Women’s hips first begin to widen during puberty, with the most dramatic skeletal changes starting around age 10 to 13 and continuing well into the mid-to-late twenties. That surprises many people who assume the skeleton is “done” by 18 or so. In reality, the female pelvis follows a complex, multi-phase trajectory shaped by hormones, pregnancy, and even lifelong bone remodeling that can add measurable width to the hips decades after adolescence ends.
Puberty Is Where It Starts
The pelvic bones are among the first parts of the skeleton to respond to the hormonal changes of puberty. In a seven-year follow-up study of pubertal girls, greater pelvis width peaked about 11 to 12 months before the first menstrual period, and lesser pelvis width peaked around 13 to 14 months before menarche. Shoulder width, by contrast, did not peak until about 18 months before menarche, which means the hips are already widening before most other skeletal growth spurts are at their fastest.1PubMed. Bone and body segment lengthening and widening: a 7-year follow-up study in pubertal girls For most girls, that translates to noticeable hip widening somewhere between ages 10 and 13, though the timing varies with individual puberty onset.
Bone is only part of the picture at this stage. The pubertal rise in estrogen also drives fat to specific depots, and research using national health survey data shows that the onset of menstruation is more closely tied to fat distribution than to overall skeletal maturity. Girls who had reached menarche stored relatively more fat in their hips and thighs compared to those who had not, even when total body fat was similar.2PubMed. Brief communication: menarche is related to fat distribution So the “hip widening” that girls and their families notice during puberty is a combination of the pelvic bones expanding and new fat padding appearing around those bones.
Why Your Hips Keep Widening Into Your Late Twenties
One of the more counterintuitive findings in skeletal biology is that the female pelvis does not reach its widest obstetric dimensions at 18 or even 21. A study of pelvic development found that after the initial pubertal divergence from the male growth path, obstetrically relevant pelvic dimensions continue expanding rapidly up to about age 25 to 30.3PubMed Central. Developmental evidence for obstetric adaptation of the human female pelvis The birth canal, in other words, keeps getting more spacious for roughly a decade after height growth has stopped. This is likely driven by estradiol levels, which are at their peak during these years. It aligns neatly with the window of maximum fertility, meaning the pelvis is at its most accommodating for childbirth precisely during the years when pregnancy is most likely.
A 2023 study tracking pelvic shape from infancy to late adulthood confirmed this timeline. Female and male developmental trajectories separate in early infancy but diverge substantially during puberty. The greatest differences in pelvic shape between the sexes are achieved at the time of maximum female fertility, and those differences continue increasing until roughly age 40 to 45.4Nature / Scientific Reports. Changes in plasticity of the pelvic girdle from infancy to late adulthood in Homo sapiens After that, the female pelvis begins changing in a pattern more similar to the male trajectory. This prolonged period of sex-specific remodeling means that a woman’s hips at 30 are a meaningfully different shape from her hips at 18, even though she stopped growing taller years earlier.
The pubic rami, the bony arches at the front of the pelvis, appear to retain particular plasticity throughout the primary childbearing years, allowing ongoing remodeling into the late twenties and potentially beyond.5Oxford Academic. Squatting, pelvic morphology and a reconsideration of childbirth difficulties
How Pregnancy Changes the Pelvis
Pregnancy adds another layer of hip widening on top of whatever developmental stage the pelvis has reached. During pregnancy, the hormone relaxin (along with other circulating hormones) induces structural changes in the fibrocartilaginous disc at the pubic symphysis, the joint at the very front of the pelvis. This softens and widens the joint, increasing mobility and making more room for delivery.6PubMed Central. The adult human pubic symphysis: a systematic review
How much the symphysis widens varies. One study measuring symphyseal width at 35 weeks of pregnancy found mean widths ranging from about 4.5 mm in women with no pelvic pain up to 7.4 mm in women with significant discomfort, a meaningful spread that underscores how differently individual women respond to the same hormonal signals.7PubMed. Symphyseal distention in relation to serum relaxin levels and pelvic pain in pregnancy Serum relaxin levels and the baby’s weight have been linked to pubic symphysis separation, though not necessarily to how severe that separation becomes.8PubMed Central. Role of relaxin in diastasis of the pubic symphysis peripartum
Many women report that their hips feel permanently wider after pregnancy, and there is some truth to that. The ligamentous laxity induced by relaxin does not always fully reverse, and the bony remodeling that occurs under pregnancy’s hormonal influence can leave lasting changes. It is common, for instance, for women to go up a shoe size during pregnancy due to ligament loosening, and the same phenomenon plays out across the pelvis. Still, the degree to which these changes persist varies enormously. Some women’s pelvic measurements return nearly to pre-pregnancy values within a year; for others, the change is permanent.
A Widening That Never Fully Stops
Even setting aside puberty, fertility-linked remodeling, and pregnancy, the bony pelvis appears to keep widening slowly across the entire adult lifespan. A study using CT scans of patients aged 20 to 80 found a strong link between increasing age and increasing pelvic width at the trochanters (the bony bumps you feel on the outside of your hips), the iliac wings (the broad upper plates of the pelvis), and between the femoral heads. The overall widening amounted to more than 20 mm between ages 20 and 80, or roughly a third of a millimeter per year.9PubMed. Surprising evidence of pelvic growth (widening) after skeletal maturity This is not a large amount in any single year, but it accumulates. Over 60 years, it is close to an inch of additional external width.
An important detail: the pelvic inlet, the internal opening through which a baby would pass, did not enlarge in that same study. So this lifelong widening is mainly happening at the outer dimensions of the pelvis and hip structure, not the birth canal. It means that the “hip spread” many people associate with middle and old age has a genuine skeletal component. Your bones are literally moving apart, independent of any changes in body fat.
