Uterine contractions are the tightening and shortening of the uterine muscles. They are a fundamental part of the birthing process, helping to dilate the cervix and move the baby through the birth canal. Monitoring contractions during pregnancy provides insights into the progression of labor and the well-being of both the parent and the baby.
How Contractions Are Monitored
Contractions are primarily monitored using external and internal electronic fetal monitoring. External monitoring involves placing a tocodynamometer (toco) on the abdomen. This device records the frequency and duration of contractions by sensing the tightening of the abdominal wall. While widely used, external monitoring does not accurately measure the true strength of contractions.
Internal monitoring provides a more precise assessment of contraction strength. This method uses an intrauterine pressure catheter (IUPC) inserted into the uterus. The IUPC measures the actual pressure inside the uterus in millimeters of mercury (mmHg), providing data on contraction intensity, frequency, and duration. Internal monitoring is only possible once the membranes have ruptured and the cervix is sufficiently dilated.
Identifying Strong Contractions on the Monitor
On a monitor, contractions appear as “peaks” or “hills” on a graph. The graph typically shows two lines; the lower line usually represents uterine contractions. The horizontal axis (X-axis) tracks time, allowing healthcare providers to determine the duration and frequency. The vertical axis (Y-axis) indicates intensity.
For external monitoring, a higher peak suggests stronger uterine activity. However, this method only shows relative strength, as the external sensor cannot measure the actual pressure within the uterus. Accuracy can be affected by device placement or maternal body habitus. With internal monitoring, the vertical axis displays the exact pressure in mmHg. Strong labor contractions typically register above 50-60 mmHg during active labor, with some reaching 80-100 mmHg as labor progresses towards delivery.
Recognizing Patterns of True Labor
The pattern of contractions on the monitor helps distinguish true labor from false labor. True labor contractions exhibit a progressive pattern, becoming longer, stronger, and more frequent over time. On the monitor, peaks become taller, wider, and closer together.
Braxton Hicks contractions are typically irregular in timing and intensity. They may not show a clear pattern of increasing strength or frequency and often subside with changes in activity or position. While Braxton Hicks contractions might register between 5-25 mmHg, true labor contractions progressively increase, starting around 40-60 mmHg in the active phase.
When to Consult a Healthcare Provider
Monitoring contractions helps determine when to contact a healthcare provider. Call a doctor or midwife when contractions become consistently strong, regular, and painful. A common guideline is the “5-1-1 rule”: contractions occurring every five minutes, lasting one minute, for at least one hour. For individuals with previous births, the guideline might be contractions every five minutes for at least one hour.
Other signs warranting immediate medical consultation include rupture of membranes (water breaking), significant vaginal bleeding, or a noticeable decrease in fetal movement. If contractions are less than 37 weeks pregnant and seem regular, or if any contraction lasts longer than two minutes, contact a healthcare provider for guidance.