Fetal Heart Rate and Gender: Is There a Link?

The old wives' tale says: if your baby's heart rate is above 140 beats per minute (bpm), you are having a girl; if it is below 140 bpm, you are having a boy. Some versions use 150 bpm as the threshold instead.

It is one of the most commonly repeated pregnancy myths. You will hear it at antenatal classes, in parenting forums, and even from well-meaning friends and relatives. The story is appealing because it feels scientific — heart rate is a real, measurable number, and the threshold gives it a satisfying air of precision.

Unfortunately, the precision is illusory. The claim has been tested in multiple studies, and the result is always the same: there is no link between fetal heart rate and sex.

Several studies have directly tested whether fetal heart rate differs between male and female fetuses. The answer is consistently no.

A 2023 systematic review and meta-analysis found no significant difference in mean fetal heart rate between male and female fetuses (p = 0.553) and concluded that first-trimester heart rate is not a reliable predictor of fetal sex (BMC Pregnancy and Childbirth, 2023). One first-trimester study of 655 fetuses found near-identical averages — 167.0 bpm for female and 167.3 bpm for male fetuses (2015). Both sexes fall well within the same range.

This matches the wider evidence. Some studies report a tiny statistical difference — male fetuses occasionally averaging a fraction of a beat per minute faster — but the overlap is so complete that heart rate cannot predict an individual baby's sex. The medical community considers the question settled.

For the broader landscape of gender prediction myths, see our complete list of old wives' tales.

If the method performs at chance, why do so many people swear by it? Three reasons:

• Confirmation bias: when the heart rate prediction happens to be right (about 50% of the time), people remember and share it as "proof." When it is wrong, it is quietly forgotten. This creates a survivorship bias that makes the myth seem more accurate than it is.
• The 50% baseline: any prediction method will be right half the time by pure chance. If you flip a coin to predict gender, you will also be "right" 50% of the time — but that does not mean coin flips predict sex.
• Variability creates the illusion: fetal heart rate varies naturally from measurement to measurement (it changes with fetal activity, sleep cycles, and gestational age). If you measure heart rate multiple times during pregnancy, you will get different numbers — and some of them will happen to match the baby's sex by coincidence.

The normal fetal heart rate range is 120–160 bpm, and it changes across pregnancy in ways that have nothing to do with sex:

These changes reflect the developing cardiac and nervous systems — the heart rate starts high in early pregnancy because the immature heart beats faster, and it gradually decreases as the baby grows and the autonomic nervous system matures. The trajectory is the same for boys and girls.

Heart rate also varies moment to moment with fetal activity: it rises when the baby moves and falls when the baby sleeps. A single measurement captures only a snapshot, and the range of normal variation is wide enough to overlap completely between the sexes.

While fetal heart rate does not predict sex, it is a valuable indicator of your baby's wellbeing. Your midwife and obstetric team monitor heart rate to:

• Confirm viability: a detectable heartbeat from about 6 weeks confirms a developing pregnancy.
• Assess fetal health: a heart rate within the normal range (120–160 bpm) is reassuring; significant deviations can indicate distress.
• Monitor during labour: continuous fetal monitoring during labour tracks heart rate patterns to ensure the baby is coping well.

So the heart rate number you hear at your scan is worth paying attention to — just not for the reason the old wives' tale suggests. It tells you about your baby's health, not their sex.

If you want a real prediction, here is how the evidence-backed methods compare:

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