Labor Onset Theories and Signs

Theories of Labor Onset

• Labor is influenced by a combination of factors from the mother and fetus
• Factors include:
  • Uterine muscle stretching, releasing prostaglandins
  • Pressure on the cervix, stimulating oxytocin release from the posterior pituitary
  • Oxytocin stimulation working with prostaglandins to initiate contractions
  • Change in the ratio of estrogen to progesterone (increased estrogen stimulates contractions)
  • Placental age triggering contractions at a set point
  • Rising fetal cortisol levels reducing progesterone and increasing prostaglandin formation
  • Fetal membrane production of prostaglandins stimulating contractions

Signs of Labor

• Preliminary signs of labor should be taught to all pregnant women
• Lightening: Descent of the presenting fetal part into the pelvis, typically 10-14 days before labor in first-time mothers
  • Associated with shooting leg pain, increased vaginal discharge, urinary frequency due to pressure on the bladder, relief from pressure on the diaphragm and shortness of breath.
  • In later pregnancies, lightening may occur on the day of labor or after it has begun.
• Increased activity level: Increased energy levels in the morning of labor, related to an increase in epinephrine (due to a decrease in progesterone). Epinephrine prepares the body for labor.
• Braxton Hicks contractions: Strong contractions felt towards the end of pregnancy; can be mistaken for true labor

Ripening of the Cervix

• Ripening of the cervix, a sign only observable through a pelvic exam, is an integral factor
• During pregnancy, the cervix feels softer than usual, similar to an earlobe's consistency (Goodell's sign)
• At term, the cervix is very soft, described as "butter-soft"

Signs of True Labor

• Uterine Contractions: The surest sign that labor has begun
  • Productive uterine contractions (involuntary, intensity can be painful in early labor)
  • Breathing exercises can help control discomfort
• Show: Cervix softens and ripens, the mucus plug that filled the canal during pregnancy is expelled; blood mixed with mucus produces a pink tinge (bloody show)
• Rupture of membranes: Labor can begin with the rupture of the membranes; can be a sudden gush or a slow seeping of clear fluid from the vagina;
  • Intrauterine infection and umbilical cord prolapse are two risks associated with ruptured membranes
  • If labor hasn't started within 24 hours, induction may be necessary.

Differentiation Between True and False Labor Contractions

• False Labor Contractions: Irregular, localized to abdomen, can stop with activity or sleep.
• True Labor Contractions: Regular, felt in lower back first, become more intense, continue regardless of activity, lead to cervical dilation.