Progesterone in oil (PIO) is most commonly injected into the upper outer quadrant of the buttock, but the specific site within that region matters more than many people realize. The ventrogluteal area, located on the side of the hip, is now widely recommended over the traditional dorsogluteal site because it sits farther from the sciatic nerve and major blood vessels. Understanding exactly where to place the needle, how deep to go, and how to rotate between sites can make a real difference in both comfort and safety over the weeks or months that PIO injections are typically required during fertility treatment.
The Two Main Injection Sites
PIO shots are intramuscular injections, meaning the medication needs to reach muscle tissue rather than fat. In practical terms, that limits you to large muscles with enough bulk to absorb an oily solution. The two sites used for PIO are both in the gluteal region, but they differ in important ways.
The dorsogluteal site is the traditional location, sitting in the upper outer quadrant of the buttock. If you imagine dividing each buttock into four squares, the injection goes into the top outer square. This is where most people picture a “butt shot,” and for decades it was the default. A study of infertility nurses found that most used the dorsogluteal site for injections and, despite saying they rotated, rarely went elsewhere.
1PubMed Central. Procedures used to prepare and administer intramuscular injections: a study of infertility nursesThe ventrogluteal site sits on the side of the hip, over the gluteus medius muscle. You find it by placing the heel of your hand on the greater trochanter (the bony bump at the top of your outer thigh) and spreading your index and middle fingers into a V shape pointing toward your hip bone. The injection goes into the center of that V. This site has a thinner layer of fat over it compared to the dorsogluteal area, which means the needle is more likely to actually reach muscle. It also sits well away from the sciatic nerve and the superior gluteal artery, both of which run through the dorsogluteal region.
Why Avoiding the Sciatic Nerve Is So Important
The sciatic nerve is the largest nerve in the body, running from the lower spine down through the buttock and into each leg. When an intramuscular injection lands too close to it or directly into it, the consequences can be severe: shooting pain, numbness, foot drop, and in some cases permanent nerve damage. The sciatic nerve is the most commonly injured nerve from intramuscular injections precisely because of its size and because the buttock is such a popular injection site.
2PubMed Central. Iatrogenic Injury to the Sciatic Nerve due to Intramuscular Injection: A Case ReportSciatic nerve injection injuries remain a persistent problem worldwide, and they are not limited to any one healthcare setting. The risk is highest at the dorsogluteal site because the nerve’s path varies slightly from person to person, and in people with less gluteal muscle mass the nerve can sit closer to the surface than expected. The ventrogluteal site essentially removes this risk because the sciatic nerve does not pass through that area. If your clinic or fertility specialist has not specifically discussed which gluteal site to use, it is worth asking about the ventrogluteal approach.
2PubMed Central. Iatrogenic Injury to the Sciatic Nerve due to Intramuscular Injection: A Case ReportStep-by-Step Injection Technique
PIO is a thick, viscous solution, so it requires a slightly different approach than a typical shot. Most protocols call for two needles: a thicker drawing-up needle (usually 18 gauge) to pull the oil out of the vial, and a thinner injection needle (typically 22 gauge, 1 to 1.5 inches long) for the actual shot. Using a fresh needle for the injection keeps the tip sharp and reduces pain at the skin surface.
Before injecting, warm the syringe. Holding it between your palms for a minute or two, or tucking it under your arm, thins the oil slightly and makes it flow more easily through the needle. Some people warm the vial itself in a cup of warm water beforehand. This is not strictly necessary, but room-temperature or slightly warm oil is noticeably more comfortable going in than cold oil straight from the refrigerator.
The basic steps once you are ready:
- Clean the site: Wipe the injection area with an alcohol swab and let it air-dry completely. Injecting through wet alcohol stings.
- Spread or pinch: For the ventrogluteal site, use your non-dominant hand to spread the skin taut. Some clinics teach the z-track method, where you pull the skin to one side before inserting the needle, then release it after withdrawing. This displaces the tissue layers so the needle track does not line up afterward, reducing leakage of oil back out through the puncture site.
