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

## TL;DR

This study creates new ultrasound-based growth charts for early pregnancy using known gestational age data, showing differences between spontaneous and ART pregnancies.

## Contribution

The study introduces novel sonographic reference charts for early pregnancy based on known gestational age rather than last menstrual period dating.

## Key findings

- New reference charts for crown-rump length, gestational sac, yolk sac, and amniotic cavity diameter were developed.
- Spontaneous pregnancies showed greater variability in growth compared to ART pregnancies.
- Traditional dating methods overestimate gestational age at the extremes of crown-rump length.

## Abstract

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.

Retrospective cohort study.

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.

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.

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

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.

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.