DALLAS (FRONTLINE MEDICAL NEWS) – Monthly ultrasound scans in the last trimester pick up just as many fetal growth and amniotic fluid problems as do scans done every 2 weeks, Suneet P. Chauhan, MD, reported at the meeting sponsored by the Society for Maternal-Fetal Medicine.

“We found that about one in three of these high-risk pregnancies was complicated by an abnormality of fetal growth or amniotic fluid,” said Dr. Chauhan of the department of obstetrics, gynecology, and reproductive sciences at the University of Texas, Houston. “But more frequent scans did not increase the frequency of identifying these abnormalities. And since there are approximately 1.7 million such high-risk pregnancies each year, these findings have significant implications on personal, departmental, and societal levels.”

However, he added, the SUN trial , which randomized women to monthly or biweekly scans, wasn’t large enough to definitively determine the optimal timing of ultrasounds in this population. “We need larger trials to determine this.”

The trial results, published in the American Journal of Obstetrics & Gynecology , comprised 228 women with singleton pregnancies complicated by medical comorbidities, putting the fetus at risk of problems with growth or amniotic fluid volume. They were randomized to ultrasound scans every 2 weeks or every 4 weeks during the last trimester. The primary outcome was identification of four pregnancy complications: fetal growth restriction, large for gestational age, oligohydramnios, or polyhydramnios.

There were also secondary outcomes of composite maternal morbidity (chorioamnionitis, wound infection, transfusion, diabetic ketoacidosis, venous thromboembolism, ICU admission, and death) and neonatal morbidity (Apgar score of less than 5 at 5 minutes, umbilical artery pH less than 7, hyperbilirubinemia, intubation, high-grade intraventricular hemorrhage, necrotizing enterocolitis, and death).

Women were eligible for the study if they had autoimmune disease, a body mass index of 40 kg/m2 or higher, a history of delivering a small for gestational age or macrosomic infant, hypertensive disease, substance abuse, or sickle cell disease.

About half had multiple risk factors, the three most common being high body mass index, diabetes (either gestational or insulin-dependent), and hypertensive disease. Their gestational age at randomization was a mean of 23 weeks. The first scan was conducted at a mean of 29 weeks.

There were 28% more scans in the 2-week group than in the 4-week group (492 vs. 382). There were also more exams for potentially concerning findings, including more scans looking at growth (359 vs. 278), biophysical profiles (99 vs. 79), and umbilical artery Dopplers (34 vs. 27). Despite the increased scans and investigations, the primary outcome was detected at similar points (31.7 vs. 32.2 weeks).

A primary outcome finding was detected in 38% of the 2-week group and 32% of the 4-week group – not significantly different. There were no significant differences in the proportion of outcomes detected in each group, including fetal growth restriction (19% vs. 16%), large for gestational age (14% each group), oligohydramnios (4% each group) and polyhydramnios (9% each group).

Infants in each group were born at about the same time – 13.5 weeks after randomization. The mean gestational age in both groups was 37 weeks, with about 28.5% less than 37 weeks at birth. There were no significant differences in the rate of cesarean deliveries, or small or large for gestational age births.

The composite maternal morbidity outcome was similar in the 2-week and 4-week groups (26% vs. 22%). There were no significant differences in any of the individual components of the outcome. No mother died.

The composite neonatal outcome was also similar between the groups (14% vs. 12%). There were no significant differences in any of the individual components. No infant died.

The study was sponsored by the University of Texas Health Science Center, Houston. Dr. Chauhan had no financial disclosures.

SOURCE: Roberts RP et al. Am J Obstet Gynecol. 2018;218:S3 .