- Researchers analysed around 80 pregnant women over their three trimesters
- They found chemical reactions in the body are the most obvious gender sign
- Those carrying female fetuses produced more pro-inflammatory cytokines
- This inflammation may explain why some women experience aches, asthma and nausea in pregnancy
Typically, the sex of a fetus is determined by an ultrasound.
But, long before modern technology made that possible, it seems the human body had its very own way of offering insight into a baby's gender.
According to experts, chemical reactions in the body provide a mother with tell-tale signs of whether she's carrying a boy or a girl.
And these can lead to the onslaught of asthma, or even the recurrence of once-ridden allergies, scientists believe.
Tell-tale signs: According to experts, chemical reactions in the body provide a mother with indicators of whether she's carrying a boy or a girl
The data, published in the Brain, Behaviour & Immunity journal, will no doubt be welcomed by those looking for alternative readings.
Dr Amanda Mitchell, a researcher at Ohio's State's Institute for Behavioural Medicine, led the analysis.
She assessed 80 pregnant women over their three trimesters for evidence of increased immune markers called cytokines.
One subject who took part in the study, Melissa Fox,suffered a renewed sensitivity to allergy triggers while pregnant with her daughter - something that didn't happen when she was carrying her son.
Girl thing: Those carrying female fetuses produced more pro-inflammatory cytokines when presented with bacteria
OTHER GENDER PREDICTION METHODS
Last April, researchers found those with extreme morning sickness may be less likely to give birth to sons.
The condition hyperemesis gravidarum - affects about one in 100 expectant mothers.
The condition can affect the baby’s development and there is a risk it will be premature or have a very low birth weight.
The Swedish study pointed to a hypothesis that a daughter is safer for a mother to pass on her genes to as weaker males are less likely to succeed.
This result, Dr Mitchell says, were evident in several other cases and seemed to reaffirm the hypothesis that gender causes different reactions in expectant mums.
She told Kidspot: ''Women carrying female foetuses exhibited a heightened inflammatory response when their immune system was challenged, compared to women carrying male fetuses.'
This comes after scientists in January found the best way of predicting the gender of an unborn child is to look at a pregnant woman's blood pressure.
Those who have hypertension - caused by a diet high in salt, smoking or drinking too much - are more likely to have a boy, research from Mount Sinai Hospital in Toronto suggested.
While the reverse is also true, experts believe - despite not knowing why.
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