How many weeks are you? Have you had a recent scan? This happened to me and I panicked! It turned out to be because I’d moved quite late in pregnancy and they had wanted me to go into the hospital and have all my bloods repeated for their records.
Yes, I suspect it's about your bloods. That's when they do the antenatal screening, so I would suspect she is calling about your results. Either something came up in them that they want to investigate further or there was a problem with the bloods and they need to redraw them.