A Cook catheter is any catheter made by Cook Medical, a company that manufactures medical devices used across more than 20 specialties. But if you’ve heard the term from a doctor or midwife, they’re almost certainly talking about the Cook Cervical Ripening Balloon, a double-balloon catheter used to help start labor. This is by far the most common reason patients encounter the name, and it’s one of the most widely used mechanical methods for labor induction.
The Cervical Ripening Balloon
The Cook Cervical Ripening Balloon is a silicone catheter with two small balloons positioned on either side of the cervix. One balloon sits inside the uterus against the inner opening of the cervix, and the other sits in the vagina against the outer opening. When both are filled with saline, they apply gentle, steady pressure to the cervix from both sides, encouraging it to soften and open. This process, called cervical ripening, prepares the body for active labor.
The device is latex-free, with an all-silicone construction designed for comfort and biocompatibility. It includes two separate valves, one for each balloon, and a thin stylet (a flexible rod) that helps guide it into position during insertion.
Why It’s Used for Labor Induction
When labor needs to be induced but the cervix isn’t ready, the cervix is typically firm and closed. Doctors measure cervical readiness using a scoring system called the Bishop score. A low score means the cervix hasn’t started the natural softening process, and simply breaking the water or starting contractions with medication may not work well. The Cook balloon mechanically encourages this ripening without using drugs.
The American College of Obstetricians and Gynecologists (ACOG) gives a strong recommendation for mechanical cervical ripening, backed by high-quality evidence. A large systematic review of 113 trials with more than 20,000 participants found that balloon catheters are similarly effective to common ripening medications in terms of cesarean delivery rates and achieving vaginal delivery within 24 hours. The key advantage: balloon catheters have a better safety profile, with significantly lower rates of excessive uterine contractions that can affect fetal heart rate.
How Insertion Works
The procedure typically begins with you in a reclined position, though the exact positioning varies by hospital. Your provider uses a speculum to see the cervix, cleans the area, then threads the catheter through the cervical canal. Once both balloons have passed through, the stylet is removed.
The uterine balloon (connected to the blue valve) is inflated first with 40 milliliters of water, then gently pulled back until it rests snugly against the inner cervical opening. The vaginal balloon (green valve) is then inflated with 20 milliliters on the outside. From there, the provider gradually adds more fluid in increments, up to a maximum of 80 milliliters in each balloon. If you feel uncomfortable during inflation, the vaginal balloon volume is reduced first. The end of the catheter is taped to your thigh to keep it in place.
What to Expect While It’s In
The balloon typically stays in place for up to 12 hours. Many women feel cramping or pressure, similar to period pain, while the device works. Once your cervix dilates to about 3 centimeters, the balloon usually falls out on its own. That’s a good sign: it means the cervix has opened enough for the next stage of induction, whether that’s breaking the water or starting a medication to bring on contractions. If the cervix doesn’t dilate sufficiently, your provider will deflate the balloons and remove the catheter to try a different approach.
Double Balloon vs. Single Balloon
The Cook catheter’s double-balloon design distinguishes it from a simpler alternative: using a standard single-balloon Foley catheter for the same purpose. A meta-analysis comparing the two found no significant difference in total time to delivery (roughly 19 hours for both). However, individual studies have shown that the double-balloon catheter produces greater improvement in cervical ripening scores and may be more effective at achieving the cervical softening needed for vaginal delivery. In practice, both are considered reasonable options, and which one your hospital uses often comes down to provider preference and availability.
Safety and Risks
Balloon catheter induction is considered a safe intervention overall. The most notable risk is intrapartum infection (infection during labor), which occurs in about 11% of cases. Postpartum infection rates are lower, around 3.3%, and neonatal infection occurs in roughly 4.6% of deliveries following balloon use.
Excessive uterine contractions happen in about 2.7% of cases, which is lower than the rate seen with medication-based ripening. For women who have had a previous cesarean section, uterine rupture occurs in about 1.9% of cases with balloon use. Other major complications are rare, occurring in less than 1% of patients. Changes in fetal heart rate patterns are seen in about 11% of cases, which is monitored closely by the care team throughout the process.
Other Cook Medical Catheters
While the cervical ripening balloon is what most people mean by “Cook catheter,” Cook Medical manufactures a wide range of catheters for other medical specialties. These include drainage catheters used after surgery, balloon catheters that widen narrowed blood vessels, microcatheters used in interventional radiology to reach tiny blood vessels for targeted treatments, and specialized catheters for fertility procedures like embryo transfer and intrauterine insemination. Cook also makes urological catheters, pressure monitoring lines for critical care, and vascular access catheters for long-term IV therapy. The specific type your doctor is referring to depends entirely on the clinical context.