One possibility is that your pregnancy is simply not far enough along to see a fetal pole or heart beat on an ultrasound. The fetal pole becomes visible in a transvaginal ultrasound
somewhere between 5 to 6 weeks of gestational age
. Heart beat appears around 6-7weeks.
If you incorrectly remembered your last menstrual period date, that can change the expected findings on an ultrasound , or if you have an irregular cycle and do not ovulate two weeks after the start of your last menstrual period, your pregnancy may not technically be 9 and half weeks even if it has been 9 and half weeks since your last menstrual period. These can lead to non visualization of fetal pole and heart rate.
In such a case you just have to wait and get a repeat ultrasound after a week or two. But as you say your pregnancy test was positive in september so the possibility of wrong dates is less.
The other possibility is a blighted ovum
. A blighted ovum is a condition where gestational sac
develops but the baby never develops enough to become visible on ultrasound.
When a woman becomes pregnant, the fertilized egg attaches to the uterine wall. At about five to six weeks of pregnancy, an embryo should be present. At about this time, the gestational sac where the fetus develops is about 18 millimeters wide. With a blighted ovum, though, the pregnancy sac forms and grows, but the embryo does not develop. That's why a blighted ovum is also called an anembryonic pregnancy.
In such a condition pregnancy usually aborts.
Third possibilty is a missed abortion
where in fetus stops growing and so heart beat does not appear.
Both of the above conditions that is blighted ovum and missed abortion present with bleeding or pain. But sometimes missed abortion is a silent miscarriage
and present first as an ultrasound finding.
For now you should keep taking folic acid tablet
Get a repeat ultrasound done after a week and see if the fetus has grown and heart beat has appeared. There is no harm in waiting for a week or two for the heart beat to appear before taking any decision of termination due to non viable pregnancy.