This is long, but I hope it will help you to feel better.
I am currently 26 weeks along with a SUA, or two vessel cord, baby. I am doing fine and so is she. I panicked for a few days after my 20 week u/s because I was reading the web. One of my good friends just had a beautiful, healthy baby girl with a SUA. They didn't even know & weren't even monitoring her. This happens a lot. PLEASE step away from the internet.
Having a SUA means literally nothing. It is perfectly normal to NOT feel lots of kicks at 20 weeks. I really started feeling them all the time at 22 weeks, which is EXACTLY when my midwife told me I would start feeling them. If you are unsure or completely worried, call your doctor.
I am being monitored with routine ultrasounds by a very experienced OB. I just had one this week and she is PERFECT. She weighs exactly what she should. Her heart and kidneys looks great. She is measuring exactly where she should be. I am not worrying anymore. She's kicking up a storm right now, as a matter of fact.
Having a SUA means NOTHING in and of itself other than there's a two vessel cord instead of three. The issue is that it can be indicative of OTHER, not necessarily related, problems. The heart, kidneys and cord form around the same time. If there was a problem with the formation of one, then there MIGHT have been a problem with the formation of something else at the same time. They'll check it out. IF I recall correctly, they told me that your risk, in a normal pregnancy, of a "defect" is 3-5% and that it increases 1.5-2% with a SUA baby. The doctor who is doing the u/s said she sees them a lot but she's only seen one baby with a problem in the years she's been practicing.