HCG levels and singleton versus twin?

[Anonymous]

Early on in pregnancy - could it be twins that show up as one (with one hiding) or do you tend to see quite clearly both sacs when it's early on?

We saw 2 sacs of equal size at the same point in pregnancy (around 5 weeks). However, I know MANY cases on infertility boards and in real life (fellow moms of twins) in which only one sac was visualized early on and another developed further within a week or so. Or one heartbeat was seen at 6 weeks and another sac appeared empty until 7 or 7.5 weeks at which time a strong heartbeat was seen. All these were IVF pregnacies and all embryos began their development at the exact same time (and the women were monitored closely by ultrasound in early pregnancy) but it just took a little while for the second embryo to catch up or be adequately visualized on ultrasound.