Maternal rest improves growth in small-for-gestational-age fetuses (<10th percentile)

Abstract

Background: Optimal management of fetuses diagnosed as small for gestational age based on an estimated fetal weight of <10th percentile represents a major clinical problem. The standard approach is to increase fetal surveillance with serial biometry and antepartum testing to assess fetal well-being and timing of delivery. Observational studies have indicated that maternal rest in the left lateral position improves maternal cardiac output and uterine blood flow. However, maternal bed rest has not been recommended based on the results of a randomized clinical trial that showed that maternal rest does not improve fetal growth in small-for-gestational-age fetuses. This study was conducted to revisit this question.

Objective: This study aimed to determine whether maternal bed rest was associated with an increase in the fetal biometric parameters that reflect growth after the diagnosis of a small-for-gestational-age fetus.

Study design: A retrospective study was conducted on fetuses who were diagnosed as small for gestational age because of an estimated fetal weight of <10th percentile for gestational age. The mothers were asked to rest in the left lateral recumbent position. Fetal biometry was performed 2 weeks after the diagnosis. All fetuses before entry into the study had a previous ultrasound that demonstrated an estimated fetal weight of >10th percentile. To assess the response to bed rest, the change in fetal biometric parameters (estimated fetal weight, head circumference, abdominal circumference, and femur length) after the recommendation of bed rest was computed for 2 periods: (1) before the diagnosis of a weight of <10th percentile vs at the time of diagnosis of a weight of <10th percentile and (2) at the time of diagnosis of a weight of <10th percentile vs 2 weeks after maternal bed rest. For repeated measures, proportions were compared using the McNemar test, and percentile values were compared using the Bonferroni Multiple Comparison Test. A P value of <.05 was considered significant. To describe changes in the estimated fetal weight without bed rest, 2 control groups in which the mothers were not placed on bed rest after the diagnosis of a small-for-gestational-age fetus were included.

Results: A total of 265 fetuses were observed before and after maternal bed rest. The following were observed in this study: (1) after 2 weeks of maternal rest, 199 of 265 fetuses (75%) had a fetal weight of >10th percentile; (2) the median fetal weight percentile increased from 6.8 (interquartile range, 4.4-8.4) to 18.0 (interquartile range, 9.5-29.5) after 2 weeks of bed rest; (3) similar trends were noted for the head circumference, abdominal circumference, and femur length. In the groups of patients who were not asked to be on bed rest, a reassignment to a weight of >10th percentile at a follow-up examination only occurred in 7 of 37 patients (19%) in the Texas-Michigan group and 13 of 111 patients (12%) in the Colorado group compared with the bed rest group (199/265 [75%]) (P<.001).

Conclusion: Patients who were prescribed 2 weeks of bed rest after the diagnosis of a fetal weight of <10th percentile had an increase in weight of >10th percentile in 199 of 265 fetuses (75%). This increase in fetal weight was significantly higher than that in the 2 control groups in which bed rest was not prescribed. This observation suggests that bed rest improves fetal growth in a subset of patients.

Keywords: Doppler velocimetry; abdominal circumference; bed rest; estimated fetal weight; femur length; fetal growth restriction; head circumference; left lateral recumbent position; longitudinal study; middle cerebral artery; small for gestational age; umbilical artery.

FIGURE 1. EFW percentile values plotted against gestational age

A, Distribution of the EFW percentiles in AGA fetuses before the diagnosis of an EFW of <10th percentile. B, Distribution of the EFW percentiles at the time of the diagnosis of an EFW of <10th percentile in SGA fetuses SGA. C, Distribution of EFW percentile measurements after 2 weeks of maternal rest. D, Percentile plots for each fetus. The blue dots are values >10th percentile, and the red dots are values <10th percentile. AGA, appropriate for gestational age; EFW, estimated fetal weight; SGA, small for gestational age. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.

FIGURE 2. Box and whiskers plots

The mean, 25th percentile, and 75th percentile are displayed from the quartile distribution of the percentile measurements for the estimated fetal weight (A), abdominal circumference (B), head circumference (C), and femur length (D). AGA, appropriate for gestational age; SGA, small for gestational age. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.

FIGURE 3. AC percentile values plotted against gestational age

A, Distribution of the AC percentiles in AGA fetuses before the diagnosis of an EFW of <10th percentile. B, Distribution of the AC percentiles at the time of the diagnosis of an EFW of <10th percentile in SGA fetuses. C, Distribution of AC percentile measurements after 2 weeks of maternal rest. D, Percentile plots for each fetus. The blue dots are values >10th percentile, and the red dots are values <10th percentile. AC, abdominal circumference; AGA, appropriate for gestational age; EFW, estimated fetal weight; SGA, small for gestational age. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.

FIGURE 4. HC percentile values plotted against gestational age

A, Distribution of the HC percentiles in AGA fetuses before the diagnosis of an EFW of <10th percentile. B, Distribution of the HC percentiles at the time of the diagnosis of an EFW of <10th percentile in SGA fetuses. C, Distribution of HC percentile measurements after 2 weeks of maternal rest. D, Percentile plots for each fetus. The blue dots are values >10th percentile, and the red dots are values <10th percentile. AGA, appropriate for gestational age; EFW, estimated fetal weight; HC, head circumference; SGA, small for gestational age. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.

FIGURE 5. FL percentile values plotted against gestational age

A, Distribution of the FL percentiles in AGA fetuses before the diagnosis of an EFW of <10th percentile. B, Distribution of the FL percentiles at the time of the diagnosis of an EFW of <10th percentile in SGA fetuses. C, Distribution of FL percentile measurements after 2 weeks of maternal rest. D, Percentile plots for each fetus. The blue dots are values >10th percentile, and the red dots are values <10th percentile. AGA, appropriate for gestational age; EFW, estimated fetal weight; FL, femur length; SGA, small for gestational age. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.

FIGURE 6. The 3 common growth trends after the initiation of maternal bed rest

The percentage and number of fetuses for each category are listed for all fetuses with an EFW of <10th percentile. A, The EFW accelerated >10th percentile after maternal bed rest and maintained the growth >10th percentile (168 [63%]). B, The EFW did not accelerate >10th percentile after maternal bed rest but maintained a normal rate of growth (49 [19%]). C, The EFW growth rate decelerated at the last examination (48 [18%]). EFW, estimated fetal weight. DeVore. Maternal rest improves fetal growth. Am J Obstet Gynecol 2024.