What Happens After Menopause
Menopause triggers a distinct shift in pelvic remodeling. Research on adult pelvic shape identifies three phases in women: the main reproductive period (roughly 17 to 37 or 40 years), a transitional pre-menopausal phase, and the postmenopausal period after about 50. During the reproductive years, estrogen-driven and pregnancy-related bone remodeling dominates. After menopause, that hormonal influence falls away and mechanical factors take over, making pelvic remodeling more similar to the pattern seen in men.10PubMed. Age dependent changes in pelvic shape during adulthood
As noted above, from about age 40 onward the obstetrically relevant dimensions of the pelvis begin to shrink. The birth canal gets somewhat narrower, and the pelvic shape shifts back toward the male developmental trajectory.3PubMed Central. Developmental evidence for obstetric adaptation of the human female pelvis This does not mean the hips look narrower from the outside, because the outer bony dimensions continue their slow lifelong expansion. It means the internal architecture changes even as the external frame keeps widening.
Menopause also reshapes the femoral neck, the column of bone connecting the ball of the hip joint to the shaft of the thighbone. A 14-year study of women transitioning through menopause found that those with narrower femoral necks at the start showed greater increases in bone area over time (a compensatory expansion), while those with wider necks at baseline lost more bone mineral content without the same compensatory growth.11Journal of Bone and Mineral Research. Femoral Neck External Size but not aBMD Predicts Structural and Mass Changes for Women Transitioning Through Menopause In practical terms, different women’s hip bones are adapting to menopause in different ways: some get wider at the femoral neck, others lose density without compensating in width. Both patterns produce similar-looking bone density scores on a standard scan but represent very different structural situations.
The Fat Shift at Midlife
Alongside these skeletal changes, menopause brings a major redistribution of body fat that alters where the hips carry their mass. Postmenopausal women had roughly five times the odds of central adiposity compared to premenopausal women, even after controlling for overall body mass.12Menopause. Association between menopause status and central adiposity measured at different cutoffs of waist circumference and waist-to-hip ratio What this means in everyday terms is that fat migrates from the hips and thighs toward the waist. The hip-to-waist ratio changes, and many women perceive their hips as looking different even if external bony width has not changed much. The “pear shape” associated with premenopausal estrogen gradually shifts toward a more “apple” distribution.
This fat redistribution is the reverse of what happens at puberty, when estrogen directs fat toward the gluteofemoral depots. With estrogen levels falling at menopause, that preferential storage fades. The hips may actually lose some soft-tissue volume even as the bones beneath them continue their slow outward drift. The net visual effect depends on which process dominates for a given woman.
Pelvic Mobility and Posture With Aging
Width is not the only thing that changes. The pelvis also loses range of motion with age, and this affects how the hips feel and function day to day. Research on pelvic tilt angles in seated subjects found that both forward and backward tilt capacity declined with aging, closely tracking the loss of lumbar spine mobility.13PubMed Central. Age-related Changes in Maximum Pelvic Anteversion and Retroversion Angles Measured in the Sitting Position As the pelvis tips less freely, sitting posture tends to become more fixed, which can contribute to lower-back stiffness. Wider hips in combination with reduced pelvic mobility may subtly alter gait as well, though the effect is modest for most people.
Hip Width and Walking Efficiency
A persistent myth holds that wider hips make walking less efficient, an idea sometimes invoked as part of the “obstetric dilemma” framing that says women’s pelvises are an awkward compromise between childbirth and locomotion. The evidence actually points in the opposite direction. A study of locomotor energetics found that a broader pelvis (specifically the upper, flared portion) is substantially more efficient for walking, with its influence on energy cost comparable to the influence of leg length.14PubMed. Energetic cost of walking in fossil hominins
More recent biomechanical modeling confirmed that the distance between hip joint centers does help predict how much force the hip abductor muscles need to generate during walking, but neither hip joint center distance nor outer hip width improved the prediction of total metabolic energy expenditure once body mass and speed were accounted for.15PLoS ONE. Hip width and metabolic energy expenditure of abductor muscles In short, wider hips may require the abductor muscles to work a bit harder per step, but they do not make walking more metabolically costly overall. The old framing that women “pay” for their wider pelvis with less efficient walking does not hold up well under direct measurement.
Genetics, Hip Shape, and Fracture Risk
Not all pelvic widening is created equal, and individual genetics play a large role in the specific shape the hip takes. A large genetic study identified distinct hip shape modes and tested whether they were linked to osteoarthritis or fracture risk. The results were striking: a more obtuse angle where the femoral neck meets the shaft was associated with higher fracture risk (about 27% higher odds), while a wider femoral neck was actually protective, associated with about 26% lower odds of hip fracture.16PubMed Central. The genetic architecture of hip shape and its role in the development of hip osteoarthritis and fracture None of the hip shape modes studied showed a causal link to osteoarthritis, but having osteoarthritis did appear to causally affect one shape mode, meaning the disease can reshape the hip rather than the other way around.
This matters for how women think about their hip anatomy as they age. A naturally wider femoral neck, one component of what people loosely call “wide hips,” may actually carry a structural advantage against fractures. Conversely, a steep neck-shaft angle is a risk factor regardless of overall hip width. Two women who both describe themselves as “wide-hipped” might have very different fracture profiles depending on the specific geometry of their proximal femur. Standard bone density scans do not capture this distinction, which is one reason fracture prediction remains imperfect even with screening.