A baby’s legs in a carrier should form an “M” shape, with the knees higher than the bottom and the thighs spread apart and fully supported. This position, sometimes called the spread-squat position, mimics how a baby naturally sits when you hold them against your chest. Getting it right matters because infant hip joints are still soft and developing, and prolonged time in the wrong position can interfere with healthy hip formation.
What the M-Position Looks Like
Imagine looking at your baby from the front while they sit in the carrier. Their bottom forms the lowest point of the letter M, their thighs angle upward and outward, and their knees are the two high points. The hips are bent (flexed) and spread apart, with the knees naturally falling at or slightly above hip level.
The key detail most parents miss is thigh support. The carrier’s seat panel should extend from one knee pit to the other, supporting the full width of both thighs. Think of it as your baby sitting in a small hammock rather than perching on a narrow ledge. When the seat is too narrow, the legs dangle straight down from the hip with little support, and the baby’s weight concentrates on a small area at the crotch instead of distributing across the thighs and bottom.
Why Leg Position Matters for Hip Development
The unhealthiest position for a baby’s hips is the opposite of the fetal position: legs held straight, stretched out, and pressed together. The International Hip Dysplasia Institute warns that any device restraining a baby’s legs in this position should be considered a risk for abnormal hip development, and that the risk increases the longer the position is maintained.
Babies are born with hip sockets made largely of soft cartilage that gradually hardens into bone over the first year. This process happens fastest during the first six months. During this window, the forces acting on the hip joint actually shape how the socket forms. In the M-position, the head of the thighbone sits deeply and securely in the socket, encouraging it to develop a proper round shape. When a baby faces inward and straddles the caregiver’s torso, the inner thigh muscles engage to grip, generating gentle forces that further benefit hip development.
Narrow-base carriers that leave the thighs unsupported to the knee joint are not recommended for prolonged use. The resulting forces on the hip may be inappropriate, especially for infants who already have loose hip joints or undiagnosed hip dysplasia.
Newborns: Legs In or Legs Out?
New parents often wonder whether a newborn’s legs should be tucked inside the carrier or positioned out through the leg openings. Current best practice among babywearing educators is legs out from birth. Some very small newborns may naturally keep their legs tucked in a frog position for the first week or two, and this is fine briefly, but it shouldn’t continue beyond the first few weeks. Starting with legs out and ensuring the carrier’s seat is adjusted narrow enough to support (but not force) the thighs in the M-position gives the best combination of comfort and hip safety from day one.
Inward Facing vs. Outward Facing
Both carrying directions can be safe as long as the baby’s legs are separated and not locked together. That said, inward-facing carrying has a clear advantage for hip health. The IHDI recommends inward-facing during the first six months, when hip development is most rapid, and notes there may be additional benefit to continuing inward-facing up to one year.
When a baby faces outward, achieving a deep M-position is harder. The baby can’t wrap their legs around your body, and many outward-facing carriers provide a shallower seat. If you do carry your baby facing out, look for a carrier specifically designed to maintain thigh support in that position, and keep outward-facing sessions shorter. Most manufacturers recommend waiting until a baby has solid head and neck control (typically around four to five months) before trying outward-facing, but remember that head control alone doesn’t mean the hips are done developing.
Signs the Fit Is Wrong
A few visual and physical cues tell you the leg positioning needs adjustment:
- Dangling legs. If your baby’s legs hang straight down with the fabric only supporting a narrow strip at the crotch, the seat is too narrow. The thighs should be supported out to the knee pit on each side.
- Knees below the bottom. In a well-fitted carrier, the knees sit at or above the level of the baby’s bottom. If the knees point downward, the baby is essentially straddling a thin band of fabric rather than sitting in a supportive seat.
- Red marks or spots on the legs. A carrier cinched too tightly around the leg openings can act like a tourniquet. In documented cases, overly tight fabric around an infant’s lower legs caused tiny broken blood vessels (visible as clusters of red or purple dots) that appeared once the pressure was released. Red creases from the fabric edge are normal and fade within minutes, but persistent spots or discoloration are not.
- Legs forced too wide. The M-position should look natural, not like a split. If the carrier forces a small baby’s legs wider than they’d naturally go when held against your chest, the seat panel is too wide for their current size.
How to Adjust for a Good Seat
Most structured carriers have some way to change the seat width. Some use snaps or toggles at the base panel; others have adjustable fabric that folds inward for smaller babies. Start by holding your baby against you without the carrier and noticing where their knees naturally fall. That spread is roughly the seat width you’re aiming for.
Once the baby is in the carrier, check from the side. You should see the thighs angling upward from the bottom to the knees, forming that clear M when viewed from the front. The fabric should reach into the crease behind each knee without bunching or cutting in. If you’re using a wrap or ring sling, spread the fabric wide across the baby’s back and bottom so the seat is created by the full width of material rather than a single gathered strip.
As your baby grows, you’ll widen the seat. A six-month-old needs a wider base than a newborn, and a toddler wider still. Revisit the fit every few weeks during the first year, since babies grow quickly and a carrier that fit perfectly last month may now leave the thighs unsupported.
Carrier Types and Leg Support
Soft structured carriers (the backpack-style ones with a waist belt and shoulder straps) generally make the M-position easiest to achieve because the seat panel is designed with width in mind. Look for models recognized as “hip healthy” by the IHDI.
Wraps and ring slings can provide excellent support when tied or adjusted correctly, because the fabric conforms to the baby’s body. The learning curve is steeper, but the positioning can be very precise. Mei tais and half-buckle carriers fall somewhere in between, offering an adjustable fabric seat with some structured elements.
Narrow-base carriers, where the baby essentially sits on a narrow strip of padded fabric with legs dangling on either side, are the ones most likely to create problems. Short trips in these carriers are unlikely to cause harm, since the IHDI notes that intermediate positions maintained briefly are probably fine. But for everyday, prolonged use, a carrier that supports the full thigh in the M-position is a better choice.