There are no reliable symptom-based signs that you are pregnant with a boy. The vast majority of folk beliefs about predicting fetal sex from pregnancy symptoms have been tested in studies and found to be no better than a coin flip. A few real biological differences do exist between pregnancies carrying male versus female fetuses, particularly in hormone levels and immune activity, but these differences are subtle, overlap heavily between groups, and cannot be felt or observed without lab work. If you want to know your baby’s sex, the only dependable routes are ultrasound imaging and blood-based DNA testing.
Morning Sickness Actually Points the Other Way
One of the most persistent beliefs is that less morning sickness means you’re carrying a boy. There is a grain of truth buried in this one, but it works in the opposite direction from what many people assume. Research published in The Lancet found that among women with hyperemesis gravidarum, the severe form of pregnancy nausea that sometimes requires hospitalization, there was a higher proportion of female offspring.1Lancet. Sickness in pregnancy and sex of child So severe nausea is weakly associated with carrying a girl, not a boy.
The key word is “weakly.” Plenty of women with terrible morning sickness go on to deliver boys, and plenty with easy first trimesters have girls. The association shows up in population-level data, not in any individual pregnancy. If you’re experiencing mild nausea and someone tells you it must be a boy, the research doesn’t back that up as a meaningful predictor.
Hormonal Differences That Actually Exist
The most well-documented biological difference between boy and girl pregnancies involves hormones, specifically testosterone and human chorionic gonadotropin (hCG). Women carrying a male fetus tend to have higher testosterone levels, particularly during the second half of pregnancy. One study found maternal testosterone gradually increased throughout pregnancy with a male fetus and was significantly higher compared to pregnancies with a female fetus during the latter months.2PubMed. Maternal testosterone and fetal sex This makes biological sense: the male fetal testes begin producing testosterone early in development, and some of it crosses into the maternal bloodstream.
The relationship between testosterone and fetal sex is also influenced by maternal genetics. Research found that specific genotype variations in mothers of male children were associated with higher total testosterone levels, meaning two women both carrying boys could still have quite different testosterone readings depending on their own genetic makeup.3PubMed Central. Maternal and female fetal testosterone levels are associated with maternal age and gestational weight gain This kind of overlap makes testosterone useless as a home test for fetal sex. You’d need a blood draw, a lab, and reference ranges, and even then the distributions between boy and girl pregnancies overlap too much to be diagnostic.
The hCG story is more complex and, frankly, a bit contradictory. In natural pregnancies, hCG levels tend to be higher when the fetus is female. One large study found hCG was about 11% higher in the first trimester and 8% higher in the second trimester when the fetus was a girl.4PubMed Central. Fetal sex differences in human chorionic gonadotropin fluctuate by maternal race, age, weight and by gestational age Another found that mean hCG in normal pregnancies carrying a female fetus was roughly 75% higher than in those carrying a male.5PubMed Central. The Effects of Fetal Gender on Serum Human Chorionic Gonadotropin and Testosterone in Normotensive and Preeclamptic Pregnancies However, a study looking specifically at pregnancies conceived through IVF with single blastocyst transfer found the reverse: initial hCG levels were actually higher in pregnancies that produced a male infant.6PubMed. Initial serum HCG levels are higher in pregnant women with a male fetus after fresh or frozen single blastocyst transfer The IVF context is unusual because the timing of implantation is controlled, but the discrepancy is a good reminder that single hormone markers don’t reliably point to one sex or the other in an individual pregnancy.
Your Immune System Responds Differently to a Boy
One of the more interesting findings in recent years is that the maternal immune system behaves differently depending on whether the fetus is male or female. Women carrying a male fetus tend to show a stronger inflammatory immune profile, while those carrying a female fetus lean toward a more regulatory immune response.7PubMed. Sex differences in innate and adaptive immunity impact fetal, placental, and maternal health Research measuring specific immune markers found that women with a male fetus had higher levels of several pro-inflammatory signaling molecules at multiple points during pregnancy.8PubMed Central. Fetal sex-based differences in maternal hormones, angiogenic factors, and immune mediators during pregnancy and the postpartum period
What does this actually mean for the pregnant person? In theory, a more inflammatory state could contribute to feeling somewhat different, but the effects are measured in lab assays, not felt as distinct symptoms. You can’t tell that your interleukin levels are elevated by how you feel day to day. These immune differences do appear to have clinical relevance for pregnancy complications and placental function, but they don’t translate into noticeable “signs” that you’re carrying a boy.
