Johns Hopkins researchers, using a novel birthing simulator designed by biomedical engineering faculty, staff and students at the University, have identified what may be the least forceful way to deliver a baby whose shoulders are stuck in the birth canal.
Shoulder dystocia, in which the baby's shoulders won't move past the mother's bony pelvis during delivery, occurs in about 5 percent of births. Of these, up to a quarter of deliveries may result in an injury to the baby's brachial plexus, the nerves that control movement and sensation in the arm. As many as 10 percent of infants may sustain some permanent damage.
An obstetrician can perform one of several maneuvers to manipulate the position of either the mother or the baby when shoulder dystocia occurs. The Hopkins researchers found that turning the baby so its spine faces the mother's belly (a technique known as anterior Rubin's maneuver) requires less force than either turning the baby so its spine faces the mother's spine, or moving the mother's legs back to try to reduce the force of the baby's shoulders against the mother's pelvis.
These results are reported in the Jan. 4 issue of the American Journal of Obstetrics and Gynecology.
"Every obstetrician is likely to face this circumstance at some point in his or her career, and the longer the baby remains stuck, the higher the risk that the baby will suffocate," says Edith D. Gurewitsch, M.D., lead author of the study and an assistant professor of gynecology and obstetrics. "While further studies are necessary before we can make definitive recommendations on the use of one procedure over another, our initial lab results demonstrate that we can measure what is happening to the baby during birth, and that we can alter our techniques to create a safer environment for delivery - a goal shared by every obstetrician."
For the study, Gurewitsch performed 30 mock deliveries using a complex birthing device designed by Hopkins faculty, staff and students to simulate shoulder dystocia. It consists of several parts: a maternal model with a three-dimensional bony pelvis, a fetal model, a force-sensing glove, and a computer-based data acquisition system.
The maternal model - composed of pleather "skin," carpet foam, foam sealer and other components - features a birth canal, a mock uterus connected to a pneumatic pump to simulate the natural pattern of uterine contractions and force from a mother's pushing, and flexible legs that can be moved to rotate the pelvis.
The fetal model consists of a cloth mannequin outfitted with a joystick device, a spring and wooden dowels representing the cervical vertebrae. Additional elements measure neck extension, rotation and stretching of the brachial plexus nerves during delivery.
To deliver the "baby" during the study, Gurewitsch wore a force-sensing glove. The custom, nylon-lycra glove has pockets sewn into it to house force-sensors, which were used to measure the traction she used in delivery. Wires emanating from the sensors connected to a computer-based data-acquisition system that stored and processed the data.
Gurewitsch performed 10 deliveries by turning the baby so its spine faced the mother's belly, 10 deliveries by turning the baby so its spine faced the mother's spine, and 10 deliveries by moving the mother's legs back.
The first maneuver was associated with the least amount of force, at 6.5 pounds, to the baby's head necessary to achieve delivery. The other techniques applied 8.5 pounds and 16 pounds, respectively. The first maneuver also produced the least amount of stretching on the baby's brachial plexus nerves, at 2.9 millimeters. The other techniques caused the nerves to stretch by 6.9 millimeters and 7.3 millimeters, respectively.
Researchers calculated that turning the baby created as much as 2 centimeters of extra space between the baby's shoulders and the mother's pubic bone, whereas raising the mother's legs produced only 1 centimeter of extra space.
"Since complicated deliveries comprise a small percentage of vaginal births, clinicians in training often do not have adequate exposure to these types of deliveries," says Robert H. Allen, Ph.D., senior author of the study and a senior engineering lecturer at Hopkins. "Our device provides an opportunity to simulate birth complications and allow clinicians to practice resolving them. Using this birthing simulator as a research tool, we may be able to glean new insights into complicated births and develop new ways to resolve them."
The device won top prize in a student design competition held in September during the international meeting of the Institute of Electrical and Electronics Engineers' Engineering in Medicine and Biology Society in San Francisco. The inventors, including Gurewitsch, Allen and Paul Gilka, manager of the laboratory that housed the work, have filed a provisional patent on the simulator.
In continuing work with the laboratory model, Gurewitsch and Allen plan to have other doctors train on the simulator to develop a better sense of how much force they apply to babies during delivery.
The current study was funded by grants from the National Center for Injury Prevention and Control, a branch of the federal Centers for Disease Control and Prevention.
Study coauthors were Esther J. Kim, Jason H. Yang, Katherine E. Outland, and Mary K. McDonald.