The worse the morning sickness, the more likely it is you're having a girl.
Most experts believe this is truly a myth. However, women who need to be hospitalized after morning sickness have the 53%-56% chances of delivering a baby girl than to 50-50% in milder cases. No one knows exactly why morning sickness (also known as hyperemesis gravidarum) occurs, though it has long been thought to relate to elevated hormone levels (including progesterone, estrogen and/or human chorionic gonadotropin, or HCG). Which hormone, if any of these, is most important, remains a matter of speculation, and several other theories have been proposed such as zinc deficiency, genetic factors and psychological factors. At least one study found that women carrying a female fetus had higher HCG levels than with a male fetus. If true, that could explain the connection.