Fetal Heart Rate Is Not a Clue
The belief that a girl’s heartbeat is faster than a boy’s is among the most widespread pregnancy folk tales, and it has been studied enough to call it conclusively false. A study of over 650 first-trimester pregnancies found the average heart rate was virtually identical between male and female fetuses, with no statistically significant difference.9PubMed Central. First trimester fetal heart rate as a predictor of newborn sex A separate study with a different methodology also found no meaningful gap, with the difference amounting to just a few beats per minute and falling well within normal variation.10Fetal Diagnosis and Therapy. Gender-Related Differences in Fetal Heart Rate during First Trimester
The myth probably persists because fetal heart rate fluctuates a great deal from moment to moment and across gestational weeks. At any given appointment, you’ll hear a number somewhere in the normal range, and confirmation bias does the rest. If the heart rate sounds high and you later find out it’s a girl, the “rule” is confirmed in your memory. If it doesn’t match, you forget it.
Cravings, Skin, and Hair
Craving salty or savory food is popularly said to signal a boy, while craving sweets supposedly signals a girl. A population-level study in Jordan that examined the relationship between food cravings and fetal sex found no significant correlation.11PubMed Central. Exploring associations between pregnancy cravings and sociodemographic, lifestyle and health factors: insights from a cross-sectional population study in Jordan Cravings during pregnancy are real, but they appear to be driven by hormonal shifts, nutritional needs, and cultural context rather than by fetal sex.
Skin changes (“glowing” with a boy, dull skin with a girl) and hair changes have also been examined. A study that systematically tested several common old wives’ tales found that, out of all the folk predictors investigated, only one showed any statistical difference at all: women carrying a male fetus reported glossier hair slightly more often, at about 45% compared to 39% for women carrying girls.12Hrčak / Southeastern European Medical Journal. He or She, What Will It Be: Old Wivesʹ Tales and Foetal Sex Prediction That gap is small enough that it would be wrong roughly half the time if used as a prediction tool. Every other folk claim tested in that study, including belly shape, complexion changes, and weight distribution, showed no difference between mothers of boys and mothers of girls.
Fetal Movement and Growth Patterns
Some women report that pregnancies with boys involve more vigorous kicking. There is a small amount of research supporting the idea that male fetuses are somewhat more physically active. One study tracking fetal and neonatal movement found that males displayed a greater number of leg movements per minute than females, both before and after birth.13PubMed. Human fetal and neonatal movement patterns: Gender differences and fetal-to-neonatal continuity However, this was measured under controlled observation conditions, not by maternal perception. Whether mothers can actually perceive this difference amid the wide natural variation in fetal activity is a different question, and a much harder one to answer. Subjective reports of “how much the baby kicks” are influenced by placental position, amniotic fluid volume, maternal activity levels, and attention.
Male fetuses do tend to be slightly larger than female fetuses from quite early in gestation. By the first trimester, measurable size differences have already appeared, with male crown-rump length slightly longer on average.14PubMed Central. Sex-specific differences in fetal and infant growth patterns: a prospective population-based cohort study From the second trimester onward, head circumference and abdominal circumference tend to be larger in males, while femur length is actually shorter compared to females. These differences grow more pronounced as pregnancy progresses and become statistically significant by around 28 weeks.15PubMed. The ultrasound estimation of sex-related variations of intrauterine growth Interestingly, male fetal growth appears more sensitive to maternal body size. Among shorter and lighter mothers, the birth weight advantage for boys was relatively small, while it widened to about 150 to 190 grams among mothers who were either tall or heavier.16PubMed Central. Sex differences in fetal growth responses to maternal height and weight
None of this helps you guess the sex at home, of course. Growth measurements are taken during ultrasound and compared to percentile charts, and those charts have always accounted for the fact that boys tend to run a bit bigger. By the time the size difference is large enough to be meaningful, the anatomy scan has long since been able to identify sex directly.
How Sex Is Actually Determined With Confidence
If you want a reliable answer rather than a guess, two methods dominate modern prenatal care. Ultrasound is the traditional approach. At 11 to 12 weeks, ultrasound can identify fetal sex with a positive predictive value of roughly 88% for boys and 97% for girls.17PubMed Central. The ultrasound identification of fetal gender at the gestational age of 11–12 weeks Accuracy improves rapidly with gestational age: success rates climb from below 50% at 11 weeks to about 90% at 14 weeks and become highly reliable by the standard anatomy scan around 18 to 20 weeks.18PubMed. The sonographic identification of fetal gender from 11 to 14 weeks of gestation Fetal position, cooperativeness, and the sonographer’s experience all influence accuracy at earlier gestational ages.
Cell-free fetal DNA testing, often bundled into noninvasive prenatal testing (NIPT), offers an even earlier and highly accurate option. A large meta-analysis covering thousands of tests found sensitivity above 95% and specificity above 98% for detecting fetal sex.19JAMA. Noninvasive Fetal Sex Determination Using Cell-Free Fetal DNA: A Systematic Review and Meta-analysis The test works by detecting Y-chromosome DNA fragments circulating in the mother’s blood. If Y-chromosome sequences are present, the fetus is male; if absent, female. Performance is weaker before seven weeks of gestation but becomes highly reliable from about seven weeks onward. A second meta-analysis of 90 studies confirmed similarly high accuracy, with sensitivity around 97% and specificity near 99%.20PubMed Central. Non-invasive prenatal diagnostic test accuracy for fetal sex using cell-free DNA a review and meta-analysis NIPT is primarily offered for screening chromosomal conditions, but sex determination comes along as part of the analysis.
