical exertion of labor requires nutritional support, and current recommendations are to consider oral hydration, electrolyte support through oral or intravenous replacement, and light solid food intake. The oral intake of hydration and nutrition is controversial in labor due to a history of fear surrounding the risk of aspiration in the rare event that general anesthesia is indicated during labor. Restriction of oral intake is not currently supported by research for low-risk labors, but protocol has been slow to change in many anesthesia orders and facilities (Singata et al., 2013).

Contraction Pattern

Contractions during the second stage can space, or pause, immediately prior to the urge to push or during pushing efforts. This may be protective of the fetal acid-base balance. The increased force of the contractions combined with maternal expulsive efforts decreases oxygen perfusion to the fetus.

Vital Signs

In the second stage, blood pressure increases by another 10 mm Hg during active pushing, and both heart rate and respiratory rate increase as well.

Cardiovascular

As noted precedingly, heart rate and blood pressure increase in the second stage. Maternal exhaustion can be impacted by this, and appropriate rest or breaks between pushing efforts may be necessary if exhaustion or abnormal vital signs occur.

Musculoskeletal

Continued position changes and shifts in pelvic diameters or change in fetal position allow for fetal descent following the cardinal movements of vaginal birth. The birthing person will also often have an adrenaline surge, causing significant shaking or tremors during the end of the first stage and second stage of labor (Gicheru et al., 2019). These appear similar to chills experienced during a fever and will typically resolve in 1 to 2 hours after birth.

Gastrointestinal

Continued slowing of gastric emptying could be a contributing factor to the nausea and vomiting experienced during the second stage of labor. Increased acidity of the slowed gastric contents may lead to acid reflux or “heartburn” being reported by the birthing person. Epidural use is associated with less slowing of gastric emptying and may contribute to lower risk for aspiration in the use of general anesthesia (Bataille et al., 2014).

Uterus and Cervix

The term uterus is significantly distended and well perfused with purposeful vasodilation through the second stage of labor. The delivery of the fetus and drainage of remaining amniotic fluid that occurs with birth results in a rapid decrease in the internal pressure exerted on the uterine wall from within. In response to this, there is rapid vasoconstriction of the vessels that supply the pelvic floor. The 500 mL of blood flow routed to that area during labor is shunted back to the central circulation to compensate for expected blood loss of the same amount (Smith, 2020). Uterine contractions continue to shorten the muscle fibers and further decrease the uterine size, which can lead to placental detachment and subsequent delivery. The cervix will decrease in dilation and effacement as well but will remain partially dilated until the placenta delivers, typically around 5 cm dilation/50 percent effacement at this stage (Martin et al., 2022).

Cardiovascular

Rapid decrease in heart rate and blood pressure to prelabor levels may be noted or can occur slowly over the first 2 weeks postpartum. Hypotension and tachycardia are late symptoms of significant blood loss and warrant precise identification and treatment of the site of the bleeding. The shift of blood volume following uterine involution can increase the risk of cardiac complications such as cardiomyopathy and pulmonary edema, especially in those with preexisting heart conditions or hypertensive disorders in pregnancy (Martin et al., 2022).

Vital Signs

In the fourth stage, the blood pressure and pulse may be slightly elevated or return to normal Significant or symptomatic decreases in blood pressure and heart rate call for careful assessment for blood loss, which can be overt or concealed. The respiratory rate returns to normal. Temperature may be slightly elevated (up to 100.4° F or 38° C) or normal (Martin et al., 2022).

Uterus and Cervix

Uterine involution continues during the fourth stage of labor. The fundus is expected to be firm, midline, and located near the umbilicus. Cervical dilation resolves, leading to a closed cervix shortly after delivery of the placenta (Martin et al., 2022).

Lochia

Bright or dark red lochia are expected for the entire fourth stage of labor. Continued measurement of this bleeding for a total quantitative blood loss can be useful in monitoring for the potential need for intervention. Quantitative blood loss is measured via calculation of the weight of blood-filled material with the weight of the material subtracted. Fundal assessment should produce only a small amount of bleeding. If continued leaking of streams of blood is noted or large clots are expressed during the fundal assessment, prompt consultation, increased monitoring, and interventions in collaboration with the health-care provider are indicated (Martin et al., 2022).

Perineum

Tenderness, edema, and a burning sensation along lacerations are to be expected. Topical sprays, ice, rest, anti-inflammatory medications, and use of a peri-bottle during urination to dilute urine can be useful tools to promote comfort during this time. Significant bruising or severe pain should be evaluated by the provider because of the risk for hematoma formation. Perineal sitz baths can also be utilized for pain control and promotion of healing. These are also available commercially if patients prefer to use them at home after discharge.

Bladder

Some postpartum patients experience decreased bladder sensation after birth. In those cases, the nurse should encourage the patient to attempt to void at regular intervals until the urge to void returns. The nurse should evaluate the patient’s bladder for distention, especially after epidural use. Some increase in voids can be seen as the body eliminates excess fluids in the first 2 weeks postpartum. Any bladder distention or decrease in urine output should be promptly reported to and evaluated by the provider. A distended bladder is one of the leading causes of postpartum uterine atony and can lead to postpartum hemorrhage (Martin et al., 2022).

Musculoskeletal

The work of labor can cause significant aches and pains that should be treated with rest, ice or heat, and support for ambulation as needed (Martin et al., 2022). If epidural anesthesia was used, it may be several hours before the birthing person is able to ambulate without assistance. The nurse should be sure to assess fall risk and call for assistance when supporting ambulation the first time after an epidural is discontinued.

Gastrointestinal

Bowel health can generate intense fear in the birthing person. The nurse should support bowel health with oral hydration, quality dietary intake with appropriate fiber, and the administration of a stool softener for any person with severe perineal tearing, hemorrhoids, cesarean birth, or those using narcotic pain medications (Martin et al., 2022).