Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) is a way to diagnose maternal problems during pregnancy. It provides an excellent image of the soft tissues, and does not use ionizing radiation making it safer than other types of imaging such as a CT Scan.
MRI had been of little use in detecting problems with unborn babies because of the difficulty of trying to capture an image of a moving baby with a technique that took a long time to take a picture. Newer ultrafast MRIs are of high enough quality they can be used to evaluate the fetal structure and overall growth, the placenta, amniotic fluid quantity, soft tissue malformations and the biochemical status.
What you need to know
With no ionizing radiation, MRI appears safe. However most physicians agree MRI should be avoided during the first trimester when your baby is at his most vulnerable time. It is also generally agreed that contrast materials (something injected into your body to help the MRI capture the information needed), should be avoided during pregnancy because it has been shown to cross the placenta.
Overall, MRI for unborn babies should only be used to detect anomalies in high risk cases when there is need for further evaluation that cannot be completed with lesser methods like ultrasound. For all other forms of information it is usually easier to get the information you need with ultrasound.
You will lie on your back on a table and be slid on the table into the bore of the magnet. It may take 20 to 60 minutes for the full procedure depending on what part of the body is being imaged. During this time you must lay perfectly still. If your baby's movements will obstruct the image you may be asked to use a mild sedative, but this is not normally necessary with ultrafast MRI.
Salomon, L.J., Ouahba, J. Delezoide, A., Vuillard, E., Oury J., Sebag, G., and Garel, C. (2006). Third-trimester fetal MRI in isolated 10- to 12-mm vetriculomegaly: is it worth it? BJOG: An International Journal of Obstetrics and Gynaecology 113(8):942-7.