A. ONSET OF LABOR
1. Labor is the process by which the fetus and products of conception are expelled as the result of regular, progressive, frequent, strong uterine contractions.
2. Theoretically labor is thought to result from:
a. Progesterone deprivation
b. Oxytocin stimulation
c. Fatal endocrine control
d. Uterine deciduas activation (release of a complex cascade of bioactive chemical agents into amniotic fluid)
B. FACTORS AFFECTING LABOR
1. PASSAGEWAY. This refers to the adequacy of the pelvis and birth canal in allowing fetal descent; factors include:
a. Type of pelvis (for example, gynecoid, android, anthropoid, or platypelloid)
b. Structure of pelvis (for example, true versus false pelvis)
c. Pelvic inlet diameters
d. Pelvic outlet diameters
e. Ability of the uterine segment to distend the cervix to dilate, and the virginal canal and introitus to distend.
2. PASSENGER. This refers to the fetus and its ability to move through the passage way, which is based on the following:
a. Size of the fetal head and capability of the head to mold the passageway.
b. Fetal presentation – the part of the fetus enters to maternal pelvis first (for example, cephalic [vertex, face, brow]: breech [frank, single or double footing complete]; or shoulder [transverse, lie])
c. Fetal attitude – the relationship of fetal parts to one anther.
d. Fetal position – the relationship of a particular reference points of the presenting part and the maternal pelvis, described with a series of three letters (side of maternal pelvis [L, left; R, right; T, transverse], presenting [O, occiput; S, sacrum; Sc, scapula; M, mentum], and the part of the maternal pelvis (A, anterior; P, posterior].
3. POWER. This refers to the frequency duration and strength of uterine contraction to cause complete cervical effacement and dilation.
4. PLACENTAL FACTORS refers to the site of placental insertion.
5. PSYCHE refers to the client’s psychological state, available support systems, preparation.
C. SIGNS AND SYMBOLS OF IMPENDING LABOR (premonitory signs)
1. Lightning is the descent of the fetus and uterus into the pelvic cavity 2 to 3 weeks before the onset of labor.
2. Braxton hicks contractions are irregular, intermittent contractions that have occurred throughout the pregnancy; become uncomfortable, and produce a drawing pain in the abdomen and groin.
3. Cervical changes, include softening “ripening” and effacement of the cervix that will cause explosion of the mucus plug (bloody show) and increased vaginal discharge.
4. Rupture of amniotic membranes may occur before the onset of labor if the woman suspects that her membranes have ruptured, she should contact her health care provider and go to the labor suite immediately so that she may be examined for prolapsed cord – a life-threatening condition for the fetus.
5. Burst of energy or increased tension and fatigue may occur before the onset of labor.
6. Weight loss of about 1 to 3 pounds may occur 2 to 3 days before the offset of labor.
7. Urinary frequency returns.
8. Backache