Timing of Serial Ultrasounds

While there is an agreement that women at risk for abnormalities of fetal growth should have
serial ultrasound examinations in the 3rd trimester, there is a lack of consensus on how
frequently these exams should be done. The American College of Obstetrics and Gynecology
recommend that an ultrasound to assess fetal growth be performed between 2 to 4 weeks;
however, there have been no prospective or randomized trials to determine whether the
optimal interval should be closer to 2 weeks or delayed to 4 weeks. Currently, only 60% of
fetuses' with abnormal growth are detected antenatally. There is equipoise of whether
ultrasound every 2 versus 4 weeks improves the detection and subsequent newborn outcomes or
merely leads to an increase in false positives and unnecessary interventions. It has been
proposed, that if delivery occurs within 2 weeks of the ultrasound, the antenatal detection
of abnormal growth may be more accurate and hence more likely to improve outcomes.
Conversely, a shorter interval may result in confusion as to whether there is actual change
in growth or merely variation in the measurement technique itself. Moreover, with the cost
of ultrasound averaging approximately $200 per examination, the interval between ultrasounds
can have major implications on public-health costs as well as the interventions that
subsequently follow if an abnormality is detected.

The purpose of this randomized controlled trial is to compare the frequency of the diagnosis
of fetal growth abnormalities when ultrasound assessment is performed at 2 versus 4 week
intervals.

Inclusion Criteria:

- Maternal age ≥ 18 years

- Singletons

- Gestational age ≥ 20 weeks to 27 weeks 6 days

- Has insurance, whether private or government issued

- High-risk pregnancy requiring serial fetal growth assessment as determined by the
treating physician.

- Dating of pregnancy by ultrasound ≤ 21 weeks and 6 days of gestation or known date of
conception in the setting of in vitro fertilization

- No known major anomalies

Exclusion Criteria:

- Known major fetal anomaly

- Multiple gestation (twins or triplets)