Latest news with #maternalage
Daily Mail
21-07-2025
- Health
- Daily Mail
Boy or girl? Chance of having a son or daughter is NOT 50/50, scientists say
From flipping a coin to guessing the outcome of a yes/no question, there are many things that have a 50/50 chance of happening. For years, it was assumed that the chance of having a son or daughter also fit into this category. But a shocking new study has revealed that this isn't actually the case. Scientists from Harvard University have discovered that some women are much more likely to have children of only one sex. In their study, the team analysed data from more than 58,000 mothers who had given birth to at least one child. Their results revealed that maternal age plays a key role in determining the sex of the babies. 'The human sex ratio has long been of interest of biologists, statisticians, demographers, sociologists, and economists,' the team explained. 'Here, we showed that within each sibship size, sex at birth did not conform with a simple binomial distribution and identified a significant intramother correlation in offspring sex.' The sex of a baby is determined by the combination of sex chromosomes inherited from the sperm and egg. While the egg always carries an X chromosome, the sperm can either carry an X or a Y. If the sperm carrying an X chromosome fertilises the egg, the embryo will be female, while the embryo will be male if it's a Y chromosome. This has long been considered to be a 50/50 split. However, in their new study, published in Science Advances, the scientists questioned whether this is really the case. 'Several coauthors, however, observed cases of friends, colleagues, first-degree relatives, or themselves that produce offspring of only one sex raising questions about chance,' the team explained. To get to the bottom of it, the team analysed data from 58,007 US women who had had at least two children. The researchers investigated the impact of eight maternal traits - height, body mass index, race, hair colour, blood type, chronotype (whether or not you're an early bird or a night owl), age at first menstruation, and the age when they had their first child. What determines the sex of a baby? The sex of a baby is determined by the combination of sex chromosomes inherited from the sperm and egg. While the egg always carries an X chromosome, the sperm can either carry an X or a Y. If the sperm carrying an X chromosome fertilises the egg, the embryo will be female, while the embryo will be male if it's a Y chromosome. Seven of these traits did not impact the sex of the baby. However, their analysis uncovered a key link between the age at which the mother had their first child, and whether or not they had boys or girls. Women who were older than 28 when they first gave birth had a 43 per cent chance of having children of only one sex. But women who were younger than 23 when they first became a mother only had a 34 per cent chance of having children of only one sex. 'Older maternal age may be associated with higher odds of having single-sex offspring, but other heritable, demographic, and/or reproductive factors were unrelated to offspring sex,' the researchers explained. The reason for this link remains unclear. However, the researchers say it could be associated with the physiological changes women go through as they age - including a shorter follicular phase, and a lower vaginal pH. 'A shorter follicular phase tends to favor Y chromosome survival, whereas a more acidic vaginal environment favors X chromosome survival,' the team explained. 'Each woman may have a different predisposition to each of these factors as they age, which could lead to a higher probability of consistently producing same-sex offspring. 'However, these mechanisms remain speculative, and more detailed data are required to confirm these hypotheses.' Overall, the findings suggest that the chance of having a boy or girl is not 50/50 after all. 'Families desiring offspring of more than one sex who have already had two or three children of the same sex should be aware that when trying for their next one, they are probably doing a coin toss with a two-headed coin,' they team concluded.
Daily Mail
15-06-2025
- Health
- Daily Mail
EXCLUSIVE Researchers pinpoint key sexual change that puts America on course for 2050 catastrophe
Women are having their first child older than ever, according to new data that suggests the already-shrinking US fertility rate could see further declines. A new CDC report analyzing births from 2016 through 2023 found that the average age of first-time moms rose by nearly a year - from 26.6 years old in 2016 to 27.5 years old in 2023. Similar increases were also observed among women having their second and third children, with the average age at birth rising by one year for second births and just short of a year for third and higher-order births. Maternal age has been rising for decades, as the fertility rate in the US has been failing - having plunged to another new low in 2023, with fewer women than at any point in history having children. The rate was 54.5 births per 1,000 women of childbearing age (15 to 44 years old) last year, a three percent fall compared to 56 in 2022. The number of babies born in the US also declined year-over-year, with just under 3.6 million live births. Dr Jamie Grifo, the program director at New York University Langone Fertility Center, told 'We're below zero population growth in the US, and have been for years. 'I think there will be a social factor. There will be a lot of issues that result from the lack of reproduction.' The number of first births at age 30 and older also grew by nearly 13 percent for mothers ages 30 to 34 (from 22.3 percent to about 25 percent) and 25 percent for mothers age 35 and older (from 10 percent to 12.5 percent) from 2016 to 2023 The most recent CDC data showed that in 2023, the total fertility rate fell to 1.62 births per woman, the lowest since the government began tracking the metric in the 1930s. Experts say the US is headed for a so-called 'underpopulation crisis' by 2050, when too few people are born to support its current economic system. A previous National Vital Statistics Report found that from 1970 to 2000, the average age of mothers in the US rose by 2.6 years, with the most significant increase occurring among first-time mothers - from 21.4 in 1970 to 25 in 2000. The number of first births at age 30 and older also grew by nearly 13 percent for mothers ages 30 to 34 (from 22.3 percent to about 25 percent) and 25 percent for mothers age 35 and older (from 10 percent to 12.5 percent) from 2016 to 2023. This could be due to the rise in availability of birth control, as well as a steadily growing number of women in the workforce who are prioritizing career over starting a family. The increase in age at the start of motherhood suggests that the fertility rate is set to fall further. The CDC data shows women on average in 2023 are having 25 percent fewer children than their mothers and 50 percent fewer than their grandmothers. Births among women in their twenties have dropped by nearly one-third. 'Monitoring trends in maternal age at birth is important because maternal age can impact the total number of births and population growth and is associated with birth outcomes for both mothers and infants,' the CDC researchers said. 'For example, higher maternal age is linked to smaller family size on average and may carry different health risks and benefits compared with younger maternal age.' Older maternal age, particularly past 35, increases some risks of pregnancy complications, including gestational diabetes and miscarriage, as well as genetic abnormalities in the baby, like Down syndrome. 'This long-term shift reflects changes in societal, educational, and economic factors influencing when women begin childbearing,' the researchers said. The foundation for higher birth ages was laid in 1960 with the debut of the birth control pill, giving women control for the first time of their childbearing years. In the years since, it's become more common for people to have children later in life for various reasons — from financial concerns and child care challenges to delaying marriage or partnership and focusing on education, careers, or personal time in early adulthood. Choosing not to have children has also become more socially accepted, with some data indicating that more people are making that choice. Some studies suggest that kids born to older parents — who tend to be college-educated and relatively affluent — often grow up to be healthier, better educated, and better behaved than peers with younger parents. And women who have children later in life report larger happiness boosts around and after their birth, compared to younger mothers. In a 2018 New York Times survey, about 25 percent of respondents said they had fewer children — or expected to — than they'd initially hoped for, often because of financial limitations or feeling they'd run out of time to reach their ideal family size.