- Insert at 90 degrees: Push the needle straight in with a smooth, quick motion. Hesitating or going slowly tends to hurt more.
- Inject slowly: Depress the plunger at a steady, slow pace. PIO is thick, so pushing too fast creates pressure in the muscle that increases soreness. A common guideline is about ten seconds per milliliter.
- Withdraw and apply pressure: Pull the needle out at the same angle you went in. Press a cotton ball or gauze over the site for a few seconds. A small amount of oil or a drop of blood at the puncture is normal.
The z-track method deserves a closer look because it is underused. The infertility nursing study found that very few nurses employed it, even though it helps prevent the medication from tracking back out along the needle path.
1PubMed Central. Procedures used to prepare and administer intramuscular injections: a study of infertility nursesFor PIO specifically, leakage is a legitimate concern. Oil-based injections are slow to absorb, and if the oil leaks out, you are not getting your full dose. Pulling the skin about an inch to one side before inserting the needle, holding it displaced throughout the injection, and then releasing after withdrawal creates a zigzag path through the tissue that seals itself.
Site Rotation and What Happens When You Don’t
PIO injections during fertility treatment often continue daily for eight to twelve weeks, which means dozens of injections into the same general area. Rotating between left and right sides is the bare minimum, but you can also move the exact injection spot within each side by about an inch each time. Keeping a simple log or alternating sides on odd and even days helps prevent hitting the same tissue repeatedly.
When rotation is inadequate, a specific complication can develop: injection-site granulomas. These are firm lumps that form when the body walls off a pocket of oil that was deposited into subcutaneous fat rather than muscle. The tissue reaction can produce an irregularly shaped mass deep in the fat layer, surrounded by inflammation, and these granulomas sometimes appear on imaging months or even years later. Radiologists have noted that gluteal granulomas from IVF-related injections can mimic soft tissue tumors on MRI, occasionally leading to unnecessary biopsies before the correct diagnosis is made.
3PubMed. Imaging features of gluteal in vitro fertilization injection granulomas, with delayed clinical presentation simulating soft tissue sarcomaThe key risk factor for granulomas is inadvertently depositing the oil into subcutaneous fat instead of muscle. This happens more often at the dorsogluteal site, where the fat layer tends to be thicker, and in people with higher body fat percentages. Using a needle long enough to reach muscle (1.5 inches for most adults) and choosing the ventrogluteal site, where the fat pad is thinner, both reduce the chance of this happening.
Managing Pain and Soreness
Even with perfect technique, PIO injections hurt. The oil itself is irritating to tissue, and daily shots into the same muscle group cause cumulative soreness. There is no way around this entirely, but several strategies make a measurable difference.
Applying a warm compress or heating pad to the injection site for ten to fifteen minutes after the shot helps the oil disperse into the muscle. Some people sit on a heating pad or take a warm bath. Gentle movement afterward, such as walking or doing a few squats, also encourages absorption by increasing blood flow to the area. Lying still immediately after injection tends to let the oil pool, which can create a more painful lump.
Massaging the site firmly for a minute or two after injection can also help spread the oil, though this is a matter of personal tolerance. Some people find it intensely uncomfortable while others consider it essential. Ice before the injection (to numb the skin) followed by heat after is another popular approach, though ice should not be applied after the shot because it slows oil absorption.
Over time, you may develop knots or hard spots in the muscle from repeated injections. These are different from granulomas, which form in fat. Muscular knots are essentially areas of localized inflammation and can often be worked out with a foam roller, a tennis ball pressed against the wall, or targeted massage. If a hard lump grows over several weeks, becomes hot or red, or starts to significantly limit your range of motion, it is worth having a provider examine it.
