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The differences between boys and girls are apparent three weeks after conception

By: April Carson

Although there are many unproven methods for guessing the sex of a baby, doctors can use maternal serum HCG levels to accurately predict whether a woman is carrying a boy or girl.MSHCG levels are usually higher in women carrying girls than in those carrying boys. A new study published today in the journal Human Reproduction found that hormonal differences between girls and boys appear less than three weeks after conception.

These findings may help explain how fetuses of each gender exert control over their mother's hormones. It could also be used to better understand pregnancy health and development. The researchers observed that two hormones, testosterone and inhibin A, were significantly higher in male fetuses than female ones.

The researchers from the Genetic Institute at Sourasky Medical Center in Tel Aviv followed 347 pregnancies that were achieved through in vitro fertilization. Yuval Yaron and colleagues tested the mothers' MSHCG levels between 14 and 20 days after fertilization, and they found some early differences on day 16.

Across all age groups and regardless of whether the mother had been pregnant before, several weeks into their pregnancies, women carrying girls showed a 18.5 percent higher hormone level than those carrying boys.

The researchers also measured the levels of other hormones that are released by the placenta during pregnancy, including estradiol, progesterone and inhibin A. The results showed that these hormone levels were significantly higher in male fetuses than female ones. This suggests that there may be differences in placental functioning between male and female fetuses, even at such an early stage in development.

We found this gender-related difference early on in pregnancy, which may help us understand how it occurs. Some genes located on the X chromosome that control protein expression may become over-expressed when there is a female fetus present, or hormones from male fetuses could be suppressing MSHCG--these are two explanations suggested by previous research into the variance.

The authors came to the conclusion that "there is a differential expression of genes by the placentas of female compared with male fetuses" because the glands needed to produce fetal hormones have not developed within the first three weeks of pregnancy. This means that there are marked physiological differences between boys and girls very early on in development. This research could help us to better understand the mechanisms of sex determination and development, providing valuable insight into how gender-based differences can develop so early in life.

Although such differences cannot correctly predict the sex of a baby, Yaron claims that the number of pregnant women with MSHCG levels either high or low enough for an accurate prediction at three weeks is very limited. "By finding other markers that show early gender-related differences," he explains, "we would be able to predict the sex of a fetus." Unfortunately, until then, parents who want to know the sex of their child will have to wait a bit longer.

Furthermore, Yaron's research has delved into the underlying mechanisms of sex determination and development. He proposes that at three weeks after conception, a process known as genomic imprinting plays a key role. This process is when a gene's expression depends on whether it was inherited from the mother or the father, and Yaron believes that this plays a major role in the differences between boys and girls at three weeks after conception.

This study was published in the journal Nature and has opened up a novel area of research that can potentially shed light on how sex differences in humans evolve over time. It is clear that Yaron's work has made an important contribution to our understanding of sexual development, and will continue to do so as his research progresses.

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About the Blogger:

April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on

To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav



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