Prelabour changes in uterus and cervix

During the prelabour period, which occurs in the weeks leading up to the onset of active labor, the uterus and cervix undergo physiological changes in preparation for childbirth.

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These changes involve alterations in the structure, function, and composition of the uterine muscle (myometrium) and cervical tissue, gradually transitioning the reproductive tract from a quiescent state to a dynamic, contractile state conducive to labor and delivery. Here are the key prelabour changes that occur in the uterus and cervix:

Uterine Changes:

1. Braxton Hicks Contractions:

• From the second trimester onward, the uterus may experience irregular, painless contractions known as Braxton Hicks contractions. These contractions help tone the uterine muscle and may become more noticeable and frequent as labor approaches.

1. Increase in Uterine Size and Tone:

• Throughout pregnancy, the uterus undergoes significant growth and enlargement to accommodate fetal development. By the prelabour period, the uterus has reached its maximum size and tone, with well-developed muscle fibers capable of generating strong, coordinated contractions during labor.

1. Effacement (Thinning) of the Cervix:

• Effacement refers to the gradual thinning and shortening of the cervix as it prepares for dilation and passage of the fetus through the birth canal. Effacement typically begins in the weeks preceding labor and is assessed as a percentage (e.g., 50% effaced).

1. Lightening (Engagement) of the Fetal Head:

• In late pregnancy, the fetal head may descend into the maternal pelvis, a process known as lightening or engagement. This descent may relieve pressure on the diaphragm and lungs, resulting in easier breathing for the mother, but may also increase pressure on the bladder and pelvis.

1. Changes in Uterine Electrophysiology:

• Electrical and contractile properties of uterine muscle cells (myocytes) undergo modifications, including alterations in ion channel activity, calcium handling, and gap junction communication, to facilitate the generation and propagation of uterine contractions.

Cervical Changes:

1. Softening (Ripening) of the Cervix:

• The cervix undergoes softening and ripening, transitioning from a firm, closed structure to a softer, more flexible consistency conducive to effacement and dilation. Cervical ripening is mediated by hormonal changes, including increased prostaglandin production and decreased collagen content.

1. Effacement (Thinning) and Dilation:

• Effacement of the cervix is accompanied by dilation, as the cervical os (opening) gradually expands to allow passage of the fetus. Effacement and dilation are dynamic processes that occur concurrently during the prelabour period, with effacement typically preceding dilation.

1. Increase in Cervical Secretions:

• Cervical glands produce increased quantities of mucus, known as cervical mucus or cervical ripening, which serves as a protective barrier and lubricant for the birth canal. Changes in mucus consistency and quantity may be observed as labor approaches, with the mucus becoming thinner, clearer, and more copious.

1. Loss of Mucus Plug (Bloody Show):

• As the cervix effaces and dilates, the mucous plug that seals the cervical canal may be expelled from the vagina, often accompanied by small amounts of blood or pink-tinged discharge. This phenomenon, known as the “bloody show,” is a common prelabour sign indicating cervical changes and impending labor.

1. Changes in Cervical Position and Consistency:

• During pelvic examinations, healthcare providers may assess changes in cervical position, consistency, and dilation as indicators of prelabour progress. The cervix may become anteriorly positioned, softer, and more centrally located in the pelvis as labor approaches.

These prelabour changes in the uterus and cervix represent the physiological adaptations that occur in preparation for childbirth. By gradually priming the reproductive tract for labor and delivery, these alterations help facilitate the onset of active labor, promote cervical effacement and dilation, and contribute to the progress of spontaneous or induced labor. Monitoring these prelabour changes through clinical assessment, pelvic examinations, and obstetric evaluation allows healthcare providers to assess readiness for labor and provide appropriate support and interventions as needed.