Self-Administration Challenges
Many people doing PIO injections are administering them at home, often with a partner’s help. The ventrogluteal site is actually easier for a partner to access than the dorsogluteal site because you can stand or lie on your side rather than bending over. The person giving the injection can clearly see the landmarks (hip bone, greater trochanter) and does not have to navigate the curvature of the lower buttock.
Giving yourself a PIO shot without help is harder but possible. The ventrogluteal site is reachable if you stand with your weight shifted to the opposite leg and twist slightly. Some people prefer to inject while standing in front of a mirror to see the landmarks. Using the dorsogluteal site on yourself is more awkward because the angle of your arm makes it difficult to maintain a steady, perpendicular insertion. If you must self-inject and have trouble reaching, the outer thigh (vastus lateralis muscle) is sometimes used as an alternative intramuscular site, though it tends to be more painful for oily injections because the muscle is smaller and the oil disperses less easily.
The Oil Carrier Matters
Progesterone in oil is not just progesterone. The oil carrier that suspends the hormone varies between formulations, and some people react differently to different oils. The most common carriers are sesame oil and peanut oil, though olive oil and ethyl oleate formulations also exist. Research on skin reactions to steroid hormones in various oil carriers found that peanut oil alone produced nonspecific reactions in roughly 89 percent of subjects, mostly itching-type allergic responses. Sesame oil, olive oil, and ethyl oleate produced lower rates of nonspecific reactions, in the range of 15 to 31.5 percent, and these tended to be milder, mostly simple redness rather than itching.
4Revue Française d’Allergologie et d’Immunologie Clinique. Contribution a l’étude de l’allergie aux hormones stéroides La réponse dermique à l’injection de divers stéroïdes en solution huileuse chez les sujets séborrhéiquesIf you have a known peanut allergy, tell your fertility clinic before starting PIO. Many pharmacies default to a sesame oil formulation, but it is worth confirming. Even without a diagnosed allergy, if you experience intensifying redness, swelling, or hives at the injection site with each subsequent shot, the oil carrier might be the culprit. Switching to a different carrier oil sometimes resolves the problem entirely.
When It Is More Than a Local Reaction
True progesterone hypersensitivity is rare but real. In a review of 24 cases, symptoms ranged from cyclical dermatitis and hives to angioedema, asthma, and in the most serious cases, anaphylaxis. About 58 percent of cases were triggered by exogenous progestogens (medications), while the remainder were reactions to the body’s own progesterone. Desensitization protocols, given either by intramuscular injection or orally, achieved symptom control in the majority of patients who underwent them.
5PubMed. Progestogen Hypersensitivity in 24 Cases: Diagnosis, Management, and Proposed Renaming and ClassificationIf your reactions seem to be worsening with each injection rather than staying the same or improving, or if you develop symptoms beyond the injection site (widespread hives, difficulty breathing, throat tightness, lightheadedness), seek medical attention promptly. Worsening local reactions over successive injections can be a sign that the immune system is sensitizing to either the progesterone itself or a component of the formulation.
Subcutaneous Progesterone as an Alternative
The pain and difficulty of daily intramuscular PIO injections have pushed researchers to study whether subcutaneous progesterone can deliver comparable results. Subcutaneous shots go into the fat layer just beneath the skin, typically in the abdomen or thigh, using a much shorter, thinner needle. The injection is simpler and substantially less painful.
An aqueous (water-based) subcutaneous progesterone preparation has been studied against traditional intramuscular PIO in frozen embryo transfer cycles. A pharmacokinetic study in postmenopausal women found that twice-daily subcutaneous progesterone achieved roughly 92 percent of the total drug exposure of a single intramuscular dose, with a higher peak concentration.
6PubMed. Comparative Bioavailability of Two Daily Subcutaneous Doses Versus a Single Dose of Intramuscular and Vaginal Progesterone Formulations in Healthy Postmenopausal FemalesClinical outcomes have been similarly encouraging. Trials comparing subcutaneous and intramuscular progesterone for frozen embryo transfer found no significant difference in clinical pregnancy rates or live birth rates between the two routes.