The Ramzi Method and Early Ultrasound Guesses
You may have encountered references online to the “Ramzi method,” which claims that placental or chorionic villi location on the right side of the uterus indicates a male fetus, and location on the left indicates a female. A study from Moldova found that about 83% of male fetuses had right-sided placental placement, and about 91% of female fetuses had left-sided placement, which superficially appears to support the idea.21Institutional Repository in Medical Sciences of Nicolae Testemitanu State University of Medicine and Pharmacy of the Republic of Moldova. The relationship between placental location and fetal gender (Ramzis method), among pregnant women in Moldova
There are good reasons to be skeptical. The original Ramzi study, which claimed over 97% accuracy, has never appeared in a mainstream peer-reviewed journal and has not been independently replicated with the same striking results. Ultrasound image orientation can be flipped depending on the probe approach, making “left” and “right” assignments unreliable unless the sonographer specifically documents laterality. Most obstetricians and maternal-fetal medicine specialists do not endorse the method. The Moldovan study is the kind of single-center finding that needs replication in larger, prospective trials before it should change anyone’s expectations. Treating it as a fun early guess is harmless, but treating it as a diagnostic tool is premature.
Placental Biology and Why Boys Are the “Riskier” Pregnancy
One area where the research is genuinely compelling, even if it has no symptom-level implications for the pregnant person, is placental biology. Male and female placentas function differently at the molecular level. Animal research has shown that female placentas upregulate genes related to growth and blood vessel formation in response to maternal diet changes, while male placentas are less adaptive.22PubMed Central. Sex-Dependent Differences in Mouse Placental Gene Expression following a Maternal High-Fat Diet Female placentas also show higher expression of certain genes involved in the placental junction zone compared to males at equivalent developmental time points.23Scientific Reports. Sex differences in placental structure and gene expression in ICR mice during embryonic development
Combined with the stronger inflammatory immune profile associated with male pregnancies, this paints a picture where carrying a boy involves a somewhat different metabolic and immunological load. Male pregnancies are associated with slightly higher rates of preterm birth and gestational diabetes in large epidemiological studies, though the absolute risk differences are small. The working theory is that the male fetus pursues a more aggressive growth strategy while investing less in placental resilience, which works fine under favorable conditions but leaves less margin when things get stressful. The female fetus, by contrast, appears to adopt a more cautious strategy with a more adaptable placenta.
Maternal Cognition and the Trivers-Willard Hypothesis
A surprising finding from a single study reported that women pregnant with boys outperformed women pregnant with girls on difficult tests of working memory and spatial ability.24PubMed Central. Exploring the influence of pregnancy on cognitive function in women: a systematic review This is the kind of finding that makes headlines and should be taken with considerable caution. It comes from one study, and pregnancy cognition research in general is difficult to do well because of all the confounding variables involved. It is an intriguing result, not an established fact.
From a broader evolutionary angle, the Trivers-Willard hypothesis predicts that mothers in better condition should bias their reproductive investment toward sons, because males tend to have higher variance in reproductive success. A mother in good condition, the theory goes, is more likely to produce a son capable of competing successfully.25PubMed Central. The Trivers-Willard hypothesis: sex ratio or investment? Evidence for this in humans is mixed and contested. Some studies have found small sex-ratio shifts associated with maternal nutrition, socioeconomic status, or stress, but the effects are tiny and inconsistent across populations. The hypothesis is more useful as a framework for understanding why evolution might have produced sex-specific differences in placental strategy and maternal physiology than as a practical predictor of anything in your own pregnancy.
Women With PCOS Carrying Boys
For women with polycystic ovary syndrome, pregnancy hormone dynamics add another layer. Women with PCOS already tend to have higher androgen levels, and research has found that carrying a male fetus compounds this effect. A clinical trial investigating metformin use during PCOS pregnancies found that the drug reduced testosterone and other androgen markers specifically in non-obese women carrying a male fetus, suggesting that the combination of PCOS and a male fetus creates a particularly pronounced androgen environment.26PubMed Central. Sustained Maternal Hyperandrogenism During PCOS Pregnancy Reduced by Metformin in Non-obese Women Carrying a Male Fetus This is relevant for PCOS management during pregnancy but again is not something you’d detect without blood work. It does, however, add context to why some women with PCOS may experience more pronounced androgen-related symptoms like acne or body hair changes when pregnant with a boy, though even this has not been confirmed in large observational studies linking subjective symptoms to fetal sex in the PCOS population specifically.