Baby Heart Rate and Gender: Does Over 140 Mean a Girl?

What does the heart rate gender theory say?

The rule usually quoted is 140 beats per minute (bpm): above it, a girl; below it, a boy. A 2017 research paper summarised the folklore as "the 120–140 bpm range for boys and the 140–160 bpm range for girls". People apply it to the number they hear at an early scan or a midwife appointment.

It is one of the most widely believed pregnancy tales, which is exactly why researchers have tested it. A US team that did so described "the prevailing lay view of females having a faster FHR" (fetal heart rate). The short version of what they found: it does not hold.

What did the studies find?

A 2023 systematic review pooled five first-trimester studies and found no significant difference in average heart rate between boys and girls (standardised mean difference 0.04, 95% confidence interval −0.09 to 0.16). Its conclusion: first-trimester heart rate "is not a reliable predictive test for fetal sex determination". If anything, the tiny differences ran the opposite way to the folklore — the reviewers noted that male fetuses show a faster heart rate, but that the difference is minimal.

Why a heart rate tells you the week, not the sex

The number you hear depends mainly on how far along you are. In a Japanese study of 57 IVF pregnancies, the embryos' heart rate rose steadily from 87 bpm at 38 days of gestation to 189 bpm at 62 days, tracking gestational age closely, with no difference between boys and girls. It then slows again: in a Portuguese study of 9,701 babies, the average baseline fell by 9 bpm between 24 and 40 weeks. It also changes with the baby's activity, slowing when the baby sleeps.

If you are not sure exactly how far along you are, the gestational age calculator works it out. When a heartbeat first shows on a scan is covered in 6 weeks pregnant.

Heart rate and gender at 8, 10 or 12 weeks

This is when the rule is most often applied, and when it makes least sense. In the West Virginia study of babies scanned at 8 to 13 weeks, both girls and boys averaged about 167 bpm — well above the 140 line. At that stage the rule would call the average boy a girl. A heart rate of 150, 160 or 170 in the first trimester says something about the week of pregnancy and nothing about the sex. What is happening at the end of the first trimester is in 12 weeks pregnant.

Is there a difference later in pregnancy?

Possibly an average one, and it still does not help you. The Portuguese study analysed heart-rate tracings from 9,701 healthy babies between 24 and 41 weeks and found the baseline "was consistently higher in females", a statistically significant difference that the authors used to build separate reference charts for boys and girls. A Canadian study of 212 women, measuring between 14 and 41 weeks, found no significant difference at any gestational age.

Even where an average difference exists, it cannot sort one baby. In the 2006 Ohio study, the gap between the girls' and boys' averages was about 3 bpm, while the spread within each group was a standard deviation of about 23 bpm — roughly seven times larger. Boys and girls overlap almost completely.

Heart rate is in good company: the other tales tested against real babies, from bump shape to the Chinese gender calendar, also came out at chance — see old wives' tales for boy or girl. The only early-scan sign with studies behind it is nub theory.

Should you use a home doppler to listen?

No. The NHS is direct about this: "Do not use a home doppler (heartbeat listening kit) to try to check the baby's heartbeat yourself. This is not a reliable way to check your baby's health. Even if you hear a heartbeat, this does not mean your baby is well."

That warning is about safety, not sex prediction, but it is the most important thing on this page if you have a doppler at home. The way to keep track of your baby later in pregnancy is to get to know their usual pattern of movements.

When to call someone

The NHS says to call your midwife or maternity unit immediately if:

• your baby is moving less than usual
• you cannot feel your baby moving any more
• there is a change to your baby's usual pattern of movements

"Do not wait until the next day – call immediately, even if it's the middle of the night." The NHS says you should start to feel your baby move between 16 and 24 weeks, and that if you have not felt your baby move by 24 weeks, you should tell your midwife. More on reduced fetal movements.

Frequently asked questions

Is a heart rate of 150 a boy or a girl?

Neither: it cannot tell you. In a 2006 study of 477 babies scanned before 14 weeks, girls averaged 151.7 bpm and boys 154.9 bpm, with no real difference. A heart rate of 150 sits well within the range seen for both, and mainly reflects how many weeks pregnant you are.

Does a fast heartbeat at 12 weeks mean a girl?

No. In a study of 655 babies scanned between 8 and 13 weeks, girls averaged 167.0 bpm and boys 167.3 bpm. Both averages are far above 140, so a fast heartbeat at this stage reflects the week, not a girl. A 2023 review of five studies confirmed the finding.

Is the heart rate gender theory true?

No. Studies in the first trimester found no meaningful difference between boys and girls, and a 2023 review called heart rate "not a reliable predictive test" for sex. One large study later in pregnancy found girls' baseline higher on average, but boys and girls overlap far too much for it to predict one baby.

Can heart rate predict gender at 20 weeks?

No. A Canadian study measuring from 14 to 41 weeks found no significant difference at any stage. By then there are far better options: see the 20-week scan and when you can find out the sex.