It's hard to imagine pregnancy care without the ultrasound.
Since the 1950s, this incredible technology has provided an essential snapshot into the womb.
Now, scientists are taking it up a notch by trying to provide a continuous window of imaging.
In the coming years, new inventions may allow prospective parents and their physicians to monitor a developing fetus for hours on end, without the need for a traditional handheld ultrasound device or a sonographer standing by.
That sounds like sci-fi, but the proof of concept already exists.
Scientists at the University of California San Diego, Stanford, and Oxford have now invented a wearable ultrasound patch, called UPatch.
Mariana Tome, study co-author and obstetrics doctor at the University of Oxford, thinks the invention could "transform pregnancy care".
"This is the kind of technology obstetrics has been waiting for," she claims.
Like a handheld ultrasound, UPatch sends high-frequency sound waves inside the body to bounce off structures.
The returning echoes are then read by special software to capture a real-time view of what's going on inside the body.
UPatch sticks to the skin of the abdomen, where it 'reads' the echoes of red blood cells deep within the vessels of a developing fetus.
It can even accurately measure anatomical features of the fetus, such as the head circumference, abdominal circumference, or femur length, thereby providing an estimated weight.
Most impressively, UPatch does all this autonomously, without the need for a trained sonographer on hand.
The patch needs to be connected to a bulky backend powering system, and it doesn't work when a mother is walking or moving too much, but it is technically hands-free.
"Babies in the womb still cannot be monitored reliably, which is a major gap in maternity care worldwide, with huge implications. Solutions are needed urgently," says Antoniya Georgieva, a reproductive health researcher at Oxford.
"The UPatch technology opens the possibility of monitoring the most important signals of fetal health over much longer periods, gain essential new knowledge of how babies' oxygen supply and wellbeing adapt inside the womb, and ultimately helping clinicians identify problems earlier."
When researchers tested the patch on 62 pregnancies within a clinical setting, it performed on par with current ultrasound devices.
For one participant, the patch even noticed a dangerous change in blood flow to the fetus, signaling preeclampsia.
"Following the detection of compromised fetal health using the UPatch, the preeclamptic participant underwent intensive monitoring and the baby was delivered by Cesarean section four days later," write the study authors.
During pregnancy, ultrasounds are regularly recommended to monitor the health of both the mother and the child.
In higher-risk pregnancies, where patients are kept in the clinic for longer periods of time, ultrasounds are done multiple times a week.
Each one of those scans, however, takes time and requires a sonographer to use a handheld device to focus on parts of the uterus.
UPatch allows patients to be monitored in bed for hours, without the need for a clinician to move the device's focus or interpret the results in real time.
If UPatch is used in conjunction with classical imaging techniques, then perhaps pregnancy outcomes could be greatly improved, its inventors argue.
"This technology could expand access to prenatal imaging in healthcare deserts and low-resource settings, where shortages of trained sonographers often delay care for high-risk pregnancies," says Tom Park, the main engineer who designed and fabricated UPatch.
After comparing the patch to current ultrasound devices, the researchers then tested the patch continuously for between 1 and 6 hours in 52 pregnant women, including those affected by preeclampsia, gestational diabetes, hypertension, or poor fetal growth.
The findings reveal differences between short-term fluctuations in ultrasound readings and longer-term changes that require closer monitoring.
Researchers hope the device can help clinicians more readily detect signs of sustained fetal distress, so they can intervene sooner.
The flexible patch is designed with electrodes and an acoustic lens, so that when it wraps around an expectant mother's abdomen, it provides a window to the entire uterus while sitting, standing, or lying down.
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It can even provide details on how blood flow rates in the umbilical artery compare to those in the fetus's brain.
"This work shows how advances in soft electronics, ultrasound engineering, and clinical science can come together to address one of the most important unmet needs in pregnancy care," says senior author and engineer Sheng Xu from Stanford.
The study is published in Nature Biotechnology.