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.
Time Frame. A baby develops a heartbeat early in the first trimester. The first trimester is the first 12 weeks of pregnancy as measured by the first day of the last period, according to MayoClinic.com. These early weeks are marked by intense hormonal changes in the womanâs body and rapid growth in the babyâs body.