Fetal sex does not determine whether a pregnant person carries high or low. The belief that girls sit high in the abdomen while boys hang low (or any variation of the claim) has no scientific support. Belly shape during pregnancy is driven by the mother’s anatomy, muscle tone, the number of previous pregnancies, and the position of the fetus in the uterus. A study of 350 mothers found that, with a single minor exception unrelated to belly shape, none of the common folk predictions about fetal sex held up when tested against actual birth outcomes.
Why People Believe It
Guessing a baby’s sex from pregnancy appearance is one of the most widespread folk traditions across cultures. The “carrying high means a girl” claim is just one entry in a long menu of supposed tells: heart rate, food cravings, skin changes, hair texture, morning sickness severity, and the shape of the bump. These ideas persist because they feel intuitive. Pregnancy is visibly dramatic, every belly looks different, and before modern imaging, there was no reliable way to know fetal sex until delivery. People filled the gap with pattern-matching, and confirmation bias did the rest. When someone guesses correctly, it gets remembered. When they guess wrong, it gets forgotten.
A study published in the Southeastern European Medical Journal tested many of these old wives’ tales at once. Researchers surveyed 350 mothers of newborns, all with singleton pregnancies delivered at or after 36 weeks, and compared the answers between those who had boys and those who had girls. The mothers were asked about their cravings, skin changes, nausea, hair quality, mood, belly shape, and other commonly cited predictors. Out of all the statements tested, only one showed a statistically significant difference: women who had girls reported slightly glossier hair during pregnancy than women who had boys, and even that finding was marginal and not clinically meaningful. No other folk predictor, including how high or low the belly sat, distinguished between male and female infants.1Hrčak / Southeastern European Medical Journal. He or She, What Will It Be: Old Wivesʹ Tales and Foetal Sex Prediction
What Actually Shapes the Bump
If fetal sex doesn’t explain belly shape, what does? The answer involves several factors, none of which have anything to do with whether you’re having a boy or a girl.
- Abdominal muscle tone: The rectus abdominis muscles run vertically along the front of the abdomen, and their tightness acts like a corset around the uterus. In a first pregnancy, these muscles are typically firmer and hold the uterus higher and more forward. In subsequent pregnancies, the muscles have already been stretched and tend to be more relaxed, letting the belly sit lower and spread wider.
- Number of prior pregnancies: First-time mothers almost always carry differently from someone on their third or fourth pregnancy. This is largely a muscle-tone effect, but it’s so consistent that parity (how many times you’ve given birth) is one of the strongest predictors of bump shape.
- Maternal height and torso length: A taller person with a long torso has more vertical space for the uterus to expand, so the bump may appear smaller and higher. A shorter torso means the uterus has nowhere to go but outward, creating a rounder, lower-looking profile.
- Fetal position: Babies move constantly in the uterus and settle into different positions at different stages. A fetus lying with its back along the mother’s front (anterior position) creates a different bump shape than one lying with its back along the mother’s spine (posterior position). Late in pregnancy, when the baby drops into the pelvis in preparation for delivery, the entire belly shifts downward regardless of sex.
- Placental location: An anterior placenta (attached to the front wall of the uterus) can make the belly appear rounder and flatter, masking fetal movement and altering the overall contour.
Each of these variables changes from one pregnancy to the next, even in the same person. A woman might carry high with her first child and low with her second, and the shift has nothing to do with having a different-sex baby. It reflects the physical realities of her body after the first pregnancy.
How Abdominal Muscles Change Across Pregnancies
One of the most significant anatomical changes that affects belly appearance is diastasis recti abdominis, a separation of the two vertical strips of muscle that run down the center of the abdomen. During pregnancy, the growing uterus pushes these muscles apart, and the connective tissue between them (the linea alba) stretches and thins. This is extremely common. The condition is not a hernia, though it can cause the abdominal wall to bulge visibly, especially when the muscles are engaged.2Ginekologia Polska. Diastasis recti abdominis — a review of treatment methods
Diastasis recti is much more prevalent in women who have had multiple pregnancies, and its presence dramatically alters how the belly looks during subsequent pregnancies. With weaker central abdominal support, the uterus shifts forward and sometimes downward, creating the classic “low carry” that folk wisdom attributes to boys. In reality, it’s a structural consequence of prior pregnancies weakening the abdominal wall. The sex of the current baby is irrelevant.
