Risk factors for rupture of the anal sphincter Buchhave, Per; Flatow, Lennart; Rydhstroem, Hakan ...
European journal of obstetrics & gynecology and reproductive biology,
12/1999, Letnik:
87, Številka:
2
Journal Article
Recenzirano
Objective: To evaluate risk factors for rupture of the anal sphincter during vaginal delivery.
Material and methods: All 292 parturients with rupture of the anal sphincter in four neighbouring ...central hospitals in southern Sweden between 1988 and 1990 were identified retrospectively. For each case a control was selected, the sole matching criterion being that the control woman was the next to give birth vaginally in the same unit as the case. Only singleton deliveries were included. For comparison of risk factors among cases and controls, McNemar’s test was used for bivariate testing; multiple regression analysis was restricted to those variables found to be significant in the bivariate analysis. Odds ratios (OR) were calculated with 95% confidence limits (CL).
Results: In all, 292 of 22,653 deliveries (1.3%) had a rupture of the anal sphincter. Of a total of 14 independent variables explored, 8 were found to be significantly associated with rupture of the anal sphincter in the bivariate testing. In the following multivariate analysis, three variables remained significantly associated with rupture of the anal sphincter: birthweight ≥4000 g (OR 2.6; CL 1.7, 3.9), primiparity (OR 2.2; CL 1.5, 3.3) and episiotomy (OR 1.7; CL 1.1, 2.6).
Conclusion: Episiotomy appears to be significantly associated with rupture of the anal sphincter. In contrast to primiparity and birthweight, the incidence of episiotomy during vaginal delivery may easily be reduced. However, only a prospective, controlled study will disclose the true negative or positive effects of episiotomy.
We study theoretically and experimentally the dynamics of a single-frequency, unidirectional ring laser with an intracavity nonlinear singly resonant OPO-crystal in a coupled resonator. We find for a ...range of operating conditions good agreement between model results and measurements of the laser and OPO power output and of the temporal development of complex dynamic phenomena such as pulse shape, pulse duration, oscillatory transients and Q-switched operation of the laser.
We present the results of an experimental investigation of multimode intensity patterns from an optical parametric oscillator operating above threshold and show that it oscillates in 10-15 transverse ...modes strongly coupled through the nonlinear crystal, which makes this setup useful for future investigation of quantum correlations in the transverse plane. We describe the experimental setup for simultaneous measurements of signal and idler near- and far-field patterns and analyze the effects of various experimental complications such as walk-off and thermal index changes on the generated patterns. We also show that the oscillator can be stabilized by optical feedback, indicating a possible route for controlling the generated intensity patterns.
The polarization properties of Bi(12)SiO(20) (BSO) crystals are investigated in detail theoretically and experimentally, and the results are used to describe the operation of an optical correlator ...for a particle image velocimeter (PIV) using a BSO crystal as the nonlinear optical element. The work is based on an extension of the optical beam-propagation (OBP) method to include all the significant optical properties of the BSO crystal when used in a two-wave mixing configuration, i.e., optical activity, field-induced birefringence, and anisotropic diffraction. The model is able to handle multiple gratings where the input beams do not have to be symmetric about the axis of propagation. Using the numerical model the polarization properties of the BSO crystal are analyzed and the operation of the correlator is explained. The model is able to take into account self-diffraction effects, and it is shown that these effects can have a significant influence in the setup employed for the optical correlator even when the diffraction efficiency is low. The predictions of the numerical model are verified by extensive experiments on the polarization state of the output of the correlator as a function of operating conditions and of the polarization state of the input beams
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