Reference intervals of gestational sac, yolk sac, embryonic length, embryonic heart rate at 6–10 weeks after in vitro fertilization-embryo transfer

BACKGROUND: Accurately determining the normal range of early pregnancy markers can help to predict adverse pregnancy outcomes. The variance in ovulation days leads to uncertain accuracy of reference intervals for natural pregnancies. While the gestational age (GA) is accurate estimation during in vitro fertilization-embryo transfer (IVF-ET). Thus, the objective of this research is to construct reference intervals for gestational sac diameter (GSD), yolk sac diameter (YSD), embryonic length (or crown–rump length, CRL) and embryonic heart rate (HR) at 6–10 gestational weeks (GW) after IVF-ET. METHODS: From January 2010 to December 2016, 30,416 eligible singleton pregnancies were retrospectively recruited. All included participants had full records of early ultrasound measurements and phenotypically normal live neonates after 37 GW, with birth weights > the 5th percentile for gestational age. The curve-fitting method was used to screen the optimal models to predict GSD, CRL, YSD and HR based on gestational days (GD) and GW. Additionally, the percentile method was used to calculate the 5th, 50th, and 95th percentiles. RESULTS: There were significant associations among GSD, CRL, YSD, HR and GD and GW, the models were GSD = − 29.180 + 1.070 GD (coefficient of determination [R(2)] = 0.796), CRL = − 11.960 - 0.147 GD + 0.011 GD(2) (R(2) = 0.976), YSD = − 2.304 + 0.184 GD - 0.011 GD(2) (R(2) = 0.500), HR = − 350.410 + 15.398 GD - 0.112 GD(2) (R(2) = 0.911); and GSD = − 29.180 + 7.492 GW (R(2) = 0.796), CRL = − 11.960 - 1.028 GW + 0.535 GW(2) (R(2) = 0.976), YSD = − 2.304 + 1.288 GW - 0.054 GW(2) (R(2) = 0.500), HR = − 350.410 + 107.788 GW - 5.488 GW(2) (R(2) = 0.911), (p < 0.001). CONCLUSIONS: Reference intervals for GSD, YSD, HR and CRL at 6–10 gestational weeks after IVF-ET were established.