Until the 14th week of pregnancy, baby boys and girls look exactly the same on ultrasound, Carr said. But he warned there's not a hard and fast relationship between morning sickness and fetal sex. Be wary of keepsake ultrasounds Carr said that he understands the psychology of expectant parents wanting to see an image of their baby. A baby's gender is determined when the egg is fertilized. You'll know soon enough; in the meantime, just buy green or yellow clothes and accessories! One popular belief is that if a woman is carrying the baby high, she is supposedly having a girl, while carrying the baby low means it's a boy. Lately, as more couples turn to in-vitro fertilization procedures to conceive a child, the issue of selecting the sex of a baby for purposes of "family balancing" rather than for medical reasons is controversial and raises ethical concerns. Early in pregnancy, there is no difference in heart rate between the sexes, Carr said. Still, Carr cautioned that although researchers may find this association holds true over an average of 1, babies studied, an individual baby boy could still have a faster heartbeat, and an individual baby girl could have a slower one. Ultrasounds were not designed for sex prediction. Another theory holds that a mother's food cravings during pregnancy may reveal the baby's sex, with sweet cravings signifying a girl and cravings for salty, sour or odd foods linked with a boy. And the only risks to the mother may come from lying flat on her back, which might make her feel dizzy, along with the discomfort of having a full bladder, he said. It can clue you in on whether you're expecting a boy or girl! A blood test for pregnant women that's been around for about three years can also determine the sex of the fetus with 98 to 99 percent accuracy, Carr said.