Written and maintained by CASRAI Editorial Board
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General device and regulatory information for laboratory, clinic and supply staff. It is not medical advice and does not replace a clinician’s guidance or a manufacturer’s instructions for use.
Short answer
A contraceptive diaphragm is a closely fitting membrane that covers the cervix completely and is used with a spermicide to prevent pregnancy. In the United States, FDA regulates it as a Class II device under 21 CFR 884.5350. A cervical cap is a related, smaller cervical barrier that has been compared with the diaphragm in randomized trials.
Definition and scope
The federal regulation, 21 CFR 884.5350, identifies a contraceptive diaphragm as “a closely fitting membrane placed between the posterior aspect of the pubic bone and the posterior vaginal fornix.” It states that the device “covers the cervix completely and is used with a spermicide to prevent pregnancy,” and that this generic type of device “may include an introducer.” Paragraph (b) classifies it as Class II (performance standards).
Three points follow directly from that wording:
- The regulation covers the diaphragm and its accessories, so an introducer sold with or for the device falls under the same device type.
- The definition builds the spermicide pairing into the device description, so the diaphragm is a barrier used with a separate product.
- The regulation’s classification line reads “Class II (performance standards).” For background on how FDA classifies devices, see What Is a Medical Device? and the Medical Device Amendments of 1976.
How the device is used in practice
The regulation describes where the device sits and what it does: it forms a barrier over the cervix and is used together with a spermicide. Fitting, handling and care of a specific product are set out in that manufacturer’s instructions for use and by the prescribing clinician, so this page does not give step-by-step instructions.
Diaphragm vs cervical cap: what the Cochrane trials found
The Cochrane review Cervical cap versus diaphragm for contraception (CD003551; literature searched to February 2012) is the clearest sourced comparison of the two devices. It identified two randomized trials, each comparing a cervical cap with a diaphragm.
| Question | What the Cochrane review reports |
|---|---|
| Which caps were tested | Two randomized trials compared a cap with a diaphragm: the Prentif cap and the FemCap. |
| Pregnancy prevention | The Prentif cap was as effective as its comparison diaphragm in preventing pregnancy, but the FemCap was not. The FemCap’s six-month pregnancy rates were not clinically equivalent to the diaphragm’s. |
| Size | The review describes the cap as smaller than the diaphragm. Product-specific details are set out in current manufacturer labeling. |
| Safety findings | The Prentif cap was associated with more cervical cell changes than the diaphragm, and fewer vaginal ulcerations or lacerations. Both devices appear to be medically safe. |
The result is specific to the products tested. “Cervical cap” is not one interchangeable product: in these trials one cap matched the diaphragm and the other did not.
Diaphragm sizes
The regulation describes a closely fitting membrane, so fit is part of the device definition. Size ranges are product-specific and are set out in each manufacturer’s instructions for use and by a clinician’s fitting; this page does not give a size chart.
Where it matters for labs, clinics and supply decisions
For staff who document, classify or stock barrier devices, the regulation supports a short checklist. Each item traces to the sources above:
- Device type: confirm the product is listed as a contraceptive diaphragm (21 CFR 884.5350) and not a different cervical device. Class II applies to this device type.
- Accessories: the regulation says the device type may include an introducer, so an introducer is covered by the same entry.
- Spermicide pairing: the regulatory definition describes the diaphragm as used with a spermicide, so records that describe the device alone are incomplete without that pairing.
- Cap versus diaphragm: do not treat the two as equivalent. The Cochrane trials found different outcomes for the two caps tested.
- Labeling: fit details are product-specific, so rely on the current manufacturer labeling. Record device identifiers as described in UDI Labeling and GUDID Submission.
Common misunderstandings
- “884.5360 is the diaphragm rule.” It is not. 21 CFR 884.5360 is the contraceptive intrauterine device (IUD) and introducer, classified Class III (premarket approval). The diaphragm is 884.5350, Class II.
- “A diaphragm works alone.” The regulation’s definition describes it as used with a spermicide.
- “All cervical caps perform like a diaphragm.” In the Cochrane review, the Prentif cap was as effective as its comparison diaphragm and the FemCap was not.
FAQ
What is a contraceptive diaphragm?
Per 21 CFR 884.5350, it is a closely fitting membrane that covers the cervix completely and is used with a spermicide to prevent pregnancy. It may include an introducer.
Is a contraceptive diaphragm regulated by FDA?
Yes. It is a Class II device under 21 CFR 884.5350, in the obstetrical and gynecological therapeutic devices subpart of Part 884.
What is the difference between a diaphragm and a cervical cap?
The Cochrane review describes the cap as smaller than the diaphragm. In its two trials, one cap (Prentif) matched the diaphragm for pregnancy prevention and the other (FemCap) did not.
Where can I find diaphragm sizes?
Sizes are product-specific. Use the manufacturer’s instructions for use and a clinician’s fitting for the product in question.
For the wider specialty context, see What Is Obstetrics and Gynecology?.
Sources
- U.S. Code of Federal Regulations, 21 CFR 884.5350, Contraceptive diaphragm and accessories: law.cornell.edu/cfr/text/21/884.5350 (checked 30 October 2026).
- 21 CFR 884.5360, Contraceptive intrauterine device (IUD) and introducer: law.cornell.edu/cfr/text/21/884.5360 (checked 30 October 2026).
- Cochrane, Cervical cap versus diaphragm for contraception (CD003551): cochrane.org/CD003551 (checked 30 October 2026).
