A superstition is a belief not based on fact. By definition, superstitions rise out of ignorance, fear of the unknown, or trust in magical thinking. Superstitions most often surround mysterious and life changing events. Pregnancy certainly qualifies as one of those events. So why do superstitions survive over time? 
One reason superstitions survive is that even though they are not based on fact, they may be based on true experience. The cause and effect may be wrong, but the result may hold up over time. In fact, some pregnancy superstitions have been supported by scientific study.  Here are 7 superstitions backed up by some real science.
- Boys are harder to deliver.
It is a common superstition that baby boys are harder on mothers than girls. Even doctors and nurses who work in delivery rooms are familiar with the experience that a hard labor and delivery usually means a boy. A study published in the British Medical Journal backs up the belief that boys cause harder labor than girls. 
The study compared about 4,000 male births to 4,000 female births. It found that boys had longer labors and were more likely to require induced labor, use of forceps for delivery, and C-section delivery. One reason may be that boy babies tend to have larger head sizes. 
- What you eat during pregnancy influences your baby’s taste.
When my oldest daughter was pregnant with her first child, she swore that her baby would roll around in her belly when she ate peach ice cream. Sure enough, my grandson is a big fan of peach ice cream. There are many superstations about how the food you eat affects your baby. My grandmother used to say that your baby would favor the foods you eat during pregnancy.
Many studies now show that food choices made by a mother during pregnancy do have an effect on the child. In fact, studies show that food flavors and smells pass into the amniotic fluid. The baby swallows this fluid and can experience the taste and smells of food. One study found that pregnant women who drank carrot juice had babies that favored carrot-flavored cereal. There is even a name for this effect. It’s called the “flavor bridge.” 
- You can affect the sex of your baby by what you eat.
There are many superstitions about food and the sex of your baby. If you want a girl, you should eat sweets. If you want a boy, you should eat meat. One superstition says that eating bananas will give you a boy.
Research done by a team from the universities of Exeter and Oxford back up the belief that diet at the time of conception really does have an influence on the sex of your baby. It is not so much what type of food you eat, but how many calories you eat. 
In the study, which included over 700 first-time mothers, women who consumed the most calories at the time of conception were more likely to have boys. The high-calorie women had sons in 56 percent of births. The low-calorie women had sons in 45 percent of births. The researchers suggest this finding may explain why male births are declining in developed countries where young women are more likely to skip breakfast or be on a low calorie diet. 
- Stay away from funerals and graveyards.
This superstition is especially strong in Chinese culture. It is part of the traditional Chinese pregnancy restrictions. Although this Chinese taboo is based on the belief that negative energy will upset the balance of yin and yang, modern scientific research backs up the negative results. Traditional Chinese medicine also advises pregnant women avoid other stressful situations like moving or making major changes in the home. 
A review of the impact of stress and anxiety during pregnancy on fetal health was published in the journal Clinical Obstetrics and Gynecology. If you accept the fact that being around death and funerals is stressful, the advice to avoid these events and places makes a lot of sense, especially if the death involves a loved one. 
The review found that stress and anxiety during pregnancy might cause stress hormones to rise in both the mother and the fetus. This fetal stress causes babies to become restless and the fetal heart rate to go. Fetal stress has been linked to increased risk of future nervous system disorders or developmental problems. 
- If you have bad morning sickness, you will have a girl.
Nausea and vomiting during pregnancy – morning sickness – is a problem for up to 70 percent of women. The superstition says that the worse your morning sickness is, the more likely you will have a girl. Severe morning sickness occurs in up to 2 percent of women. This condition is called hyperemesis gravidarum (HG). 
A review of studies that examined the link between HG and female births was published in the British Journal of Obstetrics & Gynecology. There were 13 studies reviewed and they all found that HG and female births are linked. Fifty-five percent of women with HG had baby girls compared to 49 percent of women who did not have HG. 
The probable reason for this is the pregnancy human chorionic gonadotropin (hCG). Female babies cause higher levels of hCG and higher levels of hCG cause nausea and vomiting in pregnant women. 
- If you have bad heartburn, you will have a baby with lots of hair.
This is a common superstition. About 80 percent of pregnant women have heartburn. In a study published in the journal Birth, 64 women reported their amount of heartburn and were followed through birth. The study backed up the superstation. Women with the most severe heartburn tended to have babies with full heads of hair. Women with the least amount of heartburn tended towards cue ball-headed babies. 
This link, like the link between morning sickness and female births, is probably caused by pregnancy hormones. Some of these hormones may affect both the amount of fetal hair growth and the function of the lower esophageal sphincter (LES) in the mother. Pregnancy hormones may relax the LES, which is a valve that helps keep stomach juices in the stomach. If the LES relaxes, stomach juices can flow up into the esophagus and cause heartburn. 
- Don’t tell anyone you are pregnant until three months have passed.
This don’t-count-your-chickens superstition has the most solid scientific support of all pregnancy superstitions. According to the American College of Obstetricians and Gynecologists, 10 percent of all pregnancies are lost due to miscarriage. The main cause of miscarriage is a chromosome abnormality in the fetus that stops development. Eighty percent of these miscarriages occur during the first three months of pregnancy. 
So this one makes sense. Once you get through those first three months, your chances for keeping your pregnancy go way up. That’s the best time to share your joyful news with your family and loved ones.
- Proceedings of Biological Sciences, The evolution of superstitions and superstition-like behavior.
- HealthDay, Boy, Is This a Rough Labor.
- Journal of Law and Medical Ethics, Parental Influence on Eating Behavior.
- The Telegraph, Diet before pregnancy can affect baby’s sex, new research shows.
- Asian Nursing Research, Traditional Chinese Pregnancy Restrictions, Health-Related Quality of Life and Perceived Stress among Pregnant Women in Macao, China.
- Clinical and Obstetric Gynecology, Impact of Maternal Stress, Depression & Anxiety oin Fetal Neurobehavioral Development.
- BJOG, Consequences of hyperemesis gravidarum for offspring: a systematic review and meta-analysis.
- Birth, Pregnancy folklore revisited: the case for heartburn and hair.
- The American College of Obstetricians and Gynecologists, Early Pregnancy Loss.