Several studies demonstrate decreased detection of fetal anomalies with increasing body mass index (likely related to suboptimal visualization) on routine and detailed examinations [36-40]. An anatomic survey in obese women should be considered at 20 to 22 weeks (about 2 weeks later than women of normal weight), and if incomplete, a repeat follow-up US should be considered in 2 to 4 weeks [8,40-44]. There is emerging evidence that anatomic studies performed earlier in gestation with transvaginal imaging may be helpful [36-39]. A recent Canadian publication has demonstrated that performing early anatomic evaluation by transvaginal technique in combination with routine transabdominal study at 18 to 22 weeks can result in completion rates of the anatomic study that are comparable to those in nonobese populations [21]. This method should especially be considered in completion of the anatomic study in the high-risk obese population. MRI Fetal Without and With IV Contrast MRI abdomen and pelvis with IV contrast is not recommended for fetal evaluation. There are no documented fetal indications for the use of MRI contrast, but there may be rare instances where contrast is potentially helpful in evaluating maternal anatomy or pathology, to be decided on a case by case basis [45]. MRI Fetal Without IV Contrast The International Society of Ultrasound in Obstetrics and Gynecology current guidelines recommend that fetal MRI is generally indicated following an US examination in which the information about the abnormality is incomplete. Although MRI is usually reserved for patients with a known or suspected anomaly, MRI can be helpful in screening fetuses with a family risk for brain abnormalities, as well as for assessment of fetal brain development [8,45-47]. If performed, this is ideally done at or after 22 weeks gestation [8], although an MRI performed between 18 to 22 weeks may be of value in certain clinical indications and settings [48].
Second and Third Trimester Screening for Fetal Anomaly. Several studies demonstrate decreased detection of fetal anomalies with increasing body mass index (likely related to suboptimal visualization) on routine and detailed examinations [36-40]. An anatomic survey in obese women should be considered at 20 to 22 weeks (about 2 weeks later than women of normal weight), and if incomplete, a repeat follow-up US should be considered in 2 to 4 weeks [8,40-44]. There is emerging evidence that anatomic studies performed earlier in gestation with transvaginal imaging may be helpful [36-39]. A recent Canadian publication has demonstrated that performing early anatomic evaluation by transvaginal technique in combination with routine transabdominal study at 18 to 22 weeks can result in completion rates of the anatomic study that are comparable to those in nonobese populations [21]. This method should especially be considered in completion of the anatomic study in the high-risk obese population. MRI Fetal Without and With IV Contrast MRI abdomen and pelvis with IV contrast is not recommended for fetal evaluation. There are no documented fetal indications for the use of MRI contrast, but there may be rare instances where contrast is potentially helpful in evaluating maternal anatomy or pathology, to be decided on a case by case basis [45]. MRI Fetal Without IV Contrast The International Society of Ultrasound in Obstetrics and Gynecology current guidelines recommend that fetal MRI is generally indicated following an US examination in which the information about the abnormality is incomplete. Although MRI is usually reserved for patients with a known or suspected anomaly, MRI can be helpful in screening fetuses with a family risk for brain abnormalities, as well as for assessment of fetal brain development [8,45-47]. If performed, this is ideally done at or after 22 weeks gestation [8], although an MRI performed between 18 to 22 weeks may be of value in certain clinical indications and settings [48].