Fetal Assessment During Labor

The intrapartum period refers to the time of pregnancy from the onset of labor to delivery of the newborn and the placenta.

During this period, the uterus contracts to provide the main force necessary for delivery. So intrapartum assessment of uterine activity refers to assessing the frequency, duration, and intensity of these contractions.

Of note, the assessment of the fetus during labor is always interpreted relative to uterine activity. First, let’s go over the physiology of the uterus, which is a pear-shaped, hollow, muscular organ that protects and nurtures the fetus, but also promotes its delivery during labor.

The superior part of the uterus is called the fundus, the middle part is the body and the bottom, cylindrical portion is the cervix.

Zooming in, the uterus has three layers: the outer serosal layer, or perimetrium; the middle muscular layer, or myometrium; and the inner mucosal layer, or endometrium.

The myometrium consists of smooth muscle fibers, which can tighten to produce uterine contractions in response to certain hormones, like oxytocin.

Now, the number of oxytocin receptors in the myometrium are low during most of the pregnancy, but they increase dramatically during the third trimester, reaching the greatest concentration during active labor.

The oxytocin receptors, especially those in the fundus, respond to oxytocin by promoting rhythmic synchronized endometrial contractions from the fundus towards the cervix, causing dilation and effacement, or thinning of the cervix, as well as pushing the fetus through the birth canal.

Normal uterine activity during labor involves 5 contractions or fewer in a 10 minute period, averaged over 30 minutes. Between contractions, the uterus relaxes to allow adequate blood flow to the placenta and fetus.

Now, let’s switch gears and go through some types of dysfunctional labor. First up, is tachysystole, which is defined as more than 5 contractions in a 10 minute period, averaged over 30 minutes.This is caused by the uterine muscle’s inability to properly relax between contractions, compromising blood flow to the uterus, placenta and fetus.

The most common cause of tachysystole is excessive administration of exogenous oxytocin or prostaglandins. This can cause problems like placental abruption, which is when the placenta separated prematurely from the uterine wall; as well as postpartum hemorrhage.

The fetus can also experience hypoxia due to the rapid contractions. Another type of dysfunctional labor is precipitous labor, or rapid labor, where the fetus is delivered within 3 hours from the onset of labor.

These frequent contractions can cause maternal injuries such as lacerations of the cervix, vagina, and outer genitalia; as well as placental abruption; and postpartum hemorrhage.

The fetus can also experience hypoxia due to the rapid contractions, or even injuries. On the other hand, labor dystocia, or slow, abnormal contractions, is ineffective in progressing cervical dilation and effacement, and fetal descent.

This type of dysfunctional labor is sometimes referred to as “failure to progress.” These contractions are infrequent, weak, and brief, and can slow the progression of labor; cause complete arrest of labor; result in the exhaustion of the client; as well as increasing risk for infections and neonatal sepsis.

Clients experiencing labor dystocia will often require cesarean birth.Now, the assessment of uterine activity includes frequency, duration, intensity, and resting tone, or tonus.

Frequency is calculated from the onset of one contraction to the onset of the next contraction, and is described in minutes, while duration is calculated from the onset of one contraction to the end of that contraction, and is described in seconds.

Intensity, or the strength of contraction, can be subjectively assessed by palpation of the uterus. The more intense the uterus contracts, the harder and less indentable the fundus.

It can feel like a tip of a nose in mild contractions, like a chin in moderate ones, or like a forehead during strong ones.

The relative intensity can also be measured by a tocodynamometer, which is a pressure-sensitive button placed on the fundus that detects uterine changes during a contraction.

The tocodynamometer can also measure the relative duration and frequency of the contraction. Now, the only way to accurately measure the true intensity of a uterine contraction is with an intrauterine pressure catheter, or IUPC.

The catheter is inserted through a cervix and into the uterine cavity, which requires cervical dilation of at least 2 centimeters and rupture of fetal membranes.

Finally, the resting tone is an assessment of the amount of uterine muscle tone between contractions, which should be soft by palpation, and approximately 10 mmHg with an IUPC.Alright as a quick recap… Uterine activity, which involves the frequency, duration, and intensity of contractions, is assessed during labor along with assessment of the fetus.

These contractions provide the main force necessary for delivery of the fetus. The frequency of uterine contractions is calculated from the onset of one contraction to the onset of the next, while duration is calculated from the onset of one contraction to the end of that contraction.

Intensity, or the strength of contraction, is described as mild, moderate, or strong. The resting tone is an assessment of the amount of uterine muscle tone between contractions.

During labor, the uterine muscle, called the myometrium, contracts in response to hormones like oxytocin. These contractions bring about dilation and effacement of the cervix, as well as the movement of the fetus through the birth canal.

Uterine activity can be measured by palpation, with a tocodynamometer, or an IUPC. Types of dysfunctional labor include tachysystole, which is defined as more than 5 contractions in a 10 minute period, averaged over 30 minutes.

Other types of dysfunctional labor are precipitous labor, where the fetus is delivered within 3 hours from the onset of labor, and labor dystocia, which occurs when abnormal contractions are ineffective in producing cervical