Factors influencing the likelihood of instrumental delivery success.
OBJECTIVE
To evaluate risk factors for unsuccessful instrumental delivery when variability between individual obstetricians is taken into account.


METHODS
We conducted a retrospective cohort study of attempted instrumental deliveries over a 5-year period (2008-2012 inclusive) in a tertiary United Kingdom center. To account for interobstetrician variability, we matched unsuccessful deliveries (case group) with successful deliveries (control group) by the same operators. Multivariate logistic regression was used to compare successful and unsuccessful instrumental deliveries.


RESULTS
Three thousand seven hundred ninety-eight instrumental deliveries of vertex-presenting, single, term newborns were attempted, of which 246 were unsuccessful (6.5%). Increased birth weight (odds ratio [OR] 1.11; P<.001), second-stage labor duration (OR 1.01; P<.001), rotational delivery (OR 1.52; P<.05), and use of ventouse compared with forceps (OR 1.33; P<.05) were associated with unsuccessful outcome. When interobstetrician variability was controlled for, instrument selection and decision to rotate were no longer associated with instrumental delivery success. More senior obstetricians had higher rates of unsuccessful deliveries (12% compared with 5%; P<.05) but were used to undertake more complicated cases. Cesarean delivery during the second stage of labor without previous attempt at instrumental delivery was associated with higher birth weight (OR 1.07; P<.001), increased maternal age (OR 1.03; P<.01), and epidural analgesia (OR 1.46; P<.001).


CONCLUSIONS
Results suggest that birth weight and head position are the most important factors in successful instrumental delivery, whereas the influence of instrument selection and rotational delivery appear to be operator-dependent. Risk factors for lack of instrumental delivery success are distinct from risk factors for requiring instrumental delivery, and these should not be conflated in clinical practice.
Department of Obstetrics and Gynaecology, University of Cambridge, NIHR Cambridge Comprehensive Biomedical Research Centre, Cambridge, United Kingdom; and the Population Research Center and LBJ School of Public Affairs, and Red McCombs School of Business and Division of Statistics and Scientific Computation, University of Texas at Austin, Austin, Texas.
Catherine E
CE
Aiken
Abigail R
AR
Aiken
Jeremy C
JC
Brockelsby
James G
JG
Scott
D000328:Adult; D001724:Birth Weight; D002585:Cesarean Section / Q000706:statistics & numerical data*; D002983:Clinical Competence; D005113:Extraction, Obstetrical / Q000295:instrumentation / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007748:Labor Stage, Second; D016015:Logistic Models; D008423:Maternal Age; D009772:Obstetrical Forceps / Q000706:statistics & numerical data; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult