8.1. BASIC CONCEPTS
Labor (delivery, childbirth) is the process of expulsion or extraction of gestational sac (product of conception: the fetus and parafetal structures) from the cavity of uterus after the fetus has become viable. In the light of this definition, any expulsion or extraction (vaginal or abdominal) is considered to be delivery. When the fetus is delivered, labor is not over as the afterbirth still remains in the uterus.
International classification codes:
• 047 False labor;
• 060 Preterm labor and delivery;
• 048 Prolonged pregnancy;
• 080 Single spontaneous delivery:
◊ 080.0 Spontaneous vertex delivery.
The causes of labor onset are not studied well enough (see Chapter 6.2 "Onset of Labor and Regulation of Uterine Activity").
The onset of labor is preceded, as a rule, by precursors of labor, a complex of clinical manifestations; their emergence four to two weeks prior to childbirth indicates that childbirth is near:
• fundus of uterus sinks as the presenting part engages the lesser pelvis inlet; this happens in primiparous women;
• relative decrease in amniotic fluid volume;
• «show»: profuse mucous vaginal discharge as the mucous plug is discharged from the cervix of uterus;
• some reduction in body weight;
• emergence of irregular cramplike painless sensations in the lower abdomen;
• absence of weight gain over the last two weeks.
There is another notion accepted in obstetrics: labor readiness.
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Ripeness of cervix is commonly determined using various integral scores, Bishop's score (1964) among them (Table 8.1).
A vaginal examination determines the cervical consistency, its length (or degree of effacement), patency of the cervical canal and the position of cervix in relation to the pelvic axis. Fetal station is determined in relation to the ischial spines which are