Maternal Body Composition Is Hard to Measure During Pregnancy
You might wonder whether fat distribution patterns differ depending on fetal sex, since another version of the myth claims that carrying a girl means gaining weight all over while carrying a boy means the weight stays in the belly. Researchers have looked at body composition changes during pregnancy, and the honest answer is that the measurements themselves are unreliable. During pregnancy, the normal assumptions built into body-composition tools break down. The hydration of lean tissue changes, the fetus and its supporting tissues (placenta, amniotic fluid) can’t be cleanly separated from the mother’s own composition, and standard methods like bioelectrical impedance or body density calculations produce estimates with wide margins of error.3PubMed Central. Body composition changes in pregnancy: measurement, predictors and outcomes
So even the basic premise that we could reliably detect fat-distribution differences between pregnancies with boys versus girls is shaky. The tools aren’t precise enough during pregnancy to support the claim, and no well-designed study has demonstrated that fetal sex drives maternal fat patterning. Weight gain during pregnancy is influenced by diet, pre-pregnancy body composition, hormonal shifts, and genetics, but fetal sex doesn’t appear on the list of meaningful variables.
How Fetal Sex Is Actually Determined
If belly shape can’t tell you anything, what can? Modern medicine offers two reliable routes, and both involve looking directly rather than guessing from the outside.
Ultrasound is the most familiar method. By the second trimester, a sonographer can visually identify external genitalia with high accuracy. One study found that when sex could be determined (which was possible in about 99% of cases in the second and third trimesters), the assignment was correct in virtually all of them.4PubMed Central. Accuracy of sonographic fetal gender determination: predictions made by sonographers during routine obstetric ultrasound scans Earlier in pregnancy, the accuracy drops somewhat. At 11 to 12 weeks, ultrasound sex identification was about 88% accurate for males and 97% for females, with the overall sensitivity and specificity still high but not as reliable as later scans.5PubMed Central. The ultrasound identification of fetal gender at the gestational age of 11–12 weeks A landmark study in the New England Journal of Medicine found 99% accuracy when imaging at 15 weeks or later, though the fetal position made visualization impossible in about 31% of attempts.6PubMed. Determination of fetal sex
Non-invasive prenatal testing, or NIPT, is a blood test that analyzes fragments of fetal DNA circulating in the mother’s bloodstream. It can be performed as early as the first trimester and provides sex determination with sensitivity around 99% and specificity above 99%.7PubMed. The accuracy of cell-free fetal DNA-based non-invasive prenatal testing in singleton pregnancies: a systematic review and bivariate meta-analysis NIPT is primarily used to screen for chromosomal conditions, but fetal sex determination is essentially a byproduct of the analysis, and for that purpose, the test is so accurate it’s considered diagnostic.8PubMed Central. Sex selection and non-invasive prenatal testing: A review of current practices, evidence, and ethical issues
Both methods give you an answer grounded in anatomy or genetics rather than guesswork. The contrast with belly-shape prediction is stark: one method relies on directly observing fetal structures or DNA, the other relies on eyeballing the outside of a fully clothed person and invoking tradition.
When NIPT Isn’t Perfect
NIPT’s headline accuracy numbers for sex determination are genuinely impressive, but it’s worth knowing that the test is less reliable for certain chromosomal conditions. A large study of over 34,000 NIPT results in China found that among positive results flagged for sex chromosome abnormalities (conditions like Turner syndrome or Klinefelter syndrome, which involve having an atypical number of sex chromosomes), only about 35% of cases that went on to confirmatory testing were true positives. The rest were false alarms.9PubMed. An assessment of the analytical performance of non-invasive prenatal testing (NIPT) in detecting sex chromosome aneuploidies This is a different question from simply identifying whether the fetus is male or female, which NIPT does with near-perfect accuracy. Detecting sex chromosome abnormalities is a harder task, and a positive screen for those conditions needs to be confirmed with further testing. But for the straightforward question of boy or girl, the blood test is about as close to certain as prenatal screening gets.
Twins and Belly Shape
People carrying twins often look dramatically different from those carrying singletons, and the difference gets more pronounced as pregnancy progresses. This is another illustration of why belly shape reflects the contents of the uterus and the mother’s anatomy, not fetal sex. Interestingly, each individual twin tends to be smaller than a singleton. Research comparing fetal body composition found that twins had measurably smaller abdominal areas than singletons from about 25 weeks onward, with the gap widening as pregnancy continued.10JAMA Pediatrics. Fetal Body Composition in Twins and Singletons Twin pregnancies also showed less subcutaneous fat thickness in each fetus compared to singletons. Yet despite each individual baby being smaller, the total uterine volume in a twin pregnancy is larger, and the belly typically measures bigger and sits differently because two bodies, two placentas, and a larger volume of amniotic fluid are all competing for space. The shape of the bump in a twin pregnancy tells you nothing about whether the babies are boys, girls, or one of each. It tells you there are two of them.
