The first meaning is 'metre' which is a measurement of length. If the 'm' stands alone it is metre. The second meaning is 'milliâ¦' which means a thousandth. In this case 'm' can not stand alone, we need to know what we have a thousandth of; if it is weight, length or some other thing. Example: mg means 'milligram', a thousandth of a gram. Example: mm means 'millimetre', a thousanth of a meter.
At about six weeks into pregnancy (four weeks from conception), you should be able to see your baby's heartbeat on ultrasound. The typical heart rate at this age is about 100 beats per minute.
As a general rule, 5.5 to 6.5 weeks is the earliest time that your doctor will be able to detect a fetal heart beat by trans-vaginal ultrasound. In other words, about six weeks is the earliest stage where you can hear your tiny babyâs heartbeat with an ultrasound. At that early phase, your babyâs heart rate should be about 100 beats per minute.