According to Gram Research analysis, a newborn exposed to burosumab throughout pregnancy developed temporary high calcium levels and phosphate retention for several weeks after birth because the medication crossed the placenta and remained active in the baby’s body. All abnormalities resolved by six months of age with no lasting harm, but the case demonstrates that careful monitoring of exposed newborns is necessary and doctors should approach continuing burosumab beyond mid-pregnancy with caution.
Researchers reported the first known case of a baby exposed to burosumab, a medication that treats a rare bone disease called X-linked hypophosphatemia, throughout pregnancy. The baby developed temporary high calcium levels and retained phosphate (a mineral) for several weeks after birth because the drug crossed the placenta and stayed active in the newborn’s body. By six months old, all the baby’s lab values returned to normal and the child remained healthy. This case shows that while the medication is helpful for treating the mother’s condition, doctors need to carefully monitor babies exposed to it in the womb and consider whether continuing the drug during pregnancy is safe.
Key Statistics
A 2026 case report published in Therapeutic Advances in Drug Safety documented the first known newborn exposed to burosumab throughout pregnancy, who developed prolonged phosphate retention and temporary high calcium levels that gradually normalized by six months of age.
Genetic testing in the exposed newborn excluded the familial PHEX mutation, confirming that the observed mineral metabolism abnormalities were due to transient pharmacologic exposure to burosumab rather than inherited X-linked hypophosphatemia.
The newborn exposed to antenatal burosumab demonstrated persistently elevated tubular phosphate reabsorption and low urinary phosphate excretion beyond the early neonatal period, with all biochemical values returning to normal by six months without evidence of kidney damage.
The Quick Take
- What they studied: Whether a pregnancy medication called burosumab, used to treat weak bones and low phosphate levels, affects newborns when mothers take it during pregnancy.
- Who participated: One newborn baby whose mother took burosumab throughout her entire pregnancy to manage severe bone pain and fatigue from X-linked hypophosphatemia.
- Key finding: The baby developed temporary high calcium levels and retained phosphate for several weeks after birth because the medication crossed the placenta and remained active in the newborn’s body, but all values returned to normal by six months of age.
- What it means for you: If you’re a woman of childbearing age taking burosumab for bone disease and planning pregnancy, discuss with your doctor whether to continue the medication during pregnancy. If you do continue it, your newborn will need careful blood tests to monitor calcium and phosphate levels. The good news: this case showed no lasting harm, but more research is needed.
The Research Details
This is a case report, which means doctors described what happened to one specific patient rather than studying a large group of people. The researchers followed one mother with X-linked hypophosphatemia (a rare inherited disease causing weak bones) who continued taking burosumab throughout her pregnancy. They carefully tracked the baby’s blood chemistry after birth, measuring calcium, phosphate, and related hormones at multiple time points over six months.
The doctors used genetic testing to confirm that the baby’s temporary mineral imbalances came from the medication exposure rather than from inheriting the mother’s bone disease. This was important because it proved the drug was responsible for the changes, not the baby’s own genes.
The research team documented how long the medication’s effects lasted in the newborn’s body and when everything returned to normal, providing the first real-world evidence of what happens when a baby is exposed to this drug in the womb.
Case reports are valuable when a medication has never been studied in pregnancy before. They provide the first warning signs that a drug might affect a developing baby or newborn. This case is important because burosumab is increasingly used to treat X-linked hypophosphatemia in women of childbearing age, but no one had studied what happens if they take it while pregnant. This report alerts doctors to watch for similar effects in other exposed babies.
This is a single case report, which is the lowest level of research evidence. It describes one baby, not many, so we cannot know if all exposed babies will have the same effects. However, the researchers did thorough blood testing and genetic analysis, which strengthens the findings. The fact that they ruled out genetic disease through testing makes the conclusion more reliable. More research with larger numbers of exposed pregnancies is needed to fully understand the risks.
What the Results Show
The baby was born healthy at full term with normal weight and appearance. However, within the first few weeks of life, blood tests showed the baby had higher-than-normal calcium levels (hypercalcemia) and was retaining too much phosphate instead of excreting it in urine. The baby’s parathyroid hormone (a hormone that controls calcium and phosphate) was lower than expected.
These findings persisted for several weeks after birth, which was unusual because newborns typically adjust their mineral balance quickly. The pattern of results matched exactly what would happen if the burosumab medication was still working in the baby’s body—blocking the FGF23 hormone just as it does in the mother.
By six months of age, all the baby’s calcium and phosphate levels had returned to completely normal ranges. The baby showed normal growth, normal development, and no signs of kidney damage (nephrocalcinosis), which was a concern the doctors monitored for. Throughout the observation period, the baby remained clinically well with no symptoms or complications.
