Also, avoid promising a specific gender of the baby before you have a definitive answer from an ultrasound. (helpwevegotkids.com)
Sometimes it is hard to find out the exact gender of the baby earlier: the doctor can not see it clearly or isn't sure. (infobaby.org)
What is clearer though is that this method should not be used to make decisions based on the results you get.If you are serious about knowing whether you are pregnant and the possible genders of your babies, then do not use this method. (intelligentmother.com)