Slow rising HCG levels but promising US results

Patient: Dear Ask the doctor team,I am up in the air for so many days now about my pregnancy that I can hardly stand it. I am about 6wks4 days pregnant(last period Nov 16th. I already have one healthy baby and had one ectopic pregnancy about 4mths ago that got treated with 1x MTX.This time I have extremely slow rising hcg levels while at the same time very promising ultrasound results. Neither my doctor nor the doctors at the hospital can make sense of it: One doctor advised to look at the levels as secondary and the other one diagnosed a pending mc.Ultrasound results:Dec 23rd empty gestational sac of 0,8cmDec 27th gestational sac with clear yolk sac of 0,4cmDec 30th yolk sac of 0,6cm and HEARTBEATHCG level resultsDec 23rd-27th constant at 5130Dec 30th 5.800I had zero spotting or cramping and to me it feels like a very normal pregnancy.Is there any chance for this pregnancy? Do you know of healthy pregnancies that had slow to rise HCG levels?Also do you see a correlation between slow rising levels and chromosomal defects?I have another US scheduled for next week.I am so worried! I have never had HCG levels drawn in my first pregnancy so I have no idea how they progressed the 1st time.Thank you so much and happy new year!