Why Gender Guessing Isn’t Just Harmless Fun
For most people, the “carry high, it’s a girl” game is lighthearted party conversation. But research suggests that strong expectations about fetal sex can have real psychological consequences when those expectations aren’t met. A study of primiparous women (first-time mothers) found that those whose baby’s sex didn’t match their expectations had roughly two and a half times the odds of developing postpartum depression compared to women whose expectations were confirmed. The association was statistically significant among first-time mothers but not among women who already had children.11PubMed Central. Maternal expectations of fetal gender and risk of postpartum depression
The researchers estimated that fetal gender expectations accounted for about 15% of the risk of postpartum depression in their models. That’s a substantial chunk of a serious condition. The mechanism isn’t about belly shape specifically, but the broader culture of gender prediction feeds into it. When family members, coworkers, and strangers on the street confidently declare “you’re definitely having a girl” based on how you’re carrying, it reinforces expectations. If those expectations become emotionally invested, the letdown when the actual sex is revealed can be acute, particularly for first-time parents who have no prior experience to moderate the reaction.
This doesn’t mean you need to avoid all gender speculation during pregnancy. But it’s a reminder that these predictions aren’t consequence-free, especially when they’re delivered with the authority of folk wisdom that “always works.” For first-time mothers in particular, staying open to either outcome and treating any prediction, from belly shape to heart rate myths, as entertainment rather than fact may be emotionally protective.
Other Folk Predictions and What the Evidence Shows
Belly position isn’t the only folk method that fails when tested. The same study of 350 mothers that debunked carrying height also examined cravings (sweet foods supposedly mean a girl, salty foods a boy), nausea severity (worse morning sickness supposedly indicates a girl), skin quality (acne or dull skin supposedly means a girl is “stealing your beauty”), and mood changes. None of these showed a meaningful difference between mothers of boys and mothers of girls.1Hrčak / Southeastern European Medical Journal. He or She, What Will It Be: Old Wivesʹ Tales and Foetal Sex Prediction
The single finding that did reach statistical significance, slightly glossier hair reported by mothers of boys compared to mothers of girls, is the kind of result that can easily emerge by chance when you test a large number of comparisons at once. When researchers check a dozen or more hypotheses in the same dataset, at least one is likely to cross the threshold for significance purely by luck. Even if the hair-quality finding is real, the difference was small enough to be useless as a prediction tool for an individual pregnancy.
The fetal heart rate myth deserves a special mention because it sounds more scientific than the others. The claim is that a heart rate above 140 beats per minute means a girl, while below 140 means a boy. Multiple studies have examined this, and fetal heart rate does not reliably differ by sex at any gestational age that would be relevant for prediction. Heart rate varies with fetal activity, gestational age, and the timing of the measurement, not with the chromosomes the baby carries.
When Fetal Sex Does Affect the Pregnancy
While fetal sex doesn’t change how the belly looks from the outside, it isn’t biologically irrelevant to the pregnancy. Research has identified modest associations between fetal sex and certain pregnancy complications. Male fetuses are, on average, slightly heavier at birth than female fetuses, and pregnancies with male fetuses show slightly higher rates of gestational diabetes and preterm birth in some large epidemiological studies. Female fetuses are associated with a slightly higher risk of preeclampsia in some datasets, though these findings aren’t universal across populations.
These differences are statistical tendencies visible only across thousands of pregnancies. They don’t manifest as visible changes to the mother’s body shape, and they certainly don’t produce the kind of high-versus-low carrying patterns that folk wisdom describes. The biological effects of fetal sex on the pregnancy are real but subtle, operating at the level of placental hormone production and immune signaling rather than belly contour. If fetal sex mattered enough to reshape the abdomen, you’d expect the 350-mother study to have picked up at least some difference in carrying position. It didn’t.
The disconnect between what people believe and what the evidence shows is a good example of how folk medicine can latch onto a kernel of biological truth (fetal sex does affect the pregnancy in some ways) and stretch it into a visible, dramatic claim (you can see the difference just by looking) that doesn’t follow from the underlying science. The real effects of fetal sex during pregnancy are hidden inside blood chemistry and placental function. They aren’t written on the belly.