Although ultrasound is meant to check the health of an unborn baby, it has created a lot of stress for expecting mothers. Early ultrasound can especially be stressful due to the different growth rates of babies.

So if you've had an early ultrasound, at what fetal development week can you expect to see a heartbeat? This is a question that is not easily answered.

Although the heart starts beating around the fifth week of fetal development, there are a few different factors that can affect when a heartbeat will be detected.

A heartbeat is typically seen on ultrasound between week 6 and 7. It can typically be heard by doppler between week 10 and 15.

So, if you go in for an early ultrasound and the heartbeat is not seen, or your doctor uses a doppler and can't find a heartbeat, do not worry without first considering the following possibilities:

* Are you sure of when you ovulated? A late ovulation will change pregnancy dates because most doctor's calculate from last menstrual period (LMP) rather than by ovulation date.

This is for the simple fact that most women will know when their LMP was, but will not know when they ovulated. A good sign that you ovulate late is if you typically have menstrual cycles longer than 28 days.

* Have you been told you have a tipped uterus? That causes the embryo to be located closer to your back than your front, therefore making it more difficult to see or hear a heartbeat.

* Are you overweight? The fat stores on the stomach can also make it difficult to see or hear a heartbeat.

* How old is the ultrasound machine? Older ultrasound machines do not always produce an image that has the quality to see a tiny heartbeat. Trans-vaginal ultrasounds are most effective at seeing an embryo during early pregnancy. There may be some concern if no heartbeat is seen once the embryo measures 5mm or if there is no gestational sac after week 6.

So if you're having an ultrasound before fetal development week 6, don't fret if no heartbeat is seen because it may just take a bit longer for it to be detected.