Recognition of midpelvic contraction

Abstract

A LTHOUGH pelvic contraction was recognized at least as early aa the sixteenth century, it was not until 1861 that Litzmanns set forth practical criteria for evaluating the inlet. Outlet contraction, mentioned occasionally through the years, received serious attention only after Williams’ exposition,‘X almost fifty years later. There has been a similar delay in the general acceptance of the concept of midpelvic contraction. Although occasional reference has been made to the obstetric significance of the pelvic midplane for at least fifteen years, the subject continues to receive scant attention, and the majority of recent writers ignore it. A single paragraph on the effect of “prominent ischial spines ’ ’ appears in one of four standard obstetric texts. It is strange that midpelvic capacity should be ignored or its importance denied, since for years this level has been known as “the plane of least pelvic dimensions. ” Published reports, on the contrary, indicate that interspinous measurements below the generally accepted normal of 10.5 cm. are relatively common. By manual mensuration, Hanson5 found 16.1 per cent of 1,120 obstetric patients with interspinous diameters 9.5 centimeters or less, using a specifically designed instrument. Others29 3* ‘if *O have repeatedly called attention to the frequency of midpelvic contraction. Obviously, one would expect to find midpelvic contraction in association with caontracted inlet and outlet. On the other hand, it can occur with normal inlet and outlet, according to the criteria of Litzmann and Williams. The difference between average pelvic measurements and those at the lower limits of normal demands emphasis at this point. With average manual measurements, it is doubtful that midpelvic dystocia will result. With manual measurements at. t,he lower limits of normal, serious, and even insurmountable midplane disproportion is not only possible theoretically, but also actually does occur, as exemplified by the ensuing report :