Case-control analysis of post-term induction of labor.

At Akershus Central Hospital the main indication for induction of labor is post-term pregnancy, and induction is carried out by i.v. oxytocin drip. During 3 years between 1974 and 1977, labor was induced in 11.6% of all births in this hospital. Thirty per cent of first induction attempts were unsuccessful; the success rates, implying labor contractions and delivery consequent upon induction, were slightly higher among mothers of parities 1 + than among those giving birth for the first time. Most of the induced births took place between noon and 8 p.m. In a case-control study of post-term inductions of live single fetuses in cephalic presentation, comprising 721 sets of cases and controls, unreliable term dating was more frequent among induced than among control mothers, significantly so in the para 1 + group. Mothers requiring induction were slightly shorter and slightly heavier than those with spontaneous onset of labor, and pregnancy hypertension was more frequent among the former. Labor was of shorter duration in induced cases than in those with labor of spontaneous onset, and operative intervention during delivery was significantly more frequent in the induction groups. Birth weight and crown-heel length were similar in the two groups, but Apgar scores of the infants born after induction were significantly lower than of those born after spontaneous labor, at both 1 and 5 minutes. While the frequency of diseases and injuries in the newborns were similar, more children born after induction were transferred to the intensive care unit. There was a striking preponderance of boys born after induction, both to para 0 and para 1 + mothers. In spite of matching, the comparability of cases and controls is always an object of criticism in studies like this one. Therefore, although the information obtained is valuable, there is a need for large-scale randomized studies on induction of labor.