Novel sonographic reference charts for early pregnancy based on known gestational age

Abstract

Objective: To study pregnancy dating, we developed growth charts using data from pregnancies with known gestational age. The most widely used growth charts for ultrasonographic early pregnancy variables were developed decades ago and are based on dating by the last menstrual period. The aims of the study were to create growth charts for early pregnancy (including crown-rump length, gestational sac diameter, yolk sac diameter, and amniotic cavity diameter) for last menstrual period-dated spontaneous pregnancies and pregnancies conceived through assisted reproductive technology (ART) with known gestational age; and to compare crown-rump length measurements with two established traditional charts based on last menstrual period dating.

Design: Retrospective cohort study.

Subjects: Of 1,061 singletons, 2,803 crown-rump length measurements from 716 exactly dated ART gestations with 1,143 crown-rump length measurements from 345 spontaneous pregnancies, which were dated by the last menstrual period in women with regular cycles, were compared using nonlinear quantile regression.

Exposure: A total of 716 ART pregnancies and 345 spontaneous pregnancies underwent ultrasound examinations, with a median of four visits at various points during the first trimester.

Main outcome measures: Early pregnancy dating with growth charts based on crown-rump length, gestational sac-, yolk sac- and amniotic cavity diameter.

Results: Novel reference charts for ultrasound dating of gestational age based on crown-rump length from 4 + 6 to 10 + 6 gestational weeks were created. The difference of the 10th and 90th percentile was significantly higher in spontaneous compared with ART pregnancies (P<.05). For the same crown-rump length, the gestational age of spontaneous pregnancies was estimated to be up to 4.08 days older than in ART pregnancies at the 90th percentile. Preexisting curves (Robinson/Fleming, Hadlock) aligned closely with the new reference curve mid-range but showed larger deviations at the extremes of assessed gestational ages.

Conclusion: Early pregnancy crown-rump length curves based on last menstrual period may overestimate gestational age. Using 2,803 crown-rump length measurements, we propose the current comprehensive charts for early pregnancy within a population with known gestational age for crown-rump length, gestational sac diameter, yolk sac diameter, and amniotic cavity diameter.

Keywords: Crown-rump length; first trimester; gestational sac; growth charts; ultrasound.

Figure 1

Patient inclusion flowchart. CRL= crown-rump length.

Figure 2

The 10th, 50th, and 90th percentiles of the predicted gestational age based on crown-rump length measurements, for both assisted reproductive technology pregnancies (green) and spontaneous pregnancies (red). Individual data points for spontaneous pregnancies are plotted as gray dots.

Figure 3

Crown-rump length measurements by gestational age for assisted reproductive technology pregnancies with 10th, 50th, and 90th centiles (red). Existing reference curves inserted for comparison: Hadlock curve (light green) and Robinson/Fleming curve (purple).

Supplementary Figure 1

Differences between the predicted median gestational age of the assisted reproductive technology pregnancies compared to the curve of Hadlock (light green) and the curve of Robinson/Fleming (purple).

Supplementary Figure 2

Mean gestational sac diameter measurements by gestational age with 10th, 50th, and 90th centiles for 716 assisted reproductive technology pregnancies (n = 3,190 measurements). Grey dots correspond to gestational sac diameter measurements of assisted reproductive technology pregnancies.

Supplementary Figure 3

Mean yolk sac diameter measurements by gestational age with 10th, 50th, and 90th centiles for 716 assisted reproductive technology pregnancies (n = 3,001 measurements). Grey dots correspond to yolk sac diameter measurements of assisted reproductive technology pregnancies.

Supplementary Figure 4

Mean amniotic cavity diameter measurements by gestational age with 10th, 50th, and 90th centiles for 716 assisted reproductive technology pregnancies (n = 1,320 measurements). Grey dots correspond to amniotic cavity diameter measurements of assisted reproductive technology pregnancies.