There are quite a few but we also know she is no longer pregnant now. She is past what would have been her due date if she was 19 weeks in Feb/March but no details of if she gave birth or the pregnancy was terminated.
http://www.mirror.co.uk/news/uk-news/becky-watts-murder-trial-stepbrother-6621107
How do we know she was 19 weeks at the time?