The genetic testing was particularly important: it showed the baby did not inherit the mother’s PHEX gene mutation that causes X-linked hypophosphatemia. This confirmed that the temporary mineral imbalances were caused by the medication exposure, not by the baby having the genetic disease itself. The gradual normalization of all values over six months suggested the medication was slowly cleared from the baby’s body and its effects wore off naturally. The absence of kidney damage despite the phosphate retention was reassuring, as high phosphate can sometimes cause calcium deposits in kidneys.
This is the first published case of a baby exposed to burosumab throughout pregnancy. No previous studies have examined this medication in human pregnancy because it was never formally studied before use. The findings align with what scientists would predict based on how the drug works: if it blocks FGF23 in the mother, it would likely do the same in the baby if it crosses the placenta. However, the duration and severity of effects in this newborn were longer than might have been expected, suggesting the baby’s kidneys took time to clear the drug.
This is a single case report, so we cannot know if all babies exposed to burosumab in pregnancy will have the same effects. Some babies might have more severe effects, some might have milder effects, and some might have no effects at all. We don’t know if the mother’s dose, the timing of doses, or other factors affected the baby’s outcome. The case doesn’t tell us what happens if mothers stop the medication at different points during pregnancy. More research with many more exposed pregnancies is essential before doctors can make firm recommendations about burosumab use in pregnancy.
The Bottom Line
Women of childbearing age taking burosumab should discuss pregnancy plans with their doctors before conception. If pregnancy occurs or is planned, the decision to continue burosumab should weigh the mother’s need for symptom control against potential risks to the baby. If burosumab is continued during pregnancy, newborns should receive careful blood testing for calcium and phosphate levels in the first weeks of life and periodic monitoring for several months. Doctors should watch for signs of kidney problems. (Confidence level: Low to Moderate—based on one case, not large studies.)
This information is most relevant to: women with X-linked hypophosphatemia who are pregnant or planning pregnancy; their doctors and obstetricians; pediatricians caring for exposed newborns. It’s less relevant to the general population since X-linked hypophosphatemia is rare. Men taking burosumab do not need to worry about this issue.
In this case, the temporary mineral imbalances resolved completely by six months of age. However, doctors should monitor exposed newborns for at least several months after birth to ensure normalization occurs. The medication’s effects appeared to gradually wear off over weeks to months as the baby’s body cleared the drug.
Frequently Asked Questions
Is burosumab safe to take during pregnancy?
Burosumab has never been formally studied in human pregnancy. One case report showed a baby exposed throughout pregnancy developed temporary high calcium and phosphate retention that resolved by six months with no lasting harm. However, more research is needed. Pregnant women taking it should discuss risks and benefits with their doctor.
What happens to a baby if the mother takes burosumab while pregnant?
In the reported case, the baby developed temporary high calcium levels and retained phosphate for several weeks after birth because the drug crossed the placenta. All values returned to normal by six months, and the baby remained healthy. However, this is based on one case, so effects may vary.
Does burosumab cross the placenta?
Yes, according to this case report, burosumab crosses the placenta and reaches the developing baby. The medication remained active in the newborn’s body after birth, affecting calcium and phosphate levels for several weeks before gradually clearing.
What monitoring should a newborn have if exposed to burosumab in pregnancy?
Newborns exposed to burosumab should receive blood tests measuring calcium, phosphate, and related hormones in the first weeks of life and periodic monitoring for several months. Doctors should also watch for signs of kidney problems, though the reported case showed no kidney damage.
Can a baby inherit X-linked hypophosphatemia from a mother taking burosumab?
No. Burosumab doesn’t cause genetic disease. In the reported case, genetic testing confirmed the baby did not inherit the mother’s PHEX gene mutation. The temporary mineral imbalances were from medication exposure, not inherited disease.
Want to Apply This Research?
- If you’re a pregnant woman taking burosumab, track your medication doses and the dates you take them. After delivery, if your baby is monitored for calcium and phosphate levels, log the test results and dates to share with your pediatrician and identify any patterns.
- Schedule regular prenatal discussions with your doctor about continuing or adjusting burosumab during pregnancy. After birth, ensure your baby receives recommended blood tests for mineral levels in the first weeks of life and keep all follow-up appointments for monitoring.
- Create a health record in your app documenting: (1) your burosumab doses during pregnancy, (2) your baby’s calcium and phosphate test results with dates, (3) any symptoms or concerns, and (4) follow-up appointment dates. Share this record with your pediatrician to ensure comprehensive monitoring.
This article describes a single case report and should not be interpreted as medical advice. Burosumab has not been formally studied in human pregnancy, and the safety and effects in pregnant women and exposed newborns remain largely unknown. Women of childbearing age taking burosumab who are pregnant, planning pregnancy, or have questions about medication use during pregnancy should consult with their obstetrician and the prescribing physician before making any changes to their treatment. Newborns exposed to burosumab in utero should be monitored by a pediatrician with appropriate blood testing. This information is for educational purposes only and does not replace professional medical advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.