Pregnancy requires major adaptations in calcium and bone metabolism. A particularly interesting unanswered question is whether carrying twins creates a measurably different skeletal burden from carrying one baby.
TWINBONE is designed to test exactly that comparison. The study is recruiting and uses a radiation-free ultrasound-based bone assessment called REMS during the third trimester. The scientifically important sentence, however, is the simplest one: no study results have been posted yet.
Quick answer
Does twin pregnancy increase osteoporosis or fracture risk?
We do not yet have TWINBONE results showing that it does. The study is specifically designed to compare bone mineral density and fracture-related measures between singleton and twin pregnancies, so it is highly relevant research to follow — not evidence of increased risk today.
Key takeaways
- TWINBONE is registered as NCT07508553 and is currently recruiting in Rome, Italy.
- The study plans to compare third-trimester bone mineral density between singleton and twin pregnancies using REMS ultrasound densitometry and questionnaires.
- ClinicalTrials.gov lists an estimated enrolment of 100 participants and no posted results.
- The record was first posted on ClinicalTrials.gov on April 2, 2026; August 28, 2026 is an aggregator sync date, not the original registration date.
- Pregnancy and lactation normally change calcium and bone metabolism, while pregnancy- and lactation-associated osteoporosis is considered rare.
What TWINBONE is actually asking
The official title is “Pregnancy-associated Reduction in Bone Mineral Density: a Comparative Study Using REMS Technology Between Singleton and Twin Pregnancies in the Third Trimester”. Its primary objective is to identify whether bone mineral density differs between women with singleton pregnancies and women with dichorionic or monochorionic twin pregnancies late in pregnancy.
Secondary objectives include associations between bone measures and maternal factors such as age, BMI, obstetric history, dietary calcium intake and questionnaire-based fracture risk.
Why REMS makes the study interesting during pregnancy
REMS — Radiofrequency Echographic Multi Spectrometry — uses ultrasound rather than ionizing radiation. In the TWINBONE protocol, it is used at the proximal femur during the third trimester, alongside a Fragility Score and questionnaires.
That makes it possible to investigate bone status during pregnancy without relying on the same ionizing-radiation approach used by DXA. The method itself does not guarantee that a difference between twin and singleton pregnancies will be found.
Pregnancy changes bone metabolism even without disease
Normal pregnancy and lactation require substantial calcium adaptation to support fetal skeletal development and milk production. Reviews describe physiological changes in calcium absorption, bone turnover and maternal bone mass. In most women these adaptations are temporary and do not translate into long-term osteoporosis.
Pregnancy- and lactation-associated osteoporosis, usually discussed in the context of fragility fractures in late pregnancy or postpartum, is rare. A 2026 systematic review emphasized that predictors and treatment evidence remain limited.
Why twin pregnancy is a reasonable hypothesis — but still only a hypothesis
Two fetuses require more total fetal skeletal mineralization than one, so it is biologically reasonable to ask whether maternal adaptations differ. Case reports have described severe osteoporosis after twin pregnancy, but case reports cannot establish how common a problem is or whether twin pregnancy itself caused it.
That gap is exactly why a comparative study such as TWINBONE matters. The correct editorial position today is “research to watch”, not “twin pregnancy causes osteoporosis”.
A date correction: this was not newly registered on August 28
The ClinicalTrials.gov record shows the study started on December 23, 2025, was first submitted on December 23, 2025, met quality-control criteria on March 27, 2026 and was first posted on April 2, 2026. It remains listed as recruiting with no results posted.
Some trial-aggregation websites display a sync date of August 28, 2026. That is not the same as the original ClinicalTrials.gov registration or first-posted date. TwinPare Research uses the official registry record as the source of truth.
TwinPare perspective: women’s health needs more prospective data
This study fits an important TwinPare Research theme: women’s health questions often need better prospective, well-characterized data rather than extrapolation from case reports or broad assumptions.
We will treat TWINBONE as an evidence watch. When results are posted or peer-reviewed, the article should be updated and the conclusions reassessed.
Source notes
The sources have been verified and editorially reviewed for this article. The limitations below show which level of conclusion the sources support.
- [twinbone-nct07508553] Comparison of Bone Mineral Density in the Third Trimester Between Women in Singleton and Twin Pregnancies Using Questionnaires and REMS Densitometric Examination (TWINBONE) Fondazione Policlinico Universitario Agostino Gemelli IRCCS. ClinicalTrials.gov, 2026. Evidence type: Official clinical trial registry record Limitation: Recruiting study with no results posted. Registry objectives describe what will be tested, not what has been proven. ClinicalTrials.gov
- [cohen-2024] Bone Metabolism, Bone Mass, and Bone Structure During Pregnancy and Lactation: Normal Physiology and Pregnancy and Lactation-Associated Osteoporosis Adi Cohen. Endocrinology and Metabolism Clinics of North America, 2024. Evidence type: Clinical review Limitation: Reviews normal physiological adaptation and rare PLO; it does not establish a twin-pregnancy-specific risk. PubMed
- [plo-review-2026] Pregnancy and Lactation Associated Osteoporosis: A Systematic Review Systematic review investigators. Calcified Tissue International, 2026. Evidence type: Systematic review Limitation: PLO is rare and the evidence base is limited; the review does not establish twin pregnancy as an independent causal risk factor. PubMed
- [twin-case-2008] Pregnancy- and lactation-associated osteoporosis with severe vertebral deformities: can strontium ranelate be a new alternative for the treatment? Case-report investigators. Spine, 2008. Evidence type: Single case report after twin pregnancy Limitation: A single case can generate hypotheses but cannot estimate incidence or prove that twin pregnancy caused osteoporosis. PubMed
Editorial source review
This section shows how the article's key factual claims are linked to the source.
Phrasings that require caution
- Do not state that twin pregnancy increases osteoporosis, low BMD or fracture risk before comparative results are available.
- Do not use case reports to estimate population risk.
- The ClinicalTrials.gov record currently reports no study results.
- Clinical questions about bone pain, fractures, supplements or treatment during pregnancy require professional medical assessment.
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