7PubMed Central. Comparison of intramuscular versus subcutaneous aqueous progesterone for luteal phase support in artificially prepared frozen embryo transfer cycles8F&S Reports. Subcutaneous progesterone administration provides a similar ongoing pregnancy rate compared with intramuscular progesterone administration in hormone replacement therapy frozen embryo transfer cycles
The aqueous subcutaneous preparation was also noted to be well tolerated, with mild injection-site reactions occurring at similar rates for both subcutaneous and intramuscular routes.
6PubMed. Comparative Bioavailability of Two Daily Subcutaneous Doses Versus a Single Dose of Intramuscular and Vaginal Progesterone Formulations in Healthy Postmenopausal FemalesDespite this promising data, subcutaneous aqueous progesterone is not yet universally available, and many clinics still default to intramuscular PIO because it has the longest track record. If daily intramuscular injections are creating significant difficulties for you, asking your reproductive endocrinologist about a subcutaneous option is reasonable. The clinical evidence so far suggests that outcomes are comparable.
Vaginal Progesterone and How It Compares
Vaginal progesterone (as suppositories, gel, or inserts) is the other major alternative to PIO. It works through a different pharmacological principle: rather than flooding the bloodstream with progesterone and letting it circulate to the uterus, vaginal delivery creates high local concentrations in the uterine lining through what is known as the “first uterine pass” effect. Endometrial progesterone levels are actually higher with vaginal administration than with intramuscular injection, even though serum (blood) levels are lower.
9PubMed Central. Subcutaneous progesterone versus vaginal progesterone for luteal-phase support in frozen-thawed embryo transfer: A cross-sectional studyEarly pharmacokinetic work showed that intramuscular injection was far more efficient at raising blood levels of progesterone: a 25 mg intramuscular dose achieved luteal-phase blood levels, while roughly four times that dose was needed vaginally or rectally to reach the same circulating concentration.
10American Journal of Obstetrics and Gynecology. Plasma levels of progesterone after vaginal, rectal, or intramuscular administration of progesteroneBut serum levels alone do not tell the whole story when the target organ is the uterus. Many clinics now consider vaginal progesterone adequate for certain frozen embryo transfer protocols, while still preferring intramuscular PIO in others, particularly when serum progesterone monitoring is used to guide dosing.
For the person on the receiving end, vaginal progesterone avoids needles entirely but comes with its own inconveniences: messiness from the waxy residue of suppositories, vaginal irritation, and the need for multiple daily doses with some formulations. The choice between intramuscular PIO and vaginal progesterone often comes down to your clinic’s protocol, your specific treatment plan, and your own tolerance for each route’s particular trade-offs.
Needle Gauge and Length Selection
Choosing the right needle is not a small detail when you are dealing with an oil-based medication. Too thin a needle makes drawing up the oil painfully slow and requires excessive plunger force during injection. Too thick a needle causes more tissue trauma. The general standard for injecting PIO is a 22-gauge needle, 1 to 1.5 inches long. The 1.5-inch length is preferred for most adults to ensure the needle reaches muscle through the subcutaneous fat layer, which is especially relevant at the dorsogluteal site where fat pads tend to be thicker.
For drawing up the medication from the vial, an 18-gauge needle is typical. These are noticeably wider and allow the thick oil to fill the syringe much more quickly. Always swap to the thinner injection needle after drawing up. The drawing needle is blunted by puncturing the vial’s rubber stopper, and injecting with a dulled, wide-bore needle is unnecessarily painful.
People with very low body fat may be able to use a 1-inch needle comfortably, while those with a higher body mass index may need the full 1.5 inches or even longer in some cases. If you are unsure, your clinic can help determine the right length. The key concern is that oil deposited into fat rather than muscle absorbs poorly, causes more lumps, and can lead to the granuloma formation described earlier. Getting the needle length right is one of the simplest ways to prevent that.